Hydrolagus erithacus Walovich, Ebert & Kemper, 2017, sp. nov

• Main Authors: Walovich, Kristin A., Ebert, David A., Kemper, Jenny M.
• Format: Text
• Language: unknown
• Published: Zenodo 2017
• Subjects: Biodiversity; Taxonomy; Animalia; Chordata; Holocephali; Chimaeriformes; Chimaeridae; Hydrolagus; Hydrolagus erithacus; Galapagos; Canada; Pacific; Indian; New Zealand; Jenny; Browns; Moura; Alberti; Davis Strait; Marion Island; North Atlantic; North East Atlantic; Patagonian Toothfish
• Online Access: https://dx.doi.org/10.5281/zenodo.5665110; https://zenodo.org/record/5665110

Hydrolagus erithacus sp. nov Common Name: Robin’s Ghostshark (Figures 1, 2; Table 1) Hydrolagus sp. nov. (Big black chimaera): Compagno 1999: 120. Holotype . SAIAB 200578, adult male, 1290 mm TL, 790 mm BDL, Discovery Seamount, Southeastern Atlantic Ocean, 43°46'S, 01°21'W. Paratypes . (n=8) SAIAB 200579, adult female, 1357 mm TL, 869 mm BDL, Discovery Seamount, southeastern Atlantic Ocean, 43°43S 01°23W; SAM 34432, adult female, 1220 mm TL, 765 mm BDL, R.S.A Seamount, southeastern Atlantic Ocean, 39° 40' S, 6° 40' W, 470-972 m; SAM 34434, adult male, 1185+ mm TL, 863 mm BDL, southwestern Indian Ocean, 44° 46’S, 36° 18’E, 1097 m, 31 Jan 1997; SAM 34723, immature male, 1169 mm TL, 775 mm BDL, Marion Island, southwestern Indian Ocean, 46° 49' 0.11"S, 37° 43' 59.87" E, 1000 m; SAM 35442, adult male, 1324 mm TL, 842 mm BDL, Marion Island, southwestern Indian Ocean, 46° 49' 0.11"S, 37° 45'E, 20 Feb 2000; SAM 34724, adult female, 1442 mm TL, 915 mm BDL, Marion Island, southwestern Indian Ocean, 44° 46' 0.12"S, 36° 17' 59.99"E, 600 m; SAM 35446, adult female, 1399+ mm TL, 945 mm BDL, Schmidt-Ott Seamount, southeastern Atlantic Ocean; SAM 35447, adult female, 1405 mm TL, 915 mm BDL, Schmidt-Ott Seamount, southeastern Atlantic Ocean Diagnosis. Hydrolagus erithacus is a large species at maturity (765–945 mm BDL) distinguished from all other congeners based on the following combination of characters: head bulky, large followed by stocky body, height similar from about pectoral fin origins to pelvic fin origins remaining consistent in height until the insertion of the pelvic fins, tall dorsal spine greater in height than first dorsal fin. Second dorsal fin up to 81% of total body length, uniform in height, and equal to dorsal caudal fin height. Paired claspers trifurcate, forked for approximately 20% of total length with fleshy, bulbous tips. Prepelvic tenaculae with five to seven medial spines and thick frontal tenaculum, nearly uniform in width. Coloration after preservation uniform black with no distinct markings. Comparison of mitochondrial NADH 2 gene sequences with other related species suggests a distinct lineage. Description. Morphometric measurements of the holotype are given followed in parenthesis by a range of eight paratypes and are presented in Table 1. Large bodied species (1169–1442 mm TL, 765–945 mm BDL) with bulky head 28% (27–31%) BDL and pointed snout 15% (15–18% POB) BDL (Figure 2). Body depth uniform from insertion of pectoral fins to insertion of pelvic fins. Pectoral-pelvic space 35% (29–36%) BDL, approximately twothirds (54–71%) BDL the pelvic-caudal space 51% (46–61%) BDL. Snout-to-vent length 70% (62–69%) BDL, longer than pelvic-caudal space 51% (46–61%) BDL. Eyes oval along horizontal axis, length 6% (5–7%) BDL, 17% (18–22%) HDL and height 4% (3–5%) BDL, 15% (12–17%) HDL. Skin firm, not deciduous. Holotype Paratypes (n=8) mm % BDL mm % BDL TL 1290 163 1169–1442 151–159 PCL 1025 130 935–1210 121–132 SVL 550 70 483–635 62–69 BDL 790 - 765–945 - TRL 