Yirrkala kaupii ( Bleeker, 1858 )

Hibino, Yusuke & Ho, Hsuan-Ching, 2024, Species of the snake eel genus Yirrkala Whitley, 1940 from Taiwan, with descriptions of a new species and two new records (Anguilliformes, Ophichthidae), ZooKeys 1220, pp. 45-62 : 45-62

Yirrkala kaupii ( Bleeker, 1858)

Figs 3 B , 4 , Table 1

Sphagebranchus kaupii Bleeker, 1858: 3 (type locality: Manado, Sulawesi, Indonesia); Bleeker 1864: 70 (Manado).

Ophichthys kaupi : Günther 1870: 86 (Celebes).

Sphagebranchus kaupi : Weber and de Beaufort 1916: 325 (Celebes).

? Yirrkala kaupi : McCosker 1977: 16 (listed; specimen collected from Philippines); McCosker 2014: 339 (listed).

Yirrkala kaupii : Kottelat et al. 1993: 13 (listed, Indonesia); Smith and McCosker 1999: 1669 (listed); Miesen et al. 2016: 81 (listed, Indonesia); Jamandre 2023: 160 (listed, Indonesia).

Materials examined.

• NMMB-P 36108 , 239 mm TL, ca 23°56.2'N, 121°36.5'E, jointed mouth of Mu-Gua River and Hualien River , Hualien, eastern Taiwan, ca 1 m, trap net (fyke net), 10 May 2021 • NMMB-P 38424 , 328 mm TL, NMMB-P 38425 , 331 mm TL, ca 23°27.9'N, 121°29.7'E, Jin-pu village , Fengbin township, Taitung, 26 May, 2023, collected after preserving in wine for several years .

Diagnosis.

An elongate species of Yirrkala with the following combination of characters: body bicolored, dark brown dorsally and pale ventrally, lateral line pores margined as pale blank; SO 1 + 3; dorsal-fin origin behind gill opening; lateral-line pores before anus 63–65; predorsal vertebrae 17–18, preanal 64–66, and total 151–156; MVF 17-65 - 154.

Description of Taiwanese specimens.

New record. Body elongate, subcylindrical, tip of tail laterally compressed and extremely pointed (Fig. 4 A, B ). Head moderate in size, 11.8–13.7 in TL; preanal length shorter than tail, 1.1 in tail length and 2.1 in TL.

Snout relatively longer, more than twice eye diameter, its tip pointed; distinct median groove ventrally on snout but the groove mostly not teared, its anterior tip beyond ethmoid pore; slope of dorsal surface of snout smooth, without notch or hump. Anterior nostril tubular, moderate in length, tube length about equal to pupil diameter; posterior nostril oval in shape with an inner valve, located on anteroventral margin of eye, opening ventrally, covered by a flap extending slightly below edge of mouth gape. Eye moderate in size, covered by a transparent skin; center of eye anterior to mid-jaw (Fig. 4 C ). Mouth inferior, distance from tip of snout to anterior tip of lower jaw slightly longer than eye diameter; lower jaw short, its tip relatively pointed, slightly beyond or reaching posterior base of anterior-nostril tube (Fig. 4 C ); rictus short, posterior end of gape slightly behind a vertical through posterior margin of eye; lips smooth with folds, the fold along upper lip extending from second infraorbital pore to posterior rictus, but absent in one specimen ( NMMB-P 38425 ); the fold along lower lip extending from position between first and second mandibular pores to anterior of first preopercular pore. Gill openings positioned ventrolaterally of breast, not close each side; shape of opening curved, diameter more than twice eye diameter.

Sensory pores on head developed, arrangement of those pores as follows (Fig. 3 B ): 1 (ethmoid) + 3 on supraorbital, 3 + 3 on infraorbital, 4 or 5 on lower jaw, 2 on preopercle, and 3 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, eight or nine anterior to a vertical through gill opening, 16–18 anterior to dorsal-fin origin, 63–65 anterior to mid anus, and total 116–138.

