Systematic Evaluation of Sea Stars of the Genus Heliaster from the Southeastern Pacific and Redescription of Heliaster helianthus

Abstract

Heliaster has long been considered to comprise seven nominal species of starfish distributed across the Eastern Pacific, from Baja California (Mexico) southward to central Chile. Along the southeastern Pacific coast, three taxa have been traditionally recognized: H. helianthus (Paita, northern Peru, to Concepción, central-southern Chile), H. polybrachius (Mexico to Perú), and H. canopus (Juan Fernández Archipelago and Desventuradas Islands). However, extensive morphological overlap among these forms has cast doubt on the validity of H. canopus, with some authors treating it as a synonym for H. helianthus. To clarify this ambiguity, we applied an integrative framework combining detailed morphometrics, phylogenetic inference from mitochondrial (COI) and nuclear (H3) markers, and two species delimitation approaches (bPTP and ASAP). Our sampling spanned Peru, continental Chile, and the oceanic islands of Juan Fernández and Desventuradas. Variation in ray number and relative arm length among H. helianthus, H. canopus, and H. polybrachius proved allometric, scaling strongly with body diameter rather than indicating discrete species boundaries. Molecular data show >95% sequence similarity across all nominal taxa and recover a single, well-supported clade; bPTP and ASAP likewise support one Heliaster lineage throughout the southeastern Pacific, corresponding to H. helianthus. Accordingly, we redescribe H. helianthus, designate a neotype from Quintay, Chile, and formally synonymize H. canopus and H. polybrachius under H. helianthus. Our results indicate that a single species spans the Eastern Pacific from Ecuador and Peru to central-southern Chile, including offshore islands, underscoring the value of integrative taxonomy for robust delimitation and accurate biodiversity assessments in marine invertebrates.

1. Introduction

The family Heliasteridae is represented by two genera: Heliaster Gray, 1840, which ranges from Baja California (Mexico) to central Chile, and Labidiaster Lütken, 1871, found from southern Chile to Antarctica [1]. Within Heliaster, seven nominal species have been described across the Eastern Pacific, largely distinguished by geographic distribution. These include H. kubiniji and H. microbrachius both described by Xatus, 1860 in the waters off Mexico; H. solaris A. H. Clark, 1920 and H. cumingi (Gray, 1840) in the Galapagos Islands; H. polybrachius H. L. Clark, 1907 and H. helianthus (Lamarck, 1816) along the coasts of Peru and Chile; and H. canopus (Valenciennes (MS) via Perrier 1875) restricted to the Juan Fernández Archipelago [2,3,4] (

Table 1. Morphological characteristics in species of the genus Heliaster and their geographical distribution according to different authors.

	No. of Rays	Percentage of Free Rays	Distribution
H. helianthus	30 or more	30% or more	Tropical, subtropical and temperate west coasts of South America	Mexico, Peru, Chile	West coast of South America	Paita, Callao, Caldera, Valparaiso.
H. canopus	28 or less	40–70%	Juan Fernandez Archipelago, Chile	Eastern Islands	Juan Fernandez Archipelago, Chile	Juan Fernandez Archipelago, Chile
H. cuminigi	30 or more	more than 20%	Galapagos Islands, Ecuador	Nicaragua	Galapagos Islands, Ecuador	Zorritos, Paita, Peru. Galapagos Islands, Ecuador
H. solaris	28 or less	50–70%	Galapagos Islands, Ecuador	Costa Rica	Galapagos Islands, Ecuador	Galapagos Islands, Ecuador
H. polybrachius	30 or more	more than 20%	Tropical coast of Peru	Mexico, Ecuador, Peru	West coast of tropical South America	-
H. microbrachius	30 or more	30% or less	West coast of Mexico and Central America	Mexico, Panama, Peru	West coast of Mexico and Central America	Margarita Bay, La Paz, Cape San Lucas, Mazatlan, Acapulco, Hawaiian Islands.
References	[3]	[3]	[4]	[7]	[3]	[2]

). However, the validity of several Heliaster species has long been debated. Early researchers noted that key diagnostic features, primarily the number of rays (arms) and overall body size, exhibited substantial variation and frequent overlap among the described forms. In fact, Clark [3] observed continuous gradation in ray count and body diameter rather than clear-cut differences. In addition, modern studies have confirmed that ray number increases with body size (allometry) rather than indicating discrete species [5]. This allometric correlation undermines the taxonomic value of ray count and size alone. Notably, H. canopus, the smaller form endemic to the Juan Fernández Archipelago and Desventurada Islands, was suspected even over a century ago to represent juvenile or small-bodied individuals of H. helianthus rather than a distinct species [6]. Diagnostic features such as ray count and the percentage of arm length free from the central disc (“free arms”) also vary continuously with body size [3]. This variability has led to inconsistent use of morphological thresholds across studies, with overlapping values for key traits (Table 1). Consequently, conflicting geographic assignments have been proposed for several forms, further complicating species boundaries and distributional records [2,3,4].

Taxonomic challenges in Heliaster stem largely from the brevity and vagueness of the original species descriptions. Asterias helianthus, the name initially assigned by Lamarck [8] to what is now H. helianthus, was described in only a few lines: “Sea star with a rounded disc and numerous radiating arms; the ventral surface is concave. The aboral surface is papillose and echinate, bearing small spines and papillae arranged in series. Dorsal spines are short and scattered” (translated from Latin). Additional details, translated from the original French, characterize the species as “one of the most peculiar and curious Asterias; it is orbicular, convex above, concave below, and divided in its circumference into thirty to thirty-six narrow rays, close together, arched, sometimes a little curled, and covered with small papillae arranged in longitudinal rows. Its width is 14 to 16 cm”. These concise and qualitative descriptions offer insufficient diagnostic resolution to reliably distinguish H. helianthus from other sympatric “sun star” species. Consequently, later naturalists often lumped or split specimens based on superficial resemblance to Lamarck’s type concept, perpetuating taxonomic ambiguity and frequent misidentifications within the genus. Perrier [6] explicitly questioned whether the “slight differences” used to delineate multiple Heliaster species were taxonomically meaningful. Given the pronounced morphological variability observed in Heliaster and their geographically restricted distribution, primarily the Galápagos, Juan Fernández/Desventuradas Islands, and the western coast of the Americas, Perrier speculated that these named forms might represent mere varieties of a single polymorphic species. His skepticism was particularly prescient in suggesting that Heliaster canopus could simply be a juvenile or small-bodied variant of H. helianthus, a hypothesis that aligns with modern findings and allometric interpretations of morphological variation in the genus.

The taxonomic ambiguity within Heliaster is particularly pronounced in Chile’s oceanic islands. Historical literature and museum records report the presence of both H. helianthus and H. canopus in the Juan Fernández Archipelago (JFA) and the Desventuradas Islands (DI) [9,10]. However, field surveys, both qualitative and quantitative, have consistently detected only H. canopus in the JFA [11,12]. Additionally, the Museo Nacional de Historia Natural de Chile (MNHNCL) catalogs include H. helianthus, H. canopus, and H. polybrachius from both island groups [10], underscoring persistent inconsistencies in species identifications within the genus.

