Corbulella boninensis ( Silén, 1941 )

Yang, Ho Jin, Seo, Ji Eun & Gordon, Dennis P., 2018, Sixteen new generic records of Korean Bryozoa from southern coastal waters and Jeju Island, East China Sea: evidence of tropical affinities, Zootaxa 4422 (4), pp. 493-518 : 497

Corbulella boninensis ( Silén, 1941)

( Figs 6, 7 )

Pyrulella corbula: Harmer 1926: 225 , pl. 14, fig. 4; Mawatari 1965: 601, fig. 53a, b; Mawatari & Mawatari 1980: 82, fig. 26. Non Membranipora corbula Hincks, 1880 .

Pyrulella boninensis Silén, 1941: 26 , figs 21–24.

Corbulella boninensis: Gordon 1984: 30 .

Material examined. Two colonies (NIBRIV0000805881, MBRBKW2), Munseom Island , Jeju, 20 m, collected by Ho Jin Yang.

Description. Colony encrusting, multiserial, unilaminar, unpigmented, up to 21 mm across. Autozooids roughly elongate-oval to subpyriform, longer than wide. Cryptocystal rim elongate-oval, highest part of zooid, granular, a little wider proximally, negligible distally, with minutely ridged margin. Gymnocyst smooth, narrow laterally, more-developed proximally, bearing 12–14 spines; 5–6 spines bordering orifice, proximalmost pair erect, the others leaning slightly outwards; 6–8 periopesial spines all slightly curving over membranous frontal wall, but not as far as zooidal midline.

Avicularium vicarious, with large lingulate rostrum and mandible, entire rim of rostrum strongly toothed, delimited from avicularian opesia by stout, projecting pivots; opesial cryptocyst granular, margin with 4–5 spines. Many vicarious avicularia produced by reparative budding within former autozooidal cystids, rarely vice versa.

Ooecia prominent, occupying gymnocyst of distal zooid; ectooecium smooth, calcified except for broad, crescentic membranous area covering tabula exposing smooth endooecium, apical margin of ectooecium rising to peak, frequently projecting as hollow spine. Only a pair of proximal oral spines in ovicellate zooids, and typically 7 periopesial spines.

Ancestrula not seen.

Measurements. ZL 426–607 (489) µm; ZW 242–318 (285) µm; OrL 275–404 (326) µm; OrW 155–217 (187) µm; AvL 424–662 (559) µm; AvW 265–349 (307) µm; OoL 92–156 (118) µm; OoW 274–350 (319) µm.

Remarks. The present material accords well with Silén’s (1941) species, the name of which has been long neglected in the northwest Pacific in favor of Corbulella corbula (or earlier combinations). Corbulella corbula ( Hincks, 1880) has been accorded a wide range in the western Pacific, but the type locality is in southeastern Australia and the oral spines, as illustrated by Bock (2008) and Gordon (1984, 1986), are long and stout. The material illustrated by Ryland & Hayward (1992) from Heron Island, Great Barrier Reef, may be allied to Silén’s species, but these authors described the rostral rim of the vicarious avicularium as smooth instead of strongly toothed. It is likely that there are cryptic species mistaken as C. corbula in the western Pacific.

Distribution. Japan: Ogasawara Islands; Honshu (Misaki and Mutsu Bay). Korea: Jeju Island. Depth range 20– 120 m.

Figures

FIGURES 6, 7. Corbulella boninensis (Silén, 1941), Munseom Island. 6, part of unbleached colony, slightly tilted forward, showing the strongly toothed distal rim of the vicarious avicularium (regenerated within an autozooidal cystid) and ooecia with a pointed ectooecial apex; 7, part of bleached colony, not tilted, showing autozooids, ooecium and a vicarious avicularium in an autozooidal cystid. FIGURES 8, 9. Onychocella subsymmetrica Canu & Bassler, 1929, Munseom Island. 8, autozooids, torqued avicularia and a zooid that appears to be a female (asterisk); 9, light micrograph of unbleached zooids showing scleritized open opercula (one arrowed) with lateral flanges and avicularian mandibles (thin wing on outer side too transparent to be seen). Scale bars: 6–8, 500 µm; 9, 300 µm.