Retevirgula asiana, Min, Bum Sik, Seo, Ji Eun, Grischenko, Andrei V., Lee, Sang-Kyu & Gordon, Dennis P., 2017

Min, Bum Sik, Seo, Ji Eun, Grischenko, Andrei V., Lee, Sang-Kyu & Gordon, Dennis P., 2017, Systematics of some calloporid and lacernid Cheilostomata (Bryozoa) from coastal South Korean waters, with the description of new taxa, Zootaxa 4226 (4), pp. 471-486 : 475-476

Retevirgula asiana n. sp.

( Figs 4–7 )

Material examined. Holotype: MBRBKSP031, RV Kuklipgongwon-yeoungu 1 Station I3, 34.1585° N, 126.7689° E, 29 July 2016, 42 m, west of Cheongsan Island (Cheongsando).

Etymology. Derivative of the old Latin name Asia, the region east of Europe.

Description. Colony encrusting, unilaminar, reticulate, up to 10 mm in diameter. Autozooids more or less elongate-oval, highly disjunct, arranged in quincunx, with 8–12 tubular connections to adjacent autozooids and/or heterozooids leaving large spaces between them. Gymnocyst most developed proximally, with lateral walls sloping steeply to substratum. Cryptocyst extremely narrow, smooth, the inner margin weakly scalloped between adjacent spine bases. 10–14 articulated periopesial spines, the 4 distalmost spines more erect, the others angled steeply part way across the membranous frontal wall; spine length c. 80–135 µm. Kenozooids mostly subvicarious, occasionally as large as an autozooid, generally abundant, of variable zooidal and opesial size, connected by 7–8 tubes to zooids, with a relatively large circular to subcircular opesia encircled by a smooth cryptocystal shelf; 0–2 frontal spines. Avicularia rare, smaller than and occupying the place of a kenozooid in a subvicarious position, longer than wide, the shape of the rim somewhat like a figure 8 but much less constricted; with elevated rostral rim and large combined foramen, no crossbar or pivot bars. Ooecium not seen. Ancestrula not seen.

Measurements. ZL 341–479 (375) µm, ZW 169–224 (203) µm; OpL 261–286 (275) µm, OpW 109–154 (141) µm; AvL 70 µm, AvW 56 µm.

Remarks. This is the first record of a species of Retevirgula in Korean waters. Mawatari & Mawatari (1980), however, illustrated three species of Retevirgula in modern Japanese seas. These were all originally described elsewhere, and conspecificity is unlikely owing to differences in geographic and temporal distribution, as well as character differences.

Retevirgula areolata ( Canu & Bassler, 1923) , reported by Mawatari & Mawatari (1980) from Shirayama, Wakayama Prefecture, Honshu, was originally described from the Pleistocene of California . Subsequently, Kataoka (1961) identified it in the Pleistocene of southern Japan. Retevirgula periporosa ( Canu & Bassler, 1928) , likewise reported from Shirahama, was originally described from Cuba, Florida and the Gulf of Mexico . Subsequently, Hayami (1970) identified it in the Miocene of Hokkaido . Retevirgula triangulata ( Silén, 1941) , reported by Mawatari & Mawatari (1980) from Atami in Shizuoka prefecture, Honshu, was originally described from the Ryukyu (Bonin) Islands .

Retevirgula asiana n. sp. differs from the fossil found in California and living R. areolata in having slightly fewer spines, a proportionally smaller avicularium, not found distal to an autozooid, more numerous kenozooids and larger interzooidal spaces. Retevirgula periporosa from Cuba has more spines (16–18) than R. asiana (12–14), but other characters appear similar. Based on Silén’s (1941) illustrations and description, R. triangulata has a proportionally larger avicularium with a circular rostral/opesial area. Of the mainland records for Japan, R.

periporosa and R. triangulata , both sensu Mawatari & Mawatari (1980), have similar spine numbers to R. asiana and either could be conspecific. Curiously, neither Mawatari & Mawatari (1980) nor Silén (1941) mentioned interzooidal kenozooids in any of the material they described, though they must presumably have been present; perhaps some were mistaken for avicularia.

In general appearance, R. asiana n. sp. appears closest to Retevirgula akdenizae Chimenz, Nicoletti & Boncambi, 1997 , from the Aegean Sea area of Turkey, which has a similar-shaped avicularium. This species is the only known Retevirgula from the vast area of Europe, Africa and the Indian Ocean and may possibly be an immigrant to the Mediterranean. In spite of its similarity to R. asiana , it differs in having larger zooids (mean length 470 µm, mean width 260 µm) with granules on the thin cryptocystal rim; additionally, it has 13–16 periopesial spines that are longer (300–400 µm) than in R. asiana . Avicularia are larger and may bear a spine, and the kenozooids have up to six spines.

The attribution of Retevirgula to the resurrected family-rank taxon Ellisinidae ( Vigneaux 1949) is explained by Gordon (in press). Inter alia, the ooecium in ellisinid genera is always associated with a heterozooid, either an avicularium or a kenozooid, both ooecial layers are calcified (some species of Retevirgula have, however, a small ectooecial foramen), and the zooidal cryptocyst is minimally developed, with no shelf.

Distribution. Korea: South Sea; 42 m depth on rock.

Figures

FIGURES 4 – 7. Retevirgula asiana n. sp., Stn I 3 near Cheongsan Island. 4, Unbleached zooids with periopesial spines; scalebar 400 µm. 5, Part of a colony with numerous kenozooids and an interzooidal avicularium (arrow); scalebar 200 µm. 6, Part of a colony showing kenozooids with spine bases and a retained entire spine (arrows); scalebar 400 µm. 7, Close-up of the avicularium shown in fig. 5; scalebar 50 µm.