Trichonotus somaliensis, Katayama, Eri, Motomura, Hiroyuki & Endo, Hiromitsu, 2012

Katayama, Eri, Motomura, Hiroyuki & Endo, Hiromitsu, 2012, A new species of Trichonotus (Perciformes: Trichonotidae) from Somalia and redescription of Trichonotus cyclograptus (Alcock, 1890) with designation of a lectotype, Zootaxa 3565, pp. 31-43 : 35-38

Trichonotus somaliensis , new species

[New English name: Somalian Sand diver] ( Figures 4–5 ; Tables 1–2)

Trichonotops sp. (1): Kotthaus, 1977: 51 (description). Trichonotops sp. (2): Kotthaus, 1977: 51 (description).

Holotype. ZMH 25713, 83.2 mm SL, coast of Somalia, Agassiz Trawl, 37–38 m depth.

Paratypes. 12 specimens: ZMH 25714, 7 males and 5 females, 61.3–81.5 mm SL, same data as holotype.

Non-type materials. 11 specimens: ZMH 5320, male, 72.4 mm SL, ZMH 5321, 10 females, 45.0–74.0 mm SL, Mogadishu, Somalia, Agassiz Trawl, 37– 78 m.

Diagnosis. Trichonotus somaliensis is distinguished from other congeners in having the following combination of characters: dorsal-fin rays III–IV, 44–47; anal-fin soft rays 35−38; lateral-line scales 54−56; gill rakers 5–6+18–24; entire body scaled; a longitudinal row of 12–14 blotches on body in both sexes; no elongated dorsalfin spines, but high dorsal fin overall; first dorsal-fin soft ray length in males 19–28% of SL; no free dorsal pterygiophores.

Description. Data for the holotype presented first, followed by those for the paratypes in parentheses. Dorsalfin rays III–IV, 44–47; anal-fin rays I, 35−38; pectoral-fin rays 13–14; caudal-fin rays 13–14; lateral-line scales 54−57; scales above lateral line 3.5–4.5; scales below lateral line 5.5–6; median predorsal-fin scales 7−10 (damaged in most specimens); gill rakers on 1st arch 5−6+18−24; pseudobranchial filaments 9–11; vertebrae 52–54.

Proportional measurements are shown in Table 1. Body long, slightly, cylindrical, compressed posteriorly. Snout long, pointed. Mouth large, maxilla reaching posteriorly to a vertical through anterior pupil. Lower jaw extending anteriorly beyond upper jaw tip, bordered along side by uniserial row of 16–18 short cirri; lower jaw tip slightly fleshy. Posterior rim of opercle just reaching pectoral-fin base in males, not so in females. Gill membranes free from isthmus. Gill rakers long and spinous, the longest more-or-less subequal to longest gill filaments. Tongue very narrow, slightly expanded anteriorly, tip rounded. Eye large, round, its length similar to snout, with ca. 10 hair-like “lashes” on iris flap. Suborbital skin fold slightly covering lower margin of eye, discontinuous at mid way, with 3−6 embedded scales adjacent to infraorbital cephalic sensory canal ( Fig. 5 ). Interorbital space narrow, 1/3 eye diameter. Nostrils small, closer to snout tip than to anterior margin of eye. Anterior nostrils short and tubular, posterior pore-like. Tip of infraorbital canal closely adjacent to supraorbital canal, but separated anterior to eye ( Fig. 5 ). Cycloid scales covering body; posterior edge of scales slightly angular. Lateral line along mid-body; each associated scale rhomboid with anterior edge depressed and a posterior notch. Scales on abdomen smaller than those on sides of body, 18–20 rows anterior to anus. Scales between supratemporal cephalic sensory canal and dorsal-fin origin of similar size to those on body, diagonally arrayed. A row of 3–6 embedded scales on posteroventral margin of eye, just ventral to infraorbital canal. Small scales posteriorly on pectoral-fin base, half size of body scales. Upper jaw teeth near symphysis large, canine-like, in 5–6 irregular rows, becoming small, conical, in 2–4 irregular rows posteriorly. Lower jaw teeth large, canine-like in a single row anteriorly; gradually decreasing in size and becoming conical, in 2–4 irregular rows posteriorly. Head of vomer crescentic, palatines narrow with villiform teeth. First 1 or 2 dorsal pterygiophores located between 4th and 5th neural spines; no free pterygiophores. First anal pterygiophore located below 15th or 16th vertebra.

