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Article

First Capture of the Deep-Sea Careproctus bathycoetus (Liparidae) a Century After the Fish Was Described (North Pacific)—Revised Diagnosis and Notes on Ecology

by
Natalia V. Chernova
1,* and
Ralf Thiel
2
1
Zoological Institute of the Russian Academy of Sciences, Universitetskaya nab. 1, 199034 Saint Petersburg, Russia
2
Independent Researcher, 23556 Lübeck, Germany
*
Author to whom correspondence should be addressed.
Taxonomy 2024, 4(4), 748-760; https://doi.org/10.3390/taxonomy4040040
Submission received: 1 September 2024 / Revised: 16 October 2024 / Accepted: 18 October 2024 / Published: 23 October 2024
Browse Figures
Review Reports Versions Notes

Abstract

The deep-sea snailfish Careproctus bathycoetus Gilbert et Burke, 1912 was described a century ago from a single specimen caught at a depth of 3292 m in the Kuril Basin (southern Sea of Okhotsk, western North Pacific). Until now, it was known from the holotype only. Therefore, the capture of another specimen is of great interest and provides new data on the morphology and ecology of the species. The second known specimen was collected by the international expedition “SohoBio” (2015) at a depth of 3305 m in the Kuril Basin near the type locality. This study provides a description of a rare fish, which allows us to improve the diagnosis of the species. Differences from other deep-sea snailfishes from the North Pacific Ocean are also given. At a depth of 3292–3305 m, the species lives in extreme conditions: complete darkness, temperature at about 1.9 °C, water pressure about 3300 ton/m2, low oxygen concentration, and low biomass of prey. Related Careproctus species can most likely be found in the abyssal depths of the neighboring Kuril–Kamchatka Trench.

1. Introduction

The liparid fish, Careproctus bathycoetus Gilbert et Burke, 1912, was described a century ago on the basis of a single specimen which was caught during the voyage of the research vessel “Albatross” in the southern Sea of Okhotsk at 1800 fathoms depth (=3292 m) [1]. This is probably why there have been no more catches of this species since then, although the Sea of Okhotsk is fairly well studied ichthyologically.
Careproctus bathycoetus is mentioned in numerous publications, most of which are faunistic lists and faunal reviews; some contain descriptions and/or drawings of the species, but all are from the only known specimen and reflect the data from the original description [2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21]. Informative data on this species represented a refinement of the holotype (Figure 1A,B) characters. Burke [22] provided a drawing of the teeth (Figure 1C), several body proportions and details of coloration in his classic revision of Liparidae. Stein [23] gave vertebral and fin-ray counts from a radiogram of the holotype, added a few measurements, and contributed with teeth drawing (Figure 1D) in comparative notes with other species. Finally, Sakurai and Shinohara [24] published a photograph of the holotype.
The aim of this study is to provide new information on a second known specimen of C. bathycoetus, caught during the joint Russian–German expedition SokhoBio (“Sea of Okhotsk Biodiversity Studies”). This expedition was conducted in the area of the Kuril Islands and the adjacent waters of the Sea of Okhotsk and the Pacific Ocean in July–August 2015 [25]. The study area included, in particular, the Kuril Basin in the southern Sea of Okhotsk, an isolated depression bounded by 3000 m isobaths with a maximum depth of 3374 m. The biological results in these poorly known waters are impressive. They are partly summarized in the special volume of the “Deep Sea Research Part II: Topical Studies in Oceanography” (2018, Vol. 154).
The ichthyologic materials of the SokhoBio expedition brought important results. A new species of eelpout Lycenchelys (Perciformes: Zoarcidae) from the deep sea off the Kuril Archipelago was described [26], and four new species of Careproctus (Cottoidei: Liparidae) were found in the Bussol Strait (the deepest in the Kuril Islands chain) and neighboring abyssal basins [27].

