Apterichtus succinus, Hibino, Yusuke & Kimura, Seishi, 2016

Hibino, Yusuke & Kimura, Seishi, 2016, A new species of Apterichtus (Anguilliformes: Ophichthidae) from the Marquesas Islands, Zootaxa 4117 (1), pp. 146-150 : 146-150

publication ID	https://doi.org/ 10.11646/zootaxa.4117.1.10
publication LSID	lsid:zoobank.org:pub:9E563E76-E83B-45A2-BE87-2A552F95FD14
DOI	https://doi.org/10.5281/zenodo.6055264
persistent identifier	https://treatment.plazi.org/id/734F8D4B-17C2-4E1E-ADE4-77FA3409619E
taxon LSID	lsid:zoobank.org:act:734F8D4B-17C2-4E1E-ADE4-77FA3409619E
treatment provided by	Plazi
scientific name	Apterichtus succinus
status	sp. nov.

Treatment

Apterichtus succinus View in CoL sp. nov.

Figures 1 View FIGURE 1 , 2 View FIGURE 2 , 3 View FIGURE 3 a; Table 1

Apterichtus View in CoL sp.: Delrieu-Trottin et al., 2015: 4 (listed; Marquesas Islands).

Holotype. USNM 409323, 175 mm TL, female with mature eggs (0.7–0.8 mm in diameter), 9.386’ S, 140.119’ W, Bay of Vaiehu, Ura Pou Island, Marquesas Islands, depth 25 m, flat sand bottom, collected by Jeffery T. Williams et al., 4 Nov. 2011.

Diagnosis. An elongate species of Apterichtus with the following combination of characters: tail 1.8, head 14.8, and body depth 69.8 in total length; tip of lower jaw between verticals through anterior margin of eye and mid-eye; four preopercular and five supratemporal pores; teeth conical, uniserial on jaws, a single vomerine tooth; head and breast white, body yellowish brown with numerous small orange-brown spots mainly larger than eye on head and nape but a few spots smaller than a half of eye; and VF 54-133.

Counts and measurements (in mm) of the holotype. Preanal vertebrae 54; total vertebrae 133; preanal lateral-line pores 55, 6 pores in branchial region. Total length 175; head 11.8; trunk 62.8; tail 99.4; body depth at gill openings 2.5; body width at gill openings 1.9; body depth at anus 2.2; body width at anus 2.0; head depth at branchial basket 2.9; head width at branchial basket 2.3; snout length 1.4; tip of snout to tip of lower jaw 2.1, tip of snout to rictus 4.5; eye diameter 1.1; interorbital distance 0.4; gill-opening length 1.6; isthmus width 0.5.

Description. Body elongate, subcylindrical, tip of tail strongly laterally compressed and extremely pointed ( Fig. 1 View FIGURE 1 ). Head short; preanal length much shorter than tail, 2.3 in TL. Snout short, its length slightly longer than eye diameter; its tip prominently pointed; short median groove ventrally on snout, its anterior tip below anteriormost margin of second infraorbital pore; slope of dorsal surface of snout approximately 40° relative to underside of snout. Anterior nostril tubular but extremely short; posterior nostril oval in shape with an inner valve, located on anteroventral margin of eye, opening ventrally. Eyes moderate in size, covered by a transparent skin; center of eye anterior to mid-jaw. Mouth inferior, distance from tip of snout to anterior tip of lower jaw almost equal to twice eye diameter; lower jaw short, its tip pointed and located between verticals through anterior margin of eye and center of eye; rictus short, posterior end well behind a vertical through posterior margin of eye; lips smooth, with distinct folds, fold on upper lip extending from a vertical through anterior margin of posterior nostril to posterior end of rictus. Gill openings entirely ventral, slit-like in shape, with its diameter less than twice eye diameter; anterior margins of gill openings close-set but not connected. Sensory pores on head developed, arrangement of those pores as follows ( Fig. 2 View FIGURE 2 a): 1 + 6 on supraorbital, 3 + 4 on infraorbital, five on lower jaw, four on preopercle, and five on supratemporal, one of those on mid-temporal; a single median interorbital pore. Lateral-line pores small but obvious. Lateral line almost complete except for near tip of tail. Teeth ( Figs. 2 View FIGURE 2 b, c) pointed, slightly recurved posteriorly; teeth on jaws uniserial; a single vomerine tooth on anterormost vomer, smoothly connected with upperjaw teeth; intermaxillary teeth larger and more slender than jaw teeth, arranged in a chevron shape along with edge of pre-ethmoid; intermaxillary teeth visible when mouth closed. All fins absent.

