A new wriggler of Eleotrid (Teleostei: Xenisthmidae) from Taiping Island, South China Sea Chang, Chih-Wei Shen, Kang-Ning Chen, I-Shiung Zootaxa 2025 2025-12-30 5738 1 32 37 Chang & Shen & Chen 2025 [151,385,1034,1061] Xenisthmidae Xenisthmus Animalia Perciformes 1 33 Chordata species aureus sp. nov.  ( Îĭ塘º) ( Figures 1, 2)     Holotype.NTOUP-2024-04-151, 17.0 mm SL,  April 24, 2024; coll. Y.C. Yang et al., Taiping Island, South ChinaSea, Taiwan, ROC.    Dignosis The new species can be well distinguished from other congeners by the following unique combination of features: (1) fins: second dorsal fin rays I/11; anal fin rays I/10; pectoral fin rays15; (2) squamation: longitudinal scale series 60–62; perdorsal scales 0; (3) vertebral count 10+16=26; (4) preopercular canal present with 4 pores γ, δ, ε, and ε1; and (5) specific colouration: lateral side of trunk with an upper horizontal series of 20–22 yellow spots; a median series of oblique golden yellow stripes or becoming smaller, irregular golden yellow marks; the orange red cross mark on eye, radiating into mouth and posterior area horizontally, and extending up to top eye margin to downward vertically behind the maxillary on cheek; pectoral fin base with a upper, large oblique golden yellow mark; and caudal fin base with a very small median black spot.   Description Body very slender, subcylindrical anteriorly and somewhat compressed posteriorly. Anterior head somewhat depressed. All following body proportions are listed in Table 1. Head with very narrow interorbital region. Eye large. Lower jaw more prominent. Both anterior and posterior nostrils as short tubes which pointed to opposite direction on dorsal view. Both jaws with 5–6 rows of small, conical teeth which largest in outer rows. Gill-opening rather large, extending ventrally beyond the rear vertical of preopercle. Vertebral count 10+16 = 26.  Fins. D1 VI, D2 I/11; A I/10; P 15; V I/5. All D1 rays about equal without any filamentous ray. D2 rays low with rather long fin base. The rear tips of D2 rays when depressed extending to the procurrent rays of C. Origin of A inserted below middle vertical between first and second branched rays of D2. P moderate large and oblong, its rear tip not reaching vertical line through anus in male. V well separate, no frenum, connecting membrane. C elliptical, rear edge rounded.   TABLE 1.Morphometry of  Xenisthmus aureusfrom Taiping Island, South China Sea.    Type status Holotype  Size (mm SL) 17.0  % inSL  Head length 23.6  Predorsal length 33.6  Snout to 2nd dorsal origin 53.0  Snout to anal fin origin 56.1  Prepelvic length 25.5  Caudal peduncle length 12.0  Caudal peduncle depth 11.2  First dorsal fin base 13.0  Second dorsal fin base 23.6  Anal fin base 31.4  Caudal fin length 21.5  Pectoral fin length 21.4  Body depth of anal fin origin 13.3  % inHL  Snout length 24.7  Eye diameter 18.4  Postorbital length 54.6  Cheek depth 15.5  Lower jaw length 41.8  % in caudal peduncle length  Caudal peduncle depth 93.9  Scales.Body mostly with rather small cycloid scales, predorsal area entirely naked. Upper part of operculum scaled. Cycloid scales present on pectoral-fin base. LR 60–62; TR 19; PreD 0. Prepelvic region naked.  Head lateral-line system.( Figure 1)  Canals:Nasal extension of anterior oculoscapular canal with terminal pore σ located in between anterior and posterior tube-like nostrils. Anterior interorbital sections of oculoscapular canal with paired pore λ. A single pore κ in near rear of interorbital region. Pore ω present behind orbit. Lateral section of oculoscapular canal with lateral pore α. Preopercular canal with rather more, 4 pores γ, δ, ε, and ε1.  Sensory papillae:Row aextending beyond vertical midline of orbit. Rows cshort. A single cppapilla. Row fpaired. Anterior edge of row oiwell separated to lower region of row ot. Row otinterrupted with 2 sections   Coloration while fresh Body and head semi-translucent with snow white to pale white background. Lateral side of trunk after pectoral fin base with an upper horizontal series of 20–22 yellow spots, then with a median series of oblique golden yellow stripes or becoming smaller, irregular golden yellow marks. On dorsum with 4 yellow spots below first dorsal fin base and also 11 yellow spots beneath the second dorsal fin base. The orange red cross mark on eye, radiating into mouth and posterior area horizontally, and extending up to top eye margin to downward vertically behind the maxillary on cheek. Opercle with large orange blotch on upper part. Posterior region of interorbitals with three major orang blotches. Both lips pale white and anterior tip crossing with orange red bar radiating from orbit. First dorsal fin translucent and spotless. Second dorsal fin translucent with a series of smaller yellow spots on middle area of fin membrane. Pectoral fin translucent and its base with a large oblique golden yellow mark beneath in having tiny melanophores on upper region. Pelvic fin translucent and spotless. Anal fin translucent with a horizontal row of tiny basal yellow spots or bars. Caudal fin base with a very small median black spot, and its upper and anterior regions surrounding with the very thin orange curves. Caudal fin membrane translucent with about three vertical rows of yellow spots.   Colouration in preservative Similar to live pattern, but the all brilliant, conspicuous orange, golden yellow, yellow marks or spots on body and all fins entirely faded. Some tiny darker melonophores or dots below the orange or yellow marks still present but less distinct.   Etymology The specific name,  aureus, is referred to the unique feature of its specific colouration pattern: golden-yellow (Latin:  aureus) belly marks and also smaller golden yellow marks or short bars on lateral body among all remaining congeners.   Distribution So far, the new species merely can be found from the typelocality—Taiping Island, South ChinaSea. It needs for fish biodiversity survey to nearby countries to realize the real distribution range.   Remarks The new species,  Xenisthmus aureus, is more similar to the Australian endemic species,  Xenisthmus chiby overall preserved colouration than any other nominal congeneric species in the Indo-Pacific region. However, this new species can be well distinguished from the close related species by the following morphological features: (1) fin ray counts: second dorsal fin rays I/11 (vs I/12), anal fin rays I/10 (vs. I/11), pectoral fin rays 15 (vs. 17); (2) scale counts: longitudinal scale rows 60–62 (vs. 52–57); and (3) specific colouration: lateral side of trunk with an upper horizontal series of 20–22 yellow spots; a median series of oblique golden yellow stripes or becoming smaller, irregular golden yellow marks; the orange red cross mark on eye, radiating into mouth and posterior area horizontally, and extending up to top eye margin to downward vertically behind the maxillary on cheek; pectoral fin base with a upper, large oblique golden yellow mark; and caudal fin base with a very small median black spot (vs. 11 X-shaped markings along body sides). The rare new wriggler is still need to explore more in the near future not only morphological but also molecular phylogenetic aspect. 6181489301 2024-04-24 Y. C. Yang China Taiping Island 1 33 1 holotype