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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. The Ascothoracida compnse more than 90 described species of parasitic maxillopodan crustaceans related to the Cirripedia within the Thecostraca. Their hosts inc! ude anthozoans and echinoderms. Unlike nearly all other ascothoracidans, species of the genus Synagoga are not attached to or enclosed within their hosts as adults, but remain free-swimming and are occasionally caught in plankton. Their nauplius larvae and any subsequent ascothoracid-larvae (bivalved, cypridiform stages) have not yet been described; only a post-larval juvenile form and adult males and females of different degrees of sexual maturity are known. Synagoga has a wide distribution in the Atlantic, Indian, and (present report) Pacific Oceans, but is known from very few specimens. Synagoga mira Norman (1888), several males of which were found on the antipatharian black coral Antipathes larix Esper in the Bay of Naples, was one of the first known species of the Ascothoracida (for illustrated descriptions see: Norman, 1913; Grygier, 1983a). Grygier (1983a) described S. ·normani based on a female found on an alcyonacean soft coral, Dendronephthya sp., near Mombasa, Kenya. Grygier (1990) also described S. l) Mailing address: 14804 Notley Rd., Silver Spring, MD, 20905, U.S.A. Publ. Seto Mar. Bioi. Lab., 36(5/6), 293-311, 1995. (Article 23) 294 M.J. GRYGJER & S. 0HTSUKA paucisetosa and S. bisetosa (the latter only provisionally included m this genus) based on a mature male and an immature possible female, respectively, from the bathyal Atlantic, hosts unknown, as well as an unnamed, mid-oceanic, planktonic juvenile from the eastern Indian Ocean (Grygier, 1988). Grygier ( 1983a) transferred two other species, S. metacrinicola Okada, 1926, and S. sandersi Newman, 1974, to a separate new genus, Waginella. This paper presents the description of a new species of Synagoga caught in plankton near Okinawa, Japan. A scanning electron microscopical (SEM) study of the the cuticular ornamentation of the carapace is included for comparison with that of Waginella metacrinicola (see Grygier & Ito, in press). A single adult male was collected aboard TRV "Toyoshio-maru" in the East China Sea off Okinawa between Ie-shima and Aguni-shima (11 May 1991, 26°42.90'N, 127°28.ll'E-26°42.17'N, 127°30.40'E, 19:26-20:15, oblique tow from 575 m to surface with ORI net, 0.33 mm mesh). The specimen was originally fixed and preserved in neutralized sea-water formalin. After the removal of the left carapace valve, the specimen was observed with a Nikon Optiphot differential interference microscope in a glycerine whole mount and drawings were prepared using a camera Iucida. The left thoracopods and frontal filament complex were mounted on a glass slide in glycerine jelly for detailed examination. The left carapace valve was dehydrated through an ethanol series, transferred to isoamyl acetate, critical point dried using liquid COz, mounted on a brass stub, and photographed with a JEOL JSM-T20 scanning electron microscope operating at an acceleration voltage of 20 kV. Diagnosis Ascothoracida Synagogidae Gruve1, 1905 Synagoga Norman, 1888 Synagoga ~nillipalus, sp. nov. (Figs 1-10, Table 1) Anterior pit of carapace more than 10 times deeper than inner diameter. Segment 4 of antennule with small spine and two large, densely setulose setae; segment 6 longer than segment 5, with more or less parallel margins. Oral cone reaching only to level of ends of thoracopodal protopods. Proximal exopodal segment of legs 2-5 with one strong, subapical, lateral seta instead of numerous weak ones. No medial seta on basis of thoracopod 4. Three setae on exopod of thoracopod 6. Epaulets of thoracomere 6 with numerous round spots with thin cuticle. Rami of penis each ending in four long setae. Row of 12-13 ventral spines on furcal rami; posteroventral telsonic setae longer than this spine row.

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