2. Materials and Methods

Gear. Fish were collected using an Agassiz trawl (AGT) with a frame of 350 × 70 cm and a mesh size of 10 mm. After deploying to the bottom and stopping the winch, trawling was carried out for 10 to 20 min at a vessel speed of 1 knot. Full data on the expedition work are available [25].
Environmental conditions. Water temperature and salinity measured by CTD at 10 stations during the cruise were stable between 1.9 to 2.1 °C (mean 1.91 °C) and 34.5 to 34.6 (34.59) PSU.
Preservation. Fish were removed from the trawl, immediately placed in chilled sea water, and photographed while they were fresh. They were then fixed in 4% formaldehyde solution and transferred to 70% ethanol at the laboratory about one month later.
Methods of fish study. We used traditional methods to study liparids [27,28]. Descriptions and measurements were carried out on a fixed specimen.
Ray numbers in vertical fins and vertebrae were counted from radiograph. The vertebral number includes the urostyle. The pectoral girdle was not extracted for study to avoid damaging this rare specimen.
For the cephalic pores of the sensory system, we gave Burke’s [22] pore formula, traditionally used in snailfish descriptions, which contains the number of pores according to their topography. For example, the pattern 2–6–7–1 includes the number of pores on the snout (nasal), around the eye (infraorbital + first temporal), on the lower jaw and praeoperculum, and that above the gill opening (suprabranchial pore).
Abbreviations: vertebrae (vert), dorsal (D), anal (A), pectoral (P), and caudal (C) fin rays; total (TL) and standard (SL) length, head length (HL).
Museums: National Museum of Natural History, Washington, DC, USA (USNM); Zoological Museum of Hamburg University (ZMH), at present belonging to Leibniz Institute for the Analysis of Biodiversity Change, Museum of Nature, Hamburg, Germany (LIB).

3. Results

3.1. Identification

The specimen (Figure 2) was identified as belonging to Careproctus Krøyer, 1862 [29] on the basis of diagnostic characters: nostrils in one (not two) pair; pelvic disc present (not reduced, although small); pectoral fins with fewer rays than the anal fin; absence of additional pores on the top of the head (coronal, supratemporal); body color uniform (not variegated) [13,22,28].
Compared to most of Careproctus species, the specimen has a small disc (5.7% SL or 26.6% HL) (Table 1). The reduced disc is one characteristic for the genera Elassodiscus Gilbert et Burke, 1912 [30] and Osteodiscus Stein, 1978 [23]. In the western North Pacific, two deep-water Elassodiscus species have been recorded at depths up to 1800 m. Elassodiscus tremebundus Gilbert et Burke, 1912 is known in the Sea of Okhotsk, Pacific Ocean from Hokkaido and the Kuril Islands to southeastern Kamchatka, in the Bering Sea at depths of 130–1800 m; E. obscurus Pitruk et Fedorov, 1993 was recorded off the northern Kuril Islands and southwestern and southeastern Kamchatka at depths of 161–1773 m [30,31]. However, the pelvic disc of Elassodiscus is greatly reduced, as bony rays and musculature are absent, and only the skin part is present in the form of small lobes. In our specimen, the disc is larger; bony rays and musculature are not reduced. The presence of musculature and the dermal marginal part in the disc also distinguishes this specimen from the genus Osteodiscus. On this basis, we assign our specimen to the genus Careproctus.
Careproctus currently includes about 170 nominal species [17,27,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50]. However, most of the species inhabit the shelf and upper part of the slope. Deep-water species, on the contrary, are not numerous; twelve of them were recorded at depths below 1800 m (Table 2). Our specimen differs from most of them by fin-ray numbers (dorsal 61, anal 55), shorter head (21.3% SL) and pre-anal-fin part (29.7% SL), smaller disc (26.6% HL) and eye (17.0% HL), and innumerous pectoral rays (23). The only exception is C. bathycoetus. The examined specimen is similar to the holotype of the latter species in fin-ray counts and body proportions. In both specimens, head length and width, body depth and preanal length, eye and pelvic disc diameters, width of mouth, pectoral fin position, and disc to anus distance are very similar. In addition, the new specimen was caught near the type locality of the species.
Below we provide the characters of the examined specimen and the updated diagnosis of the species.

