Oxuderces, NEXIPINNIS (CANTOR, 1849)

Jaafar, Zeehan & Parenti, Lynne R., 2017, Systematics of the mudskipper genus Oxuderces Eydoux & Souleyet 1848 (Teleostei: Gobiidae: Oxudercinae) with resurrection from synonymy of O. nexipinnis (Cantor 1849), Zoological Journal of the Linnean Society 180 (5), pp. 195-215 : 207-210

OXUDERCES NEXIPINNIS ( CANTOR, 1849)

FIGURES 2 , 3B , 4A , 5A , 6 , 7A , 8A , 9A , 10B , 14 ;

TABLE 1

Apocryptes nexipinnis Cantor, 1849: 1170 (type locality, Sea of Penang, Malaysia)

Apocryptes cantoris not Day, 1871 (in part Day, 1876, specimens from Madras, India)

Apocryptichthys livingstoni Fowler, 1935: 162 (type locality, Paknam , Thailand)

Syntypes examined: BMNH 1860.3.19.568-69, 2 undet., 65.0 – 67.8 mm SL, Sea of Penang, Malaysia.

Other type material examined: Apocryptichthys livingstoni holotype: ANSP 63091, male, 73.2 mm SL, mouth of Me Nam Chao Praya, Paknam, Thailand.

Other material examined: Sixty-four specimens, 19.9 – 80.6 mm SL. RMNH.PISC 12091, male (66.8 mm), 2 females (65.9 – 73.0 mm), east coast Java Island, Indonesia; RMNH.PISC 12092, 5 males (63.0 – 76.4 mm), 14 females (60.0 – 79.9 mm), east coast Java Island, Indonesia; RMNH.PISC 12433, female (55.6 mm), Java Island, Indonesia; RMNH.PISC 12750, female (79.4 mm), Surabaya, Indonesia; RMNH.PISC 33844, female (57.6 mm), Indonesia; RMNH.PISC 17382, female (72.0 mm), Pulau Weh, Sumatra, Indonesia; USNM 119547, female (64.0 mm), off Tachalon, Gulf of Thailand; USNM 278447, female (43.6 mm), southern side of river mouth, Muar river, Johore, Malaysia; USNM 279359, 12 males (19.9 – 50.0 mm; 1 C&S, 35.7 mm), 14 females (22.1 – 31.5 mm; 1 C&S, 47.9 mm); USNM 288662, 1 male (C&S, 39.7 mm), 2 females (C&S, 21.6 – 26.8 mm), southern side of river mouth, Muar river, Johore, Malaysia; ZRC 39777, male (80.6 mm), Sungai Selising, Matang mangroves, Perak, Malaysia; ZRC 53919, 3 males (50.3 – 53.2 mm), 3 females (33.4 – 53.3 mm), Matla mudflats, Jharkali, South 24 Parganas, West Bengal, India.

Differential diagnosis: Oxuderces nexipinnis is differentiated from O. dentatus by the following characters: first hemal spine terminating above midlength of first anal-fin pterygiophore (vs. extending ventrally below mid-length of first anal-fin pterygiophore; Fig. 10 ); mouth superior (vs. terminal); conspicuous dermal invagination posterior to the point of attachment of pelvic-fin base (vs. dermal invagination absent; Fig. 6 ); head relatively long (27.3 – 30.3%SL vs. 25.1 – 27.7%SL).

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Description: Head markedly depressed, wider than deep, head length 27.3 – 30.3%SL, head width 32.6 – 44.4%HL, head depth 30.4 – 42.7%HL. Eye diameter 8.7 – 16.3%HL; interorbital distance 3.0 – 4.8%HL, eye without dermal cup. Snout profile pointed, snout length 12.0 – 15.5%HL. Mouth superior, lower jaw terminating just anterior to upper jaw, gape wide; jaw length 41.3 – 59.7%HL; distinct notch in middle of upper lip between two medial teeth. Teeth in both jaws caninoid, unevenly spaced, in single row; one or two prominent and elongate canines on each side of premaxillary symphysis, canine teeth extending slightly anteroventrally and reaching beyond lower jaw when mouth closed, teeth decreasing in length posteriorly; teeth in lower jaw more uniform in size, teeth all shorter than medial canine teeth of upper jaw, teeth absent posteriorly, no canine tooth on each side of symphysis internal to anterior margin of lower jaw. Body compressed and gracile; body depth at anus 8.6 – 12.9%SL, body width at anus 4.5 – 7.3% SL. Predorsal long, predorsal length 28.2 – 31.6%SL. D1 and D2 connected by membrane for entire height, base of D1 and D2 54.9 – 59.4%SL; base of anal fin 35.9 – 40.4%SL. No membrane connecting D2 or A to caudal fin. Pelvic fin short and rounded, not reaching genital papilla, pelvic-fin length 14.0 – 18.2% SL. Pectoral-fin length moderate, 14.0 – 19.2%SL. Caudal fin long, lanceolate, 20.8 – 24.8%SL. D1 with six spinous dorsal rays (VI); all elements of D2 and A fins segmented; D2 with 25 – 26 elements, A fin with 24 – 26 elements; pectoral rays 21 – 24; caudal fin segmented rays 17; dorsal procurrent rays 5, ventral procurrent rays 4. Two epural bones. Lateral longitudinal scale count 50 – 54, scales on body small and embedded in skin anteriorly, and increasing in size posteriorly. All specimens without scales on dorsal region anterior to D1, ventral region of the head, cheek, operculum and pectoral-fin base except for largest specimen examined (ZRC 39777, 80.6 mm) which has cheek scales and 14 predorsal midline scales; all scales small and embedded. Raised and distinct free-neuromast rows on head. Conspicuous dermal invagination posterior to point