320 41 275–383 35–44 HDL 225 28 219.9–282 27–31 PD1 225 28 245–295 28–35 PD2 419 53 431–515 53–57 PP1 245 31 231–380 29–42 PP2 575 73 531–655 69–75 POB 120 15 113.5–163.4 15–18 PRN 85 11 32.5–105 4–12 POR 109 14 46.5–130 5–15 SNL 107 14 97.8–137.8 12–15 EYL 46.4 6 44– 58 5–7 EYH 35.1 4 26.5–44.5 3–5 D1P1 150 19 152.3–260 19–28 D1P2 384 49 357–450 43–49 D2P1 270 34 220–285 25–34 D2P2 190 24 157.3–285 20–31 IDS 90 11 65.1–106.9 8–12 DCS 13.6 2 4.5–22.9 1–3 PPS 276 35 233.6–310 29–36 PCS 400 51 361–555 46–61 PRS 250 32 161–235 21–27 P1AM 279 35 263.4–300.2 31–38 P1FW 163 21 155.8–171.2 18–22 P1BW 93 12 80.8– 99 9–13 P1BH 75 9 83.1–108.1 9–12 P2AM 164 21 159.1–183.6 18–22 P2FW 62 8 93.1–115.3 10–14 P2BW 44 6 36.8–91.7 4–12 P2BH 127 16 35.5–67.5 4–7 DSA 200 25 174.8 21 D1B 128 16 107.7–128 12–16 D1H 92.8 12 96.7–129.6 11–15 D2B 600 76 557–745 71–81 D2AH 29.7 4 27.1–37.2 3–5 D2 PH 36.8 5 28.5–38.7 3–5 D2MH 30.2 4 29.3– 40 3–5 CDM 185 23 176.1–196.8 21–25 ......continued on the next page Holotype Paratypes (n=8) Pectoral fins large and triangular; pectoral fin length 35% (31–38% P1AM) BDL, 1.7–1.9 times pectoral fin width 21% (18–22% P1FW) BDL, with a strait anterior margin tapering distally to a rounded apex. Pelvic fin length 21% (18–22% P2AM) BDL, equal to pectoral fin width 21% (18–22% P2FW) BDL and nearly half the pectoral fin length. Pectoral and pelvic anterior margins weakly convex, overall oval in shape. Fins remain intact and do not fray after preservation. First dorsal fin triangular with straight medial edge, base 16% (12–16%) BDL terminating to a low membrane connecting to second dorsal fin in a gentle slope. Dorsal spine 25% (21%) BDL robust, curving anteriorly and taller than the first dorsal fin height 12% (11–15%) BDL; dorsal spine when depressed is slightly shorter than or just reaches origin of second dorsal fin. Second dorsal fin base long 76% (71–81%) BDL and uniform in height along entire length. Second dorsal fin curves downward toward caudal insertion, but does not meet dorsal body margin before dorsal caudal margin begins. Caudal ventral margin 39% (30–36%) BDL generally longer than caudal dorsal margin 23% (21–25%) BDL. Caudal dorsal height 4% (3–5%) BDL nearly equal to average second dorsal height 4% (3–5%) BDL, slightly taller than caudal ventral height 4% (3–4%) BDL. No caudal filament observed in available specimens. Paired claspers trifurcate, forked for ~20% total length of clasper (17–22% BDL). Medial branch slender with small tip, lateral branches with bulbous tips, extending one-third the length of the clasper, covered in small denticles (Figure 2). Frontal tenaculum stalk thick and nearly uniform in width. Bulb round with slender, sporadically arranged spines. Prepelvic tenaculae rectangular in shape with 5 to 7 robust medial spines. Intraspecific variation of oral (O), preopercular (POP) and infraorbital (IO) canals was observed. In half of the specimens the O and POP canals share a common branch from the IO, in the remaining the O and POP canals connect separately to the IO canal. Coloration. Body coloration and fins a uniform black with no distinctive patterns or markings based on preserved specimens. Claspers variable in color from black to pale tan, tips light yellow. Frontal tenaculum dark on dorsal surface, light on ventral. Prepelvic tenaculae tan in color along medial edge near spines, darkening to black along on distal and medial edge posterior to spines. Etymology. The species name erithacus derives from the avian genus of the robin (Aves: Passeriformes: Muscicapidae: Erithacus Cuvier, 1800). Named after