AppearanceAdults of the three non-sand Coryphopterus gobies have divided pelvic fins and a characteristic black patch at the vent. C. personatus is very common in shallow-water where it hovers over coral heads in large groups, while C. hyalinus takes its place on coral walls and in deeper water. The two species can look quite similar underwater. On close examination, C. personatus has a single midline anterior dorsal interorbital pore, while C. hyalinus has a pair of pores side-by-side. In addition, C. personatus adults (over 12 mm SL; it is not true for juveniles) can be distinguished by an unmarked central patch on top of the head vs. a mostly uniform scattering of melanophores on adult C. hyalinus and the obvious stripe behind the mid eye in adult C. lipernes.
Juveniles develop the single interorbital pore by about 10 mm SL. The pelvic fins are fused in small juveniles and divide only after about 12 mm SL. The location of the vent within the black spot is an unreliable character on juveniles and small adults.
Body relatively thin, long and narrow with a large eye and a terminal mouth. Paired fins medium to long at transition, dorsal and anal-fin bases relatively short, caudal peduncle long and narrow, procurrent caudal-fin rays 7-10 (7-9 spindly). Lightly marked mostly along the lower body: melanophores on the ventral midline at the isthmus and the pelvic-fin insertion (usually streaks). Then there is a row along the anal-fin base, usually six or often seven, paired and one per side between the third and ninth element (often merged into a streak on each side). Then after a space there is a row of midline melanophores, usually seven, sometimes eight, unpaired (but often merged into a streak), extending along the caudal peduncle ending near the start of the procurrent caudal-fin rays. Internal melanophores are present at the dorsal surface of the swim bladder and around the gut near the vent (none on the head). Series of transitional larvae show development of the eye from a slightly narrowed vertical oval slightly tilted forward with a small posterior-inferior extension of the iris to round and notably larger. The extension has several surface melanophores overlying it (vs. C. glaucofraenum, comparative photograph below). Rare individuals show abnormal enlargements of this extension. There is often a prominently speckled "eyebrow" membrane over the upper half and posterior of the eyeball that appears detached from the pigmented iris below. Transitional larvae develop a scattering of iridophores between the eyes and in a stripe behind the upper eye. Melanophores start as a few scattered on top of the head developing into a loose cluster on the dorsal surface of the head behind the eye (not a stripe). Melanophores later develop in a tight group on the abdominal wall forward of the vent.
Larval C. personatus look much like larvae of the typical sand goby, but are missing the melanophores at the jaw angle and on the caudal fin. Occasional individuals with 10/10 can be similar to rare unmarked variants of the sand gobies; only the low pectoral-fin ray count would be definitive. Larval C. personatus have a larger eye than many of the sand goby larvae with more extensive dorsal membrane stippling, although these characters may be subtle. Transitional stage C. personatus diverge from the two other non-sand Coryphopterus species as follows: from C. hyalinus by developing spots scattered on the top of the head (vs. an unmarked central region) and having rows of melanophores along the posterior dorsal quadrant (1 to 2 o'clock) of the ocular rim (vs. an unmarked area); from C. lipernes by developing a prominent patch of melanophores along the abdomen to the vent (vs. a simple ring around the vent). As larger recruits, C. personatus diverge from the two other species by retaining a mostly unmarked body (vs. speckling on the posterior half of the body).
Modal fin-ray counts of D-VI,11 A-11 and Pect-15 indicate Coryphopterus personatus. The distinguishing features of later juvenile and adult C. personatus are mostly not present on recruits and small juveniles.
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