Allinectes pycnosoma (Gilbert & Burke, 1912), 2025

Allinectes pycnosoma (Gilbert & Burke, 1912) , new combination

Stout Snailfish

Figure 1 View FIGURE 1 ; Tables 1 View TABLE 1 and 2 View TABLE 2

Careproctus pycnosoma Gilbert & Burke, 1912b: 372 View in CoL , fig. 14, pl. 46-3 (original description, compared with C. ectenes, in key). Type locality: Japan, off Simushir Island, Kuril Islands, Japan, 419 m (229 fms) depth, Albatross station 4803.— Burke 1930: 108, fig. 24 (description, key).— Orr & Busby 2001: 57 (compared with Prognatholiparis ptychomandibularis).— Chernova et al. 2004: 13 (checklist, possibly in Allocareproctus).— Orr & Busby 2006: 13 (compared with Allocareproctus).— Parin et al. 2014: 314, 324 (checklist, Russia, possibly in Allocareproctus or a synonym of A. jordani).— Murasaki et al. 2018: 240, table 2 (list of characters, compared with C. surugaensis).

Allocareproctus pycnosoma View in CoL : Sheiko & Fedorov 2000: 31 (questionably a senior synonym of A. jordani, C. curilanus, and C. gilberti Jordan & Thompson, 1914).— Parin et al. 2002: S111 (senior synonym of A. jordani, C. curilanus, and C. gilberti Jordan & Thompson, 1914).

Careproctus pycnosoma View in CoL non Gilbert & Burke 1912b: Kido 1985: 14 ([= Allocareproctus tanix]; compared with C. curilanus and C. ectenes).— Kido 1988: 198 (compared with A. jordani).— Mecklenburg et al. 2002: 608 (after Kido 1985; questionably a synonym of A. jordani and C. curilanus).— Murasaki et al. 2018: 241, table 2 (list of characters, compared with C. surugaensis).

Holotype. USNM 73340 About USNM , 39.0 mm, Japan, Kuril Islands , off Simushir Island, 46.7°N, 151.75°E, 419 m (229 fms) depth, 24 June 1906, Albatross Station 4803 . GoogleMaps

Diagnosis. Distinguished from all other species of Allinectes by a combination of pectoral fin shallowly notched and shorter (upper lobe 56.2% vs. 60.6–83.9% HL in other species of Allinectes ), snout blunt, anterior dorsal-fin rays slightly elongate, body typically shorter posterior from anal-fin origin (60.6% vs. 58.4–72.9% SL), and higher counts of pectoral-fin rays (39 vs. 28–37) and pyloric caeca (17 vs. 6–11). Most similar to Allinectes istiophorus and A. busbyi , differing in peritoneum and stomach pale (vs. both dark in A. istiophorus and A. busbyi ), anterior dorsal-fin rays shorter (vs. moderately to strongly elongate). Further differing from A. curilanus and A. ectenes in its blunt non-protruding snout (vs. protruding in A. curilanus and A. ectenes ), lower counts of vertebrae and median-fin rays (vertebrae 49, dorsal-fin rays 45, anal-fin rays 39 vs. 53–59, 48–54, 42–49, respectively, in the other two species combined). Differing further from A. attenuatus and A. nanstanorum in peritoneum pale (vs. dark in A. attenuatus and A. nanstanorum ), and deeper body at anal-fin origin (61.9% vs. 38.8–51.7% HL) and at pelvic disk (73.3% vs. 44.2–67.1% HL).

Description. Body moderately elongate, slightly tapered, robust and rounded anteriorly, compressed posteriorly; depth at pelvic disk 73.3% HL; depth at anal-fin origin 61.9% HL. Head moderately large, 26.9% SL, width 57.1% HL, stout, nape slightly elevated. Snout blunt, not projecting, shorter than orbit, 76.5% OL, 24.8% HL. Mouth slightly inferior; upper jaw 28.6% HL, maxilla extending to anterior rim of orbit, oral cleft extending anterior to anterior rim; mandible 28.6% HL. Premaxillary and mandibular teeth trilobed, forming broad bands. Orbit moderate, 32.4% HL, suborbital depth to upper jaw 10.5% HL, to lower jaw 34.3% HL. Interorbital space broad, bony distance 23.8% HL, convex. Nostril on short tube at level with dorsal part of orbit.