Biogeographically, the JFA and DI form a single marine ecoregion characterized by exceptionally high levels of endemism [13]. Many marine species in these islands have evolved in isolation, resulting in some of the highest proportions of endemic fishes and invertebrates globally [14]. Nevertheless, recent molecular studies have revealed that several taxa, particularly among fish and mollusks, previously considered endemic to these islands, are genetically conspecific with their mainland counterparts [15,16]. Despite exhibiting morphological or coloration differences, DNA evidence indicates that these forms do not represent distinct species but rather belong to a broader continental lineage. This lack of genetic divergence may be explained by the relatively recent geological origin of islands. Santa Clara, the oldest island in the JFA, is approximately 5.8 My old, while the others are considerably younger [17]. Marine colonization likely occurred during the Pliocene-Pleistocene, a timeframe insufficient for lineages such as Heliaster to evolve reproductive isolation (e.g., [16]). Consequently, it is plausible that the insular form H. canopus has not been isolated long enough from the mainland H. helianthus to warrant recognition as a separate species. Emerging evidence from integrative taxonomic studies supports the hypothesis that Heliaster helianthus constitutes a single, widespread species distributed throughout the Eastern Pacific, from the coasts of Ecuador, Peru, and Chile to their oceanic islands. This study embraces that perspective and seeks to resolve the taxonomy of Heliaster by integrating morphological and genetic evidence, ultimately testing the validity of nominal species previously considered distinct.

The study aims to resolve the persistent taxonomic uncertainty surrounding nominal Heliaster species in the Southeastern Pacific, including the Juan Fernández Archipelago and the Desventuradas Islands, by applying, for the first time, an integrative approach that combines morphometric analyses, phylogenetic inference (COI and H3 markers), and molecular species delimitation techniques.

2. Materials and Methods

2.1. Sampling

A total of 53 sea stars belonging to the genus Heliaster were collected from the Pacific Ocean between 2009 and 2025, encompassing sites along the coasts of Chile and Peru, as well as Robinson Crusoe Island (JFA) and San Ambrosio Island (DI) (see Figure 1 and

Table A1. Specimens collected in this study including sampling year, locality and coordinates. *: Neotype.

Species	Code	Locality	Collection	Latitude	Longitude	COI	H3
Heliaster polybrachius	HPPP01	Pucusana, Perú	2013	−12.4799	−76.8009	PX112071	PX136096
Heliaster canopus	HCID01	San ambrosio Island	2018	−26.3380	−79.8732	PX112064	PX136089
Heliaster canopus	HCJF01	Robinson Crusoe Island	2009	−33.6213	−78.8453
Heliaster canopus	HCJF02	Robinson Crusoe Island	2009	−33.6361	−78.8301	PX112065	PX136090
Heliaster canopus	HCJF04	Robinson Crusoe Island	2009	−33.6420	−78.8247	PX112066	PX136091
Heliaster canopus	HCJF05	Robinson Crusoe Island	2009	−33.6420	−78.8247	PX112067	PX136092
Heliaster canopus	HCJF07	Robinson Crusoe Island	2009	−33.6213	−78.8453
Heliaster canopus	HCJF08	Robinson Crusoe Island	2025	−33.6405	−78.8143
Heliaster canopus	HCJF09	Robinson Crusoe Island	2025	−33.6405	−78.8143
Heliaster canopus	HCJF10	Robinson Crusoe Island	2025	−33.6405	−78.8143
Heliaster canopus	HCJF11	Robinson Crusoe Island	2025	−33.6405	−78.8143
Heliaster canopus	HCJF12	Robinson Crusoe Island	2025	−33.6405	−78.8143
Heliaster canopus	HCJF13	Robinson Crusoe Island	2025	−33.6361	−78.8301
Heliaster canopus	HCJF14	Robinson Crusoe Island	2025	−33.6420	−78.8247
Heliaster canopus	HCJF15	Robinson Crusoe Island	2025	−33.6420	−78.8247
Heliaster helianthus	HHLP01	Lobitos, Perú	2014	−4.4526	−81.2891	PX112069	PX136094
Heliaster helianthus	HHLP02	Lobitos, Perú	2014	−4.4526	−81.2891	PX112070	PX136095
Heliaster helianthus	HHTI08	Tres Islas, Iquique	2014	−20.3149	−70.1383	PX112073	PX136098
Heliaster helianthus	HHTI20	Tres Islas, Iquique	2014	−20.3149	−70.1383	PX112074	PX136099
Heliaster helianthus	HHLM01	Los Molles, Chile	2025	−32.2398	−71.5111
Heliaster helianthus	HHQT04	Quintay, Chile	2018	−33.1911	−71.7025	PX112072	PX136097
Heliaster helianthus	MNHNCL EQUI-17521 *	Quintay, Chile	2022	−33.1828	−71.6856
Heliaster helianthus	HHAL01	Algarrobo, Chile	2023	−33.3580	−71.6644
Heliaster helianthus	HHET01	El Caleuche, El Tabo	2019	−33.4567	−71.6716	PX112068	PX136093
Heliaster helianthus	HHET02	El Caleuche, El Tabo	2025	−33.4567	−71.6716
Heliaster helianthus	HHET03	El Caleuche, El Tabo	2025	−33.4567	−71.6716
Heliaster helianthus	HHET04	El Caleuche, El Tabo	2025	−33.4567	−71.6716
Heliaster helianthus	HHET05	El Caleuche, El Tabo	2025	−33.4567	−71.6716
Heliaster helianthus	HHET06	El Caleuche, El Tabo	2025	−33.4567	−71.6716
Heliaster helianthus	HHET07	El Caleuche, El Tabo	2025	−33.4567	−71.6716
Heliaster helianthus	HHET08	El Caleuche, El Tabo	2025	−33.4567	−71.6716
Heliaster helianthus	HHET09	El Caleuche, El Tabo	2025	−33.4567	−71.6716
Heliaster helianthus	HHET10	El Caleuche, El Tabo	2025	−33.4567	−71.6716
Heliaster helianthus	HHET11	El Caleuche, El Tabo	2025	−33.4567	−71.6716
Heliaster helianthus	HHET12	El Caleuche, El Tabo	2025	−33.4567	−71.6716
Heliaster helianthus	HHET13	El Caleuche, El Tabo	2025	−33.4567	−71.6716
Heliaster helianthus	HHET14	El Caleuche, El Tabo	2025	−33.4567	−71.6716
Heliaster helianthus	HHET15	El Caleuche, El Tabo	2025	−33.4567	−71.6716
Heliaster helianthus	HHET16	El Caleuche, El Tabo	2025	−33.4567	−71.6716
Heliaster helianthus	HHET17	El Caleuche, El Tabo	2025	−33.4567	−71.6716
Heliaster helianthus	HHET18	El Caleuche, El Tabo	2025	−33.4567	−71.6716
Heliaster helianthus	HHET19	El Caleuche, El Tabo	2025	−33.4567	−71.6716
Heliaster helianthus	HHET20	El Caleuche, El Tabo	2025	−33.4567	−71.6716
Heliaster helianthus	HHET21	El Caleuche, El Tabo	2025	−33.4567	−71.6716
Heliaster helianthus	HHET22	El Caleuche, El Tabo	2025	−33.4567	−71.6716
Heliaster helianthus	HHET23	El Caleuche, El Tabo	2025	−33.4567	−71.6716
Heliaster helianthus	HHET24	El Caleuche, El Tabo	2025	−33.4567	−71.6716
Heliaster helianthus	HHET25	El Caleuche, El Tabo	2025	−33.4567	−71.6716
Heliaster helianthus	HHET26	El Caleuche, El Tabo	2025	−33.4567	−71.6716
Heliaster helianthus	HHET27	El Caleuche, El Tabo	2025	−33.4567	−71.6716
Heliaster helianthus	HHLC01	Las Cruces, Chile	2025	−33.5005	−71.6351
Heliaster helianthus	HHLC02	Las Cruces, Chile	2025	−33.5005	−71.6351
Heliaster helianthus	HHLB01	La Boca, Chile	2025	−33.9197	−71.8492
Stichaster striatus	SSME 01	Mejillones	2013	−23.0988	−70.4601	PX112084	PX136109
Granaster nutrix	GNBF01	Bahía Fildes, Antártica	2022	−62.1995	−58.9592
Granaster nutrix	GNBF02	Bahía Fildes, Antártica	2022	−62.1995	−58.9592
Odontaster validus	OVES01	Escudero, Antártica	2022	−62.1995	−58.9592	PX112075	PX136100
Odontaster validus	OVES02	Escudero, Antártica	2022	−62.1995	−58.9592	PX112076	PX136101
Patiria chilensis	PHB01	Desembocadura, Biobio	2020	−36.8125	−73.1749	PX112082	PX136107
Patiria chilensis	PHQT01	Quintay	2018	−33.1911	−71.7025	PX112083	PX136108
Parvulastra calcarata	PCJF01	Robinson Crusoe Island	2009	−33.6361	−78.8301	PX112077	PX136102
Parvulastra calcarata	PCJF04	Robinson Crusoe Island	2009	−33.6361	−78.8301	PX112078	PX136103
Parvulastra calcarata	PCJF06	Robinson Crusoe Island	2009	−33.6361	−78.8301	PX112079	PX136104
Parvulastra calcarata	PCJFS1	Robinson Crusoe Island	2019	−33.6308	−78.8797	PX112080	PX136105
Parvulastra calcarata	PCJFS2	Robinson Crusoe Island	2019	−33.6308	−78.8797	PX112081	PX136106

