Diagnosis: The modal fin-ray count of D-XIX,11 A-II,19 and P-13 is shared by the 19-spined trio of L. gobio, L. guppyi, and L. kalisherae, as well as by Malacoctenus aurolineatus (but the latter usually with 14 pectoral-fin rays). Note that almost 90% of L. gobio individuals have 19 dorsal-fin spines. The fin-ray count falls within the upper or lower range for most other Labrisomus species and both M. delalandii and M. gilli. (DNA) Ecology: The palehead blenny is a somewhat common small blenny found generally in shallow mixed coral habitats. The species is widespread in the region, found in Florida, the S. Gulf of Mexico, the Bahamas, and across the Caribbean Sea except NE Venezuela. Unfortunately, the 19, 20, and 21-spined Labrisomus are very similar morphologically and are frequently confused in guidebooks and photographs. All six species share the blunt-headed and goggle-eyed appearance, at least as juveniles, i.e. the snout length (bony orbit to jaw tip) is less than two-thirds of the orbit diameter. Adult palehead blennies are recognized in the field mostly by the absence of an opercular ocellus, the dark bars not extending onto the fins, and relatively even-length dorsal-fin spines. Additional characters often cited are an "unmarked" lower head and the lower portion of the bars on the body being lighter and narrower than the upper parts, although the variation in the intensity of markings in the group make these unreliable. Juveniles are particularly difficult to separate, since the distinguishing markings for each species are either not well-developed or shared by other species at this early stage (but see description below). L. gobio larvae are rare in collections. Description: (pre-transitional larvae have not been identified, but are likely identical among the 19-spined Labrisomus, see L. guppyi) Transitional stage: L. gobio larvae in transition develop metamorphic melanophores over the head and body simultaneously. The head is mostly uniformly speckled with fine melanophores; on the body there is a series of about 9 dark bars, alternating lighter and darker, with unpigmented bands between them. Juveniles: L. gobio juveniles have prominent dark bars on the body that do not extend onto the fins, with the second body bar (under the 10-15th dorsal-fin spines) widening on the upper body to touch the bases of about 5 or 6 spines. The last dark bar, on the tail, ends as a straight vertical line or slight crescent. Although there can be a dark spot on the operculum, it is not an ocellus with a thin rim. The first dorsal-fin spine is relatively long, about half the body depth at the dorsal-fin origin, and similar in length to the mid-fin spines. Analogues: The juveniles of the 19- and 20-spined Labrisomus are blunt-headed, compared to the 18-spined Labrisomus (other than L. albigenys), i.e. the snout length (bony orbital margin to the tip of the closed jaw) is less than two-thirds the bony orbit diameter. Small juveniles of the blunt-headed Labrisomus are difficult to identify to species, especially since some species described with opercular ocelli can have only a diffuse dark spot on the operculum when young. In addition, those species described without ocelli can often have an outlined dark spot on the operculum (but not a thin-rimmed ocellus) as juveniles. Juvenile L. gobio are best identified by the dark bars on the body that do not extend onto the fins and the second body bar widening to reach about 5 or 6 dorsal spine bases (vs. 3 or 4 in other species). They can be further separated from L. guppyi juveniles who have not yet developed a distinct opercular ocellus by a longer first dorsal-fin spine (2 to 2.5 into body depth at the dorsal-fin origin vs. 2.5 to 3) and fewer dark bands on the pelvic fins (often faint and no more than 4). Juvenile L. kalisherae share the long first dorsal-fin spine but have the pigment on the base of the caudal fin outlining three light spots vs. ending as a mostly straight vertical line in L. gobio (and L. guppyi). Juvenile L. bucciferus and L. haitiensis also have three outlined spots on the caudal-fin base (and even longer first dorsal-fin spines and higher fin-ray counts). L. albigenys are best distinguished by their very short first dorsal-fin spine and lower fin-ray counts. The remaining Labrisomus juveniles are distinguished from L. gobio by longer snouts, opercular ocelli, and fin-ray counts, i.e. L. nigricinctus and L. nuchipinnis (as well as L. conditus and L. cricota, both with less distinct ocelli), and L. filamentosus (blunt-snouted but with longer first dorsal-fin spines).
