Acropoma profundum, Okamoto, 2014

Okamoto, Makoto, 2014, Acropoma profundum, a New Species of Lanternbelly (Teleostei: Perciformes: Acropomatidae) from the Solomon Islands, Species Diversity 19 (1), pp. 9-14 : 10-12

Acropoma profundum sp. nov.

[New English name: Solomon’s Lanternbelly]

( Figs 1 , 2A , 3A )

Holotype. MNHN 2002-3878 , 40.1 mm SL, female, 09°00′00″S, 159°49′10″E, Solomon Islands, western South Pacific , 1169–1203 m depth, 26 September 2001.

Diagnosis. A species of Acropoma distinguished from its congeners by its long, U-shaped luminous gland, which extends from the throat to just in front of the anal-fin origin.

Description. Dorsal-fin rays VII–I–I, 10. Anal-fin rays III, 7. Pectoral-fin rays 15. Pelvic-fin rays I, 5. Caudal fin: upper and lower procurrent caudal-fin rays 11+10; principal caudal-fin rays 9+8. Vertebrae 10+15. Gill rakers 5 (including 1 rudiment)+12 on first gill arch of right side; 5 (including 1 rudiment)+13 (including 1 rudiment) on first gill arch of left side, total 17–18. Lateral line scales ca. 44; scales above lateral line 3; scales below lateral line 8.

Body moderately elongate, compressed, dorsum slightly elevated, ventral profile less arched, caudal peduncle moderately deep. Head large, slightly compressed. Mouth large, gape oblique; posterior margin of maxilla reaching to below anterior margin of pupil; lower jaw projecting when mouth closed. Single row of villiform teeth on vomer and palatines. Teeth on both jaws small conical; one or two rows anteriorly on upper jaw; single row on lower jaw. Pair of inwardly directed canine teeth near symphyseal region of both jaws. Tongue toothless, rounded, and broad at tip. Snout short and rounded, its length subequal to interorbital width. Eye large, round, orbital diameter subequal to postorbital length; bony rim of orbit raised above upper profile of head. Two closely positioned nostrils, both elliptical, anterior nostril with thin dermal flap. Interorbital space slightly elevated, medially flattened. Preopercle margin smooth. Posterior margin of opercle with two weak spines. Posteroventral margin of interopercle weakly serrated. Subopercle thin, anteroventral margin weakly serrated, posteriorly extended to form thin flap. Lower end of gill opening extending to vertical drawn through anterior margin of eye. Anus nearer to pelvic-fin base origin than to origin of anal fin ( Fig. 3A ). Scales weakly ctenoid, thin, extremely deciduous. Body and head covered with scales. Two separated dorsal fins, eighth spine of dorsal fin lacking any connection with fin membrane (cf. eighth isolated dorsal-fin spine of Okamoto and Ida 2002); first dorsal fin originating slightly posterior to vertical drawn through pectoral fin base, spines weak. Pectoral and pelvic fins slender. Anal fin originating slightly anterior to vertical drawn through middle of second dorsal fin base; anal fin spines moderately developed, first spine extremely small, third spine longest; proximal radial of first pterygiophore with trough-like recess. Caudal fin forked. Supraneural bones 3 (0/0/0+2/1+1/1/1). Luminous gland long and U-shaped, extending from throat to just in front of anal fin base ( Fig. 2A ).

Measurements of holotype, as percentage of SL: head length 34.8; head width 15.3; head height 22.6; body depth 29.1; body width 14.0; caudal-peduncle depth 12.7; caudalpeduncle length 23.1; orbital diameter 12.5; interorbital width 8.3; postorbital length 13.0; upper-jaw length 16.1; lower-jaw length 19.2; snout length 9.9; pre-1st-dorsal-fin length 40.8; pre-2nd-dorsal-fin length 63.6; pre-pectoralfin length 37.4; pre-pelvic-fin length 39.7; pre-anus length 50.1; pre-anal-fin length 68.6; 1st anal-fin spine length 1.6; 2nd anal-fin spine length 4.7; 3rd anal-fin spine length 8.3; pelvic-fin spine length 10.9; 1st dorsal-fin base length 16.6; 2nd dorsal-fin base length 16.6; anal-fin base length 12.5; luminous gland length 41.0; (length of dorsal-fin spines, pectoral-fin length, and pelvic-fin length not measured owing to broken tips).

Color in alcohol ( Fig. 1 ). Body and head light brown except for dark brown opercle; bases of anal and pelvic fins black; caudal and pectoral fins and posterior half of pelvic fin translucent with creamy-white tinge; minute melanophores scattered on dorsal and anal fins, base of caudal fin, and anterior half of pelvic fin; various sizes of melanophores scattered on ventral surface of body; anus pale.

Distribution. Currently known only from the Solomon Islands, western South Pacific, at a depth of 1169–1203 m.

Etymology. The specific name is a Latin adjective, “ profundus ” (meaning “deep”), referring to the depth where this species was collected, deeper than all its congeners.