). In addition to Heliaster, specimens of other sea star genera, Patiria, Parvulastra, Stichaster, Odontaster, and Granaster, were collected from Antarctica, continental Chile, and the JFA (see Table A1). All specimens were preserved in 95% ethyl alcohol for subsequent morphological and genetic analysis in the laboratory (Table A1 and

Table A2. Morphological measurement of field-collected Heliaster species. *: Neotype.

Code	Species	N° of Rays	R (mm)	r (mm)	Free Rays (%)	Maximum Diameter (mm)
HHPP01	H. polybrachius	30	37.27	29.45	20.98	88.48
HCID01	H. canopus	14	32.00	14.70	54.06	56.70
HCJF01	H. canopus	27	36.95	21.92	40.68	74.84
HCJF02	H. canopus	25	44.46	25.27	43.16	85.27
HCJF08	H. canopus	23	45.13	17.25	61.78	78.02
HCJF09	H. canopus	24	37.69	19.36	48.63	65.01
HCJF10	H. canopus	25	38.06	21.96	42.30	75.18
HCJF11	H. canopus	24	30.33	11.45	62.25	59.30
HCJF12	H. canopus	24	42.39	24.69	41.76	82.48
HCJF13	H. canopus	24	51.36	26.26	48.87	95.86
HCJF14	H. canopus	26	67.16	40.09	40.31	128.95
HCJF15	H. canopus	23	36.74	19.04	48.18	71.26
HHME01	H. helianthus	17	17.41	5.48	68.52	33.68
MNHNCL EQUI-17521 *	H. helianthus	33	91.72	61.54	32.90	170.93
HHLM01	H. helianthus	35	92.82	64.84	30.14	206.75
HHAL01	H. helianthus	48	107.93	75.08	30.44	213.56
HHET02	H. helianthus	31	39.15	23.05	41.12	84.70
HHET03	H. helianthus	36	69.90	44.05	36.98	134.10
HHET04	H. helianthus	37	82.45	55.05	33.23	156.20
HHET05	H. helianthus	31	61.00	43.00	29.51	126.00
HHET06	H. helianthus	37	82.00	58.00	29.27	172.01
HHET07	H. helianthus	34	71.00	46.00	35.21	145.10
HHET08	H. helianthus	31	67	42.00	37.31	133.00
HHET09	H. helianthus	35	145.00	89.00	38.62	275.00
HHET10	H. helianthus	36	94.00	59.00	37.23	185.00
HHET11	H. helianthus	37	147.00	93.00	36.73	282.00
HHET12	H. helianthus	37	113.00	68.00	39.82	252.10
HHET13	H. helianthus	39	85.00	59.00	30.59	173.20
HHET14	H. helianthus	42	101.00	63.00	37.62	204.00
HHET15	H. helianthus	35	106.00	65.00	38.68	219.00
HHET16	H. helianthus	39	106.00	68.00	35.85	224.10
HHET17	H. helianthus	40	91.00	58.00	36.26	185.20
HHET18	H. helianthus	36	81.00	52.00	35.80	178.10
HHET19	H. helianthus	37	92.00	67.00	27.17	213.00
HHET20	H. helianthus	36	81.00	53.00	34.57	159.10
HHET21	H. helianthus	40	94.00	63.00	32.98	194.10
HHET22	H. helianthus	36	116.00	72.00	37.93	253.00
HHET23	H. helianthus	37	114.00	70.00	38.60	224.20
HHET24	H. helianthus	35	105.00	68.00	35.24	202.00
HHET25	H. helianthus	35	107.00	75.00	29.91	204.00
HHET26	H. helianthus	39	104.00	72.00	30.77	198.00
HHET27	H. helianthus	37	113.00	73.00	35.40	224.00
HHLC01	H. helianthus	24	26.60	9.7.00	63.53	49.66
HHLC02	H. helianthus	33	55.60	33.4.00	39.93	100.50
HHLB01	H. helianthus	30	35.05	18.05	48.50	63.20

).

