Lamnostoma taiwanense, Chiu & Shao & Huang & Chen, 2018

Chiu, Yung-Chieh, Shao, Kwang-Tsao, Huang, Shih-Pin & Chen, Hong-Ming, 2018, The freshwater snake eel genus Lamnostoma (Anguilliformes: Ophichthidae) in Taiwan, with description of a new species, Zootaxa 4454 (1) : -

Lamnostoma taiwanense sp. nov. Chiu, Huang & Shao

¤ wmẘü

Common name: Taiwan Snake Eel

Figures 5A–5C , 6A–6B , 7C , 8 , 9A–9C ; Table 1

Holotype. TOU-AE 7152 (354 mm TL), mature female with ca. 1.0 mm egg diameter in belly, Juan-wei , Yi-lan county, northeastern Taiwan, 2 Jul. 2014, coll. N.- C. Hsu.

Paratype. ASIZP 74900 (323 mm TL), sex unknown, Lan-yang River , Yi-lan county, northeastern Taiwan, 6 Sep. 2006, coll. S.- C. Lee.

Measurements of the holotype. TL 354 mm. HL 35 mm, PD length 47 mm, TR 152 mm, Tail 168 mm, DGO 11.4 mm, IOW 1.4 mm, UJ 12.6 mm, LJ 10.6 mm, ED 2.0 mm, S 5.2 mm, ventral width between gill opening 2.8 mm.

Diagnosis. The 3rd POP present, arranged in a triangle; lower jaw with 47–49 teeth; white spots on lateral sides of head forming parallel arches, not meeting posteriorly and lower arch clearly displayed each spot with a hillshaped papilla; others arranged along lateral-line and extending to tail tip with series of additional non-pore spots above lateral-line each separated by 5–6 lateral-line pores.

Description. Head cylindrical, uncompressed; Snout relatively long, sharp, with lip present. Eye situated above middle of upper jaw. Posterior margin of anterior nostril and anterior end of posterior nostril with slender labial papilla; posterior nostril situated within midpoint of 1 st and 2nd IO pore and the posterior edge of eye. Gill opening wide, ventral, anterior duplicate gill membrane present.

Body moderately stout. Tail slightly shorter than body, comparatively stout relative to other congeners. Vent placed after midpoint of body. HL 9.9–10.2% TL, TR 42.1–42.9 % TL, tail 47.5–47.7% TL; distance between dorsal fin origin and gill opening about 30.3–34.3% HL, ventral width between gill opening 8.0–9.1% HL. All fins low, pale, unspotted.

Teeth on both jaws uniserial, sharp, recurved, conical and pointed: teeth on intermaxilla (5) and vomer (13 in holotype and 14 in paratype) bigger than others, teeth on maxilla 41–50 on each side, and 47–49 on each side of lower jaw, strongly recurved.

Cephalic pores: SO 1 + 4, IO 4 + 2, POM 4 + 3, ST 3, F 1. Lateral-line pores: PGLL 10, PDLL 15, PALL 65, TLL 129.

Vertebral counts: 14 before dorsal fin origin, 64 before vent, total 138.

Coloration: deep brownish dorsally, becoming whitish below rictus, the 2nd row of white spots (lower one on the head) distinct; lateral white spots on head with series of hill-shaped papilla, and clearly displayed completely; numerous white spots, one on each lateral-line pore, with additional spots above lateral-line each separated by 5–6 pores along full length of body.

Size. The maximum size attains to 354 mm TL.

Etymology. The specific name recognizes the type locality, Taiwan.

Distribution. Only known from the mouth of Lan-yang River in northeastern Taiwan.

Remarks. Compared with the five valid species of the genus Lamnostoma , L. taiwanense can be distinguished by having three preopercular pores, the third which is absent in all other congeners. This new species is most similar to Lamnostoma polyophthalmum in having a similar combination of morphological features of that include the lateral-line, mean vertebral formula, and head coloration; Lamnostoma taiwanense differs from L. polyophthalmum in having the third POP, a higher number of teeth on the lower jaw (47–49), a slightly shorter tail, a longer snout in relation to the head length, and a concentration of dense fine melanin along the ventral side of the body from the lower jaw to the belly ( Figure 8 ). The white spots on the lateral side of the head of the new species looks like a second row of lateral-line pores, however, the position of the true lateral-line, the lower row of white spots along the head are on a series of hill-shaped papillae which stain with alcian blue and alizarin red-S ( Figure 9A–9C ). The presence of papillae coinciding with the 2nd row of lateral white spots may also be an important diagnostic morphological feature.

Discussion. The distribution of cephalic papillae is also a useful morphological feature for identifying gobies and sleepers ( Huang et al., 2016; Nakabo, 2013). Many species of fresh and brackish water fishes are included in the red data book of fish in Taiwan ( Chen et al., 2012). In this study, the complete taxonomic survey of freshwater eels is beneficial for understanding their diversity and distribution in Taiwan, and it may be an important reference for future changes to the conservation act.

Figures

FIGURE 5. Lamnostoma taiwanense sp. nov., holotype, TOU-AE 7152, 354 mm TL. A. Lateral view of the whole body. B. Left view of head. C. Top view of head. Bar = 10 mm. Abbreviation: DFO, dorsal fin origin.

FIGURE 6. Lamnostoma taiwanense sp. nov., holotype, TOU-AE 7152, 354 mm TL. A. Lateral view of head showing the arrangement of cephalic pores. B. Illustration of dentition. Abbreviation: F, frontal pore; ST, supratemporal pores.

FIGURE 7. Lateral view of head of three Lamnostoma species in this study. A. L. mindora. White spots forming a “Y”; B. L. polyophthalmum. Spots arranged in an arch, the two rows of spots not meeting posteriorly the lower very faint ventrally. C. L. taiwanense sp. nov. Lower spots on a series of hill-shaped papillae, all spots clearly defined.

FIGURE 8. Lamnostoma taiwanense sp. nov., paratype, ASIZP 74900, 323 mm TL. Dense-fine melanin along ventral side of body. Bar = 10 mm.

FIGURE 9. Lamnostoma taiwanense sp. nov., holotype, TOU-AE 7152, 354 mm TL. A. Right side of lateral-line pores on head. B. Same tissue as A. cleared and stained. C. Lower row of white spots along the head on a series of hill-shaped papillae.