Arachnoidella cf. protecta ( Harmer, 1915 )

Seo, Ji-Eun, Chae, Hyun Sook, Winston, Judith E., Zágoršek, Kamil & Gordon, Dennis P., 2018, Korean ctenostome bryozoans-observations on living colonies, new records, five new species, and an updated checklist, Zootaxa 4486 (3), pp. 251-283 : 259-263

Arachnoidella cf. protecta ( Harmer, 1915)

( Fig. 7 )

cf. Arachnoidea protecta Harmer, 1915: 50 , pl. 3, figs 7–11.

Material examined. MBRBK 1704 . Two colonies on small rock from west of Cheongsan Island , S. Jeolla Province, 34.1585° N, 126.7689° E, 42 m, collected 29 July 2016 by RV Kuklipgongwon-yeoungu 1 in a grab sample.

Description. Colony forming network of stolons and zooids sparsely distributed over about 2 cm 2 area on rock collected from 42 m depth ( Fig. 7A ). Zooids brown to dark brown, clavate to subpyriform, or even subquadrangular, dilatation tapering abruptly to caudal portion as long as or shorter than dilatation. Cuticular frontal wall convex, sloping upwards to proximal part of dark-rimmed orifice, quadrate distally and tilted slightly toward distal end of zooid ( Fig. 7B–E ). Zooid length (non-caudate portion), mean 0.261 mm (range 0.188–0.340 mm, N = 5), zooid width, mean 0.253 (range 0.233–0.275 mm, N = 5). Internal anatomy and tentacle number unknown.

Remarks. Gordon (1986) proposed that the name Arachnoidella be used for the marine species formerly assigned to Arachnoidea , a decision we have followed here.

The only specimen found was on a small dried rock already in the MBRBK collection, discovered by DPG when examining rock and shell samples for cheilostomes. Although the specimen was reconstituted in aqueous trisodium phosphate, no internal anatomy remained, only the cystid structure and do not form of the orifice. Many of the stolonate portions were missing.

Twelve species of Arachnoidella are known so far. The geographically closest are two abyssal species from south of Japan (d’Hondt & Mawatari 1987), neither of which is at all similar to the Korean material. Our material appears closest to Arachnoidella protecta ( Harmer, 1915) , described from Indonesia (0–32 m), although zooid shape in Harmer’s material is variable, and mostly not clavate. Harmer (1915) gives no information on internal structure. A publication by Chimenz Gusso et al. (1998) described A. protecta from the Mediterranean, giving measurements larger than those of Korean material and drawings of external morphology, including zooids with extended peristomes showing a long setigerous collar, but no tentacle crown or internal structure. Additional specimens of living or alcohol-preserved specimens from Korea are needed to clarify the species’ morphology and anatomy and confirm its specific identity.

Distribution. Korea: South Sea: Cheongsan Island, 42 m depth.

Figures

FIGURE 7. Arachnoidella cf. protecta (Harmer, 1915), west of Cheongsan Island, south Sea (MBRBK1704). A. Remains of a colony encrusting subtidal rock. B. Five reconstituted zooids, showing dilatations and some caudae and peristomes. C. Cuticularized outlines of six zooids visible. D. Chain of zooids in lateral view. E. Compound-microscope image of a single detached autozooid, showing weakly irregular margins, indication of opening of peristome, and caudate proximal end. Scale bars: B–E = 0.25 mm.