2.2. Material Examined

In the present study, 11 individuals of H. canopus were collected: one from San Ambrosio Island (SCBUCN–7749) and ten from the Juan Fernández Archipelago (Chile). Additionally, four specimens of H. helianthus were collected from continental Chile, and one specimen of H. polybrachius was obtained from Pucusana (Peru) (Table A1). Complementing this field collection, 110 Heliaster specimens housed in the invertebrate collection of the National Museum of Natural History of Chile (MNHNCL) were examined and measured (

Table A3. Morphological measurement of Heliaster species from MNHNCL specimens, collected in Chile.

Code	Species	Locality	Latitude	Longitude	N° of Rays	R (mm)	r (mm)	Free Rays (%)	Max. Diameter (mm)
MNHNCL-EQUI-15416	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	24	85	41	51.76	158
MNHNCL-EQUI-15416	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	26	83	39	53.01	168
MNHNCL-EQUI-15416	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	26	77	48	37.66	158
MNHNCL-EQUI-15416	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	23	33	21	36.36	70
MNHNCL-EQUI-15416	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	27	71	40	43.66	136
MNHNCL-EQUI-15416	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	25	82	45	45.12	175
MNHNCL-EQUI-15416	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	26	82	52	36.59	165
MNHNCL-EQUI-15416	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	26	81	51	37.04	152
MNHNCL-EQUI-15416	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	25	60	34	43.33	125
MNHNCL-EQUI-15416	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	26	96	54	43.75	187
MNHNCL-EQUI-15416	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	25	62	38	38.71	115
MNHNCL-EQUI-15416	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	27	65	41	36.92	142
MNHNCL-EQUI-15416	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	23	47	25	46.81	100
MNHNCL-EQUI-15416	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	27	73	40	45.21	129
MNHNCL-EQUI-15416	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	28	53	33	37.74	108
MNHNCL-EQUI-15416	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	25	64	36	43.75	124
MNHNCL-EQUI-15407	H. canopus	Santa Clara Island	−33.7066	−78.9393	22	49	29	40.82	100
MNHNCL-EQUI-15407	H. canopus	Santa Clara Island	−33.7066	−78.9393	25	68	37	45.59	132
MNHNCL-EQUI-15407	H. canopus	Santa Clara Island	−33.7066	−78.9393	25	82	43	47.56	165
MNHNCL-EQUI-15415	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	24	58	31	46.55	116
MNHNCL-EQUI-15415	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	24	54	31	42.59	115
MNHNCL-EQUI-15415	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	27	69	41	40.58	135
MNHNCL-EQUI-15415	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	23	58	32	44.83	117
MNHNCL-EQUI-15406	H. canopus	Santa Clara Island	−33.7066	−78.9393	25	46	21	54.35	94
MNHNCL-EQUI-15406	H. canopus	Santa Clara Island	−33.7066	−78.9393	25	55	28	49.09	108
MNHNCL-EQUI-15406	H. canopus	Santa Clara Island	−33.7066	−78.9393	25	50	23	54.00	104
MNHNCL-EQUI-15406	H. canopus	Santa Clara Island	−33.7066	−78.9393	25	46	26	43.48	111
MNHNCL-EQUI-15406	H. canopus	Santa Clara Island	−33.7066	−78.9393	23	62	33	46.77	125
MNHNCL-EQUI-15372	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	23	34	17	50.00	71
MNHNCL-EQUI-15372	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	22	47	30	36.17	93
MNHNCL-EQUI-15408	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	27	69	41	40.58	149
MNHNCL-EQUI-15408	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	25	65	40	38.46	126
MNHNCL-EQUI-15408	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	25	48	28	41.67	89
MNHNCL-EQUI-15408	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	25	68	38	44.12	132
MNHNCL-EQUI-15405	H. canopus	Santa Clara Island	−33.7066	−78.9393	34	53	33	37.74	105
MNHNCL-EQUI-15405	H. canopus	Santa Clara Island	−33.7066	−78.9393	30	45	23	48.89	83
MNHNCL-EQUI-15405	H. canopus	Santa Clara Island	−33.7066	−78.9393	35	55	38	30.91	108
MNHNCL-EQUI-15405	H. canopus	Santa Clara Island	−33.7066	−78.9393	39	51	39	23.53	104
MNHNCL-EQUI-15405	H. canopus	Santa Clara Island	−33.7066	−78.9393	31	50	33	34.00	99
MNHNCL-EQUI-15405	H. canopus	Santa Clara Island	−33.7066	−78.9393	33	49	33	32.65	94
MNHNCL-EQUI-15940	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	23	41	22	46.34	92
MNHNCL-EQUI-15940	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	22	33	18	45.45	73
MNHNCL-EQUI-15611	H. canopus	Alejandro Selkirk Island	−33.7000	−79.0000	21	36	18	50.00	72
MNHNCL-EQUI-15611	H. canopus	Alejandro Selkirk Island	−33.7000	−79.0000	21	33	19	42.42	69
MNHNCL-EQUI-15611	H. canopus	Alejandro Selkirk Island	−33.7000	−79.0000	24	36	21	41.67	69
MNHNCL-EQUI-15611	H. canopus	Alejandro Selkirk Island	−33.7000	−79.0000	23	37	20	45.95	74
MNHNCL-EQUI-15675	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	24	77	44	42.86	152
MNHNCL-EQUI-15675	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	25	59	36	38.98	121
MNHNCL-EQUI-15675	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	27	62	35	43.55	127
