Beania discodermiae boninensis Silén, 1941

(Fig. 25; Table 23)

Beania discodermiae var. boninensis Silén, 1941: 95, figs 120–123.

Material examined. Lectotype (designated here) UPSZTY 2456 A, the best preserved specimen among the syntypes UPSZTY 2456 A–C, Bonin Islands (Ogasawara), east from Chichijima, Japan; depth 100–135 m. Leg. Prof. S. Bock 1914 . Paralectotypes: the remaining specimens.

Description. Colony loosely encrusting, reticulate, supported above the substrate, and fixed to it, by rootlets (Fig. 25A, D).

Autozooids elongate oval (mean L/ W2.20), disjunct, each connected to the quincuncially arranged neighbours by six connecting tubes (230–275 µm long and 30–60 µm in diameter), one distal, two distolateral, two proximolateral, and one proximal (Fig. 25A); frontal surface entirely occupied by the frontal membrane and the oval opesia (Fig. 25B); opercular region transversely D-shaped.

Opesial spines unjointed, thin (5–15 µm in diameter) and short (30–45 µm long), 3–4 erect spines placed distally and at least 8–10 spines placed laterally starting just below the opercular region, overarching the frontal membrane and opesia but not reaching the midline, no spines proximally (Fig. 25A–C).

Single or paired, shortly pedunculate bird’s-head avicularia budding from distolateral vertical wall of each autozooid (Fig. 25A, B, E); rostrum directed distolaterally, 135–190 µm long, strongly curved downward and sometimes with a thin denticulation laterally (Fig. 25C); mandible needle-shaped (Fig. 25A, B); crossbar complete.

Dorsal side of autozooids concave, smooth and nodular (Fig. 25D, E).

Ovicells not observed.

Remarks. Silén (1941) pointed out the smaller size of both autozooids and avicularia as the main difference between this subspecies and Beania discodermiae (Ortmann, 1890) . Silén (1941) specified that in the new subspecies autozooids and avicularia were consistently four-fifths of those in the nominal species, probably based on his own observations. A revision of the type specimens of B. discodermiae is essential to ascertain the validity of this subspecies. Specimens from New Zealand, initially identified as B. discodermiae boninenis (Gordon 1984), belong to a distinct new species that differs in avicularium shape and possesses longer interdigitating lateral spines (D.P. Gordon, personal communication, July 2023).

The cap-like ooecium, illustrated in fig. 123 of Silén (1941) and referred to a specimen from locality 32, was not observed in the syntypes available, which are from locality 33 and 34. However, no material labelled as B. discodermiae boninensis was found from locality 32 in the collection. Locality numbers refer to the list provided in Silén (1941). The autozooid in Fig. 25C has a modified distal end compared to the other autozooids in the colony. The central distal spine is seemingly reduced, while the external distal spines, which appear more robust and arched than usual, are moved in a more lateral position. Modifications of the distal spines were observed in zooids of other species of Beania having a vestigial ooecium (Souto et al. 2018), suggesting that this zooid might also be fertile.