3.2. Description

Family Liparidae
Genus Careproctus Krøyer, 1862
Careproctus bathycoetus Gilbert et Burke, 1912
Gilbert and Burke 1912 [1], p. 368, fig. 10; Pl. 45 fig 2 (southern Sea of Okhotsk, “Albatross”, station 5030, depth 1800 fathoms). Burke 1930 [22], p.129, fig. 50 (teeth, additional measurements). Stein 1978 [23], p. 19–20, fig. 7 (teeth, radiogram counts). Kido 1988 [13], p. 210 (repeated data from Stein 1978). Sakurai and Shinohara 2008 [24], p. 40, fig. 1A (photo of holotype).
Holotype: USNM 73337, female, 181 mm TL, 163 mm SL. Sea of Okhotsk, 46°29′30″ N, 145°46′ E, “Albatross”, 29 September 1906, Station D 5030, depth 3292 m, 9-ft Agassiz beam trawl, Albatross North Pacific Expedition. Photo of holotype examined (http://n2t.net/ark:/65665/3101f154c-1e84-4d93-adf6-6193ddf10e23, accessed 12 August 2024).
Additional specimen examined: ZMH 28670, immature female with developing eggs, 175 mm TL. Sea of Okhotsk, 46°09′ N, 145°59′50″ E; 3305 m depth; 11 July 2015; RV “Akademik M. Lavrentyev”, cruise 71, St. 1–11; Agassiz trawl. Collector Irina Eidus.
Original description. “Dorsal 61; anal 55; pectoral 23; pyloric caeca 9. Body deepest at front of dorsal, greatly compressed and rapidly tapering posteriorly. Head short and heavy; occiput slightly swollen; a low median interorbital ridge; width and depth of head about equal. Snout moderately deep, truncate, projecting slightly beyond mouth; nostril in front of middle of eye, provided with a raised rim. Mouth wide, maxillary reaching vertical from posterior margin of pupil. Teeth rather long and slender, somewhat curved, all simple, without trace of lateral lobes, arranged in about 12 oblique rows on the half of each jaw. Gill opening not extending below upper pectoral ray. Dorsal origin above tip of opercular flap. Caudal slender apparently with six rays, joint to anal for about one-third its length. Pectoral notched; the lower lobe of six rays reaching half way between vent and anal. Disc small rather deeply cupped, placed behind vertical from posterior margin of eye. Color uniform jet black; mouth dusky; gill cavity and peritoneum also black” [1] (p. 368).
Previous data for holotype. Burke ([22]) gave same numbers of dorsal and anal fin rays as well as pyloric caeca like in the original description; he confirmed the number of caudal fin rays (6) but gave another number of pectoral fin rays (21 not 23). “Depth 5.7 in length without caudal; head 5. Eye 4.8 in head; disc 6.9. Body very attenuate posteriorly; the posterior fourth of the body not as deep as the diameter of eye. Teeth simple, rather stout, recurved (Figure 1C). Gill slit above the base of pectoral fin. Anterior mandibular pores separated by the diameter of the pupil. Lower lobe of pectoral 1.5 in the head. Disc small, deeply cupped. Color black; lips of the pores and the ventral surface of the disc black; peritoneum black; stomach pale” [22] (p. 129).
Stein [23] (p.19) gave the standard length of the holotype as 160 (not 163) mm and noted distinctly recurve sharp teeth (Figure 1D), the upper pectoral fin ray on a level with the posterior of the maxillary, and two suprabranchial pores. From radiogram, he counted vertebrae 67, dorsal 61, anal 55, and caudal 7 (not 6) fin rays. Pectoral rays 22 (not 23 or 21), including 10 rays in upper lobe, 5 in notch, 7 in lower lobe. Pyloric caeca 9. Head length (20.6% SL) and body depth (18.2%) are similar with values from original description. Other proportions were presented in % HL (Table 1).
Examined specimen ZMH 28670. Vertebrae 64 (precaudal 8, caudal 56); dorsal 59 and anal 53 fin rays, caudal fin principal rays 7 (4 upper and 3 lower, principal); procurrent rays are undefinable, either on individual or on x-rays (Table 1). Head comparatively small (4.7 in SL), pre-anal-fin part short (3.4 in SL). Body depth about equal to head length (86.9%HL), strongly compressed; about one-third of SL in posterior portion thinning whiplash-like. Head depth 1.3 larger than head width. Eye 5.9 in HL (1.7 in orbit); pupil round; interorbital 1.9 larger than eye. Gill opening 2.5 longer than eye diameter, not reaching to upper ray of pectoral fin (at length of one-third eye diameter) (Figure 3). End of operculum levels with upper margin of eye. Lower jaw shorter than upper jaw. Mouth width 53.7% HL; upper and lower jaw length 50.7 and 45.7%. Chin rounded (not angled). Teeth are simple and form oblique series, on upper and lower jaw 4 and 3 rows each near symphysis; in full oblique row in front 6 and 4 teeth each. Cephalic sensory pores 2–6–7–1 (suprabranchial pore one); pores small; chin pores not close together. Two rows of free sitting neuromasts are present along the body, lateral (about 23) and dorsal (about 8) (Figure 4).
Predorsal distance slightly longer than head length (114% HL). Disc small and wrapped inward anteriorly, not fleshy; disc length 1.6 larger than eye, width slightly less; longitudinal diameter of its central part one-third of disc length. Distance from anus to anal-fin origin slightly larger than disc to anus length. Pectoral fin notched, with 23 rays, 15 in upper lobe (counting the shortest notch ray) and 8 in lower. Upper pectoral ray levels with middle of suborbital distance; lengths of upper pectoral lobe slightly shorter than head. Lower pectoral lobe 84%, and notch ray 60% of upper pectoral length. Distance mandible to pectoral symphysis (34.0%HL) about one-third of length from pectoral symphysis to front of anal fin (100.3%). Length of caudal fin a half of HL; dorsal and anal covers the caudal fin at 27 and 28% of caudal length. Skin without prickles. Ovaries with eggs 1–3 mm, at previtellogenic phase. Color (in alcohol) uniform light brown; pectoral fins and abdomen darker; peritoneum black, stomach pale; digestive tract becomes increasingly pigmented in brown towards the end (anus); mouth cavity pale to light brown; gill cavity brown.
Updated diagnoses. Careproctus bathycoetus is a deepwater species distinguished by a combination of characteristics. Vertebrae 64–67, D 59–61, A 53–55; P 22–23, C 7. Head small, about 21% SL, pre-anal-fin length short, about 30% SL. Body attenuated, with thin posterior one-third. Pelvic disc cap-shaped, not fleshy and small (about 27% HL); anus behind disc at a distance of 6% SL. Eye 17.0% HL; teeth simple, curved; gill opening not reaches upper pectoral ray. Pectoral fin notched. Pyloric caeca 9. Skin black or brown, peritoneum black.

