Rhamphostomella tatarica ( Androsova, 1958 )

Grischenko, Andrei V., Gordon, Dennis P., Taylor, Paul D., Kuklinski, Piotr, Denisenko, Nina V., Spencer-Jones, Mary E. & Ostrovsky, Andrew N., 2022, Taxonomy, ecology and zoogeography of the Recent species of Rhamphostomella Lorenz, 1886 and Mixtoscutella n. gen. (Bryozoa, Cheilostomata), Zootaxa 5131 (1), pp. 1-115 : 67-70

Rhamphostomella tatarica ( Androsova, 1958)

( Figs 20 , 33C, D )

Escharopsis tatarica Androsova, 1958, p. 168 , fig. 98.

Escharopsis tatarica: Kluge et al. 1959, p. 213 ; Kluge 1961, p. 141.

Posterula tatarica: Denisenko 2013, p. 185 .

Material examined. Holotype: ZIRAS 1 /3701, single colony, RV Toporok , Stn 12, 6 July 1947, eastern Tatar Strait , coastal waters of southern Sakhalin Island, Sea of Japan, depth 117 m, boulders, beam-trawl, collector Z.I. Kobjakova. Paratype: ZIRAS 2 /3852, single colony , RV Toporok , Stn 29, 21 August 1949, Tatar Strait, Sea of Japan, depth 43 m, silted sand with shells, dredge, collector Z.I. Kobjakova.

ZIRAS 7 /50548, two colony fragments , MFRT Rodino, 12 September 1992, about 32 km from Cape Hayryuzova, western Kamchatka shelf, Sea of Okhotsk , 57°36.2ʹ N, 156°09.0ʹ E, depth 78–81 m, crab trap, collector A . V. Grischenko .

Measurements. ZIRAS 7/50548, western Kamchatka, Sea of Okhotsk ( Fig. 20A–M ). ZL, 0.82–1.20 (1.01 ± 0.10). ZW, 0.37–0.78 (0.53 ± 0.07). ZD, 0.43–0.54 (n = 2). OrL, 0.21–0.29 (0.25 ± 0.02). OrW, 0.24–0.31 (0.28 ± 0.02). OeL, 0.29–0.36 (0.31 ± 0.02) (n = 10). OeW, 0.39–0.45 (0.42 ± 0.02) (n = 10). Av(s)L, 0.13–0.20 (0.16 ± 0.02). P(m)N, 19–30 (25). P(oe)N, 9–18 (15) (n = 10).

Description. Colonies encrusting, multiserial, unilaminar ( Fig. 20A ), irregular in form; largest among our fragments was about 13 × 7 mm; bright brown when alive, light brown when dry. Zooids large, oblong hexagonal, pyriform, rectangular or irregular in shape ( Fig. 20A, D–G ), arranged in checkered pattern, demarcated by fine sinuous sutures between lateral and transverse walls recognizable in all colony parts.

Frontal shield umbonuloid ( Fig. 20A ), thin, dimpled with reticulate appearance, flat or moderately convex in young zooids ( Fig. 20A, D ), becoming more convex in older zooids ( Fig. 20E–G ). Frontal shield with angular marginal areolae ( Fig. 20A, B, D–H ), separated by short narrow interareolar ridges in young zooids ( Fig. 20A, D ), becoming more elongate and distinctly larger with age and, thus occupying noticeably larger area on frontal shield ( Fig. 20F–H ). Umbonuloid component very extensive, occupying about 90% of length of frontal shield (89% in one measured zooid), with fine parallel lineation and accretionary banding ( Fig. 20I ). Ring scar indistinct ( Fig. 20I, L ).

Primary orifice ( Fig. 20A, B, J ) submerged, transversely oval; distal and lateral margins formed by upper terminal part of distal transverse wall, bearing wide, flared shelf distally ( Fig. 20A–C ). Distal margin of orifice shallowly rounded, proximal margin with median oval sinus flanked by blunt or acute projection on each side ( Fig. 20A–C, J ). Condyles absent.

Secondary orifice ( Fig. 20C ) transversely oval, with deep, median U-shaped sinus in proximal margin, cormidial; sinus formed by ridges flanking primary orifice that continue into peristome, forming prominent peristomial “denticle” on one side and another “denticle” from proximo-interior corner of suboral avicularian cystid on other. Secondary orifice distally formed by vertical concave thickening of proximal shield of daughter zooid ( Fig. 20B– D ), proximally restricted by thin-walled peristome incorporating cystid of suboral avicularium on one side and high lappet with terminal denticle on opposite side. In ovicellate zooids, avicularian cystid and lappet both connecting to proximolateral corners of ooecium ( Fig. 20E ). Extensions of lateral walls of contiguous distolateral zooids growing as secondary calcification over ooecium, as two converging lobes that sometimes meet. Together with peristomial lappet and avicularian cystid, these lobes forming complete or incomplete circle ( Fig. 20F–H ), conferring tubular, transversely oval to irregular outline to peristomial orifice. No oral spines.

