Naupliar Development of Hansenocaris furcifera Ito (Crustacea : Maxillopoda : Facetotecta) from Tanabe Bay, Japan

Abstract

Five naupliar stages of Hansenocarisfurcifera Ito, 1989, the first of which is Nauplius y Type IX sensu Ito, are described in detail, based upon specimens originally collected in Tanabe Bay on the Pacific coast of Honshu, Japan, and reared in the laboratory. The naupliar sequence was determined by connecting partial series of exuviae of separately cultured individuals. The five naupliar stages, which are planktotrophic, are all metanauplii with a pair of setiform maxillular rudiments, and no orthonauplius stage was found. The surface structure of the first naupliar stage was studied by SEM. In front of the first antennae lies a pair of small protuberances with central pores, which are identified as the termini of the head gland instead of frontal filaments. Most of the body surface has a very fine, mesh-like texture, but the dorsocaudal organ and at least part of the window do not. The dorsal plates are deliniated by prominent, chitinous ridges about I Jlm high. Some new terminology is introduced to describe the developmental changes of the plates. Remarkable alterations in the Elongate and Intercalary plates are noticed through naupliar development. The setal ornamentation of the antennule changes through the first four naupliar stages, but that of the antenna and mandible remains unchanged.