4. Comparisons

Counts and basic measurements of the studied specimen, such as head length and width, predorsal and preanal lengths, body depth, and disc length coincide well with those of the holotype (Table 1). Some differences are minor and can be explained by individual variability, fish fixation methods, or measurement accuracy. Thus, in the studied specimen, length from mandible to anus 18.5% SL vs. 21.0% and from disc to anus 6.1 vs. 5.5%; upper pectoral-fin lobe longer (17.8% SL vs. 15.0%). We found only one suprabranchial pore, not two as reported by Stein; this feature should be checked in the future on new materials.
Burke [22] mentioned that C. bathycoetus differs from congeners in attenuated body, low number of pectoral rays and coloration. He noted also: “in the reduction of the pyloric caeca and pectoral rays and the slender body this species most closely resembles the typical Paraliparis. It could not, however given rise to the latter group of species because the primitive Paraliparis had trilobed teeth” [22] (p. 130).
Gilbert and Burke [1] distinguished C. bathycoetus among congeners by innumerous rays in pectoral fin and related it to C. colletti. The latter species is known from the Japan, Okhotsk and Bering seas and the Gulf of Alaska at 64–1350 m. Careproctus bathycoetus differs from it in pectoral-fin (22–23 vs. 25–31) and caudal-fin ray number (6–7 vs. 8–10), lower body (17.5–18.5% SL vs. 18.9–30.7%) which is attenuated posteriorly (vs. deep up to the end) [1,13].
Stein [23] was of the opinion that the most similar pair of Careproctus is C. bathycoetus and C. oregonensis, described by him from Cascadia Abyssal Plain off Oregon at a depth between 1900 and 2818 m. In his opinion, the latter species differs in having parallel-sided, blunt, lobed, or simple canines instead of distinctly recurved, sharp teeth in C. bathycoetus; the upper pectoral fin ray is on a level with the lower margin of the orbit, not even with the posterior of the maxillary as in C. bathycoetus.
Kido [13] considers C. bathycoetus to be most similar to C. nigricans (Sea of Okhotsk, 500–1340 m), without giving further details. But C. bathycoetus differs from C. nigricans (original description) by fewer pectoral rays (22–23 vs. 27–30); smaller eye (17.0 vs. 23.3–28.5% HL); color black or brown vs. body grey, blackish posteriorly; peritoneum black vs. grey [6].
Careproctus bathycoetus differs from other Careproctus known in the North Pacific below the depth 1800 m (Table 2). It differs from C. brevipectoralis in having more numerous counts (vert 64–67 vs. 55, D 59–61 vs. 49, A 53–55 vs. 43), fewer pectoral-fin rays (22–23 vs. 26), smaller eye (17.0 vs. 26.4% HL) and disc (26.6 vs. 41.5% HL).
It differs from C. cyanogladius by larger counts (vert 64–67 vs. 63, D 59–61 vs. 57–58, A 53–55 vs. 50) and fewer pectoral rays (22–23 vs. 29–31), as well as in having a notched pectoral fin (vs. unnotched). It differs from C. cypselurus in having fewer pectoral rays (22–23 vs. 33–40), a more posterior position of anus (vs. at posterior edge of disc), in simple teeth (a few with small cusps). It differs from C. furcellus in having a more posterior position of anus (vs. close behind disc) and a notched pectoral fin (vs. unnotched) with fewer rays (22–23 vs. pectoral 32–37). It differs from C. globulus in having a smaller eye (17.0% HL vs. 29%) and disc (26.6% HL vs. 38.1%) as well as by more numerous counts (vert 64–67 vs. 46, D 59–61 vs. 42, A 53–55 vs. 36). It differs from C. laperousei in having a smaller disc (26.6% HL vs. 37.0%), a more posterior position of anus (vs. close behind disc), and more numerous counts (vert 64–67 vs. 57, D 59–61 vs. 53, A 53–55 vs. 45). It differs from C. opisthotremus by the position of anus closer to disc (in the latter, closer to anal fin than to pelvic disc), smaller eye (3.6–4.2% SL vs. 5%) and disc (3.0–5.7% SL vs. 8%). It differs from C. pulcher by higher counts (vert 64–67 vs. 46, D 59–61 vs. 42–43; A 53–55 vs. 35–36) but fewer pectoral rays (22–23 vs. 31–32) and in having a smaller eye (17.0% HL vs. 28.2–28.5%) and disc (26.6% HL vs. 31.4–32.3%). It differs from C. roseofuscus in having a larger gill slit (41.2% HL), whereas in the latter, it is reduced to small opening (3% HL), and counts: D 59–61 (vs. 57), A 53–55 (vs. 48), but pectoral 22–23 (vs. 30).