Teeth pointed, slightly recurved posteriorly; teeth on maxilla, vomer and dentary uniserial; maxilla comprising 19 (right) / 25 (left) teeth and mandible comprising 21 / 23 teeth in NMMB-P 36108 ; intermaxillary with four or five teeth arranged in two rows or a chevron shape.

Median fins low but obvious; origin of dorsal fin behind gill opening, ending anterior to tip of tail about 1 eye diameter; origin of anal fin slightly behind anus, ending same as dorsal fin; caudal and pectoral fins absent.

Coloration. No information of fresh coloration. After the preservation by alcohol (ca 60 %) directly, body clearly bicolored, generally darkish brown dorsally and pale yellowish brown ventrally; numerous melanophores present dorsally, the border going down toward tip of tail; lateral-line pores margined by pale spots blank at least anterior to anus, but in tail the pattern gradually faded; head darker dorsally, lower jaw also dusky; dorsal fin dusky but margin pale yellowish white; eye with whitish margin by skin covering eye; anal fin pale yellowish white except dusky tip of tail ca 1 / 2 HL.

Distribution.

Manado, Sulawesi, Indonesia (holotype) and eastern Taiwan. In both places, this species was collected from rivers, but there is no detailed information for the holotype.

Ecological note.

One specimen was collected from a river mouth together with many Lamnostoma spp. , a genus which is commonly found in the freshwater environments. However, the species might be rare because only one individual was found among approximately 200 individuals of Lamnostoma .

Remarks.

Sphagebranchus kaupii is one of the oldest names in the genus Yirrkala , and it lacks detailed morphological information except for the original description ( Bleeker 1858). Based on YH’s investigation, the only known Bleeker specimen, deposited in the Natural History Museum ( BMNH 1867.11. 28.304), should be regarded as the holotype because its similar length agrees with the original description (e. g. 342 mm TL vs 362 mm TL in the original description) (Fig. 5 ).

Our specimens closely match the holotype in body proportions and vertebral counts in the original description. Bleeker (1858) noted that it has drop-shaped markings on the lateral line, which are also found in our specimens. Although Günther (1870) mentioned that it has uniform body coloration, it is assumed that holotype specimen was once dried and bleached beforehand because its very poor present condition had been caused by the drying process. There are several differences in the proportions of the head, snout, eye, and upper-jaw lengths between the original description of S. kaupii and Taiwanese specimens (Table 1 ). The Taiwanese population is possibly an undescribed species, but the morphological differences could also be due to intraspecific variation or differences in the method of preservation, or the time in preservative. As we were unable to directly observe the holotype and the number of specimens observed was limited, we refrain from considering it a separate species.

Most of congeners of Yirrkala have a dorsal fin that originates around, and usually slightly behind, the gill opening (see above). Only four species, Y. gjellerupi , Y. kaupii , Y. insolitus , and Y. omanensis , have the origin of the fin located more than half a head length behind the gill opening. Moreover, the latter two species are unique because their dorsal-fin origins are situated far behind, near the anus. Yirrkala kaupii is most similar to Y. gjellerupi in the vertebral counts and body proportions, including head length, tail length, and snout length. Both species inhabit rivers far from the river mouth ( McCosker et al. 2007). However, Y. kaupii can be distinguished from Y. gjellerupi by the position of the rictus (behind a vertical through posterior margin of eye, vs before), and the presence of a small protrusion along around margin of posterior nostril (vs absent).

Figures

Figure 3. Line drawing of lateral head A Yirrkala nkust sp. nov., holotype, NMMB-P 38652, 496 mm TL B Yirrkala kaupii, NMMB-P 38424, 328 mm TL C Yirrkala omanensis, KMNH VR 100616, 216 mm TL. Arrows indicate ethmoid = 1 st supraorbital (lefts), interorbital (middles) and mid-temporal (rights) pores.

Figure 4. Preserved specimen of Yirrkala kaupii, NMMB-P 36108, 239 mm TL A whole body (dorsal view) B whole body (ventral view) C enlarged view of head (lateral). AN anus DO dorsal-fin origin.

Figure 5. Holotype of Sphagebranchus kaupii, BMNH 1867.11. 28.304, 342 mm TL A whole body B lateral view of head C dorsal view of head. All photos provided by Natural History Museum.