Chiloconger dentatus ( Garman , 1899 )

Smith, David G. & Karmovskaya, Emma S., 2003, A new genus and two new species of congrid eels (Teleostei: Anguilliformes: Congridae) from the Indo­West Pacific, with a redescription and osteology of Chiloconger dentatus, Zootaxa 343, pp. 1-19 : 3-9

Chiloconger dentatus ( Garman, 1899)

( Figs. 1–6 )

Atopichthys dentatus Garman, 1899: 330 , pl. 66 (figs. 3–3a) Atopichthys obtusus Garman, 1899: 337 , pl. 67 (figs. 4–4a) Chiloconger labiatus Myers and Wade, 1941: 66 , pl. 7 Paraconger dentatus, Raju, 1985: 8 , fig. 4

Gorgasia obtusa, Raju, 1985: 11 , figs. 5F1, 5F2, 6.

Study material (15 adult specimens, 80–270 mm TL; 2 larval specimens, 80–100 mm SL): LACM 21559 (holotype of Chiloconger labiatus , 82 mm TL), Port Utría, Colombia, 6° 01' N, 77° 22' W, 15–30 fm (27–55 m), 25 Feb. 1938, mud and sand bottom. Others: CAS 38794 (1: 80), Costa Rica, 9° 19’ 32” N, 84° 29’ 30” W, 42 fm (77 m), 1 March 1938, “Zaca” 214­D­1; LACM 24206 (1: 145), Pacific, Panama, 7º 49’ N, 82º 23’ 30” W, 54 fm (99 m), 27 March 1939, green mud; LACM 33590­4 (1: 193), Costa Rica, 9º 30’ 00” N, 84º 45’ 12” W, 135–102 fm (247– 187 m), 17 May 1973; SIO 62–701 (1: 214), 23º 58.3' N, 111º 01.0’ W, 50 fm (92 m), 4 Dec. 1962, 0 250–0 320 hr, 16­ft otter trawl; SIO 65–227 (1: 222), 24º 12.3’ N, 111º 29.7’ W, 56–58 fm (102–106 m), 27 June 1965, 4­ft otter trawl; UCLA W56–118 (1: 250), Pacific, Mexico, Sinaloa, 25 miles SE of Bahía Topolobampo, Gulf of California, 7–13 June 1956; UCR 334­12 (1: 270), Costa Rica, near Puntarenas; UCR 681­2 (93–109), Costa Rica, Isla del Caño, N. side, 16 March 1972; UCR 686­1 (3: 81–93), Costa Rica, Isla del Caño, 17 March 1972; USNM 195586 (1: 268), Pacific, Mexico, Sinaloa, 25° 18’ N, 108° 48’ W, 2 miles south of entrance of Bahía Topolobampo, 7– 13 June 1956; USNM 316123 (ex UCR 489­18) (1: 237), Costa Rica, Puntarenas Province, Golfo de Nicoya, 26–29 Oct. 1970; MCZ 28421 (larva, holotype of Atopichthys obtusus , 100 mm SL), off Colombia, 7° 33' N, 79° 17' W, 8 March 1891, "Albatross" 3386; MCZ 28427 (larva, holotype of Atopichthys dentatus , 80 mm SL), off Panama, 2° 34' N, 82° 29' W, 4 March 1891, "Albatross" 3375.

Diagnosis. A moderately elongate, small congrid eel of the subfamily Bathymyrinae , with short, bluntly­rounded snout and a dark margin on the dorsal fin anteriorly. Total vertebrae 118–122, preanal LL pores 19–27, predorsal length 20–26 % TL.

Description. Measurements, as % TL: preanal 38.7–49.1, predorsal 20.1–26.2, head 16.8–20.1, depth at anus 4.3–7.8; as % head length: snout 14.0–19.3, eye 13.8–20.9, upper jaw 22.1–32.5, gill opening 10.4–24.4, interbranchial 10.4–28.1, pectoral fin 15.9–37.4. Meristic characters: preanal LL pores 19–27, POM pores 6–7, IO pores 3 or 4, SO pores 3 or 4, STC pores 0, branchiostegal rays 9–10, pectoral rays 16–18, predorsal vertebrae 13– 14, preanal vertebrae 42–44, total vertebrae 118–122.

