Dictyosoma tongyeongensis Ji & Kim, 2012, sp. nov.

Dictyosoma tongyeongensis sp. nov.

(New English name: Korean prickleback; New Korean name: Min-gue-mul-bae-do-ra-chi) (Figs 2 –3)

Holotype. NIBR-P0000017843, 280.0 mm SL, male, South Sea of Korea (N 34°50'25", E 128°25'06"), caught by fish trap at 12 m, 5 June, 2010, collected by Jin Koo Kim.

Paratypes. NIBR-P0000017844, 254.0 mm SL, male, South Sea of Korea (N 34°43'94", E 128°38'17"), caught by fish trap at 8.0 m, 11 June, 2009, collected by Hwan Sung Ji; PKU 3560, 257.0 mm SL, male, South Sea of Korea (N 34°50'25", E 128°25'06"), caught by fish trap at 10 m, 10 June, 2010, collected by Jin Koo Kim; PKU 3561, 279.0 mm SL, male, South Sea of Korea (N 34°50'25", E 128°25'06"), caught by fish trap at 10 m, 10 June, 2010, collected by Hyuck Joon Kwun. PKU 3562, 279.0 mm SL, male, South Sea of Korea (N 34°50'25", E 128°25'06"), caught by fish trap at 10 m, 10 June, 2010, collected by Hyuck Joon Kwun. PKU 3568, 249.0 mm SL, male, South Sea of Korea (N 34°50'25", E 128°25'06"), caught by fish trap at 10 m, 10 June, 2010, collected by Jung Hwa Ryu.

Diagnosis. Dorsal-fin rays LVIII–LXII, 8–10; anal fin rays II, 45–47, total number of vertebrae 70–74; dorsal contour of head almost straight; pelvic fin absent; 3rd lateral line extends with zigzag from pectoral fin to caudal-fin base. No blackish-brown blotches on the head; a single white oblique band on cheek; many small pale brown rounded spots present at the caudal region.

Description. Body and head greatly compressed and elongated (Fig. 2). Eyes located dorsolaterally on head, snout short and rounded, lips thick. Dorsal contour of head almost straight (Fig. 3A–C). Teeth small, but sharply conical, maxillary teeth in two rows but multiserial anteriorly. Vomerine and palatine teeth conical, multiserial. Mandibular teeth in two rows at anterior end, but followed by a single row of teeth (Fig. 4). Dorsal-fin origin above the middle of pectoral fin. Dorsal and anal fins confluent with caudal fin without any notches. Pectoral and caudal fins rounded. Pelvic fin absent. Body with embedded small cycloid scales. Cephalic-sensory canals and pores weakly developed. Supraorbital canal (SPO) connected to interorbital canal (ITO); posterior postorbital canal (PPO) connected to 2nd lateral line; occipital canal (OC) connected to 1st lateral line (Fig. 3A`–C`). Lateral line system forming complicated network: first lateral line (upper most) extending below dorsal contour of body to caudal-fin base; second running below first lateral line in parallel and connecting with first lateral line near caudalfin base; third showing zigzag form from pectoral-fin base to caudal-fin base; fourth extending midventrally to anus, then dividing into two lines running along anal-fin base. These four longitudinal lateral lines are connected with each other by numerous transverse branches (Fig. 5).

Coloration when fresh. Body, uniform brown dorsally, pale whitish ventrally. No blotches present on head. A single white oblique band on cheek (Fig. 3A). Many small pale brown rounded spots present on the caudal region.

Coloration in preservative. Body uniform dark brown dorsally, pale whitish ventrally. A single white oblique band on cheek (Fig. 3A).

FIGURE 3. Lateral view of head and cephalic sensory canals. A, A`: Holotype of Dictyosoma tongyeongensis, NIBR- P0000017843, 299.0 mm TL; B, B`: Dictyosoma burgeri type B, PKU 3559, 279.5 mm TL; C, C`: Dictyosoma rubrimaculatum, HUMZ 185421, 120.1 mm TL. Abbreviations: SPO, supraorbital canal; IFO, infraorbital canal; ITO, interorbital pore; APO, anterior postorbital canal; PPO, posterior postorbital canal; OC, occipital canal; PO, preopercular canal; MN, mandibular canal; 1st, first longitudinal lateral line; 2nd, second longitudinal lateral line; 3rd, third longitudinal lateral line; 4th, fourth longitudinal lateral line.

Distribution. Southern coast of Korea.

Etymology. The specific name, tongyeongensis, refers to the name of type locality (Tongyeong).

Remarks. Our six specimens were identified to the genus Dictyosoma by the following morphological combinations, suggested by Yatsu et al. (1978) and Hatooka (2002): 1) lateral line system forming a complicated network, 2) pelvic fin absent or rudimentary, 3) skin embedded with small cycloid scales, and 4) dorsal and anal fins confluent with caudal fin without any notches. The genus Dictyosoma is characterized by the lateral line system, which consists of three or four complicated lateral lines on each side of body. In particular, species can be classified by the absence or presence of the 3rd lateral line. D. tongyeongensis is more similar to D. rubrimaculatum than to D. burgeri in having the 3rd lateral line complete (Fig. 4). We also found differences in the dorsal contour of head between D. tongyeongensis and the two other congeneric species. The dorsal contour of the head of D. tongyeongensis is almost straight, while that of both D. burgeri and D. rubrimaculatum is gently convex (Figs. 3B, C, 7A–C). Yatsu et al. (1978) documented that D. burgeri and D. rubrimaculatum have a distinctive blackishbrown blotch on the upper region of the opercle. In contrast, D. tongyeongensis has no blotch (Fig. 3A).