Cystid of suboral avicularium small, slightly elevated, with dimpled surface and one communication pore ( Fig. 20A–H ), asymmetrically placed proximally on left or right of orificial margin and slightly overhanging it. Frontal surface (rostral/postmandibular areas) of avicularium to one side of zooidal midline, facing distally or obliquely upwards. Rostrum lingulate, with slightly curved distal end, directed distolaterally ( Fig. 20B–H ), extending over surface of neighbouring zooid ( Fig. 20D–G ). Palate lingulate, foramen elongate oval with distal cryptocystal shelf; opesia semicircular. Crossbar complete.

No adventitious avicularia.

Ovicells initially hyperstomial, rapidly becoming subimmersed and sometimes appearing endozooidal through overgrowth of ooecium by secondary calcification encroaching from walls of surrounding lateral and daughter zooids ( Fig. 20F–H ). Ooecium formed by distal autozooid, ooecial fold developing at colony periphery concurrently with formation of frontal shield of distal zooid. Ooecium smooth ( Fig. 20F–H ), with scattered circular or oval pseudopores, some occluded by secondary calcification; proximal margin arched.

Zooids interconnected by 2‒3 mural pore chambers in each distolateral wall ( Fig. 20M ) and two multiporous septula (sometimes with individual pores in between) in basal half of transverse walls ( Fig. 20B ).

Basal wall of zooids fully calcified, smooth, flattened, with fine transverse parallel lineation in places ( Fig. 20K ). Boundaries between zooids visible basally as fine, sinuous incisions.

Ancestrula and early astogeny not observed.

Remarks. Androsova (1958) attributed her new species to Escharopsis Verrill, 1880 based solely on the absence of a lyrula in the primary orifice. At the same time, Escharopsis lacks evenly pseudoporous ooecia; instead, there are either no pseudopores or just a single central pseudopore. Denisenko (2013) placed this species in Posterula Jullien, 1903 , but the peristomial secondary orifice with an asymmetrically set suboral avicularium and ovicells with numerous pseudopores warrant placement of this species in Rhamphostomella .

Ecology. Rhamphostomella tatarica has been recorded from depths of 30–117 m, on gravel and mollusc shells.

Distribution. The species was originally described from the northern part of the Sea of Japan, including off Kholms, Tomari, Ilyinskoye and Belinskoye along the southwestern coast of Sakhalin Island (47°03.0ʹ N, 142°00.0ʹ E to 48°15.0ʹ N, 142°08.0ʹ E) and from Primorye near capes Zolotoy (47°18.0ʹ N, 139°00.0ʹ E) and Syurkum (50°05.0ʹ N, 140°41.0ʹ E). It was subsequently reported by Kluge et al. (1959) and Kluge (1961) from the western part of southern Sakhalin and at Primorye. We obtained specimens from the western Kamchatka shelf of the Sea of Okhotsk. Based on these records, R. tatarica is a Pacific Asian high-boreal, sublittoral species.

Figures

FIGURE 20. Rhamphostomella tatarica (Androsova, 1958). ZIRAS 7/50548 (western Kamchatka, Sea of Okhotsk).A. Colony margin with young and developing zooids. B. Distal view of marginal zooids, showing developing ooecia, details of orifice and multiporous septula in distal transverse wall. C. Orifice with suboral avicularium. D. Non-ovicellate zooids in young part of colony. E. Zooids with developing ooecia in young part of colony. F, G. Ovicellate zooids in older part of colony. H. Lateral view of distal half of ovicellate zooid. I. Interior of frontal shield, showing umbo, ring scar and areolae. J. Internal view of primary orifice. K. Basal surface of colony. L. Interior of frontal shield, showing ring scar and exterior wall microstructure of umbonuloid component. M. Lateral view of zooid, showing frontal shield and lateral wall with mural pore chambers. Scale bars: A, D, G, K, 500 μm; B, E, F, H, 250 μm; C, I, J, 100 μm; L, 50 μm; M, 200 μm.

FIGURE 33. Type specimens of Rhamphostomella and Mixtoscutella species. A, B. Rhamphostomella sibirica (Kluge, 1929). Lectotype, ZIRAS 1/50730 (Laptev Sea). C, D. Rhamphostomella tatarica (Androsova, 1958). Paratype, ZIRAS 2/3852 (Tatar Strait, Sea of Japan). E, F. Rhamphostomella spinigera Lorenz, 1886. Lectotype, NHMW 92535 (Jan Mayen). G. Mixtoscutella ovata (Smitt, 1868). Lectotype, SMNH-Type-9303 (Red Bay, west Spitsbergen, Svalbard and Jan Mayen). H. Mixtoscutella ussowi (Kluge, 1908). Lectotype, ZIRAS 4/2331 (estuary of Mezen River, White Sea). Scale bars: A–F, H, 250 µm; G, 500 µm.