Description: Body relatively thin, narrow, and long with a large eye and a terminal, small mouth. Pectoral fins medium, reach to vent. Pelvic fins very short. Dorsal and anal-fin bases long, caudal peduncle short and relatively wide. Melanophores on the fin-ray membranes typically occurring in in four groups: at the mid and rear dorsal fin and the forward and rear anal fin. Each melanophore group covers from one to five fin spines or rays. Most, but not all, larvae have a sub-surface melanophore at the top of the head behind the skull, sometimes two or three. Many of the larvae also have a small melanophore on the body at the ventral midline just after the last anal ray (often unnoticed adjacent to the large anal-fin membrane melanophores). Unlike other larval Halichoeres, this species has internal melanophores along the dorsal peritoneal cavity. The one transitional larva captured had begun to develop surface melanophores on the head. Transitional recruits of H. poeyi have a mid-dorsal fin ocellus, a spot on the caudal peduncle just behind the base of the last dorsal ray, a white-edged black spot on the upper base of the central caudal-fin rays, a chain-link patch pattern along the lateral midline, and colored striping on the top of the head. Some variants lack the chain-link pattern and have melanophores uniformly covering the upper and lower sides of the body with a mid-lateral band with no melanophores. Transitional recruits on the reef commonly retain the larval melanophores behind the skull and remnants of the larval melanophores on the fin membranes.
Diagnosis: The fin-ray count of D-IX,11 A-III,12 and Pect-13 indicates Halichoeres and is shared by most of the Caribbean species. Larvae with a total of four patches of melanophores on the dorsal and anal fins (missing the anterior patch of dorsal fin melanophores) represent H. poeyi (confirmed by DNA sequencing).
