(Figs 12–14)
Hippothoa hyalina: Okada 1929: 17, pl. 1, fig. 4, pl. 4, fig. 3; Androsova 1958: 130, fig. 48; Kubanin 1976: 33; Gontar 1978: 14.
Celleporella hyalina: Soule et al. 1995: 183, pl. 66 (cum syn.); Liu et al. 2001: 536, pl. 36, figs 1–2. Celleporella hyalina species complex: Dick et al. 2005: 3724, fig. 9; Grischenko et al. 2007: 1097, fig. 19.
Material examined. NIBRIV0000325933, Jinchon-ri, Baengnyeong Island. Other material: Woosuk University collection—Baengnyeong Island: Hwadong (11 colonies), Junghwadong (3 colonies), Dumujin (24 colonies), Jinchon-ri (51 colonies), Yeonhwa-ri (21 colonies); mostly on rocky substrata, plus shell and crustose coralline algae (Clathromorphum). East Sea: Namae port (1 colony), on the basal side of a bryozoan.
Description. Colony encrusting, initially unilaminar, up to 15 mm in diameter, developing additional autozooids and reproductive zooids at a later stage, which increases the thickness of the crust; these frontally budded zooids are orientated irregularly. Autozooids more or less elongate-oval, the gymnocystal frontal shield highly convex, highest suborally where there may be an umbo, typically with weaker transverse ridges across other parts of the shield. Orifice evenly rounded, the near-circular shape interrupted by a stout, slightly upturned pair of condyles that mark the entrance to the sinus; distal rim of orifice somewhat cowl-like, rising up behind the operculum, which is more or less flat; sinus occupying c. 60% of the proximal rim at the level of the condyles regardless of variability in orifice width. Typically 1–3 holes in the interzooidal furrows between zooids, these representing the frontal expressions of pore-chambers from which additional zooids, mainly reproductive, will be budded.
Male zooids produced adventitiously, shorter and narrower than autozooids; orifice about half the width of autozooidal orifices but otherwise similar. Female zooids also budded adventitiously, these short, more or less triangular, the frontal shield rising to the suboral region; orifice mostly concealed by ooecium, but much wider than in autozooids, with a broad shallow poster; ectooecium more or less smoothly calcified, with 13–19 funnel-like pseudopores, sometimes ringed.
Ancestrula oval, smooth, with a sinusoid orifice; early astogeny asymmetrical, with a daughter zooid arising on one side distolaterally, in turn giving rise to a daughter from a proximolateral position.
Measurements. ZL, 357–442 (392) µm; ZW, 195–241 (215) µm; OrL, 93–109 (99) µm; OrW 84–106, (93) µm; ♂ OrL, 49–76 (62) µm; ♂ OrW, 52–66 (58) µm; OoL, 130–157 (141) µm; OoW, 202–234 (216) µm; AnL, 280 µm; AnW, 220 µm; AnOrL, 87 µm; AnOrW, 77 µm.
Remarks. The synonymy given above is restricted to the North Pacific and is not exhaustive. Dick et al. (2005) and Grischenko et al. (2007) have suggested that C. hyalina in the North Pacific may both be a species complex inasmuch as there is some morphological variation (see Morris 1976, 1980). The ancestrula and early astogeny in the present material match what Cancino & Hughes (1988) have described for C. hyalina from Britain, which is generally consistently unilateral (although occasional deviations may occur from the standard pattern at the same locality). This concordance in early astogeny between the material from Britain and Korea could support conspecificity inasmuch as early astogeny of multiserial hippothoids has been regarded as species-specific (e.g. Ryland & Gordon 1977); as noted above, however, molecular evidence points to a complex of cryptic species (see also Gómez et al. 2007).
Distribution. The nominal species was first described from Western European seas (Linnaeus 1767) and has subsequently been accorded a near-cosmopolitan distribution. In the northeastern Pacific, material attributed to C. hyalina has been recorded from Alaska to California (Soule et al. 1995), while in the northwestern Pacific the species has been accorded a distribution from the Arctic (Kluge 1962; Androsova 1977), Sea of Okhotsk (Kubanin 1976), Kurile Islands (Gontar 1978), Sakhalin and the Japan Sea (Androsova 1958). More recently, with the integration of micromorphological (SEM) and molecular characters, additional species have been recognized from different parts of the Northern Hemisphere that were (or would have been) once attributed to C. hyalina, e.g. Celleporella angusta Álvarez, 1991, Celleporella reflexa Dick & Ross, 1988 and Celleporella osiani Hughes & Wright, 2014. Grischenko et al. (2007) noted differences in the numbers of ooecial pseudopores in populations in Akkeshi Bay, Hokkaido. Further studies are needed on northern Pacific populations to determine the extent and geographical distribution of morphological variation. Published depth ranges are from 0–55 m (e.g. Hayward & Ryland 1999). Korea: Baengnyeong Island.