Diagnosis: Long thin larvae with a short round pelvic-fin sucking disk and modal fin-ray counts of D-VI,11 A-11 Pect-20 indicate the river gobies of Sicydium. The taxonomy and range of species in this genus are generally unresolved and numerous species have been described (Bussing 1995). According to Lyons (2005) the northern Central American coastal species is S. gymnogaster, found from Veracruz, Mexico to Honduras, but this Yucatan-caught larvae is a DNA match to an adult from St. Thomas USVI, indicating that the species limits and/or phylogenetics are in question.
Description: Body thin, long, and narrow with a medium-sized round eye and a terminal small mouth. Pectoral fins very short, pelvic fins very short. Dorsal and anal-fin bases short and caudal peduncle narrowing, 10-14 procurrent caudal-fin rays. On the head there are melanophores lining the premaxilla and the dentary at the tip of the lower jaw and a pair of large melanophores at the rear edge of the brain case. A large sub-surface melanophore is placed behind the pectoral-fin base on each side of the body. Along the ventral midline there is a large melanophore at the mid-abdomen and then paired at the base of the mid-anal-fin. Internal melanophores overlie the posterior swim bladder and extend down to the vent. A large deep internal vertical melanophore underlies the last anal-fin ray extending to the lateral midline, where it surfaces and spreads as a large dendritic surface melanophore with characteristically long filamentous extensions. Melanophores are concentrated at the base of the mid and upper caudal-fin segmented rays.