Moderately elongate, round in cross section anteriorly, becoming more compressed posteriorly, anus before midlength ( Fig. 1­1 ). Dorsal­fin origin over posterior part of appressed pectoral fin, continuous around end of tail with caudal and anal fins; caudal fin broadly rounded, its rays reduced in length, shorter than adjacent dorsal and anal rays; anal­fin origin immediately behind anus; pectoral fin well developed. Gill opening a nearly vertical slit slightly below middle of body, its upper end slightly below upper edge of pectoral­fin base, thus not completely enclosing the pectoral fin (the original illustration in Myers and Wade, 1941, pl. 7, reproduced in slightly modified form here as Figure 1 , was wrong in this regard); interbranchial nearly equal to gill opening.

Head ( Fig. 1­2 ) deepest about midway between pectoral fin and snout tip, tapering anteriorly and posteriorly from this point; snout short, equal to or slightly less than eye diameter. Eye large. Anterior nostril tubular, near tip of snout; posterior nostril a rounded pore with a slightly raised rim, near anterior margin of eye, distinctly below mideye level. A broad, well developed upturned flange on upper lip, beginning on side of snout about 1­ 2 nostril diameters behind anterior nostril, deepest at middle of length, narrowing posteriorly, ending under anterior part of eye, somewhat before rictus, enclosing an excavated space. A prominent downturned flange on lower lip.

Head pores small, often difficult to see ( Fig. 1­2 ; Fig. 2 , left). Supraorbital canal with three or four pores; a small pore (ethmoidal pore) near tip of snout, near edge of lip; a second somewhat larger pore above the preceding, at level of anterior nostril and about one nostril diameter anterior to nostril; a small papilliform pore immediately above base of anterior nostril, which is either the third supraorbital pore or the adnasal pore; a small pore directly above posterior nostril. Infraorbital canal with three or four pores (depending on which canal the small pore above the anterior nostril belongs to); a pore on upper lip just below anterior end of labial flange; a small pore on upper lip near posterior end of labial flange and shortly anterior to rictus; a small pore on side of head directly behind rictus, slightly behind a vertical through posterior edge of eye; no pores in postorbital section of canal. Preoperculomandibular canal with 4–5 pores before rictus and 2 pores behind (one specimen had 1 pore here on one side). No pores in supratemporal commissure.

Teeth small, conical ( Fig. 1–3 ; Fig. 2 , right). Intermaxillary teeth in two transverse rows, forming a roughly semicircular patch, separated from vomerine patch. Vomerine teeth in a slightly elongate patch, broadest anteriorly, narrowing posteriorly. Maxillary teeth irregularly triserial, not forming a cutting edge. Mandibular teeth in approximately four series at anterior end of jaw, narrowing posteriorly to three or two series, not forming a cutting edge.

Gas bladder loosely attached to body wall by mesentery, extending from anterior end of stomach to slightly beyond posterior end of stomach. Stomach ends about halfway between pectoral fin and anus.

Color light brown, with minute dark specks dorsally and laterally; dorsal fin with a dark margin anteriorly, fading to a faint line posteriorly. Anal and caudal fins without a dark margin. Esophagus black, stomach pale. Holotype of C. labiatus has remnants of larval pigmentation: a row of small melanophores along lateral midline, not quite one per segment; a few melanophores on ventral midline, including two under liver. Six other specimens, 81–145 mm TL, also show traces of larval pigment.

Osteology. Neurocranium ( Fig. 3 ) moderately short, triangular in dorsal view, orbital and antorbital portion relatively narrow in dorsal or ventral view; lateral ethmoid process present, relatively slender; sphenotic, pterosphenoid, and prootic fused into a single unit; supraoccipital present; otic bullae slightly inflated.

Maxilla and mandible ( Fig. 4 ) typical of Congridae ; maxilla with a well developed pedicel anteriorly and an expanded, ventrally deflected flange at posterior end.

Suspensorium ( Fig. 4 ) relatively short, inclined anteriorly; pterygoid broad, well developed.

All four opercular elements ( Fig. 4 ) present, well developed; posterior margin of opercle smooth.

Pectoral girdle ( Fig. 4 ) complete, well developed. Supracleithrum well developed, expanded dorsally forming three lobes; cleithrum without a sharp bend dorsally; scapula and coracoid both well developed, embedded in a cartilaginous matrix; four actinosts.