Dictyosoma burgeri has no pelvic fins, but D. rubrimaculatum has small pelvic fins. Dictyosoma tongyeongensis is likely to be closely related to D. burgeri in having no pelvic fins. In meristic characters, the number of segmented anal fin rays is also diagnostic for the three species: i.e. 45–47 in D. tongyeongensis, 41–45 in D. burgeri, and 38–42 in D. rubrimaculatum (Table 2). Although the number of vertebrae somewhat overlaps, D. tongyeongensis has more numerous vertebrae than the other two species; 70–74 in D. tongyeongensis, 69–72 in D. burgeri, and 63–68 in D. rubrimaculatum (Table 2). A similar tendency is seen in the number of dorsal-fin spines (58–62 in D. tongyeongensis, 54–58 in D. burgeri, and 52–56 in D. rubrimaculatum) (Table 2). In the number of infraorbital pores, D. tongyeongensis is more similar to D. burgeri than to D. rubrimaculatum (9 + 3 in D. tongyeongensis, 8–9 + 3–4 in D. burgeri and 8–9 + 1–2 in D. rubrimaculatum) (Table 1). The anal-fin base length as a percentage of standard length also distinguishes the three species: 55.4%–57.7% in D. tongyeongensis, 52.6%–55.9% in D. burgeri, and 49.8%–55.2% in D. rubrimaculatum (Table 1).

Vertebrae

Counts n 63 64 65 66 67 68 69 70 71 72 73 74 75 D. tongyeongensis sp. nov. 6 1 1 1 1 1 holotype 1 D. burgeri type A (64) (1) (30) (27) (6)

D. burgeri type B 20 (82) 2 (10) 9 (34) 7 (33) 2 (5) D. rubrimaculatum 20 2 2 3 5 5 3

continued.

Dorsal fin spines

Counts n 52 53 54 55 56 57 58 59 60 61 62 D. tongyeongensis sp. nov. 6 1 3 1 holotype 1 D. burgeri type B 20 2 3 6 3 6 D. rubrimaculatum 20 3 4 8 5

continued.

Anal fin rays

Counts 38 39 40 41 42 43 44 45 46 47 D. tongyeongensis sp. nov. 1 3 1 holotype 1 D. burgeri type A (7) (24) (27) (4) (1) D. burgeri type B 2 (2) 8 (23) 6 (40) 3 (19) (1) D. rubrimaculatum 3 4 9 1 3

Parenthese indicate reference data of Yatsu et al. (1978)

Dictyosoma tongyeongensis was compared with D. burgeri and D. rubrimaculatum using 529 base pair sequences of the mitochondrial DNA cytochrome oxidase subunit I (COI). Kimura’s genetic distance was very small between D. tongyeongensis and D. burgeri (0.011), and considerably large between D. tongyeongensis and D. rubrimaculatum (0.075) (Table 3). Although D. tongyeongensis was closest with D. burgeri in genetic distance, the two species were well distinguished by six DNA variations of #307, #319, #328, #370, #520 and #553 (Table 4). Our mtDNA result was similar with that of Katafuchi et al. (2011). Katafuchi et al. (2011) reported that Ditrema temminckii and Ditrema viride are genetically very close (D = 1.1%–1.4%), although they are separate species. Notwithstanding, in order to clarify whether our specimens are hybrids between D. burgeri and D. rubrimaculatum, nuclear DNA was further analyzed. A total of 800 base pair sequences of the recombination mtDNA COI 1 2 3 4 5 6 7 Dictyosoma tongyeongensis sp. nov. (1)

Dictyosoma tongyeongensis sp. nov. (2) 0.000

Dictyosoma tongyeongensis sp. nov. (3) 0.000 0.000

Dictyosoma tongyeongensis sp. nov. (4) 0.000 0.000 0.000

Dictyosoma burgeri type B (5) 0.011 0.011 0.011 0.011 Dictyosoma burgeri type B (6) 0.011 0.011 0.011 0.011 0.000 Dictyosoma burgeri type B (7) 0.011 0.011 0.011 0.011 0.000 0.000 Dictyosoma rubrimaculatum (8) 0.075 0.075 0.075 0.075 0.062 0.062 0.062 FIGURE 5. Dictyosoma showing the difference in lateral line structure. (A) D. tongyeongensis, NIBR-P0000017843; (B) D. burgeri type B, PKU 3559; (C) D. rubrimaculatum, HUMZ 185421. 1st, first longitudinal lateral line; 2nd, second longitudinal lateral line; 3rd, third longitudinal lateral line; 4th fourth longitudinal lateral line.

activating gene 2 (RAG2) were used. Kimura’s genetic distance was the same between D. tongyeongensis and D. burgeri (0.004) and between D. tongyeongensis and D. rubrimaculatum (0.004) (Table 3). In spite of very close relationship among the three species, they were well distinguished by five DNA variations of #64, #148, #246, #331 and #712 (Table 4). The RAG2 gene has been used to evaluate intrageneric and intraspecific relationships (Clements et al., 2004; Wang et al., 2007). For example, Clements et al. (2004) reported that mean distance between species within the genus Odax ranged from 0.7–0.8%. Our results of RAG2 sequences data within the genus Dictyosoma ranged from 0.4%. Although D. tongyeongensis shows small distance between D. burgeri and D. rubrimaculatum, the neighbor-joining tree shows the reciprocal monophyly of D. tongyeongensis, with high bootstrap support (99; Fig. 6A –B). Accordingly, we conclude that D. tongyeongensis is a distinct species.