Reptadeonella yeonbora n. sp.

(Figs 10–13)

Etymology. Alluding to the distinctive pale lavender colour of new zooids at the colony margin—in the Korean language, bora is purple, yeon is light or pale.

Material examined. Holotype: NIBRIV0000805883, one of seven colonies found at Munseom Island, Seogwipo, Jeju Island, 24 December 2016, 20 m, on oyster shell, collected by Ho Jin Yang. Paratype: NIBRIV0000805884, same data as for holotype.

Description. Colony encrusting, multiserial, unilaminar, up to 23 mm across, color pale lilac or lavender at growing edge, pigmentation darker purple in older parts of colony, with scattered, darker bluish-purple pigment granules that may be lost from surface, which then appears white. Autozooids variably subhexagonal to suboval, frontal shield lightly hummocky, with 16–20 areolar pores distributed over granular surface. Spiramen single in periancestrular zooids, becoming divided and compound with 2–4 foramina in succeeding zooids. Peristomial orifice roundly transversely D-shaped with straight or gently concave proximal margin and raised, generally thickened distal margin that can appear cowl-like, with row of areolar pores around margin.

Avicularium single, median suboral, inclined obliquely frontalwards with tip forming part of peristomial rim; rostrum triangular, mandibular pivots very short; opesial cryptocyst narrow, descending, smooth. Rostral gymnocyst smooth, edged with boundary line, merging with orificial peristome.

Female zooids not determinable with certainty and possibly variable; only one zooid seen that was distinctly larger, with a wider orifice and more-complex compound spiramen.

Interzooidal communications in small recesses along zooidal margins. Ancestrular complex interpreted as a triad, more or less triangular, with median zooid flanked by zooids angled outwards to left and right.

Measurements. ZL 347–472 (405) µm; ZW 157–246 (200) µm; OrL 39–63 (49) µm; OrW 66–95 (82) µm; AvL 74–109 (89) µm; AvW 53–75 (63) µm.

Remarks. Twenty-two Recent Reptadeonella species have previously been described (Bock 2016). Of these, only Reptadeonella yeonbora n. sp. has a spiramen that can be both single and compound. Additionally, only one other species, Reptadeonella cucullata Almeida, Souza, Sanner & Vieira, 2015 from Brazil, has a denticulate spiraminal rim; the simple spiramen of Reptadeonella violacea (Johnston, 1847) from Europe can have tiny granules around its margin but these are not true denticulations and the species also differs in colour and astogeny. Reptadeonella yeonbora n. sp. has the northernmost range of any Pacific species belonging to this genus.

The form of the ancestrular complex has not been noted for many species. That in the type species, R. violacea (Johnston, 1847) and Reptadeonella insidiosa Jullien in Jullien & Calvet, 1903 comprises six zooids (Hayward & Ryland 1999). On the other hand, Tilbrook (2006) described three in Reptadeonella cellulanus Tilbrook, Hayward & Gordon, 2001 and Reptadeonella hystricosus Tilbrook, 2006, but these zooids are set at an angle of 120° to each other, whereas the zooids in the ancestrular triad of R. yeonbora n. sp. are aligned in a fan-shaped arrangement.