Stephanollona boreopacifica Yang & Seo & Gordon 2018, n. sp.

Stephanollona boreopacifica n. sp.

(Figs 32–34)

Etymology. Alluding to its distribution in the North Pacific (Greek, boreas, north).

Material examined. Holotype: NIBRIV0000805893, one of two colonies found at Munseom Island, Seogwipo, Jeju Island, 24 December 2016, 20 m, on oyster shell, collected by Ho Jin Yang.

Description. Colony encrusting, multiserial, unilaminar, but with some frontal budding in one mature colony, up to 16 mm across. Autozooids lacking clear boundaries except at growing edge. Lepralioid frontal shield porcellanous, with 3 small areolar-septular pores along each lateral margin. Orifice cleithridiate, with longitudinally oval anter merging into deep, rounded-U-shaped sinus; condyles narrow, on sloping proximolateral shoulders of anter; distal rim of anter beaded, high-arched; weakly concave proximal margin with low, sloping condyles in corners. Oral spines 5–6, long.

Avicularia adventitious, numerous, dimorphic. Most zooids with 1 or 2 elongate latero-oral avicularia directed distad or obliquely so, rostrum elongate-triangular with rounded tip and extensive palatal shelf; rostral foramen triangular, into which projects relatively long ligula from crossbar; opesial foramen transversely oval or circular, bordered by smooth, wide cryptocystal shelf. One or both elongate avicularia replaced by small oval avicularia, obliquely orientated, with toothed rostral rim, thin crossbar, and knob-like ligula on rostral side of crossbar; 1–2 additional such avicularia may occur on frontal shield in colony center where some frontal budding of zooids takes place.

Ooecium recumbent on distal zooid, smooth, with shallow frontal tabula and extremely narrow labellum; secondary calcification encroaches around distal part of ooecium, with sometimes 1–2 small associated avicularia on ooecia in central parts of mature colony. Four oral spines seen in ovicellate zooids.

Interzooidal communications via mural septular pores. Ancestrula not seen.

Measurements. ZL 274–445 (361) µm; ZW 204–363 (264) µm; OrL 103–138 (124) µm; OrW 70–85 (77) µm; AvL 179–304 (261) µm; AvW 72–81 (77) µm; OoL 141–221 (165) µm; OoW 134–191 (169) µm.

Remarks. This is the first record of the genus from the western Pacific north of Australia. Stephanollona eopacifica (Soule, Soule & Chaney, 1991b), the only other species from the North Pacific (on and just north of the equator at the Galápagos Islands) is similar, but has a much broader orificial sinus and a ligulate avicularian crossbar. Of the 15 other Recent species, none has the combination of 5–6 oral spines, both kinds of avicularia (oval and elongate) having a well-developed ligula (columella), and ooecia crowned with avicularia in parts of the colony. Two species that are closest in morphology are Stephanollona longispinata (Busk, 1884) from the South Atlantic and Stephanollona ignota Hayward & Cook, 1983 from eastern South Africa. Both species have ligulate avicularia and similar-shaped orifices, but zooid size is great than in S. boreopacifica n. sp., B. longispinata has acutely triangular elongate avicularia and a more-developed ooecial labellum, and S. ignota has 6–7 oral spines and a nodular frontal shield.