Caragobius Smith and Seale, 1906

Edward O. Murdy & Koichi Shibukawa, 2003, A revision of the Indo-Pacific fish genus Caragobius (Gobiidae: Amblyopinae)., Zootaxa 301, pp. 1-12 : 3-5

Caragobius Smith and Seale, 1906

Caragobius Smith and Seale, 1906 : 418 (type species: Caragobius typhlops Smith and Seale, 1906 , by original designation and monotypy)

Trypauchenophrys Franz, 1910 : 68 (type species: Trypauchenophrys anotus Franz, 1910 , by original designation and monotypy).

Caragobioides Smith, 1945 : 571 (type species: Caragobius geomys Fowler, 1935 , by original designation and monotypy).

Included Species. Caragobius comprises two species, C. rubristriatus and C. urolepis .

Diagnosis. The genus is unique within the Amblyopinae in having: 3-7 anal-fin pterygiophores anterior to first hemal spine (AP); fifth hypural absent; and ribs lacking on 3rd precaudal vertebra. The other features useful in distinguishing it from all other Trypauchen-Group members are: pectoral fins broadly rounded, symmetrical dorsoventrally; head slightly depressed; no fang-like teeth; no opercular pouch; eyes rudimentary; and pelvic fins rounded.

Description. Total dorsal-fin elements 36-52; first dorsal fin with six flexible spines; first element of second dorsal fin segmented, or segmented and branched, all others segmented and branched rays; dorsal-fin base long and broadly joined with caudal fin. A short, longitudinal fleshy ridge anterior to dorsal fin. Total anal-fin elements 31-45, first element spinous or segmented, or segmented and branched, all other elements segmented and branched; anal-fin height approximately equal to second dorsal-fin height; anal-fin membrane broadly joined with caudal fin. Pectoral-fin rays 16-20, pectoral fin short and rounded posteriorly; all pectoral-fin rays segmented and branched, except, occasionally, dorsalmost and/or ventralmost just segmented. Pelvic-fin rays I, 5, with well developed frenum and connecting membrane forming cup-shaped disc. Caudal fin long and pointed, with 12-15 segmented rays (typically 13 in a 7+6 arrangement), and 10-12 branched rays (typically 11 in a 6+5 arrangement). Ray associated with epural typically is very short and bifid, ray associated with ultimate hemal spine typically is very short and simple. Procurrent rays typically absent; when present, are rudiments.

Head slightly depressed with body compressed. Scales cycloid, anteriormost small, embedded, non-imbricated; posteriormost larger and slightly overlapping.

Upper and lower jaws with two rows of slender, sharp-tipped canine teeth that are slightly curved inward. Outer-row teeth slightly larger than those of inner row; outer-row teeth of lower jaw approximately equal in size to those of upper jaw; 10-27 teeth in outer row of upper jaw; 12-28 teeth in outer row of lower jaw. No palatine or vomerine teeth present.

Mouth large and oblique, jaws terminating posteriorly at the vertical with, or just anterior to, posterior naris. Tongue thin, tip free from floor of mouth. Isthmus moderate to broad. No barbels present.

Eye rudimentary, but distinct, covered by skin, slightly smaller than diameter of posterior naris. Posterior naris located immediately anteromedial to eye; anterior naris at tip of a very short flap that slightly overhangs upper jaw.

Cephalic sensory canals and pores absent. Sensory papillae present on head and anteriorly on body, but difficult to observe without magnification. Sensory papillae on head scattered, not forming a discernible pattern except for those along mandible, which follow the jaw line. Sensory papillae on body represented by a longitudinal, midlateral raised fold of tissue with smaller dermal ridges radiating dorsally and ventrally. Sensory papillae lacking on posterior 30-40% of body.

Gill rakers low, fleshy, and unossified; gill opening narrow, extending only the height of the pectoral-fin base.

Osteology. Spinous dorsal-fin pterygiophore formula 3-1221, rarely 3-1221+1 or 3- 1311+1 [in these latter two, the sixth spine shares its interneural space with the first pterygiophore associated with the first dorsal-fin soft ray]. Precaudal vertebrae 10, rarely 9 or 11; caudal vertebrae 18-22 or 25-27. Pterygiophore of the second soft dorsal-fin ray (typically the posteriormost pterygiophore inserting in 7th interneural space) has a middle radial. Epurals 2. Basihyal spatulate. Symplectic with a posteriorly directed arm that cartilaginously joins the hyomandibula; this arm creates a small oblong-shaped gap between dorsal aspect of symplectic and the hyomandibula. Dorsoposterior tip of metapterygoid in contact with inner surface of hyomandibula. Infrapharyngobranchial 2 lacking. Uncinate process on epibranchial 3 present. Frontal crest present but low. Four pectoral fin radials with three fossa, largest one between radials 2-3, smallest between 1-2. Long dorsallydirected flange anteroventrally on subopercle. Atlas with well developed parapophyses, in contact with first epineural. Epineurals present from 1st precaudal vertebra through 9th to 12th caudal vertebra. Well-developed ribs on 4th through 9th precaudal vertebrae, ribs on 10th precaudal vertebra slightly reduced. Epineurals fused with ribs on precaudal vertebrae 4-8. In one cleared & stained specimen from Fiji (USNM 241794), middle radial of ultimate pterygiophore in anal and dorsal fins forked; all other middle radials of anal and dorsal fin pterygiophores simple and not forked. Hypural 5 absent.

Comparison with Brachyamblyopus . As mentioned above, Caragobius has been confused with Brachyamblyopus . However, Caragobius is easily distinguished from Brachyamblyopus as follows: in C. rubristriatus , scales extending from the vertical with 3rd or 4th dorsal-fin spine to caudal peduncle, whereas in C. urolepis , no scales ventral to spinous dorsal fin (vs. scales extending from predorsal area to caudal peduncle in Brachyamblyopus ); total elements in anal fin 31-45 in Caragobius (vs. 28-31 in Brachyamblyopus ); jaw length/SL 0.048-0.070 in Caragobius (vs. 0.070-0.081 in Brachyamblyopus ); no interneural gap in Caragobius (vs. interneural gap present in Brachyamblyopus ); AP=3-7 (vs. AP=2); 18 or more caudal vertebrae (vs. 16 caudal vertebrae); and first ribs on precaudal vertebra 4 (vs. first ribs on precaudal vertebra 3).

Key to the species of Caragobius

1a. Total elements in dorsal fin 43 or fewer, typically 38-40; total elements in anal fin 36 or fewer, typically 32-35; anal-fin pterygiophores anterior to first hemal spine 4-7, typically 5 or 6; caudal vertebrae 18-22, typically 20 or 21; longitudinal scale rows extend from just posterior to mid-body to caudal peduncle. (India, Thailand, Indonesia, Japan, Philippines, Fiji) .......................................................................... C. urolepis

1b. Total elements in dorsal fin 43 or more, typically 48-50; total elements in anal fin 35 or more, typically 40-43; anal-fin pterygiophores anterior to first hemal spine 3-5, typically4; caudal vertebrae 25-27; longitudinal scale rows extend from just posterior to distal tip of pectoral fin to caudal peduncle. (northern Australia) ........ C. rubristriatus