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Open AccessFeature PaperReview

How Many Sipunculan Species Are Hiding in Our Oceans?

1
Department of Marine Biology, Texas A&M University at Galveston, Galveston, TX 77554, USA
2
Zoology Department, Institute of Biological Sciences, Federal University of Minas Gerais, Pampulha, Belo Horizonte, Minas Gerais 31270-901, Brazil
*
Author to whom correspondence should be addressed.
Academic Editor: Luc Legal
Diversity 2021, 13(2), 43; https://doi.org/10.3390/d13020043
Received: 30 December 2020 / Revised: 19 January 2021 / Accepted: 20 January 2021 / Published: 24 January 2021
(This article belongs to the Special Issue Systematics and Biodiversity of Annelids)
Sipuncula, long considered a separate phylum, are now commonly included in the Annelida based on phylogenomic analyses. The sipunculan body consists of an unsegmented trunk and a retractable introvert, usually with a set of tentacles at its anterior end. Unlike other annelids, they have no chaetae, but the introvert is often adorned with proteinaceous hooks that can be important taxonomic characters. Other external taxonomic characters include the tentacles (number, shape and arrangement), body papillae and, in some cases, hardened shields, as well as length ratios. Many species require dissection for correct identification to reveal internal characteristics, such as introvert retractor muscles, nephridia and contractile vessels. Here we summarize the state of the current knowledge of species diversity in sipunculans. We emphasize molecular studies, conducted over the past two decades, that have revealed multiple complexes of cryptic or pseudocryptic species. It has become obvious that diversity is significantly higher than the current taxonomic scheme accounts for, but formal species descriptions are lagging behind. Although the major branches in the sipunculan phylogeny have become increasingly consolidated, the internal relationships within most branches are still in flux. View Full-Text
Keywords: annelida; invertebrates; peanut worms; cryptic species; pseudocryptic; species complex annelida; invertebrates; peanut worms; cryptic species; pseudocryptic; species complex
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MDPI and ACS Style

Schulze, A.; Kawauchi, G.Y. How Many Sipunculan Species Are Hiding in Our Oceans? Diversity 2021, 13, 43. https://doi.org/10.3390/d13020043

AMA Style

Schulze A, Kawauchi GY. How Many Sipunculan Species Are Hiding in Our Oceans? Diversity. 2021; 13(2):43. https://doi.org/10.3390/d13020043

Chicago/Turabian Style

Schulze, Anja; Kawauchi, Gisele Y. 2021. "How Many Sipunculan Species Are Hiding in Our Oceans?" Diversity 13, no. 2: 43. https://doi.org/10.3390/d13020043

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