Oxuderces, EYDOUX & SOULEYET, 1848

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 : 201-206

GENUS OXUDERCES EYDOUX & SOULEYET, 1848

Oxuderces Eydoux & Souleyet, 1848: 181 (type species Oxuderces dentatus Eydoux & Souleyet, 1848 , type by monotypy)

Composition: Two allopatric species: O. dentatus Eydoux & Souleyet, 1848 ( Figs 3A , 11 , 12 ) and O. nexipinnis ( Cantor, 1849) ( Figs 2 , 3B , 6 , 14 ). The distribution of each species is shown in Figure 13 .

Differential diagnosis: Oxuderces is differentiated from all other oxudercine gobies by five putative synapomorphies: (1) single, anterior interorbital pore C that sits in a fleshy, interorbital trough supported internally by expanded, curved medial margins of the frontal bones and lined externally with a thick epidermis and thin dermis (vs. no fleshy, interorbital trough, medial margins of the frontal bones expanded but not curved, and epidermis extremely thin and dermis thick); (2) highly thickened epidermis over the eye (vs. a thickened dermis); (3) neural spine of the fourth vertebra broad and spatulate (vs. narrow and pointed); (4) anterior ceratohyal elongate and notched posterior to insertion of fourth branchiostegal (vs. not elongate, or elongate but not notched); and (5) acute angle

between metapterygoid – symplectic – quadrate strut and the anguloarticular (vs. angle obtuse).

Description: Anterior portion of head markedly depressed; snout profile broadly pointed; gape wide; distinct notch in middle of upper lip between two medial premaxillary teeth; lips thick, posterior lower lip protruding distally. Roof of mouth with fleshy palp that is elliptical and with pointed tips, palp studded with papillae. Teeth in both premaxilla and dentary in single row; one or two prominent, elongate canine teeth on each side of premaxillary symphysis, canine teeth extending slightly anteroventrally and projecting beyond lower jaw when mouth closed, all teeth on premaxilla caninoid; dentary with discontinuous caninoid teeth; no canine tooth on each side of symphysis internal to anterior margin of dentary; dentary with small dorsally directed flange on each side just posterior to posterior-most tooth. Maxillo-dentary ligament with finger-like projections on dorsoposterior sides of lower lip; dentary with ligament on each side attaching medially just posterior to posterior-most tooth and antero-medially to flange ( Murdy, 1989: fig. 73). Gill opening restricted, beginning from the region anterior to midpoint of pectoral-fin base, coursing anteroventrally, and ending just dorsal to pelvic-fin origin. Eyes positioned anterodorsally but not meeting medially, no dermal cup or membrane covering ventral portion of eye. Thickened dermal layer (or secondary cornea) over dorsal portion of eye, extending, and gradually thinning out ventrally and posteriorly ( Figs 4 , 5 ). Single anterior interorbital sensory pore (pore C) at anterior edge of fleshy trough or groove; trough covered externally by thickened dermal layer extending from dorsal area of eyes; a pair of anterior oculoscapular canal pores present. Posterior nostril large, anteroventral to eye; anterior nostril opening ventrally at tip of pendulous short tube overlapping upper jaw. Sphenotic bones small, not contacting eyes. Frontal bone elongate; lateral processes on medial portion of frontal distinct; frontal bone fused, forming interorbital bridge, slightly curved, not overlapping ethmoid anteriorly ( Fig. 5A ). Maxilla and premaxilla terminating posterior to eye, maxilla not reaching retroarticular. Palatine terminating before mid- If a specimen was damaged or abnormal (e.g. it has obvious parasites), we did not record data; this is noted in the table by the abbreviation DNT. Data for the holotype of O. dentatus are not included in the range reported for the species.

ectopterygoid. Ectopterygoid thin and elongate, meeting with quadrate posteriorly ( Fig. 7A ). Metapterygoid terminating at hyomandibular junction; angle between metapterygoid – symplectic – quadrate strut and anguloarticular acute (vs. angle obtuse). Preopercle subcrescent-shaped, thin, meeting hyomandibula dorsally. Basihyal bone triangular with continuous cartilaginous anterior margin. Branchiostegal rays 5, rays thin. No laminar processes on parapophyses of fourth vertebrae; neural spine of fourth vertebra broad and spatulate. D1 and D2 connected by membrane for entire height, shallow indentation separating D1 and D2 due to varying height of fin elements. No membrane connecting D2 or A to caudal fin. D1 with six spinous elements, each spine with associated pterygiophore; spaces between first five D1 spines subequal, base of sixth spine positioned approximately midway between base of fifth D1 spine and first element of D2; all elements in D2 and A fins are segmented rays; penultimate and ultimate rays of D2 and A fins supported by single pterygiophore; caudal fin lanceolate, with 17 segmented rays; pelvic fin short and rounded, not reaching genital papilla. Caudal peduncle cartilage elongate, reaching anterior extent of penultimate vertebra. Vertebrae slightly elongate, vertebrae number 10 + 16, two epural bones present. Dense network of capillaries close to epidermal surfaces, especially on head. Males with triangular, conical genital papilla, with posterior tip pointed; females with bulbous, rectangular genital papilla. No other observed external sexual dimorphism.

