Ilyophis maclainei Tighe, Smith & Merrett 2024, sp. nov.
Creators: name: Tighe, Kenneth A.
name: Smith, David G.
name: Merrett, Nigel R.
name: Frable, Benjamin W.
name: Zajonz, Uwe
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Anguilliformes
Synaphobranchidae
Ilyophis
Ilyophis maclainei

description: Ilyophis maclainei Tighe, Smith & Merrett, sp. nov.
urn:lsid:zoobank.org:act: 294A1599-5A76-467D-B8C5-B7DBF6B28D12
Figures 4‒9, Table 1‒2
Ilyophis arx (not of Robins, 1976). Saldanha & Merrett 1982: 633 (listing of one specimen from Porcupine Sea-Bight, eastern North Atlantic). Merrett & Saldanha 1985: 730‒735 (description of northeastern Atlantic specimens). Robins & Robins 1989:238 (suggestion that northeastern Atlantic population was not Ilyophis arx). Sulak & Shcherbachev 1997: 1163, 1172, 1188 (key, identification as llyophis arx, distribution).
Holotype: BMNH 1995.4.19.31 (male, 242 mm TL), Discovery Collection Station 50710, Goban Spur, off SW Ireland, northeastern Atlantic Ocean, 49° 30’ 06” N, 13° 19’ 54” E; 1800–2000 m; date: 17 October 1979.
Paratype: BMNH 1995.3.29.1 (male, 263 mm TL), Discovery Collection Station 50711, Porcupine Sea-Bight, off SW Ireland, northeastern Atlantic Ocean; 49° 53’ N, 15° 36’ E; 4788 m; date: 18 October 1979.
Referred Specimen: Discovery Collection Station 50517 (female, 237 mm TL, portion of specimen cataloged as BMNH 1996.3.8.2, see remarks below), Goban Spur, off SW Ireland, northeastern Atlantic Ocean, 49° 33’ 30” N, 13° 28’ 00” E; 1785–1794 m; date: 7 June 1979.
Diagnosis. A species of Ilyophis with the following characters. Body covered with scales in an irregular basket-weave pattern. Trunk moderate (about 20% of TL). Dorsal-fin origin above posterior half of pectoral fin. Gape moderate, extending at most to posterior half of eye. Teeth not compound. Intermaxillary teeth conical and acute with approximately 16‒18 teeth in the tooth patch. Vomerine teeth abutting the rear of intermaxillary patch with approximately 25 teeth irregularly biserial anteriorly becoming uniserial posteriorly. Both intermaxillary and vomerine teeth set in beds of papillose tissue. Maxillary teeth arranged in bands of one to four (medially) to one irregular row, with anterior teeth somewhat enlarged. Dentary teeth arranged in bands with roughly three to five series of teeth, with anterior ones (in two rows) the largest. Lateral line extends to approximately 70‒75% the length of body. Cephalic lateralis pores: supraorbital pores (SO) 3, infraorbital pores (IO) 6 (including adnasal pore just posterior to anterior nostril), preoperculomandibular pores (POM) 8‒9, 7‒8 pores in mandibular region and the eighth or ninth pore in a preopercular position. Total vertebrae 131‒134.
Description. Measurements of holotype: total length 240 mm, preanal length 76 mm, predorsal length 36.4 mm, head length 30.0 mm, trunk length 46 mm, snout length 11.8 mm, upper jaw length 14.0 mm, eye diameter 3.3 mm, interorbital width 6.6 mm, gill opening 2.8 mm, intrabronchial distance 5.8, pectoral fin length 7.8 mm, depth at anus 9.9 mm. Meristics and proportional morphometrics of the holotype and paratype are presented in Table 1. Rest of description based on data presented by Merrett & Saldanha (1985). However, it should be noted that the two specimens available for examination have shrunk since originally measured by Merrett and Saldanha (1985).
