Chaperiopsis boninensis (Silén, 1941)

(Fig. 11; Table 12)

Chaperia transversalis var. boninensis Silén, 1941: 48, fig. 65.

not Chaperiopsis (Chaperiopsis) boninensis: Gordon, 1984: 35, pl. 6, fig. B.

Material examined. Holotype by original designation UPSZTY 2464, Bonin Islands (Ogasawara), east from Chichijima, Japan; depth 100–135 m. Leg. Prof. S. Bock 1914.

Description. Colony encrusting, multiserial, unilaminar; the holotype consisting of two dozen zooids lacking ovicells.

Autozooids oval to rhomboidal, longer than wide (mean L/ W 1.32), distinct, separated by deep furrows, quincuncially arranged (Fig. 11A, B). Gymnocyst smooth, forming a short triangular shelf proximally (70–80 µm), lodging the base of the pedunculate avicularium; a narrow moon-shaped band of granular cryptocyst extending proximally and laterally, outlined by a raised rim indented by spines distolaterally.

Opesia oval, occupying about half of the frontal surface (mean OpL/ZL 0.51); occlusor laminae not visible; four robust distal spines, 30–40 µm in diameter, the most external pair cervicorn, branched thrice, 250–315 µm long, the distalmost pair bifurcated, 130–215 µm long (Fig. 11A).

Adventitious avicularia of two types: type 1 sessile, placed distally to almost each autozooid, teardrop-shaped with acutely triangular rostrum directed distally and two blunt condyles, mandible same shape and size as the rostrum (Fig. 11B); type 2 pedunculate with a 150–280 µm long stalk, placed on the proximal gymnocyst of most autozooids, directed perpendicular to the surface of the colony, same shape of the sessile avicularia but on average slightly longer, the rostrum oriented proximally (Fig. 11B).

Ovicells not observed.

Remarks. The main diagnostic feature of this species is the long-stalked, pedunculate proximal avicularium. Gordon’s (1984) records of this species from several stations in the Kermadec Ridge across a great depth range (35–635 m) turned out to be conspecific with Chaperiopsis tintinnabula Hayward & Thorpe, 1988 (Gordon et al. 2009).