Pylocheles (Pylocheles) mortensenii (Boas, 1926)

Pylocheles Mortensenii Boas, 1926: 40, figs. 1, 5, 6, 10A, 11B, 13, 14, 18, 25A.

Pylocheles (Pylocheles) mortensenii. — Forest, 1987: 51, figs. 2a, 3a, 5a, b, 7a, 8a–i, 9a–d, 10a, b, 12a–d, 41a, pl. 2C.

Material examined. Ten specimens, cl = 2.0– 2.3 mm; three dissected (examination and description by Saito & Konishi 2002).

Remarks. Although Saito & Konishi (2002) referred to their larvae as a first zoea, they noted the stalked condition of the eyes, existence of a mandibular palp, well developed pereopods, six pleonal somites and the occurrence of uropodal buds. However, the presence of only four natatory setae on the exopods of each first and second maxilliped was viewed as a typical first zoeal character.

The antennule of P. (P.) mortensenii was described as being incompletely segmented and lacking processes, although Saito & Konishi’s (2002, fig. 3A) figure might be interpreted as having the bud of one ramus (presumably the exopod) developed but lacking aesthetascs. Clearly, the antennule was in an early stage of development. The antenna as described and illustrated also appeared to be of an early zoeal stage, whereas the mandible, with its two-segmented palp was comparable to mandibular development seen in a late stage zoea. The maxillule was described as reduced, but whether this condition was a reflection of lecithotrophy or transition to the juvenile state is uncertain. The first and second maxillipeds had the endopods reduced, but appeared typically zoeal in structure, in contrast to the third maxilliped where the endopod had five incipient segments.

Saito & Konishi (2002) concluded that the larvae of Pylocheles (P.) mortensenii were free-swimming upon hatching, and while not cultured, the authors suggested that at least one subsequent larval stage would follow. Although staked eyes and developing pereopods, uropods, and pleopod buds are indicative of advanced development, the generally typical early zoeal stage antennule and antennal of the larvae would sustain their conclusion.