Body moderately elongate, laterally compressed posteriorly (Fig. 5A). Body tapers gradually to caudal, deepest body depth anteriorly, near anus. Dorsal-fin origin near posterior half or just behind tip of pectoral fin, predorsal length ca. 14–15 % TL. Trunk length moderate (ca. 18–19 % TL), contained about 5 times in TL. Preanal length approximately 3 times in TL, preanal fin length about 31% of TL. Head length moderate (ca. 10–12 % TL) (Fig. 5B). Gill slits crescentic and horizontal, located ventrally just anterior to and below pectoral fin base. Anterior nostril tubular, directed anterolaterally. Posterior nostrils round, just in front of eye. Eye relatively small (10.3–14.3 % HL). Pectoral fin moderate in size (3.2–3.7 % TL, 25–36 % HL) with 15 rays. Gape extends to near posterior half of eye. Snout plicate (Fig. 6A), three main plicae on each side of mid-line, outermost least developed. Outer margins of first and second plicae bear some four and eight papillae respectively, other minute papillae occur along all plical ridges. Tip of lower jaw also plicate (Fig. 6B), two main plicae on each side of mid-line, outermost least developed. Teeth conical, arranged in bands along maxillary, dentary and intermaxillary/vomer [Fig. 7]. Teeth not compound. Maxillary teeth in two to four rows (medially) reducing to one irregular row posteriorly, with anterior teeth somewhat enlarged. Dentary teeth in three to five irregular rows, with anterior ones (in two rows) larger. Intermaxillary teeth with 16–18 strong teeth concentrically arranged around tooth patch with inner teeth slightly larger. Vomerine teeth abutting intermaxillary tooth patch with two irregular rows anteriorly (with 10–11 teeth each) and converging to single row posteriorly (with three to four teeth), total number of vomerine teeth 24–25. Both intermaxillary and vomerine teeth surrounded by papillae. Cephalic lateralis pores (Fig. 5B): supraorbital pores three, first located between first and second plicae on snout. second on snout at level of the dorsal rim of anterior nostril, third on dorsal of snout above adnasal pore; infraorbital pores six, first (adnasal pore) just posterior to dorsal rim of anterior nostril, second on lip just posteroventral to base of anterior nostril, third on lip one third of the way between anterior and posterior nostrils, forth on lip anteroventral to posterior nostril, fifth on lip just ventral to the anterior margin of the eye, sixth on lip slightly posterior to posterior margin of eye; preoperculomandibular pores eight to nine, first very small and located within plicae at tip of lower jaw, remaining 6–7 mandibular pores spaced progressively far apart along jaw, last mandibular pore located approximately below rictus, 1–2 preopercular pores located posteriorly in the opercular region. Only the paratype has 2 preopercular pores which are on the left side of the head and are set very close together in a pair. Lateral line incomplete, relatively long; pores extend to approximately 75% length of body. Three to six pores anterior to pectoral-fin base, 7–10 pores anterior to dorsal-fin origin, 29–32 pores anterior to anus, 88–94 total pores. Scales present all over body, except head, arranged broadly in classic basket-weave pattern (Fig. 8A–D). Number, shape, and disposition variable. Scales generally elongate in shape, but length may vary between 2–3 scale width [type α scales (Fig. 8B) or 10–15 or more times scale width [type β scales (Fig. 8C–D). Disposition of scale types variable between specimens and not necessarily bilaterally symmetrical on an individual. Type α scales present in only one specimen (Fig. 8A), one patch on left side on belly posterior to left pectoral fin and two patches on right side, one between lateral line and dorsal profile, posterior to right pectoral fin, and second on beginning of caudal region between lateral line and ventral profile. Type β scales are most common and present on all three specimens. Vertebral numbers: predorsal 8–9, preanal 31–32, total 131–134.
Remarks. The Referred Specimen listed above (Discovery Collection Station 50517) was one of the original three specimens described by Merrett & Saldanha(1985). This specimen was also examined by Sulak& Shcherbachev (1997). Since then, most of the specimen has apparently been lost. Only the gonads of this female specimen are still in existence and are cataloged at the Natural History Museum as BMNH 1996.3.8.2. However, since much of the data on the northeastern Atlantic population provided by Merrett & Saldanha (1985) was based on this specimen, we have included it in the description. If the body of this specimen is ever found, it should be reunited with BMNH 1996.3.8.2.