MNHNCL-EQUI-15222	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	24	42	27	35.71	82
MNHNCL-EQUI-15222	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	20	40	21	47.50	81
MNHNCL-EQUI-15222	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	25	46	29	36.96	79
MNHNCL-EQUI-15222	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	25	37	23	37.84	74
MNHNCL-EQUI-15222	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	27	35	19	45.71	71
MNHNCL-EQUI-15260	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	24	37	21	43.24	73
MNHNCL-EQUI-15260	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	26	74	42	43.24	141
MNHNCL-EQUI-15260	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	24	67	35	47.76	129
MNHNCL-EQUI-15590	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	22	71	42	40.85	131
MNHNCL-EQUI-15590	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	26	56	34	39.29	117
MNHNCL-EQUI-15590	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	25	39	24	38.46	73
MNHNCL-EQUI-15590	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	25	34	21	38.24	72
MNHNCL-EQUI-15590	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	25	41	29	29.27	88
MNHNCL-EQUI-15248	H. canopus	San Ambrosio Island	−26.3439	−79.8714	23	23	11	52.17	45
MNHNCL-EQUI-15409	H. canopus	Robinson Crusoe Island	−33.6167	−78.8667	23	35	16	54.29	78
MNHNCL-EQUI-15410	H. canopus	Santa Clara Island	−33.7066	−78.9393	26	57	33	42.11	126
MNHNCL-EQUI-15612	H. canopus	San Ambrosio Island	−26.3439	−79.8714	24	31	22	29.03	63
MNHNCL-EQUI-15748	H. canopus	Juan Fernandez Archipelago	−33.6167	−78.8667	24	39	22	43.59	78
MNHNCL-EQUI-15910	H. canopus	Alejandro Selkirk Island	−33.7000	−79.0000	21	25	9	64.00	55
MNHNCL-EQUI-15936	H. canopus	Alejandro Selkirk Island	−33.7000	−79.0000	23	30	19	36.67	64
MNHNCL-EQUI-15116	H. helianthus	ND	ND	ND	36	90	54	40.00	155
MNHNCL-EQUI-15116	H. helianthus	ND	ND	ND	34	84	61	27.38	168
MNHNCL-EQUI-15188	H. helianthus	Iquique	−21.0906	−70.1356	35	70	51	27.14	138
MNHNCL-EQUI-15188	H. helianthus	Iquique	−21.0906	−70.1356	33	55	31	43.64	112
MNHNCL-EQUI-15379	H. helianthus	Las Cruces	−33.5012	−71.6362	38	88	65	26.14	179
MNHNCL-EQUI-15379	H. helianthus	Las Cruces	−33.5012	−71.6362	37	99	74	25.25	190
MNHNCL-EQUI-15109	H. helianthus	Cobija, Tocopilla	−22.5500	−70.2667	32	102	64	37.25	205
MNHNCL-EQUI-15109	H. helianthus	Cobija, Tocopilla	−22.5500	−70.2667	34	108	67	37.96	212
MNHNCL-EQUI-15106	H. helianthus	Los Vilos, Coquimbo	−31.9090	−71.5175	38	74	57	22.97	152
MNHNCL-EQUI-15106	H. helianthus	Los Vilos, Coquimbo	−31.9090	−71.5175	34	95	64	32.63	191
MNHNCL-EQUI-15108	H. helianthus	Cobija, Tocopilla	−22.5500	−70.2667	26	36	23	36.11	69
MNHNCL-EQUI-15108	H. helianthus	Cobija, Tocopilla	−22.5500	−70.2667	27	39	28	28.21	80
MNHNCL-EQUI-15679	H. helianthus	Iquique	−20.4764	−70.1864	25	29	19	34.48	56
MNHNCL-EQUI-15679	H. helianthus	Iquique	−20.4764	−70.1864	25	23	12	47.83	49
MNHNCL-EQUI-15218	H. helianthus	Santa Clara Island	−33.7066	−78.9393	24	42	25	40.48	85
MNHNCL-EQUI-15218	H. helianthus	Santa Clara Island	−33.7066	−78.9393	25	43	23	46.51	87
MNHNCL-EQUI-15218	H. helianthus	Santa Clara Island	−33.7066	−78.9393	24	73	37	49.32	156
MNHNCL-EQUI-15239	H. helianthus	Alejandro Selkirk Island	−33.7000	−79.0000	24	37	22	40.54	75
MNHNCL-EQUI-15739	H. helianthus	Las Cruces	−33.5012	−71.6362	26	31	19	38.71	64
MNHNCL-EQUI-15021	H. helianthus	El Tabo	−33.4500	−71.6333	23	25	17	32.00	46
MNHNCL-EQUI-15096	H. helianthus	Iquique	−20.2194	−70.1719	34	42	29	30.95	79
MNHNCL-EQUI-15103	H. helianthus	Los Vilos, Coquimbo	−31.9090	−71.5175	36	98	63	35.71	198
MNHNCL-EQUI-15104	H. helianthus	Los Vilos, Coquimbo	−31.9090	−71.5175	37	67	48	28.36	131
MNHNCL-EQUI-15105	H. helianthus	Los Vilos, Coquimbo	−31.9090	−71.5175	38	88	61	30.68	171
MNHNCL-EQUI-15107	H. helianthus	Los Vilos, Coquimbo	−31.9090	−71.5175	33	98	69	29.59	195
MNHNCL-EQUI-15119	H. helianthus	Quintero	−32.7667	−71.5333	36	81	63	22.22	162
MNHNCL-EQUI-15120	H. helianthus	Quintero	−32.7667	−71.5333	36	113	79	30.09	226
MNHNCL-EQUI-15121	H. helianthus	Quintero	−32.7667	−71.5333	37	65	49	24.62	129
MNHNCL-EQUI-15122	H. helianthus	ND	ND	ND	43	137	104	24.09	274
MNHNCL-EQUI-15176	H. helianthus	ND	ND	ND	38	58	43	25.86	118
MNHNCL-EQUI-15188	H. helianthus	Iquique	−21.0906	−70.1356	36	71	44	38.03	140
MNHNCL-EQUI-15278	H. helianthus	El Tabo	−33.4500	−71.6333	18	16	10	37.50	36
MNHNCL-EQUI-15374	H. helianthus	Quintero	−32.7667	−71.5333	32	70	44	37.14	141
MNHNCL-EQUI-15594	H. helianthus	Isla Negra	−33.4380	−71.6917	18	17	9	47.06	35
MNHNCL-EQUI-15371	H. polybrachius	Robinson Crusoe Island	−33.6167	−78.8667	22	42	25	40.48	83
MNHNCL-EQUI-15371	H. polybrachius	Robinson Crusoe Island	−33.6167	−78.8667	24	30	19	36.67	61
MNHNCL-EQUI-15368	H. polybrachius	San Ambrosio Island	−26.3439	−79.8714	20	27	15	44.44	49
MNHNCL-EQUI-15368	H. polybrachius	San Ambrosio Island	−26.3439	−79.8714	22	27	14	48.15	65
MNHNCL-EQUI-15370	H. polybrachius	Robinson Crusoe Island	−33.6167	−78.8667	19	31	17	45.16	64
MNHNCL-EQUI-15373	H. polybrachius	Robinson Crusoe Island	−33.6167	−78.8667	26	34	19	44.12	71
MNHNCL-EQUI-15399	H. polybrachius	Alejandro Selkirk Island	−33.7000	−79.0000	24	37	21	43.24	75