5. Distribution

Two known specimens were collected in the southern part of the Sea of Okhotsk in the deep-sea Kuril Basin very close to each other, within the same degree of latitude and longitude: 46°29′30″ N, 145°46′ E (the type) and 46°09′ N, 145°59′50″ E (examined specimen) (Figure 5) at similar depths of 3292 and 3305 m.
It is not correct to classify that the species is of “temperate boreal distribution” [16] (p. S110). Geographically, the locality lies inside the temperate boreal latitudes, but the deep-sea Kuril Basin is not part of the shelf area to which this zonation is applicable. Depths below 3000 m are regarded as the upper abyssal zone; and the Kuril Basin is isolated from the deep Pacific Ocean [25]. Therefore, C. bathycoetus is an abyssobenthic species, and more likely, an endemic species of the Kuril Basin.

6. Ecology

The Kuril Basin is the deepest and oldest part of the Sea of Okhotsk, formed during the Early Oligocene–Late Miocene [53] or even earlier, the Late Paleocene—Early Oligocene [54]. The Basin is 3300 m deep and about 250 km wide at maximum [55] and borders the open Pacific Ocean by the Kuril chain, with water exchange through straits between islands. Deep-ocean Pacific waters enter the Kuril Basin through deepest channels, the Bussol (2318 m depth and width 83.3 km) and Krusenstern (1920 m and 66.7 km) straits, and descend into the Kuril Basin [56].
Information about the deep-sea fauna of the Kuril Basin is scarce, and invertebrate animals are better known than fish. The abyssal fauna is influenced by the influx of deep-sea waters from the Pacific Ocean, and the two regions share many invertebrate species [57,58,59]. In contrast, no similarities to the bathyal depths of the Sea of Japan were found, since there were historically no opportunities for the exchange of deep-sea faunas [58]. Therefore, for the abyssobathial fish of the Kuril Basin, it is more likely to expect similarities with the Pacific fauna, namely, with the fauna of the ultra-abyssal Kuril–Kamchatka Trench, which borders the Kuril chain on the Pacific side.
Living conditions in the Sea of Okhotsk are extremely harsh. The average duration of the ice period in the south of the sea is 120–130 days. In winters, 65 to 99% of the sea area is covered with ice. Surface waters are characterized by temperatures ranging from −2.0 °C in winter to 18 °C in summer. The underlying water layer, cooling in winter, maintains negative temperatures (up to minus 1.8 °C). Below is an intermediate water mass of warmer Pacific waters with temperatures from 2 to 2.5 °C. In the area of maximum depths, the bottom water mass (below 1300–1500 m) has a stable temperature of 1.8–1.9 °C and a salinity of 34.6–34.7‰ [56].
The bottom of the Kuril Basin is a plain, located on average at a depth of 3300 m. Bottom sediments are represented by silty clay with a very soft (almost liquid) greenish-brown oxidized surface layer of 2–11 cm thick [60]. Oxygen concentration decreases with depth, with values 0.7 mL L−1 at 1500 m (saturation 9.2%) [59], and on the abyssal plain of the Kuril Basin 1.7–1.9 mL L−1 [61].
As on other deep-sea plains, the bottom fauna of the Kuril Basin lives mainly at the expense of sinking organisms of surface production. The main part of the Kuril Basin has low benthic biomass (~30.5 g m−2) and is characterized by immobile filter feeders including the pogonophora Lamellisabelle, bryozoans Kinetoskias, sponges, and octocorallia Radiceps. The deepest part of the Kuril Basin has a biomass of ~102 g m−2 and is dominated by bottom feeders and detritophagous animals including the polychaete families Maldanidae, Terebellidae, Capitellidae, and Travisia, the holothurians of the families Molpadiidae and Psychropotes, echiurids, and ophiuroids [62].
In general, the abyssal meio-, macro-, and megafauna of the Kuril Basin is quite specious and in the southeastern part, near the Bussol Strait, is similar in composition to the abyssal Pacific fauna of the slope of the Kuril–Kamchatka Trench [25]. This group of species, common to the two regions, includes predominantly eurybathic animals adapted to cold.
Strictly abyssal species have also been found [25,62,63]. In this group, the majority are species not found in neighboring waters of the Pacific Ocean. For example, among 27 Gastropoda species (from 11 families Vetigastropoda and Caenogastropoda), collected in the Kuril Basin, only six species were shared with the Pacific side of the Bussol Strait [63]. Thus, the abyssal fauna of the Kuril Basin includes a number of obvious endemics to the Basin (and the Sea of Okhotsk).
Endemism of fishes from the southern Sea of Okhotsk was briefly commented [64], and C. bathycoetus named among the deep-sea endemics. Considering the above data, it can be concluded that this abyssobenthic fish inhabits depths of 3292–3305 m and survives under extreme environmental conditions: complete darkness, at temperatures of about 1.8–1.9 °C, at enormous water pressure (about 3300 ton/m2), and with a low oxygen concentration and a low biomass of prey. Comparisons with congeners have not revealed similar relatives among the known deep-sea species of the genus. Taking into account data on the invertebrate fauna, related species can most likely be found in the abyssal depths of the Kuril–Kamchatka Trench.

