Diagnosis: The modal fin-ray count of D-XVIII,11 A-II,18 and P-13 indicates Labrisomus nigricinctus and L. albigenys. This fin-ray count falls within the lower range for Malacoctenus aurolineatus and M. versicolor, as well as for many of the remaining 18 and 19-spined Labrisomus species. (DNA) Note: This larval identification is pending DNA confirmation, but is likely from the process of elimination: the larva differs in several ways from the L. albigenys series described above (the L. albigenys identification is based on the fin-ray counts and a very different DNA sequence from adult L. nigricinctus from the same site). The remaining species of Labrisomus and Malacoctenus that could possibly share the low fin-ray count of this larva have different larvae, all clearly identified here with DNA-sequence confirmation. The remarkably small size of the larva (for Labrisomus) matches the observation by Springer (1959) that juvenile L. nigricinctus as small as 12 mm SL are collected on the reef. Ecology: The spotcheek blenny is a small blenny found mostly in tidepools and shallow eroded reef and thus rarely noticed underwater. They are found throughout the Caribbean, as well as Florida, the Gulf of Mexico, and the Bahamas, but not NE Venezuela or Brazil and its offshore islands. The species is common only in clear water and high-energy sites: the outer Keys in Florida, the Bahamas and Antilles, and the barrier reef and atolls of Belize. Their larvae are rare in collections. Description: Pre-transitional larvae: Body long, moderately narrow, and thin with a medium round eye, pointed snout, and relatively small terminal mouth. Long continuous dorsal and anal fins with a short and narrow caudal peduncle. Pectoral fins long, reaching past the vent, and pelvic fins long and thread-like. On the head there are two small off-center melanophores overlying the midbrain lobes. There is a cheek melanophore on each side. There are no melanophores along the dorsal or caudal-fin bases. Along the ventral midline there is a melanophore at the isthmus and deep at the pelvic-fin base. Along the anal fin there is a melanophore at the base of each anal-fin soft ray except the last, which is closely followed by a single larger melanophore along the ventral midline of the caudal peduncle. Internal melanophores comprise only the basic complement: the nuchal midline, otic capsule, and overlying the abdominal organs. Juveniles: L. nigricinctus juveniles are quite distinctive with a prominent round opercular ocellus, a pointed snout with a small terminal mouth, no spot on the first few dorsal-fin spines, and sometimes narrow dark bars on the body that extend onto the dorsal fin. Analogues: L. nigricinctus larvae share fin-ray counts and some morphology with L. albigenys, but differ by having a melanophore along the ventral midline of the caudal peduncle, one or two cheek melanophores, and no deep melanophore associated with the anal-fin row. These two species are intermediate in size and appearance between Labrisomus and Malacoctenus, but, notably, have lower fin-ray counts than all Malacoctenus except the rare individual of M. versicolor or M. aurolineatus. Larvae of M. versicolor can be distinguished by their relatively long first dorsal-fin spines (vs. short in the two Labrisomus species) and more numerous head spots. M. aurolineatus larvae also have a longer first dorsal-fin spine and have a set of additional larval melanophores (along the soft dorsal-fin and caudal-fin bases and internally over the vertebral column). M. macropus, M. erdmani and M. gilli larvae have similar light markings, but no melanophore at the isthmus (or the pelvic-fin base in the former two) and higher fin-ray counts. The remaining Malacoctenus species have many more head spots. The remaining Labrisomus larvae are larger with larger mouths and usually with many more melanophores over the cranium, dorsal and caudal-fin bases, and internally over the vertebral column. Juvenile L. nigricinctus are separated from other Labrisomus species by the small mouth, pointed snout, and well-delineated round opercular ocellus. In morphology they appear more similar to Malacoctenus juveniles, however no Malacoctenus share the obvious ocellus on the operculum. Juvenile L. nuchipinnis, L. guppyi, and L. filamentosus can share the opercular ocellus, but are distinguished by less-pointed snouts, larger mouths, and indistinct bars. The 19- and 20-spined Labrisomus species all have a much blunter snout, less than two-thirds the bony orbit diameter.
