The wormfishes are tiny and rarely-seen relatives of the gobies. There are only two Caribbean genera: Cerdale floridana and the genus Microdesmus with five regional species. Fortunately, fin-ray counts clearly distinguish the regional species, which share almost all other larval characters and markings. Despite the small size of the adults, the larvae are large and not uncommon in larval collections.
The dartfishes of the family Ptereleotridae have been taxonomically mobile in recent years and some taxonomists now include them in the wormfish family Microdesmidae. I place them here alongside the family Eleotridae because they are also gobioids and share the clearly-divided pelvic fins of the eleotrids. Larval ptereleotrids most closely resemble the "long" larvae of my Group 4 gobies. There are only two dartfishes in the region, a pair of sibling species that vary only slightly in color: their larvae are likely identical.
Larval microdesmids are long and worm-like with a prominent mid-body swim bladder. They have a characteristically blunt, hooked, and protruding lower jaw and more, usually many more, than 35 elements in the dorsal fin and 23 in the anal fin. These features easily distinguish them from the gobies and other gobioids. Wormfish larvae are morphologically similar to the larval pikeblennies of Chaenopsis, but the latter have long and thread-like pelvic fins while larval wormfishes have inconspicuous pelvic fins. Transforming eel larvae of many families may superficially resemble larval microdesmids, but the eels do not have a normal caudal fin as do the microdesmids and chaenopsids.