).

Given the loss of Lamarck’s original Asterias helianthus type specimens, we designate an adult specimen from Quintay, Chile (33°10′58″ S, 71°41′06″ W) as the neotype of Heliaster helianthus. This specimen has been formally deposited in the Museo Nacional de Historia Natural de Chile (MNHNCL EQUI-17521).

2.3. Comparative Material Examined

We examined seven specimens from the invertebrate collection of the Musée National D’Histoire Naturelle de France (MNHN), including: Heliaster canopus (See Figure 2c,d), type material: two syntypes from the Juan Fernández Archipelago (Collection Hombron & Jacquinot 1841; MNHN-IE-2014-424-01 & MNH-IE-2014-424-02); Heliaster canopus: Chile, Collection Cotteau G. 1894 (MNH-IE-2017-1389); Heliaster helianthus (See Figure 2a,b): Caldera (Chile), Collection envoi de M. Agassiz 1864 (MNH-IE-2017-669); Heliaster cuminingi: Peru (MNH-IE-2017-1831); Heliaster kubiniji: Acapulco (Mexico), Collection envoi de M. Agassiz 1864 (MNH-IE-2017-1350); Heliaster microbrachius: California (EEUU) (MNH-IE-2017-665). It was also examined six specimens from the invertebrate zoology collection of the National Museum of the American Latino, Smithsonian Institution: Heliaster canopus: Juan Fernández Archipelago (Chile), collected by Dr. Waldo L. Schmitt 1926 (USNM-E3771); Heliaster helianthus: Salaverry (Peru), collected by Dr. Waldo L. Schmitt 1926 (USNM-E3554); Heliaster kubiniji: USNM-EO32619; Heliaster microbrachius: Collected by Dr. Waldo L. Schmitt 1926 (USNM-EO32624); Heliaster microbrachius: Baja California (Mexico), collected by the United States Fish Commission in 1911 (USNM-2017); Heliaster microbrachius (holotype): San Jose Island (Panama), collected by A. Wetmore & J. P. Morrison 1944 (USNM-E3554) (

Table A4. Morphological measurement of Heliaster species from museum specimens.

Code	Species	Locality	N° of Rays	R (mm)	r (mm)	Free Rays (%)	Diameter (mm)
USNM-E03771	H. canopus	Juan Fernandez Is., Chile	24	46.15	24.82	46.22	84.92
USNME-3554	H. helianthus	Salaverry, Peru	29	35.06	24.16	31.09	74.03
USNME-032619	H. kubiniji		18	68.57	58.30	14.98	128.57
USNM-2017	H. microbrachius	Baja California, Mexico	36	96.00	70.00	27.08	174.00
USNM-E02624	H. microbrachius		42	68.30	55.00	19.47	140.00
USNME-6767	H. microbrachius	Perlas Archipelago, Panama	24	65.45	46.06	29.63	139.39
MNHN-IE-2014-424-01	H. canopus	Juan Fernandez Is., Chile	23	35.14	20.27	42.32	70.95
MNHN-IE-2014-424-02	H. canopus	Juan Fernandez Is., Chile	24	38.44	19.01	50.55	78.17
MNHN-IE-2017-1389	H. canopus	Chile	24	36.15	20.00	44.67	70.00
MNHN-IE-2017-669	H. helianthus	Caldera, Chile	33	56.25	40.00	28.89	117.50
MNHN-IE-2017-1831	H. cuminingi	Perú	42	49.09	39.09	20.37	89.09
MNHN-IE-2017-1350	H. kubiniji	Acapulco, Mexico	24	68.57	31.43	54.16	135.71
MNHN-IE-2017-665	H. microbrachius	California, EEUU	33	50.00	37.70	24.60	101.10

).

2.4. Morphological Measurements

For each specimen, whether collected in the field or sourced from a museum collection, we recorded the total number of rays and measured the length of each ray in millimeters. We calculated the major radius (R), defined as the distance from the center of the oral disc to the tip of the longest ray, and the minor radius (r), defined as the distance from the disc center to its outer edge, and the percentage of free ray was calculated as (R − r/R) × 100. The maximum body diameter (mm) was recorded for each individual and used as a proxy for body size (Table A2 and Table A3).

2.5. Molecular Protocol for Gene Amplification and Sequencing

DNA was extracted from the ambulacral feet of each specimen following the protocol described by Haye et al. [18], based on the saline extraction method of Aljanabi and Martinez [19]. DNA concentration and purity were measured with a spectrometer (Nanodrop Lite), and DNA quality was verified by electrophoresis on a 1.5% agarose gel.

Partial sequences of the mitochondrial Cytochrome Oxidase I (COI) and nuclear Histone 3 (H3) genes were amplified using echinoderm-specific primers (COI: [20], H3: [21]). Polymerase Chain Reaction (PCR) mixture included 1.5 mM MgCl₂, 1× reaction Buffer (50 mM KCl, 10 mM Tris-HCl, pH 8.0), 0.22 mM dNTPs, 0.4 pmol/μL of each primer, 0.1 U/μL Taq DNA polymerase, and 3 ng/μL template DNA [18].

Thermal cycling conditions varied by region: COI: Initial denaturation at 94 °C for 10 min, followed by 35 cycles of denaturation at 94 °C for 1 min, annealing at 50 °C for 45 s, and extension at 72 °C for 1 min, with a final extension at 72 °C for 10 min. H3: Initial denaturation at 94 °C for 3 min, followed by 35 cycles at 94 °C for 30 s, annealing at 50 °C for 45 s, and extension at 72 °C for 1 min, with a final extension at 72 °C for 10 min. PCR products were sequenced bidirectionally by Macrogen Inc. (Seoul, Republic of Korea). Sequence editing and alignment were performed manually using ProSeq v.2.9 software [22].

2.6. Phylogenetic Analysis

Phylogenetic reconstructions were performed using Maximum likelihood (ML) and Bayesian inference (BI) approaches, based on a partitioned dataset comprising COI and H3 gene sequences, each assigned distinct substitution models. ML analyses were performed using the IQ-TREE online server [23], employing a hill-climbing Nearest Neighbor Interchange (NNI) search strategy [24]. Substitution models were selected using ModelFinder [25], incorporating codon-position partitioning. Node support was evaluated using 1000 ultrafast bootstrap replicates [26]. All trees were rooted with Ophiura robusta (Ayres, 1852) as the outgroup (

Table 2. List of species employed in the phylogeny and their corresponding Genbank accession numbers for the COI and H3 genes.

Species	COI	H3
Heliaster helianthus	JQ918254	JQ918206
Stichaster striatus	JX130053	EU707677
Odontaster validus	GQ294396	EU707663
Ophiura robusta	MG935300	KP113641

), based on its well-supported phylogenetic position as sister to Asteroidea [1].

Bayesian analyses were performed in MrBayes v.3.2 [27], using partition-specific models identified by ModelFinder (COI: GTR+G+I, H3: K2+G). Each Markov Chain Monte Carlo (MCMC) run consisted of four chains over ten million generations, with sampling performed every 1000 generations. Convergence and effective sample size (ESS) were assessed across independent runs using Tracer v.1.5 [28]. The initial 1000 trees from each run were discarded as burn-in, and a majority-rule consensus tree was constructed. The final topology was visualized and edited in FigTree v.1.4 [29].

2.7. Species Delimitation

Species boundaries within the genus Heliaster were assessed using two complementary approaches: (1) the Bayesian Poisson Tree model (bPTP, [30]), applied to the phylogenetic tree generated by IQ-TREE, and (2) the Assemble Species by Automatic Partitioning method (ASAP, [31]), based on JC69 genetic distance for both COI and H3 gene sequences.

3. Results

3.1. Taxonomic Account

Asteroidea de Blainville, 1830;

Forcipulatida Perrier, 1884;

Heliasteridae Viguier, 1879;

Heliaster Gray, 1840;

Heliaster helianthus (Lamarck, 1816).

