Ilyophis arx

Ilyophis arx C. H. Robins 1976

Ilyophis arx Robins, 1976 Ilyophis arx C.H. Robins in Robins & Robins 1976: 245, Figs. 4, 6, 7b, 8. Holotype: ANSP 133808. Type locality: Southeastern Pacific , Galapagos Islands, 01° 48’ S, 90° 19’ W, 3522 m.

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

description

Description. Body moderately elongate, laterally compressed posteriorly (Fig. 2). Body tapers gradually to caudal, deepest body depth anterior to anus. Dorsal-fin origin near posterior half or just behind tip of pectoral fin, predorsal length ca. 14 – 18 % TL. Trunk length moderate, contained about 4 times in TL. Preanus length approximately 3 times in TL, preanal-fin length about 36 % of TL. Head length moderate (ca. 10 – 14 % TL). Gill slits crescentic and horizontal, located ventrally just anterior to and below pectoral fin base. Anterior nostril tubular, directed anterolaterally. Posterior nostril round, just in front of eye. Eye relatively small (9 – 14 % HL). Pectoral fin moderate in size (3.2 – 3.7 % TL, 10 – 27 % HL) with 15 rays. Gape extends to near posterior half of eye. Snout plicate, two main plicae on each side of mid-line, outermost least developed. Tip of lower jaw also plicate, two main plicae on each side of mid-line and occasionally one smaller plica lateral to the main plicae for a total of six. Teeth conical, arranged in bands along maxillary, dentary and intermaxillary / vomer. Teeth not compound. Maxillary teeth in two to four rows (medially) reducing to one

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

diagnosis

Diagnosis. A species of Ilyophis with the following characters. Body without scales. Trunk relatively long (about 21 ‒ 29 % of TL). Dorsal-fin origin (DFO) above posterior third of pectoral fin. Gape of mouth moderate, extending to near rear margin of eye. Teeth not compound. Intermaxillary teeth conical with approximately 16 ‒ 24 teeth in the tooth patch, inner teeth on the patch nearly twice as large as the outer teeth. Vomerine teeth contiguous with intermaxillary teeth with approximately 25 ‒ 30 teeth irregularly biserial to triserial anteriorly and uniserial posteriorly. Both intermaxillary and vomerine teeth set in beds of papillose tissue. Maxillary teeth small, set in irregular rows, 3 rows anteriorly to 6 rows posteriorly. Dentary teeth similar to maxillary teeth except they are slightly larger and more uniform in size anteriorly. Lateral line short, confined to anterior half of body (ca. 35 ‒ 45 % of TL). Cephalic lateralis pores: supraorbital (SO) 3, infraorbital (IO) 5 (including adnasal, AD), preoperculomandibular (POM) 6 ‒ 10. Total vertebrae 129 ‒ 136.

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

discussion

Comparative remarks. Ilyophis arx 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). Head length differentiates I. arx from Meadia abyssalis (Kamohara, 1938) and M. roseni Mok, Lee & Chan, 1991 (head length less than trunk in I. arx versus greater than trunk in M. abyssalis and M. roseni). Vertebral counts also distinguish these species (128 ‒ 137 versus 173 – 178 in M. abyssalis and 198 – 206 in M. roseni). The third species of Meadia, M. minor Vo & Ho, 2021, which has a head length less than trunk, can be differentiated from I. arx by its lower vertebral count (128 ‒ 137 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 lack of scales distinguishes Ilyophis arx from I. brunneus, l. blachei, l. nigeli and I. maclainei sp. nov. Ilyophis arx can also be differentiated from three of these species by its lower vertebrae number (128 ‒ 137 versus 145 – 151 in I. brunneus, 177 – 188 in l. blachei and 140 – 152 in l. nigeli). It can be disting

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