Dorsal-fin spines flexible, not filamentous, dorsal fin height equal to twice body depth in males, equal to body depth in females. Anal-fin spine flexible, shorter than adjacent soft rays in both sexes. Anal-fin rays unbranched, except for last ray. Caudal fin rounded in males, double truncate in females, uppermost and undermost rays short, unbranched. Pectoral fin uppermost 2 rays and lowermost 3 rays unbranched, other rays branched. Pelvic fin insertion anterior to pectoral-fin base, extending beyond anus only in males; spine shorter than 1st soft ray, 3rd soft ray subequal to longest 4th soft ray. First 2 dorsal pterygiophores located between 6th and 7th neural spines; 2 free pterygiophores between 6th and 7th spines. First anal pterygiophore located below 15th vertebra.

Tip of infraorbital canal closely adjacent to supraorbital canal, but separated anterior to eye. Infraorbital canal with 8–9 pores; mandibular canal with 3 pores, continuous with preopercular canal; preopercular canal with 11 pores, upper 2 pores with 2 rows ( Fig. 5 B).

Color when fresh. Unknown.

Color in alcohol ( Fig. 4 ). Ground color of body uniformly yellowish-brown. Upper half of eye black, lower white. 12–14 brownish markings on and above lateral line, size equal to eye in both sexes. All fins whitish with translucent membrane. No black markings on anterior dorsal fin in females.

Distribution. Known only from Somalia, in a depth of 37– 78 m.

Etymology. The specific name is derived from the type locality.

Sexual dimorphism and morphological changes with growth. Male and female Trichonotus show remarkable differences in body size, morphology and coloration (e.g., Shimada & Yoshino 1984, Randall & Tarr 1994; Clark & Pohle 1996). Kusen et al. (1991) reported that Trichonotus filamentosus underwent protogynous hermaphroditism, following an examination of body sizes, otoliths and gonads. We suggest that T. somaliensis is also protogynous, due to males being larger than females. The body sizes of the largest females and smallest males of T. somaliensis and T. arabicus examined herein indicated that sexual changes probably occur at ca. 75 and 105 mm SL, respectively, female and male size ranges overlapping between 69.6 and 74.1 mm SL in T. somaliensis . However, sexual changes in T. cyclograptus cannot be confirmed since no female specimens have been found. Analyses of 32 measurements in T. somaliensis and T. arabicus indicated that the relative lengths of the dorsal, pelvic and caudal fins changed with growth ( Fig. 7 ), the length of the dorsal fin becoming significantly greater at ca. 69.6–83.2 mm SL in T. somaliensis , and ca. 106.8–135.9 mm SL in T. arabicus , indicating male morphs ( Fig.

7A). Pelvic and caudal fins also became relatively longer with growth, their proportions clearly changing at ca. 70 mm SL in T. somaliensis and ca. 100 mm SL in T. arabicus ( Fig. 7 B, C).

Comparisons. Among the species of Trichonotus lacking elongated dorsal-fin spines, Trichonotus somaliensis is most similar to T. arabicus (Arabian Gulf and Oman) and T. cyclograptus (Bay of Bengal) (also having only 3–4 dorsal-fin spines and a darkly marked or lined body). However, the present new species differs from the aforementioned in having 54−57 lateral-line scales (vs. 55–57 in T. arabicus and 57−59 in T. cyclograptus ) (Table 2), no free pterygiophores (vs. 1 or 2), 12–14 body markings in both sexes (vs. 14 and 12 in males), a short snout, its length 24–28% of HL (vs. 26–28% and 26–28%), the 1st dorsal-fin soft ray length in males 19.4–27.4% of SL (vs. 13.8–17.4% and 14.5%), the dorsal-fin length in males19.4–27.6% of SL (vs. 17.6–22.8% of SL and 17.8% of SL) ( Fig. 7 A) and a small body size in males, 69.1–83.2 mm SL (vs. 106.8–141.4 mm SL and 106.2–109.7 mm SL), in addition to the above-mentioned growth related differences. Trichonotus somaliensis also has a unique character within the genus Trichonotus , i.e., presence of 2 rows of 3rd and 4th preopercular pores (vs. single row). Female Trichonotus somaliensis can also be distinguished from female T. arabicus by markings on the body, i.e., a longitudinal row of 12–14 blotches (vs. a longitudinal stripe above the lateral line).

Figures

FIGURE 4. Preserved specimens of Trichonotus somaliensis. (A) ZMH 25713, holotype, male, 83.2 mm SL; (B) ZMH 25714, paratype, female, 74.0 mm SL.

FIGURE 5. Cephalic sensory pore system in Trichonotus somaliensis, ZMH 25713, 83.2 mm SL. (A) dorsal view, (B) lateral view, (C) ventral view. Arrows indicate “ doubled ” pores. Bar indicates 5 mm.

FIGURE 7. Relationships of (A) 1 st dorsal-fin ray length, (B) longest pelvic-fin soft ray length, (C) longest caudal-fin ray length in Trichonotus arabicus (triangles), T. cyclograptus (square), T. somaliensis sp. nov. (circles).