Robin Leslie of South African Department of Agriculture, Forestry and Fisheries (DAFF), a fanatic birder, in recognition of his help and support on this project, and his overall contribution to Chondrichthyan research in southern Africa. Distribution. Hydrolagus erithacus is currently known from the southeastern Atlantic and southwestern Indian oceans, between latitudes 39° to 47° S, from depths of 470–1,000 meters (Figure 3). Based on the depth distribution of similarly sized species and accounts from the Patagonian toothfish (Dissostichus eleginoides ) fishery operating within its range, this species likely occurs to depths in excess of 2,000 meters (R. Leslie, DAFF unpublished data). Biological notes. A large bodied species growing to at least 945 mm BDL, 1405 mm TL. Smallest observed mature individuals were 842 mm and 765 mm BDL for males and females, respectively. Largest immature male individual was 775 mm BDL, no immature females were observed. Internal examination of a mature female specimen (SAM 34724) measuring 915 mm BDL revealed a fully developed uterus and oviducal glands with several oocytes measuring approximately 30 mm in diameter. Fragments of possible crab appendages were recovered from the digestive tract of the holotype specimen, indicating a diet of crustaceans and other benthic fauna. Comparisons. Hydrolagus erithacus is the second largest Hydrolagus species described to date, and can clearly be differentiated from the small-bodied chimaerids in the genus (e.g. H. africanus , H. alberti, H. alphus, H. barbouri, H. colliei, H. macrophthalmus, H. mirabilis, and H. mitsukurii ). Hydrolagus africanus occurs nearest in geographic proximity to H. erithacus , but does not overlap in distribution, and is a much smaller species (<500 mm BDL, <900 mm TL and size at maturity> 300 mm) (Walovich et al. 2015). The anterior second dorsal fin height of H. africanus is taller (4–8% vs. 3-5% BDL) and the second dorsal height taller across its entire length (2–7% vs. 3–5% BDL D2 PH, 1–6% vs. 3–5% BDL D2MH). The coloration of fresh H. africanus is silver and brown and when preserved turns a uniform light brown. Additionally, the uniform black color of H. erithacus separates it from the patterned species such as H. alphus , H. colliei, H. marmoratus, H. mccoskeri , and H. novaezealandiae . The seven species most similar to H. erithacus in color and body size are compared. Three species of these large bodied Hydrolagus are known only to occur in the North Atlantic, H. affinis, H. pallidus and H. lusitanicus (Ebert & Stehmann 2013). Hydrolagus affinis relative to H. erithacus differs proportionally by having a smaller snout to second dorsal fin distance (47–55% vs. 53–57% BDL), head length (23–31% vs. 27-32% BDL), prepectoral fin length (28–34% vs. 29–42% BDL), pre-orbital length (12–14% vs. 15–18% BDL), dorsal caudal margin (16–21% vs. 21–25% BDL) and dorsal caudal height (2–4% vs. 3–5% BDL). Hydrolagus affinis has been described as having 4–6 medial spines on the prepelvic tenaculae (Hardy & Stehmann 1990), however investigation of additional specimens reveals a slightly wider spine count range (4–8 spines, average 6). Hydrolagus pallidus is distinct from H. erithacus based on a shorter head length (23–30% vs. 27–31% BDL), prepectoral fin length (26–34% vs. 29–42% BDL) and pectoral fin length-to-width ratio (1.3–1.7 vs. 1.7–1.9). Previously reported pectoral fin length-to-width ratios are less than 1.5 for H. pallidus (Hardy & Stehmann 1990; Ebert & Stehmann 2013), however an additional specimen measured by the authors was outside this