Comparisons. Acropoma profundum is similar to two previously described species, A. argentistigma and A. japonicum , particularly in having a U-shaped luminous gland, a trough-like recess in the proximal radial of the first anal-fin pterygiophore, and its anus situated nearer to the pelvic-fin base origin than to that of the anal fin ( Fig. 3A ). It differs from them in the length of the luminous gland, the posterior ends of which extend almost to the anal-fin origin in A. profundum ( Fig. 2A ) but only just reach past the anus in A. argentistigma and A. japonicum ( Fig. 2B, E ). In addition to morphological differences, the smallest size at sexual maturity is about 70 mm in total length in A. japonicum (ca. 55 mm SL; Okuda et al. 2005; Yamada et al. 2007), whereas the holotype of A. profundum (smaller at 40.1 mm SL) is already a mature female with a great number of mature eggs.

Acropoma profundum can be distinguished from the other known congeneric species, A. boholensis , A. hanedai , and A. lecorneti , in having a U-shaped luminous gland (vs an elongate luminous gland with the anterior ends not contiguous in A. boholensis and A. hanedai , and an O-shaped luminous gland in A. lecorneti ; Figs 2C, D, F ). In addition, the proximal radial of the first anal-fin pterygiophore of A. profundum differs from that of these three species in having a trough-like recess (vs lacking a trough-like recess or being hollow in A. boholensis and A. lecorneti , and being hollow in A. hanedai ; Yamanoue and Matsuura 2002; Yamanoue and Toda 2008). The location of the anus of A. hanedai , midway between the origins of the pelvic and anal fins, is unique within the genus ( Figs 2D , 3B ). The anus of all its congeners, including A. profundum , is located nearer to the pelvic-fin origin than to that of the anal fin ( Figs 2 A–C, E, F). In addition to the above-mentioned features, A. profundum also differs from A. boholensis in the count of pectoral-fin rays (15 vs 16 in A. boholensis ), and from A. lecorneti in body proportions (body depth 29.1% SL vs 25% SL in A. lecorneti ).

Remarks. Although a large number of specimens of Acropoma were examined in museums worldwide, no additional specimens of the new species were found. The holotype of A. profundum is a 40.1 mm SL mature female. Although the holotype is small, important diagnostic characters of the genus (the shape of the luminous gland, form of the proximal radial of the first anal-fin pterygiophore, and the position of the anus) do not change with growth, as is evident from examination of specimens of various sizes of congeners ( A. argentistigma , 59.0– 107.5 mm SL; A. hanedai , 41.9–193.0 mm SL; A. japonicum , 24.7–143.7 mm SL). Nor is there any geographical variation or sexual dimorphism in these features. Their expression in A. profundum thus serves well to distinguish the new species from its congeners.

The holotype of A. profundum has mature ovaries full of relatively large eggs at several stages of development (the most fully developed eggs are ca. 0.4 mm in diameter). Except for A. lecorneti , the other congeneric species mature at ca. 55–100 mm SL, and do not reach more than 200 mm SL ( Okamoto and Ida 2002; Yamanoue and Matsuura 2002; Okuda et al. 2005; Yamada et al. 2007). Acropoma lecorneti is the largest species in the genus, described by Fourmanoir (1988) and Yamanoue and Toda (2008) from the holotype and an additional specimen measuring 326 mm SL and 221 mm SL, respectively. Although they did not describe the state of the gonads of A. lecorneti , the specimens surely are adults. Thus, A. profundum seems to attain sexual maturity at the smallest size among the species within the genus.

Acropoma profundum is the deepest-living species of the genus, the holotype having been captured at a depth of 1169–1203 m. Acropoma japonicum and A. hanedai have been collected on the continental shelf and continental slope at depths of 50 to 400 m in the Indo-Pacific by bottom trawl ( Brüss and Ben-Tuvia 1983; Yamakawa 1985; Mohsin and Ambak 1996; Randall and Lim 2000; Shinohara et al. 2005; Yamada et al. 2007; Javadzadeh et al. 2012). The holotype of A. lecorneti was collected at a depth of 360 m off the west coast of New Caledonia ( Fourmanoir 1988). Although the depths at which A. argentistigma and A. boholensis occur are currently unknown, the two species have been collected by trawl and landed in fish markets of Southeast Asia and India ( Okamoto and Ida 2002; Yamanoue and Matsuura 2002; Yennawar et al. 2012), which suggests that they are found on the continental shelf and in nearby waters.

Figures

Fig. 1. Acropoma profundum sp. nov., holotype, MNHN 2002-3878, 40.1mm SL, Solomon Islands.

Fig. 2. Schematic diagram of the luminous glands of all six known species of Acropoma. A, Acropoma profundum sp. nov.; B, A. argentistigma; C, A. boholensis (after Yamanoue and Matsuura 2002); D, A. hanedai; E, A. japonicum; F, A. lecorneti (after Yamanoue and Toda 2008).

Fig. 3. Ventral view of the abdomens of two species of Acropoma. A, Acropoma profundum sp. nov., holotype, MNHN 2002- 3878, 40.1mm SL; B, A. hanedai, FRLM 32251, 61.2mm SL, Taiwan.Arrows point to the anus.