Etymology: Greek in origin, derived from the word ‘ oxyderkes ’ meaning ‘sharp-sighted’ ( Murdy, 1989). Gender masculine.

Remarks: The genus Oxuderces , and type species O. dentatus , was first described by Eydoux and Souleyet based on a single specimen collected from Macao along with some 200 other fish species aboard the corvette La Bonite between 1836 and 1837 ( Bauchot, Whitehead & Monod, 1982; Figs 1 , 11 ). The unique character of the holotype that prompted its description as a new genus and species (Eydoux & Souleyet, 1848:181) was a peculiar gill opening interpreted by Springer (1978:1) as ‘... continuous across the isthmus and restricted to the ventral surface of the head’. The holotype and, until 1978, the sole scientific specimen identified as O. dentatus also lacks pelvic fins ( Fig. 12A ; Springer, 1978: fig. 4b). Springer (1978) concluded that the absence of pelvic fins in the holotype was abnormal, although it was not considered so by Eydoux & Souleyet (1848) who compared Oxuderces to the ‘anarrhiques’, the French vernacular for wolffishes, currently classified as the family Anarhichadidae , which typically lack pelvic fins. Although Eydoux & Souleyet (1848) placed their new genus in the family Gobioides , congruent with the modern Gobiidae , classification of Oxuderces has been unstable ( Springer, 1978). It has been subsequently placed in its own family, the Oxudercidae (G unther €, 1861; Gill, 1872, 1893; Reeves, 1927; Chu, 1931), which was classified alternatively as a trachinoid ( Berg, 1940; Fowler, 1956; Schultz, 1960; Golvan, 1965; Lindberg, 1971), blennioid ( Gosline, 1968) or gobioid fish (G unther €, 1880; Boulenger, 1904; Jordan, 1905). Many of these ichthyologists who reclassified O. dentatus did not examine the holotype or, even if they did, were probably diverted to a search for close relatives among other fishes that also lacked pelvic fins, such as the wolffishes. No other specimen of Oxuderces has been identified without pelvic fins.

A

After examining the holotype, Springer (1978) returned Oxuderces dentatus to the family Gobiidae , a decision followed by all subsequent workers (e.g. Hoese, 1984; Murdy, 1989; Pezold, 1993).

The monotypic Apocryptichthys Day, 1876 , allied historically with Oxuderces , was described for Apocryptes cantoris Day, 1871 . Confusion surrounding the identity of Apocryptichthys cantoris stemmed from the inconsistent descriptions in the literature and figures by Day (1871, 1876, 1889; and see Springer, 1978: 10 for a tabulated summary). These descriptions varied from publication to publication. The original description of Apocryptichthys and the figure included of the type specimen Apocryptes cantoris ( Day, 1876) conform to Oxuderces (probably referring to AMS B.8336 from Madras), whereas the original description of Apocryptes cantoris (probably referring to BMNH 1870.5.18.23 from the Andaman Islands) conforms to Scartelaos histophorus ( Valenciennes, 1837) . Springer (1978) designated a lectotype for Apocryptes cantoris Day, 1871 (BMNH 1870.5.18.23) from an unspecified number of syntypes and classified the species in the genus Boleophthalmus Valenciennes, 1837 . Murdy (1989) reclassified this species in Scartelaos Swainson, 1839 , a decision with which we concur, as does V. G. Springer (pers. comm.). As the original description of Apocryptichthys may be interpreted to include Oxuderces , we have included Apocryptichthys , in part, in our treatment of Oxuderces .

Ecological note: Published information on the biology and natural history of Oxuderces may refer to what we now recognize as three allopatric species classified in two genera. We interpret information on specimens from eastern China to refer to O. dentatus , that on specimens from the Indo-West Pacific, excluding China, to refer to O. nexipinnis , and that on specimens from northern Australia and New Guinea to refer to Apocryptodon wirzi . General information on O. dentatus may refer to either one of the species of Oxuderces .

Figures

Figure 1. Illustration of the holotype of Oxuderces dentatus Eydoux & Souleyet (1848: pl. 8, fig. 3) from the original description. Image courtesy of the Smithsonian Institution Libraries.

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 11. Holotype of Oxuderces dentatus Eydoux & Souleyet (1848), MNHN A.1822, 77.5 mm SL.

Figure 12. Oxuderces dentatus, head and anterior portion of the body in ventral view. A, MNHN A.1822 (holotype, 77.5 mm SL) has pectoral fins and lacks pelvic fins. B, USNM 85846 (80.3 mm SL) has fully formed pectoral and pelvic fins. The arrow in A points to the area where the pelvic fins have either been lost or never developed. Anterior is to the left.

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.