Hypohyals absent; ceratohyal and epihyal moderately short; nine branchiostegal rays in specimen examined, posteriormost ray expanded near base into a posteriorly directed lobe; glossohyal moderately stout with a ventral keel; urohyal slender, shaft compressed, not trifurcated posteriorly. ( Fig. 5 )

Branchial arches ( Fig. 5 ) typical of Congridae ; first three basibranchials ossified, fourth cartilaginous, fifth absent; first two hypobranchials ossified, third cartilaginous, fourth and fifth absent; five ceratobranchials present and ossified, fifth slender and reduced; lower pharyngeal tooth plates moderately developed; first through fourth epibranchials, second and third infrapharyngobranchials present; upper pharyngeal tooth plate moderately developed, undivided.

Anteriormost epineurals not fused to neural arch; abdominal vertebrae with broad, almost horizontally inclined parapophyses; pleural ribs present; caudal vertebrae with epicentral processes. In specimen examined, first rib on 12th vertebra, dorsal­fin origin over 13th–14th vertebra, first closed hemal arch on 47th vertebra, total vertebrae 117+ (caudal skeleton missing). ( Fig. 6 )

Ossicles in cephalic lateralis canals incompletely ossified, outlines unclear in specimen examined.

Distribution and habitat. Found along the western coast of Mexico, Central and South America from the southern Gulf of California to Colombia, in depths of 27– 247 m. It has not been recorded from any of the oceanic islands of the eastern Pacific.

Remarks. Chiloconger dentatus is unusual among congrids in having far fewer lateral­line (LL) pores than vertebrae. The number of preanal LL pores, 19–27, is barely more than half the number of preanal vertebrae, 42–44. This species was first described by Garman (1899) from two then­unidentified leptocephali, Atopichthys dentatus and Atopichthys obtusus , the former premetamorphic and the latter metamorphic. Raju (1985: 8) assigned A. dentatus to Paraconger , based on similarities to known larvae of that genus. He erroneously assigned A. obtusus to the heterocongrine genus

Gorgasia . Grove and Lavenberg (1997: 179) cited all three names and selected dentatus as the valid name.

Figures

FIGURE 1. Chiloconger dentatus (from Myers and Wade, 1941, pl. 7). Note: the figure has been modified here to show the correct position of the upper end of the gill opening.

FIGURE 2. Chiloconger dentatus. Left, head showing position of nostrils and pores; right, upper dentition (one side of specimen illustrated is damaged).

FIGURE 3. Neurocranium of Chiloconger dentatus in dorsal (top) view, lateral (middle) view, and ventral (bottom) view. BO, basioccipital; BS, basisphenoid; EP, epiotic; EX, exoccipital; F, frontal; lep, lateral ethmoid process; PEV, premaxillary ethmovomerine complex; P, parietal; PRO, prootic; PS, parasphenoid; PTO, pterotic; PTS, pterosphenoid; SOC, supraoccipital; SPH, sphenotic. Note: right otic region damaged.

FIGURE 4. Chiloconger dentatus. Upper and lower jaws (upper left); suspensorium (upper right); opercular apparatus (lower left); pectoral girdle (lower right). AC, actinost; CL, cleithrum; CO, coracoid; HM, hyomandibula; IOP, interopercle; OP, opercle; POP, preopercle; PTG, pterygoid; QU, quadrate; SC, supracoracoid; SCL, supracleithrum; SOP, subopercle.

FIGURE 5. Chiloconger dentatus. Hyoid arch (left) and branchial arch (right). BB, basibranchial; BR, branchiostegal rays; CB, ceratobranchial; CH, ceratohyal; EB, epibranchial; EH, epihyal; GH, glossohyal; HB, hypobranchial, IB, infrapharyngobranchial; LP, lower pharyngeal tooth plate; UH, urohyal; UP, upper pharyngeal tooth plate. Glossohyal and urohyal in ventral (top) and lateral (bottom) view, anterior end to left; ceratohyal, epihyal and branchiostegal rays of left side, dorsal view; branchial arches, ventral elements in ventral view, dorsal elements left side in dorsal view.

FIGURE 6. Chiloconger dentatus, vertebrae. A, anteriormost four vertebrae, left side. B, Abdominal vertebra, anterior view. C, Abdominal vertebra, left lateral view. D, Caudal vertebra, left lateral view. E, Caudal vertebra, anterior view. EN, epineural; EP, epipleural; EPR, epicentral process; PP, parapophysis; PR, pleural rib.