7. Conclusions

A century after the description of the deep-sea snailfish Careproctus bathycoetus, a second specimen was identified among the samples of the international expedition “SohoBio” (2015) from the Kuril Basin (southern Sea of Okhotsk, western North Pacific Ocean). The study of this rare fish has made it possible to improve the diagnosis of the species. Distinguishing characters from other deep-sea congeners from the North Pacific Ocean are given. This snailfish lives at a depth of 3292–3305 m in extreme conditions: in complete darkness, at temperatures of about 1.8–1.9 °C, water pressure about 3300 ton/m2, with a low oxygen concentration and a low biomass of benthic food organisms. Careproctus bathycoetus is an abyssobenthic fish, endemic to the Kuril Basin. Related Careproctus species can most likely be found in the abyssal depths of the neighboring Kuril–Kamchatka Trench.

Author Contributions

Conceptualization, methodology, N.V.C.; investigation, N.V.C. and R.T.; writing—original draft preparation, N.V.C.; writing—review and editing, visualization, N.V.C. and R.T. All authors have read and agreed to the published version of the manuscript.

Funding

This research of N. Chernova was funded within the framework of the Federal theme of the Zoological Institute, Russian Academy of Sciences No. 122031100285-3. Research of Ralf Thiel received no external funding.

Data Availability Statement

The data generated in this study are available from the corresponding author upon request.

Acknowledgments

We sincerely thank Mrs. Irina Eidus (LIB) who collected the material on board of research vessel and transported it to the fish collection of the ZMH as well as for taking the ratiographs of the new specimen. Many thanks also to Thilo Weddehage (LIB) for taking the photographs of the new specimen. We are very grateful to reviewers for their comments that helped improve this manuscript.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