range (1.7). Hydrolagus pallidus turns white to creamy grey colored in fixative, whereas H. erithacus turns a uniform black. Hydrolagus lusitanicus appears to reach similar body lengths as H. erithacus , however the species was poorly described, did not use standard measurement methods for comparison to other Hydrolagus species, and did not provide any maximum size or size at maturity information (Moura et al. 2005). However, H. lusitanicus has a larger pectoral fin length-to-width ratio (1.9–2.3 vs. 1.7–1.9), longer first dorsal fin base length (19–20% vs. 13– 16% BDL), and a distinct coloration from H. erithacus , being a uniform rose to light brown with irregular spots and violet-blue fins. Hydrolagus purpurescens from the central and western North Pacific is poorly known, but can be separated from H. erithacus by a longer snout-to-vent length (68–72% vs. 62–69% BDL), shorter distance from first dorsal fin origin to pectoral fin origin (20–21% vs. 19–28% BDL), and greater eye length (6–8% vs. 5–7% BDL) and eye height (4–6% vs. 3–5% BDL). Second dorsal fin height is taller and with a slight dip at the center (4–5% BDL), while remaining a consistent height in H. erithacus . The eastern Pacific H. melanophasma has a shorter snout-to-vent length (57–60% vs. 62–70% BDL), larger eyes (22–26% vs. 17–22% HDL), longer pectoral fin anterior margin (39–41% vs. 31–38% BDL), and fewer prepelvic tenaculae spines (3–4 vs. 5–7 spines) (James et al. 2009). Hydrolagus trolli, found in the waters off New Zealand and New Caledonia, is a slightly smaller species, reaching sexual maturity at 550–650 mm BDL (Didier & Séret 2002). Hydrolagus trolli has a greater range of snout-to-vent lengths (63–75% vs. 62–69% BDL), longer pre-orbital length (14–19% vs. 15–18% BDL), smaller head (22–26% vs. 23–39% BDL), shorter caudal dorsal height (3–4% vs. 3–5% BDL), shorter caudal ventral margin (30–36% vs. 28–40% BDL) and fewer medial spines on the prepelvic tenaculae (4–5 vs. 5–7 spines). Hydrolagus trolli is a uniform pale, blue-grey when fresh, becoming brown to purple when fixed, compared to the uniform black coloration of H. erithacus. Hydrolagus homoncyteris is a medium bodied (667 mm maximum BDL) species from southeast Australia and New Zealand, whose diagnostic short, round pelvic fins (13–18% BDL) make it distinguishable from the larger, oval shaped pectoral fins of H. erithacus (18–22% BDL) despite its similar uniform, black coloration (Didier 2008). The tree topology of the maximum likelihood analysis of sequence data at the NADH 2 gene locus suggests five distinct clades, corresponding to H. africanus , H. affinis . H. pallidus , H. trolli and H. erithacus (Figure 4). Rhinochimaera atlantica and Harriotta raleighana were used to root the tree. Hydrolagus africanus is clearly distinguishable from the other four species based on sequence data. However, the remaining four species show limited sequence divergence at this locus, indicating two potential scenarios: (1) these are valid species, or (2) that they represent populations of a single species. The inference suggests separate species, since they fall out into their respective species lineages and show geographic structure. However, this topological pattern is also typical of little movement between populations of the same species, limiting gene flow due to isolation by distance. Interestingly, H. affinis and H. pallidus are known to overlap in distribution, and here, are recovered as their respective species, indicating two unique species. While we suggest Hydrolagus erithacus as a new species distinct from