Analogues: (post-anal fin single melanophore, small: <7 mm SL) Among the taxa with divided pelvic fins and the single melanophore behind the anal fin, several types have small larvae. Larvae of Psilotris batrachodes are most similar and often have a post-dorsal fin spot as well (although it is typically smaller than the ventral spot). When the dorsal melanophore is present, Psilotris batrachodes can be distinguished by the lower fin-ray counts (especially the short anal fin) and a narrower caudal peduncle. Psilotris alepis larvae have only a ventral spot and Gobulus myersi have abdominal ventral midline spots.
Description: Body somewhat thick, long, and narrow with a relatively small round eye and a terminal mouth. Larvae are usually hunched-over, with the head mostly bent below the level of the lateral midline of the body. Head relatively broad and flattened, not much wider than the caudal peduncle. Pectoral fins long, dorsal and anal-fin bases short and placed well back on the body, caudal peduncle relatively wide. Internal melanophores around the sacculus and on the dorsal surface of the swim bladder. A surface melanophore around the gut near the vent and large solitary melanophores on the caudal peduncle placed just behind the last dorsal and anal-fin rays. Transitional larvae become more flattened and develop tiny melanophores on the mid-upper and lower jaw and a scattering of leukophores on top of the head between the eyes.
Diagnosis: Modal fin-ray counts of D-VII,10 A-9 and Pect 16 and divided pelvic fins indicates Pycnomma roosevelti. The appearance and fin-ray counts are quite similar to the Psilotris, but a strong mode at this count of fin elements excludes the Psilotris species. P. alepis larvae have fewer pectoral-fin rays and lack the dorsal melanophore. Psilotris boehlki and P. celsa both have a strong modal anal-fin-ray count of 10 and are therefore excluded. An adult Pycnomma roosevelti from the Saba Bank matches the transitional larva in morphology, especially the long body with a small flattened head (and relatively small round eyes), the placement of the anal fin far back on the body, the wide caudal peduncle, and the rounded caudal fin. The hunched-over appearance, with the head placement mostly below the lateral midline of the body, occurs in both the larvae and adult from Saba. In addition, the larval melanophores on the body at the end of the dorsal and anal fins match markings at the same location on the Saba specimen. (PE) G19a