Synonymized names

Asterias helianthus Lamarck, 1816;

Stellonia helianthus (Agassiz, 1835);

Asteracanthion helianthus (Müller & Troschel, 1842);

Heliaster canopus (Valensiennes (MS) in Perrier, 1875)—in this study

Heliaster polybrachius H.L. Clark, 1907—in this study.

Type locality: Unknown.

Type material: Lost.

3.2. New Diagnosis

Large disc (>150 mm). Adult specimens (>100 mm) with 22–48 rays. The percentage of free arms ranged from 22% to 54%. Abactinal plate ridges bearing 8–15 robust spinelets. Marginal plates are indistinguishable from actinal plates. Adambulacral plates with nine or ten spines, grading smaller distally. Three rows of spines along the dorsal surface of each ray.

3.3. Redescription

Large sea star with a maximum diameter of 274 mm; disc broad and relatively long, with robust rays. Larger specimens (>100 mm) with 22–48 rays. The percentage of free arms ranged from 22% to 54% in larger specimens. The designated neotype (R = 91.72 mm, r = 64.84 mm, percentage of free arm: 32.9%; Figure 3, Table A2) exhibits a densely spined abactinal surface (Figure 3a,b,e,f,i,j). Three prominent zigzag rows of white spines are aligned along each ray (Figure 3b,f,j). The madreporite is positioned closer to the anus than to the disc edge; small and oval-shaped, with irregularly radiating spinose ridges (Figure 3a,e,i). Each ray has numerous ambulacral furrows with large lateral white spines (Figure 3). Live specimens exhibit a striking black and white coloration with irregular maroon blotches and speckles abactinally. Spines and madreporite are yellowish to whitish (Figure 3a,e,i).

3.4. Distribution

Based on a synthesis of published literature, museum records, and newly collected specimens, the geographic distribution of Heliaster helianthus extends from Ecuador (2° S) to Concepción, Chile (37° S). Notably, the species exhibits a marked decline in frequency towards the southernmost extent of its range (Figure 4).

3.5. Habitat

This species inhabits the mid to high intertidal zone of rocky shores, favoring wave-exposed and semi-exposed environments [32], and extends into the shallow subtidal, typically at depths less than 10 m (Figure 5; [4]). Ontogenetic habitat shifts have been documented: juveniles are found in sheltered microhabitats such as boulder fields and crevices within the upper intertidal, whereas larger individuals tend to inhabit deeper areas subject to stronger wave action [32].

3.6. Neotype Designation and Type Locality

Heliaster helianthus (Lamarck, 1816) lacks original name-bearing type material, and the protologue does not specify a precise type locality. To stabilize the taxonomic identity of this species, in this study, we designate a neotype in accordance with Article 75.3 of the International Code of Zoological Nomenclature. Available online: https://www.iczn.org/the-code/the-code-online/ (accessed on 13 October 2025).

Neotype. MNHNCL EQUI-17521, collected at Quintay, Valparaíso Region, Chile (33°10′58″ S, 71°41′06″ W; Figure 6), and deposited in the Marine Invertebrate Zoology collection of the Museo Nacional de Historia Natural de Chile (MNHNCL). By this act, the type locality of H. helianthus is restricted to Quintay, Chile. This locality lies within the confirmed native range of the species based on historical and contemporary records.

Lamarck [8] diagnosis, rounded disc; numerous, narrow radiating arms (30–36); a concave oral surface; aboral surface with small papillae and spines arranged in rows, is consistent with the neotype, which exhibits a broad disc, 35 arms, a papillose and echinate aboral surface, and short dorsal spines arranged longitudinally (see Section 3.3). Its measurements and coloration fall within the observed variation of the species and match subsequent taxonomic accounts [3].

Compliance with ICZN Art. 75-3: Purpose and need (75.3.1): the neotype is designated to resolve long-standing taxonomic confusion and stabilize usage of Clark, 1907 H. helianthus in the southeastern Pacific. Diagnosis/definition (75.3.2): the taxon is defined by an explicit diagnosis and comparative morphology consistent with the protologue. Consistency with original material (75.3.3): the neotype conforms to the characters given by Lamarck (1816) and subsequent redescriptions. Loss/unavailability of original material (75.3.4): no original name-bearing type is extant or traceable. Type locality (75.3.5): the neotype originates as near as practicable to the historical range, with this designation, the type locality is fixed to Quintay, Chile. Clarification of status (75.3.6): the designation resolves competing usages arising from historical synonymy among nominal Heliaster taxa. Repository (75.3.7): the neotype is housed in a recognized, publicly accessible museum (MNHNCL), ensuring permanent preservation and availability for study. This neotype designation provides a definitive reference for the application of the name Heliaster helianthus, thereby stabilizing nomenclature and resolving confusion among nominal Southeastern Pacific Heliaster species.

3.7. Morphological Variability

Morphological variation among Heliaster species is associated with both specimen diameter and habitat. As shown in Figure 7, the number of rays, ray length (largest and smallest radius), and proportion of free arms are positively correlated with specimen diameter (Figure 7A–D). Additionally, these traits vary across sampling localities. Most individuals of H. canopus and H. polybrachius from JFA and DI exhibit fewer rays (<30) and a lower proportion of free arms (<40%) compared to H. helianthus from the continent (Figure 7A,D). These interspecific differences suggest that both developmental constraints and environmental factors may shape arm morphology and regenerative capacity across habitats.

3.8. Phylogeny and Species Delimitation

Bayesian inference based on concatenated COI and H3 sequences, including both GenBank records and newly generated sequences, yielded a consensus tree with high posterior probability across most nodes (PP = 0.85–1.0). The resulting topology was congruent with that obtained from ML analysis using IQ-TREE, which exhibited strong bootstrap support (BS = 75–100) throughout (Figure 8). Both approaches (ML and BI) recovered a well-supported monophyletic clade comprising H. canopus, H. polybrachius, and H. helianthus (BS = 95, PP = 1.0; Figure 8).

Species delimitation analyses (bPTP and ASAP) yielded broadly congruent partitions of the broader asteroidean dataset, recovering 6 and 8 candidate species overall, six of which were represented by multiple individuals (Figure 8). Specifically, bPTP method delimited seven entities with strong support (PP = 0.75–1.0), largely mirroring the groupings recovered by ASAP method (Figure 8). ASAP, based on JC69 genetic distances for COI and H3 separately, identified 6–7 species depending on the locus, with only minor discrepancies involving Granaster and Stichaster species (Figure 8). These counts refer to the intergeneric dataset, not to Heliaster per se. All methods grouped a single Southeastern Pacific Heliaster lineage corresponding to H. helianthus.