A First dorsal-fin anterior elements

of attachment of pelvic-fin base, invagination deep and appearing as a ‘pit’ ( Fig. 6 ).

Coloration: Preserved specimens uniformly light to dark brown with black spots on dorsal region of head and nape. Darkened brown to black upper lip and pectoral-fin base. Dark brown spot between 20 th and penultimate rays, positioned at mid-height of D2. Murdy (1989: 20) based his description of live coloration on material from Peninsular Malaysia that he had identified as O. dentatus (= O. nexipinnis here): ‘Head and trunk greyish blue; 7 greyish-blue spots along lateral midline starting at a point equal to origin of first dorsal fin and ending at a point equal to about 75% of the length of D2; a suffusion of shiny, bluish scales on posterior half of trunk; 6 dusky, saddle-like blotches on dorsum starting at terminus of D1 with 4 across the base of D2 and 1 on caudal peduncle; D1 translucent; D2 translucent except for a thin, faint dusky stripe through the median part of fin and a large black ocellus near distal tips of last 4 rays; caudal, anal and pelvic fins translucent; pectoral fin translucent but with a large, dusky blotch on upper base; nape with dusky reticulations; anterior nostril with a black anterior margin; venter shiny white.’ In the Malacca Straits, along the western coast of Peninsular Malaysia, Takita, Agusnimar & Ali (1999: 132) identified O. nexipinnis (reported as O. dentatus ) by the characteristic ‘...bright green eyes and depressed head, and a dark spot posteriorly on the dorsal fin’. They reported that O. nexipinnis occurs on the mudflats of Bengkalis and Penang islands in Peninsular Malaysia, at sites facing the sea and not influenced by freshwater inflow ( Takita et al., 1999). At Teluk Bahang in Penang Island, this species was found low on the intertidal zone, an area which was exposed for only several days per lunar cycle, prompting the hypothesis that O. nexipinnis is probably active underwater ( Takita et al., 1999). This hypothesis is corroborated by Polgar & Bartolino (2010) who found larger individuals of O. nexipinnis (reported as O. dentatus ) in the lower intertidal zones (more aquatic) and smaller individuals in higher intertidal zones (more terrestrial) at their study site in Tanjung Piai, Johor, along the western coast of Peninsular Malaysia.

Etymology: Latin, ‘ nexus’ meaning ‘tied together’ and ‘ pinnis ’ meaning ‘fins’, referring to the continuous dorsal fins.

Distribution and ecological note: Oxuderces nexipinnis is distributed in the Indo-West Pacific, here reported from the southern part of the South

1 mm

China Sea, Gulf of Thailand, Java Sea, Andaman Sea and Bay of Bengal ( Fig. 13 ). This species lives on intertidal soft-bottom habitats, predominantly mudflats. Adults have been observed to swim through the muddy substrate with only a thin film of water above them, through which they would occasionally poke their heads ( Murdy, 1989, reported as O. dentatus ). This species has been reported to store air in its burrows, especially in the spawning chambers ( Ishimatsu et al., 1998, reported as O. dentatus ). In Malaysia, it is a common prey of homalopsine snakes such as Bitia hydroides (see Jayne, Ward & Voris, 1995, reported as O. dentatus ) and Cerberus rynchops (see Jayne, Voris & Heang, 1988, reported as O. dentatus ).