Comparative remarks. Ilyophis maclainei can be distinguished from all members of the genera Atractodenchelys, Dysomma Dysommina, and Linkenchelys by the lack of compound teeth in the dentition (versus at least vomerine teeth compound). Ilyophis maclainei is distinguished from Meadia abyssalis and M. roseni by its head length shorter than its trunk (versus head length longer than trunk). Finally, it can be distinguished from a third species in the genus Meadia, M. minor, by its higher vertebral number (131–134 versus 118–122 in M. minor).
Morphometric, meristic, and morphological data for all described species of the genus Ilyophis are presented in Table 2. The presence of scales distinguishes I. maclainei from other members of the genus Ilyophis except I. brunneus, l. blachei and l. nigeli. Ilyophis maclainei is differentiated from those three species by its lower vertebrae number (131–134 versus 145–151 in I. brunneus, 177–188 in l. blachei and 140–152 in l. nigeli). I. maclainei can be distinguished from I. arx with which it had previously been confused not only by the presence of scales (versus no scales in I. arx), but also by its longer lateral line (ca. 70–76% TL versus ca. 35–46% TL in I. arx), the correlated higher number of lateral line pores (88–94 versus 31–47 in I. arx), and a lower number of preanal fin vertebrae (33–34 versus 37–42 in I. arx).
Etymology. We take pleasure in naming this new species after our colleague James Maclaine, Senior Curator of Fishes at The Natural History Museum, United Kingdom, for his dedication to the collections under his care, and especially his hard work in incorporating the collections of the Institute of Oceanographic Sciences/National Oceanography Centre into the Natural History Museum, United Kingdom.
Distribution. Ilyophis maclainei is known only from the three specimens which were collected in the vicinity of the Porcupine Sea-Bight and Goban Spur areas, off SW Ireland at a depth range of 1785 to 4788 m (Fig. 9).
Whether the species is endemic to this area or might be more widely distributed in the slope region of the eastern North Atlantic is unknown.
Comparative Specimens Examined. Ilyophis brunneus: USNM 44403 (holotype, 380 mm TL), Eastern Pacific Ocean, Galápagos Islands, Near San Cristóbal Island [Chatham Island], 0° 36' 30" S, 89° 19' 00" W, Albatross station 2808, depth 634 fathoms (1160 m). USNM 185665 (1, 312 mm TL), Gulf of Mexico, off Mississippi Delta, 28° 58’ N, 88° 11’ W, Oregon station 2822, depth 1143 m. USNM 195901 (1, 414 mm TL), Gulf of Mexico, off Alabama, 28° 55’ N, 87° 49’ W, Oregon station 2022, depth 1646 m. USNM 197115 (1, 403 mm TL) North Atlantic Ocean, Straits of Florida, north of Cay Sal Bank. 24° 24’ N, 80° 00’ W, depth 400–400 fathoms. USNM 212185 (1, 262 mm TL), Southern Caribbean Sea, off western Venezuela, 11° 44’ N, 68° 43’ W, depth 1006 m. Ilyophis saldanhai: MMF 27080 (2, 354– 382 mm TL), MMF 27081 (1, 409 mm TL); North Atlantic Ocean, Mid-Atlantic Ridge, Broken Spur Hydrothermal Vent Field. 29 08’N, 43 13” W. 3020 m.
description: Published as part of Tighe, Kenneth A., Smith, David G., Merrett, Nigel R., Frable, Benjamin W. & Zajonz, Uwe, 2024, Redescription of the eel Ilyophis arx Robins, 1976 (Anguilliformes: Synaphobranchidae: Ilyophinae) with a description of a new species of Ilyophis, and a taxonomic synopsis of the Ilyophinae, pp. 35-57 in Zootaxa 5506 (1) on pages 44-48, DOI: 10.11646/zootaxa.5506.1.2, http://zenodo.org/record/13746099