Description: Body relatively thin, long, and narrow with a medium eye and a terminal, medium mouth. Pectoral fins long, reaching to or past vent. Pelvic fins medium, extending about two-thirds the way to the vent, with a flat frenum not forming an obvious cup. Dorsal and anal-fin bases medium length and caudal peduncle medium length and width, procurrent caudal-fin rays usually 6 (5-6 spindly). A single melanophore on the caudal peduncle ventral midline just after the last anal fin and internal melanophores only at the dorsal surface of the swim bladder and sometimes around the gut near the vent.
Diagnosis: Fused pelvic fins and modal fin-ray counts of D-VII,11 A-10 and Pect-17 overlaps many species of the numerous Gobiosoma/Elacatinus group, but matches the mode only for the allopatric set of Gobiosoma hildebrandi (Panama), G. schultzi (Venezuela), G. yucatanum (Yucatan to Honduras), and then the pair of Tigrigobius saucrus and T. dilepis. G710 G7S1110
Analogues: (solitary post-anal-fin spot) Pre-transitional Gobiosoma hildebrandi larvae can only be distinguished from their co-ocurring congeners by fin-ray counts (but there is overlap); the combination of 11/10 p-17 vs. 12/10 p-16 in G. spes and 12/11 p-16 in the T. gemmatus type. This group is distinguished by having flat pelvic frenums vs. obvious cup-shaped pelvic fins in T. saucrus and T. dilepis. At transition, G. hildebrandi develop outlined scales along the posterior body (vs. naked in newly-settled G. spes).