Free neuromasts present ( Burke 1930). Gill opening small, 22.9% HL, upper margin at dorsal rim of orbit, extending ventrally to above pectoral-fin ray 1.

Dorsal-fin rays 45 ( Tables 1 View TABLE 1 , 2 View TABLE 2 ), anteriormost rays slightly longer than succeeding rays, tips free and not embedded in skin ( Gilbert & Burke 1912b), forming a slight notch ( Burke 1930), anteriormost rays now broken, tips of more posterior rays not exserted. Anteriormost dorsal-fin pterygiophore inserted between neural spines 2 and 3. Pre-dorsal-fin length 27.2% SL.

Anal-fin rays 39 ( Tables 1 View TABLE 1 , 2 View TABLE 2 ); one anal-fin pterygiophore anterior to first haemal spine, bearing single ray, tips of all rays not exserted ( Gilbert & Burke 1912b: pl. 46-3). Anal-fin origin below vertebra 11 (caudal vertebra 1), pre-anal-fin length 39.5% SL.

Pectoral fin shallowly notched, with 39 rays ( Tables 1 View TABLE 1 , 2 View TABLE 2 ). Upper lobe relatively short, 56.2% HL, with 30 rays, extending well beyond anus to anal-fin origin, longer than lower lobe. Lower lobe short, 33.3% HL, with 9 rays, extending to anus, well short of anal-fin origin; dorsal rays lengthening to slightly longer rays, ventral rays gradually shortening to ventralmost ray near pectoral symphysis. Tips of all rays 5–20% free of membrane. Notch shallow. Uppermost pectoral-fin ray level with ventral rim of orbit. Insertion of lowermost pectoral-fin ray below midorbit.

Pelvic disk moderate, round, length and width 27.6% HL, anterior lobe slightly developed, flat, distance from tip of snout to pelvic disk 15.4% SL. Anus below anterior part of dorsal fin, closer to disk than anal-fin origin, distance from disk 25.7% HL, distance to anal-fin origin 40.0% HL; distance from snout to anus 27.7% SL, 102.9% HL.

Principal caudal-fin rays 11 ( Kido 1985). Depth at base of caudal fin 15.0% HL.

Vertebrae 49, precaudal 10, caudal 39 ( Tables 1 View TABLE 1 , 2 View TABLE 2 ). Pleural ribs 3, anteriormost small, others long and slender, present on vertebrae 8–10. Hypural plate composed of dorsal and ventral plates with short distal split.

Skin relatively thick; prickles absent. Pyloric caeca 17, short, and bluntly pointed ( Kido 1985).

Coloration. In life, dusky gray, lighter about head and snout ( Gilbert & Burke 1912b; Burke 1930). In preservation, body and fins pale. Peritoneum, orobranchial cavity, stomach, intestines pale, and urogenital papilla pale.

Distribution. The holotype and only known specimen of Allinectes pycnosoma was collected in the Kuril Islands off Simushir Island ( Fig. 1 View FIGURE 1 ) at a depth of 419 m.

Life history. The holotype of 39 mm is immature ( Kido 1985).

Etymology. The specific epithet is from the Greek πυκνός, meaning thick, and σῶμα, meaning “body,” likely an allusion to its thick head relative to A. ectenes , with which it was compared in the original description ( Gilbert & Burke 1912b).

Remarks. I tentatively allocate A. pycnosoma to Allinectes based primarily on the description of the dorsal fin by Gilbert & Burke (1912b) and Burke (1930), as well as its possession of other morphological characters typical of the genus. Both descriptions were based on the holotype and only known specimen ( Orr & Busby 2006) and indicate that the dorsal fin was similar to that of A. ectenes in having the anterior rays either “not shortened” ( Gilbert & Burke 1912b) or longer than succeeding rays and forming a shallow notch ( Burke 1930: 109), a diagnostic character for Allinectes . The specimen is in fair condition overall, although the dorsal-fin rays are clearly broken. However, even though broken, the second dorsal-fin ray is longer than in slightly larger specimens of the small species A. curilanus and longer than in comparable specimens of Allocareproctus , to which it had been tentatively assigned ( Sheiko & Fedorov 2000).