New Species of Synagoga (Crustacea : Ascothoracida) from Plankton off Okinawa, Japan, with a SEM Study of the Carapace

Abstract

A free-swimming adult male of the ascothoracidan crustacean Synagoga millipalus sp. nov. is described from plankton in the East China Sea off Okinawa, Japan. This is the first Pacific record of the genus. The new species is distinguished at length from its most similar congener, S. paucisetosa Grygier from the bathyal equatorial Atlantic. The ornamentation of the carapace is described by scanning electron microscopy. The inner surface has a continuous but regionally differentiated, submarginal palisade of partly fused spines as well as lanceolate guard setae with distally pointing barbs, a deep anterior pit, concentric zones of pores, and a cluster of minute pores at the posterior angle. The external surface has rimmed pores and hair sensilla, but most of the diverse outer integumental organs reported from another morphologically generalized ascothoracidan, Waginella metacrinicola (Okada), are absent. Two of the five pairs oflattice organs ( = cardic organs) along the hinge line have anterior rather than posterior pores. This orientation differs from that of other ascothoracidans and tends to weaken a recent analysis, using Ascothoracida as the outgroup, of lattice organ variation among the cyprid larvae of Cirripedia.