similar Hydrolagus species based on the molecular data, we caution that this inference is the tree topology for only a single mitochondrial gene and may not correspond to the species tree based on multiple markers. It may be necessary to analyze a suite of independent molecular markers to infer a robust species tree. The NADH 2 gene it should be noted is a fast-evolving protein-coding mitochondrial gene, and thus, is regarded as a useful marker for assessing species differentiation. Comparative material. Material examined of H. alphus , H. macrophthalmus , H. mccoskeri , H. melanophasma , H. mitsukurii , and H. novaezealandiae is listed in Barnett et al . (2006), Quaranta et al . (2006), James et al . (2009), and Ebert et al . (2013). Hydrolagus affinis (13 specimens): AMNH 78355, adult female, 1080 mm TL, 740 mm BDL, Tenerife Island, Eastern Central Atlantic, 28° 6’16. 15”N, 16° 8’39. 77W, 0 1 Oct 1986; AMNH 78358, adult male, 1035 mm TL, 690 mm BDL, Tenerife Island, Eastern Central Atlantic, 28° 6’16’5”N, 16 °8’ 39.77 W, 0 1 Oct 1986; AMNH 78365, adult male, 980 mm TL, 655 mm BDL, Tenerife Island, Eastern Central Atlantic, 28° 6’16.15”N, 16° 8’39.77”W, 0 1 Oct 1986; AMNH 78367, adult male, 1122 mm TL, 760 mm BDL, Tenerife Island, Eastern Central Atlantic, 28° 6’16. 15”N, 16° 8’39’77”W, 0 1 Oct 1986; AMNH 78368, adult male, 1045 mm TL, 721 mm BDL, Tenerife Island, Eastern Central Atlantic, 28° 6’16.15”N, 16° 8’ 39.77W, 0 1 Oct 1986; AMNH 78378, adult female, 1185 mm TL, 760 mm BDL, North Atlantic Ridge, 46°49'18.0"N 27°36'18.0"W; AMNH 78379, immature male, 920 mm TL, 568 mm BDL, North Atlantic Ridge, 46°49'18.0"N 27°36'18.0"W; AMNH 78380, adult female, 1215+ mm TL, 840 mm BDL, North Atlantic Ridge, 46°49'18.0"N 27°36'18.0"W; ANSP 174645 (1 of 3), adult male, 1080 mm TL, 700 mm BDL, Northwestern Atlantic Ocean; ANSP 178569, adult male, 1002 mm TL, 657 mm BDL, Davis Strait, North Atlantic Ocean, 63° 37' N, 56° 37' W, 1415 m, 7 Nov 2001; USNM 38021, adult male, 945 mm TL, 624 mm BDL, Nova Scotia, Canada, 44° 30' 00''N, 58° 30' 00''W, 366 m; USNM 94399, adult female, 1121+mm TL, 853 mm BDL, Browns Bank, Massachusetts, USA; USNM 387795, immature male, 996 mm TL, 653 mm BDL, Bear Seamount, Atlantic Ocean, 39 °55’21.36”N, 67° 25’55.91”W, 1197 m, 19 Apr 2005 Hydrolagus africanus (42 specimens): CAS 241488, 3 male, 1 female, Western Cape, South Africa, 3459'38.4" S, 01820'04.8" E, 631 m, 10 Feb 2015; CAS 241490, 1 male, 1 female, Western Cape, South Africa, 31°27'33.0"S 15°52'07.2"E, 543 m, 28 Feb 2015; CAS 241491, male, Western Cape, South Africa, 30°56'57.6"S 15°27'53” E, 725 m, 5 Mar 2015; CAS 241492, 2 male, Western Cape, South Africa, 30°19'20.4"S 14°54'38.4"E, 511 m, 6 Mar 2015; CAS 241493, female, Western Cape, South Africa, 30°19'20.4"S 14°54'38.4"E, 511 m, 6 Mar 2015; SAIAB 186459, adult female, 393+ mm TL, 321 mm BDL, Durban, South Africa, 30° 05.244' S, 31° 22.969' E, 25 Aug 2010; SAIAB 14040 A, adult female, 620 mm TL, 293 mm BDL, Mombasa, Kenya, 4° 16’ 59.99” S, 40° 6’ 59.99” E, 10 Dec 1908; SAIAB 14040 B, adult male, 655 mm TL, 413 mm BDL, Mombasa, Kenya, 4° 16’ 59.99” S, 40° 6’ 59.99” E, 10 Dec 1908; SAIAB 17324 A, adult male, 459 mm TL, 285 mm BDL, Durban, South Africa, 29° 51' 0" S, 31° E, Sept 1967; SAIAB 25211, adult male, 790 mm TL, 325 mm BDL, 22 Jan 1984; SAIAB 25712, adult male, 443 mm TL, 304 mm BDL, Western Cape, South Africa, 28° 22' 59.99" S, 14° 25' 18&qu : Published as part of Walovich, Kristin A., Ebert, David A. & Kemper, Jenny M., 2017, Hydrolagus erithacus sp. nov. 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