Coloration. Ground color of body light reddish brown except white head and nape; head and nape with vivid reddish oval or circular spots, mostly equal to or slightly larger than eye diameter, only a few spots smaller than half of eye diameter ( Fig. 3 View FIGURE 3 a); remainder of body with numerous faint brown dots; iris light blue. In alcohol preservative, body mostly pale yellow, with faint pale brown spots on head and nape.

Etymology. The scientific name succinus , the Latin name of amber, refers to its coloration and the shape of its head and nape markings.

Distribution. Known only a single specimen collected from shallow sandy bottom (25 m depth) of the Marquesas Islands.

Remarks. The combination of preopercular and supratemporal pore counts is one of the most important diagnostic characters in the genus ( McCosker & Hibino, 2015). Although the present new species agrees with Apterichtus ansp ( Böhlke, 1968) , Apterichtus caecus ( Linnaeus, 1758) , Apterichtus gracilis ( Kaup, 1856) and Apterichtus jeffwilliamsi McCosker & Hibino, 2015 in those counts, the new species differs from A. ansp and A. gracilis in the presence of spots on the head (vs. absent) and the number of vomerine teeth (1 vs. 3–4 in A. ansp and 2–3 in A. gracilis ). It differs from A. caucus in the size of spots on the head (large spots equal to or longer than eye vs. smaller than eye), the number of vomerine teeth (1 vs. 8–14), and the location of lower-jaw tip (between verticals through anterior margin of eye and mid-eye vs. anterior to anteriormost margin of eye). Apterichtus succinus also differs from A. jeffwilliamsi in its snout length and profile (snout length 11.9% HL vs. 13.4–17.8% HL; profile 40° vs. 30°), size of spots (generally equal or larger than eye vs. smaller than eye diameter), and the shape of the anterior nostril (short tube vs. simple hole without tube). The present new species closely resembles Apterichtus klazingai Weber, 1913 in the location of its lower-jaw tip, the presence of head spots, snout profile of 40°, and in total vertebral count. The former species differs from the latter in its count of preopercular pores (4 vs. 3). Apterichtus klazingai is the most widespread species, known from South Africa to French Polynesia, and it has high variation in its coloration or vertebral counts. Nevertheless, there is no variation in its counts of preopercular and supratemporal pores as far as our materials of 66 specimens collected from various localities. As stated above, these counts are very important to identify species of Apterichtus because all congeners have a unique combination of counts with minor exceptions ( Hibino et al., 2014; McCosker & Hibino, 2015). Consequently, the above difference is regarded as an interspecific difference. In addition, the new species can be distinguished from A. klazingai by having fewer preanal vertebrae (54 vs. 56–63, mean 58) ( Table 1), a single tooth on prevomer (generally absent); shorter head (14.8 in TL vs. 12–14 in TL), and larger spots on head and nape (mostly equal or larger than eye with a few spots smaller than a half of eye, vs. various but generally smaller than eye, exceptionally with larger spots with numerous smaller spots smaller than a half of eye) ( Fig. 3 View FIGURE 3 ).

Total vertebrae

133 134 135 136 137 138 139 140 141 142

Apterichtus succinus sp. nov. 1

Apterichtus klazingai 3 2 2 5 9 6 4* 2 1? Preanal vertebrae

? 5 4 5 5 5 6 5 7 5 8 5 9 6 0 6 1 6 2 6 3 Apterichtus succinus sp. nov. 1

Apterichtus klazingai 5 5 12 8 2 1 1*

*including holotype.

In the Marquesas Islands, numerous endemic fishes were found including Apterichtus mysi McCosker & Hibino, 2015 ( McCosker & Hibino, 2015; Delrieu-Trottin et al., 2015). The new species is also possibly endemic in that area. Although Apterichtus flavicaudus ( Snyder, 1904) and Apterichtus moseri ( Jordan & Snyder, 1901) were recorded from these islands by Randall & Earle (2000), those records were probably based on misidentification of A. mysi and A. klazingai , respectively, and McCosker & Hibino (2015) excluded these records from each distribution without explanations. All specimens recorded in Randall & Earle (2000) are deposited in the Bishop Museum, but there were no specimens of those species from Marquesas during YH and JMc’s revisionary work. Most of these formerly identified as A. flavicaudus were designated as paratypes of A. mysi . A. moseri is endemic to Japanese waters ( McCosker & Hibino, 2015). Consequently, only A. mysi , A. klazingai , and A. succinus are now known to occur in the Marquesas Islands.