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Figure 1. Careproctus bathycoetus, holotype USNM 73337, 181 mm TL: lateral view (A) and ventral view with the position of pelvic disc and anus (B) [1]; teeth [22] (C) and [23] (D).
Figure 1. Careproctus bathycoetus, holotype USNM 73337, 181 mm TL: lateral view (A) and ventral view with the position of pelvic disc and anus (B) [1]; teeth [22] (C) and [23] (D).
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Figure 2. Careproctus bathycoetus, examined specimen, 175 mm TL, ZMH 28670; lateral (A), ventral (B) and dorsal (C) views.
Figure 2. Careproctus bathycoetus, examined specimen, 175 mm TL, ZMH 28670; lateral (A), ventral (B) and dorsal (C) views.
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Figure 3. Careproctus bathycoetus, ZMH 28670; locations of suprabranchial pore (sbr), free neuromasts of medial row (n), the sixth preoperculomandibular pore (pm6); lower end of gill slit (1) and base of upper pectoral-fin ray (2) are shown.
Figure 3. Careproctus bathycoetus, ZMH 28670; locations of suprabranchial pore (sbr), free neuromasts of medial row (n), the sixth preoperculomandibular pore (pm6); lower end of gill slit (1) and base of upper pectoral-fin ray (2) are shown.
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Figure 4. Careproctus bathycoetus, ZMH 28670; disposition of suprabranchial pore (yellow arrow) and free neuromasts (white arrows), in two rows (medial and dorsal), is shown.
Figure 4. Careproctus bathycoetus, ZMH 28670; disposition of suprabranchial pore (yellow arrow) and free neuromasts (white arrows), in two rows (medial and dorsal), is shown.
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Figure 5. Map showing the catch locations of the holotype (red asterisk) and of our specimen ZMH 28670 (green asterisk) in the Kuril Basin. The map was generated based on the 60 Arc-Second Global Relief Model of NOAA National Centers for Environmental Information [52].
Figure 5. Map showing the catch locations of the holotype (red asterisk) and of our specimen ZMH 28670 (green asterisk) in the Kuril Basin. The map was generated based on the 60 Arc-Second Global Relief Model of NOAA National Centers for Environmental Information [52].
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Table 1. Morphometry and counts of Careproctus bathycoetus, holotype and examined specimen.
Table 1. Morphometry and counts of Careproctus bathycoetus, holotype and examined specimen.
CharactersHolotype USNM 73337ZMH 28670
Gilbert et Burke [1]Stein [23]Our Data
TL, mm181.0–175.0
SL, mm163.0160.0157.5
%SL%SL% HL%SL% HL
Head length, HL21.020.6 21.3
Snout length8.0 9.042.4
Eye diameter4.2 3.617.0
Orbit 17.0 6.229.3
Postorbital length 10.348.4
Head width14.0 13.161.5
Head depth– 17.180.6
Body depth17.518.2 18.586.9
Body depth above anal-fin origin 12.458.2
Body width 7.434.6
Predorsal length23.0 24.2113.7
Pre-anal-fin length29.5 29.7139.7
Mandible (tip of snout) 1 to anus21.0 81.8 (101.5) 118.587.2
Mandible (tip of snout) 1 to disc(13.0) 1 39.27.635.5
Mandible to pectoral-fin symphysis 7.234.0
Disc length3.0 15.55.726.6
Disc width 3.516.4
Disc central-part length 1.78.1
Anus to anal fin 10.549.3
Disc to anus5.5 23.46.128.7
Disc to anal fin 15.371.9
Upper pectoral fin-lobe length15.0 82.417.883.9
Pectoral notch rays length3.5 10,649.9
Lower pectoral fin-lobe length15.0 77.215.070.4
Pectoral symphysis to anal fin 21.3100.3
Interocular width9.0 6.932.2
Bony interorbital width 3.918.2
Gill slit length5.5 8.841.2
Gill slit to pectoral-fin base distance 1.36.0
Upper jaw length9.2 10.850.7
Lower jaw length 40.19.745.7
Width of mouth11.5 11.453.7
Caudal fin length 11.152.2
Dorsal fin confluent caudal fin 3.014.0
Anal fin confluent caudal fin 4.914.6
Counts
Vertebrae 67 64
Dorsal fin rays6161 59
Anal fin rays5555 53
Caudal fin raysca. 67 7
Pectoral fin rays2322 23
1 The data in parentheses are when measured from the tip of the snout to the disc.
Table 2. Deep-sea Careproctus from the North Pacific Ocean recorded at a depth greater than 1800 m, with characters in bold distinguishing them from the examined specimen.
Table 2. Deep-sea Careproctus from the North Pacific Ocean recorded at a depth greater than 1800 m, with characters in bold distinguishing them from the examined specimen.
