Integripelta japonica, SP. NOV.

INTEGRIPELTA JAPONICA SP. NOV.

(FIG. 2C, D)

Eurystomella bilabiata:? Kataoka 1960: 396, pl. 41, fig. 3;? Hayami 1970: 330, pl. 36, fig. 3;? Hayami 1974: 222, pl. 69, fig. 2a, b;? Seo 1996: 301.

Material examined

Holotype: SMBL Type no. 399, 34°50.568¢N, 131°05.554¢E, 89–94 m, near the island of Mi-shima, north of south-west Honshu (Yamaguchi Prefecture) [Seto Marine Biological Laboratory Station 13-1, 29 September 1998].

Paratypes: SMBL Type no. 400, and NIWA P-1218, same locality as holotype.

Description

Colony encrusting, multiserial, unilaminar. Dried colonies hyaline. Autozooids contiguous, quincuncially arranged, 0.47–0.75 mm long (0.62 ± 0.07 mm), 0.32–0.57 mm wide (0.45 ± 0.07 mm). Gymnocystal frontal shield not elevated, no umbo or carina, smoothsurfaced, lacking fenestrae. Orifice somewhat more D-shaped than hat-shaped, the anter high-arched with the proximal corners bluntly condyle-like, the proximal rim of the poster straight or scarcely concave, the lateral corners curving obliquely distad towards the short indentations and adjacent excavations. Orifice of maternal zooids mostly not dimorphic, more or less identical in size and shape (0.30–0.36 mm wide at the proximal margin) to that of autozooids (0.24– 0.30 mm); distal kenozooidal chamber very small, not extending to the basal wall, the central foramen tiny, rounded or slit-like. No basal pore-chambers, interzooidal communications comprising a row of uniporous septula along each lateral wall. Ancestrula not seen.

Etymology

From japonica (L.) Japanese.

Remarks

Integripelta japonica has almost certainly previously been confused with I. bilabiata. The two species appear similar, but published SEM micrographs (Cook & Chimonides, 1981) allow comparison of the key taxonomic features, permitting ready discrimination of the two species. In I. bilabiata the autozooidal orifice is proportionately larger than in I. japonica (almost half the size of the zooid) with larger proximolateral excavations on the edge of the gymnocyst (see Cook & Chimonides, 1981; fig. 5D, arrows), the maternal orifice is dimorphic, a low umbo and/or carina is often present, and the ‘ooecial kenozooid’ is larger with a larger foramen. In his original description, Hincks (1882) noted that the zooids in I. bilabiata were ‘short’ and that the ‘ooecium’ had a ‘large foramen’ (see also Hincks, 1884). The above synonymy is suggested by the published illustrations of specimens described by Kataoka (1960) and Hayami (1970, 1974). We have not examined these specimens, but the relative proportions of the orifice in relation to the entire zooid strongly indicate that they were I. japonica, not I. novella, which is somewhat intermediate between I. bilabiata and I. japonica in the zooid length:orifice length ratio.

Distribution

Southern Japan Sea off south-western Honshu, 89–94 m (Seto Marine Biological Laboratory Collection).?Also Japan Sea, western Honshu, 151 m (Kataoka, 1960), and Early Miocene of south-west Hokkaido and central Honshu (Hayami, 1970, 1974).