4. Discussion

This study supports the idea that several nominal multiarmed sea stars from the Southeastern Pacific are conspecific and represent a single taxonomic entity: Heliaster helianthus. Integrative evidence from morphology and phylogeny indicates that H. helianthus is the sole representative of the genus at these latitudes, with a distribution encompassing the coasts of Peru and Chile, as well as the Chilean Oceanic Islands, including the Juan Fernández Archipelago and the Desventuradas Islands.

4.1. Morphology

Traditional morphometric traits in asteroids often provide limited discriminatory power, underscoring the need for improved diagnoses. In our study, morphological features such as ray number and relative arm length scale strongly with overall body size (Figure 7), rendering them unreliable for distinguishing Heliaster species in the Southeastern Pacific. The positive association between ray number and diameter corroborates previous observations [3,5]. On this basis, Perrier [6] and Clark [4] proposed that H. canopus may represent a juvenile form of H. helianthus.

Our data are consistent with the hypothesis that H. helianthus from the Juan Fernández Archipelago (JFA) attains reproductive maturity at smaller sizes than conspecifics from continental Peru and Chile (mean diameters ~25 mm vs. ~35 mm). This pattern may reflect developmental plasticity and/or environmental differences (e.g., resource regimens, temperature, hydrodynamics) rather than species-level divergence, a phenomenon documented in other echinoderms and marine invertebrates inhabiting heterogeneous environments. This inference remains tentative and would benefit from direct evidence (e.g., gonad staging/histology, size at maturity curves) before being treated as a life-history generalization.

Among the variables analyzed, the rows of spines along the dorsal surface of each ray are the most important trait to differentiate Heliaster species. The percentage of free rays, interpreted in a geographic context, emerged as informative morphological trait. Nevertheless, it appears to capture within-species phenotypic structure rather than discrete species boundaries. Examination of type specimens (MNHN) and additional museum material (SM; MNHNCL) confirmed substantial size-associated variation in this genus (Figure 7, Table A3), supporting the conclusion that several previously named forms are junior synonyms of H. helianthus.

Based on the morphological congruence between the neotype and Lamarck’s original (albeit brief) description, we treat H. canopus and H. polybrachius as junior synonyms of H. helianthus. Size differences between continental and insular populations are consistent with the “Island Rule” patterns in marine invertebrates [33], but we frame this as a working hypothesis, not as a taxonomic conclusion, pending targeted tests that integrate morphology, environment, and demography.

4.2. Species Delimitation and Phylogeny

All lines of evidence support the recognition of a single species encompassing the nominal Heliaster taxa from the Southeastern Pacific. Species delimitation analyses (bPTP and ASAP) and the phylogenetic results are fully consistent. Although the intergeneric Asteroidea dataset yields 6–8 candidate species overall, within Heliaster, all analyses converge on one cohesive lineage corresponding to H. helianthus.

In the phylogeny, Heliaster (family Heliasteridae) is recovered as sister to Stichasteridae Perrier, 1885, specifically to a clade comprising Granaster and Stichaster. This relationship is congruent with previous studies [1,34] and reinforces the close evolutionary affinity between Heliaster and Stichasteridae. Although Heliasteridae includes two genera (Heliaster and Labidiaster), our sampling targeted Heliaster only. Incorporating Labidiaster will be essential to fully resolve intrafamilial relationships. Notably, prior multilocus phylogenies (COI, 12S, 16S, 18S, 28S, and H3) consistently recover both genera within a well-supported monophyletic Heliasteridae [1,34].

The delimitation results indicated that H. canoups and H. polybrachius are junior synonyms of H. helianthus, echoing Clark [4] taxonomic conclusions. Because material was unavailable, we could not include H. cumingi/H. solaris (Galápagos Islands) or H. kubiniji/H. microbrachius (North Pacific). Future research should determine whether these names are conspecific with H. helianthus or represent distinct species, using an integrative framework that couples dense geographic sampling with morphology explicitly accounting for allometry and independent genetic markers. Clark [4] hypothesized that H. cumingi could be a synonym of H. helianthus, if corroborated, the range of H. helianthus would extend to the Galápagos Islands.

4.3. Distribution

Our study provides an updated overview of the geographical distribution of H. helianthus along the Southeastern Pacific. Based on original collections, museum specimens, and literature, we confirm its presence from Ecuador to South-Central Chile (Figure 4), including Chile’s oceanic Islands (Juan Fernández Archipelago and Desventuradas Islands).

The wide geographic range of H. helianthus is particularly notable given the limited dispersal potential typically associated with benthic echinoderms. Although larval development in Heliaster has not been described in full detail, Heliaster species are reported to possess planktotrophic larvae with a planktonic duration exceeding two to three months before metamorphosis [35]. Such durations could facilitate long-distance dispersal via the Humboldt Current System, a major oceanographic feature that flows northward along the Peru and Chile coasts and can connect with oceanic islands through mesoscale eddies and upwelling filaments [36].

Supporting this inference, Haye et al. [18] detected no significant population structure in H. helianthus along the Chilean coast, suggesting high gene flow and limited isolation by distance. The morphological variation observed between island and continental populations, especially in body size, is therefore best interpreted as local adaptation rather than evidence of cryptic speciation. Together, these lines of evidence indicate a single, highly connected species with near-continuous distribution (in line with Perrier’s hypothesis), despite substantial geographic distances and ecological gradients.

4.4. Biogeographic and Evolutionary Implications

The broad geographic distribution of H. helianthus across both continental margins and remote islands provides key insights into Southeastern Pacific biogeography. Its apparent lack of genetic structure [18], coupled with extended planktonic larval duration [35], strongly suggests high dispersal capacity and/or historical connectivity. This aligns with studies of other regional taxa [15,16] that infer colonization of oceanic islands such as JFA and DI during the Pliocene–Pleistocene, facilitated by transient oceanographic connections, suggesting that the isolation has been recent or intermittent.

From an evolutionary perspective, our results highlight that morphological differentiation in insular populations does not necessarily indicate speciation. The treatment of H. canopus and H. polybrachius as junior synonyms of H. helianthus illustrates a broader pattern: insular populations may retain phenotypic distinctions driven by environmental differences or growth allometry while remaining genetically and taxonomically conspecific. This cautions against inferring species limits from morphology alone and emphasizes the value of integrative approaches in marine taxonomy.

5. Conclusions

Our results show that the nominal multiarmed sea stars of the southeastern Pacific represent a single taxonomic entity: Heliaster helianthus. Concordant morphological and phylogenetic evidence indicate that H. helianthus is the only Heliaster inhabiting this region. We redescribe H. helianthus, designate a neotype from Quintay (Chile), and formally synonymize H. canopus and H. polybrachius under H. helianthus. Its broad distribution, from northern Peru to south-central Chile, including the Juan Fernandez Archipelago and the Desventuradas Islands, likely reflects a combination of high dispersal potential and historical connectivity. More broadly, this study underscores the value of integrative taxonomic approaches in avoiding taxonomic inflation and in clarifying the evolutionary and biogeographic dynamics of marine invertebrates.