Remarks: Apocryptes nexipinnis , described by Cantor (1849), was classified in the genus Oxuderces , and synonymized with O. dentatus by Murdy (1989). We resurrect this name from synonymy as Oxuderces nexipinnis . The BMNH syntypes are the left sides (heads and bodies) of two individuals that have been dried, filleted and stuffed with cotton wool ( Fig. 14 ). Cantor (1849) did not indicate the number of specimens he had on hand and reported the total length of the specimen (or specimens) on which he based his description as 3 3/ 8 inches, or 85.7 mm TL. He further indicated that the caudal fin comprised 1/5 of the TL, which would mean that the specimen (or specimens) was approximately 68 mm SL. The BMNH syntypes measure approximately 67.8 mm SL (possibly a male) and 65 mm SL (possibly a female). Although the larger specimen is closer in size to that given by Cantor (1849), we do not designate it as a lectotype because both specimens are extremely distorted, as well as incomplete, and we cannot identify either with certainty as the primary specimen on which the description was based.

Figures

Figure 2. Oxuderces nexipinnis (Cantor, 1849), ZRC 53919, 53.2 mm SL, West Bengal, India. Scale bar = 1 cm.

Figure 3. Dorsal view of the head including interorbital region of (A) Oxuderces dentatus (ZRC 53939) and (B) Oxuderces nexipinnis (ZRC 53919). Arrow points to interorbital trough or groove. A sensory pore C sits in the anterior portion of the trough. C, Apocryptodon wirzi (AMS I23993.007), there is a single sensory pore D, and no trough; D, Apocryptodon glyphisodon (USNM 99874), there is a paired sensory pore E and no trough. Scale bar = 3 mm.

Figure 4. Histological sections through the head of (A) Oxuderces nexipinnis (USNM 427099) and (B) Apocryptodon wirzi (USNM 432509). The paired adductor arcus palatini lie on either side of the parasphenoid and the intermandibularis spans the lower jaw and connects the dentaries. Bone is bright red, cartilage light blue, muscle and connective tissue dark blue to purple. Scale bar = 0.5 mm.

Figure 5. Enlargement of the histological sections of Figure 4 through the mid-dorsal region of (A) Oxuderces nexipinnis (USNM 427099) and (B) Apocryptodon wirzi (USNM 432509). Bone is bright red, cartilage light blue, muscle and connective tissue dark blue to purple.

Figure 6. Dermal invagination or pouch (arrow) at point of attachment of the pelvic-fin base in Oxuderces nexipinnis (ZRC 53919, 53.2 mm SL). Anterior is to the right.

Figure 7. Line drawings of the jaw and jaw suspensorium of (A) Oxuderces nexipinnis (USNM 279359) and (B) Gnatholepis sp. (USNM 287166). Angle between metapterygoid–symplectic–quadrate strut and anguloarticular is acute in O. nexipinnis, in which the preopercle is relatively thin and subcrescent-shaped. In contrast, the angle between the strut and the anguloarticular is obtuse, and the preopercle is wider and broadly crescent-shaped in Gnatholepis sp. Bone is stippled, cartilage is represented by open circles.

Figure 8. Line drawings of the hyoid bar in (A) Oxuderces nexipinnis (USNM 279359), (B) Apocryptodon wirzi (USNM 287292) and (C) Gnatholepis sp. (USNM 287166). The anterior ceratohyal posterior to insertion of the fourth branchiostegal ray is elongate and notched (arrow) in O. nexipinnis, elongate and not notched (arrow) in A. wirzi, and not elongate and not notched in Gnatholepis sp. Branchiostegal rays 3–5 are distinctly thinner in A and B. Bone is stippled, cartilage is represented by open circles. Only the proximal portion of the five branchiostegal rays is drawn.

Figure 9. Line drawings of several anterior vertebrae and associated elements of the first dorsal fin in (A) Oxuderces nexipinnis (USNM 279359) and (B) Gnatholepis sp. (USNM 287166). The neural spine of the fourth vertebra (arrow) is broad and spatulate and directed posteriorly in O. nexipinnis and relatively thin and pointed and directed dorsally in Gnatholepis. Bone is stippled, cartilage is represented by open circles.

Figure 10. Line drawings of the last precaudal and the first two caudal vertebrae and associated elements of the anal fin in (A) Oxuderces dentatus (USNM 86954) and (B) Oxuderces nexipinnis (USNM 279359). In O. dentatus, the hemal spine extends to a point at about mid-length of the first anal-fin pterygiophore; in O. nexipinnis the hemal spine terminates closer to the proximal tip of the first anal-fin pterygiophore. Bone is stippled; cartilage is represented by open circles.

Figure 13. Distribution map of Oxuderces dentatus (solid circles) and Oxuderces nexipinnis (solid triangles). Each symbol represents one catalogued museum lot. Distributional limits are approximated by a solid line.

Figure 14. Apocryptes nexipinnis Cantor, 1849, syntypes, BMNH1860.3.19.568-69 (2), dried, filleted and stuffed with cotton wool. Anterior is to the left. Top: the larger of the two syntypes, approximately 67.8 mm SL. Middle: the same specimen as the top, rotated on the horizontal axis. Bottom: the smaller of the two syntypes, approximately 65 mm SL.