SpeciesDistribution and DepthMain Characters References
C. batialis Popov, 1933Peter the Great Bay, Japan Sea, 1225–1980 m Head 28.8% SL; eye 14.8% HL, disc 21.1%; disc to anus less than a half of disc; D 58, A 46, P 30[12,51]
C. bathycoetus Gilbert et Burke, 1912Southern Sea of Okhotsk, 3292 mHead 21.0% SL, preanal 29.5, eye 4.2, disc 3%; anus mid distanced from disc and front of anal fin; vert 67, D 61, A 55, P 22[1]
C. brevipectoralis Chernova, Thiel et Eidus, 2020Kuril Basin in the Sea of Okhotsk; 3301 mHead 17.7% SL, preanal 34.0%; eye 26.4% HL, disc 41.5%; vert 55, D 49, A 43, P 26[17]
C. cyanogladius Kai, Endo et Nakayama, 2021Northern Honshu Island 2698–3223 mPectoral fin without a notch; vert 63, D 57–58, A 50, P 29–31 [45]
C. cypselurus (Jordan et Gilbert, 1898)Northern Honshu to Kuril Islands, SE Kamchatka, Bering Sea, British Columbia, Washington; (rarely 35) 400–1600 (rarely 1993) mHead 23.5 (18.3–23.5) * % SL, eye 4.5% SL (17.0–22.7% HL), disc 5% SL or 13–22 (13.1–17.5)% HL; anus at posterior edge of disc; teeth acute, a few with small cusps; D 59 (59–64), A 55 (53–58), P 33 (33–40)[13] *
[30]
C. furcellus Gilbert et Burke, 1912Sea of Okhotsk, Pacific Hokkaido, Kuril Islands, Bering Sea and Aleutian Islands, Gulf of Alaska; (rarely 98) 175–882 (rarely 1270) mHead 27.5 (17.1–27.0) * % SL, (eye 13.7–25.0% HL), disc 6% SL, or 13–22 (11.7–19.6)% HL;
anus close behind disc; (vert 67–72), D 62 (61–65), A 57 (54–59); pectoral fin unnotched, 36 (32–37)		[13] *
[30]
C. globulus Chernova, Thiel et Eidus, 2020Pacific side of the Bussol Strait; 2350–2358 mHead 24.4% SL, preanal 34.9%; eye 29% HL, disc 38.1%; vert 46, D 42, A 36, P 24[17]
C. laperousei Chernova, Thiel et Eidus, 2020Northern slope of the Kuril–Kamchatka Trench; 4796–4803 mHead 22.5% SL, preanal 31%; eye 16.7% HL, disc 37.0%; anus closer to disc than to anal fin; D 53, A 45, P 26[17]
C. nigricans Schmidt, 1950Okhotsk Sea and Honshu (Iwate Prefecture); 500–2005 mHead 22.4–24.0 (18.0–19.9) * % SL, preanal–; teeth three-lobed (simple); eye 23.3–28.5 (20.4–24.0)% HL, (disc 12.4–14.4%HL); anus behind disc; (vert 62–67), D 56 (67–61), A 52 (51–55), P 27–30 (29–32)[6]
[13] *
C. opisthotremus Gilbert et Burke 1912Vicinity of Aleutian Islands (Agattu, Umnak); 1913–2562 m Head 30% SL, preanal–; eye 5% SL, disc 8%; anus nearer anal fin than ventral disc[30]
C. pulcher Chernova, Thiel et Eidus, 2020Pacific side of the Bussol Strait; 2350–2358 mHead 25.5–26.3% SL, preanal 39%; eye 28.2–28.5% HL, disc 31.4–32.3%; vert 46, D 42–43, A 35–36, P 31–32[17]
C. roseofuscus Gilbert et Burke, 1912Sea of Okhotsk, Kuril Islands, southeastern Kamchatka; 72–810 (1950) mHead 26% SL, preanal–; eye 5, disc 5.5%; gill slit reduced to small opening, 3% HL; disc separated from anus by a distance slightly exceeding its own diameter; D 57, A 48, P 30 [1]
* Data from Kido [13] in brackets, if different from those of Gilbert and Burke [30] or Shmidt [6]. Data are not entirely consistent, as some are absent in references.
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Chernova, N.V.; Thiel, R. First Capture of the Deep-Sea Careproctus bathycoetus (Liparidae) a Century After the Fish Was Described (North Pacific)—Revised Diagnosis and Notes on Ecology. Taxonomy 2024, 4, 748-760. https://doi.org/10.3390/taxonomy4040040

AMA Style

Chernova NV, Thiel R. First Capture of the Deep-Sea Careproctus bathycoetus (Liparidae) a Century After the Fish Was Described (North Pacific)—Revised Diagnosis and Notes on Ecology. Taxonomy. 2024; 4(4):748-760. https://doi.org/10.3390/taxonomy4040040

Chicago/Turabian Style

Chernova, Natalia V., and Ralf Thiel. 2024. "First Capture of the Deep-Sea Careproctus bathycoetus (Liparidae) a Century After the Fish Was Described (North Pacific)—Revised Diagnosis and Notes on Ecology" Taxonomy 4, no. 4: 748-760. https://doi.org/10.3390/taxonomy4040040

APA Style

Chernova, N. V., & Thiel, R. (2024). First Capture of the Deep-Sea Careproctus bathycoetus (Liparidae) a Century After the Fish Was Described (North Pacific)—Revised Diagnosis and Notes on Ecology. Taxonomy, 4(4), 748-760. https://doi.org/10.3390/taxonomy4040040

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