Rhamphostomella aspera, Grischenko & Gordon & Taylor & Kuklinski & Denisenko & Spencer-Jones & Ostrovsky, 2022

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 : 40-43

Rhamphostomella aspera n. sp.

( Fig. 11 )

Diagnosis. Colony encrusting, multiserial. Zooids very large, broadly hexagonal. Frontal shield thickened, strongly convex, roughly granulated, with shaggy appearance. Marginal areolae separated by prominent radially arranged interareolar ridges continuing to apex of suboral avicularium, giving striated appearance to zooid. Umbonuloid component extensive. Primary orifice roughly quadrangular with round angles and ill-defined rounded lateral condyles. Proximal margin straight with broad low prominence. Pair of short, ephemeral, tubular oral spines often present. Secondary orifice oval or quadrangular, cormidial. Suboral avicularian cystid very large, occupying one-third to half of frontal shield, elevated, with acute conical apex, partially overhanging orifice, covered by interareolar ridges; frontal surface facing laterally to proximolaterally, occasionally proximally. Rostrum semioval, blunt. Crossbar complete, with small ligula. No adventitious avicularia. Ovicells hyperstomial, wider than long. Ectooecium smooth with sparse pseudopores; no secondary calcification. Pore chambers in distolateral wall and 1‒2 multiporous septula in transverse walls. Basal surface of zooids fully calcified, tightly cemented to substratum.

Material examined. Holotype: ZIRAS 1/50542 , colony encrusting sponge, IMB Collection, RV Akademik Oparin , 41st Expedition, Stn 63/ 53, 29 July 2011, northward from Iturup Island, South Kuril Islands, Sea of Okhotsk, 45°45.1ʹ N, 148°33.2ʹ E – 45°44.5ʹ N, 148°33.5ʹ E, depth 264– 274 m, Sigsbee trawl, collectors A.P. Tsurpalo and A.V. Chernyshev.

Etymology. Latin, asper, rough, shaggy, alluding to the coarsely granular surface of the zooids that contrast strongly with the smooth spherical ooecia.

Type locality. Northward from Iturup Island , South Kuril Islands, Sea of Okhotsk, 45°45.1ʹ N, 148°33.2ʹ E – 45°44.5ʹ N, 148°33.5ʹ E, depth 264– 274 m.

Measurements. ZIRAS 1/50542, Iturup Island, Kuril Islands, Sea of Okhotsk ( Fig. 11A–M ). ZL, 1.33–1.95 (1.58 ± 0.17). ZW, 0.85–1.30 (1.01 ± 0.09). ZD, 1.13–1.19 (n = 2). OrL, 0.40–0.51 (0.44 ± 0.03). OrW, 0.39–0.46 (0.43 ± 0.02). OeL, 0.42–0.55 (0.49 ± 0.04) (n = 10). OeW, 0.57–0.68 (0.62 ± 0.04) (n = 10). Av(s)L, 0.33–0.43 (0.38 ± 0.02). P(m)N, 19–31 (25). P(oe)N, 9–18 (12) (n = 10).

Description. Colony encrusting, multiserial, unilaminar ( Fig. 11A ), patch-like, about 11 × 16 mm in size, yellow when dry. Zooids very large, broadly hexagonal to oval, widest in midlength, arranged in checkered pattern, demarcated by fine sutures between lateral and transverse walls. Boundaries between zooids clearly visible in both young and old parts of colony.

Frontal shield umbonuloid ( Fig. 11A, I ), thickened, strongly convex, with rough surface composed of pointed granules conferring a shaggy appearance, with circular areolae along raised margins (sometimes forming double rows for a short distance) ( Fig. 11B–F ), separated by elongate, prominent, radially arranged interareolar ridges connected with cystid of suboral avicularium, frequently continuing to apex and thus giving a striated appearance to zooid. Areolae diminishing in size in older parts of colony. Umbonuloid component extensive, occupying about 80% of length of frontal shield (78% in one measured zooid), with fine parallel lineation and accretionary banding ( Fig. 11I, L ). Ring scar indistinct ( Fig. 11I, L ), nevertheless forming regular boundary between umbonuloid exterior wall and extra-umbonuloid interior wall microstructure.

Primary orifice ( Fig. 11C, I, J ) quadrangular with round angles to hoof-shaped, often longer than wide; distal and lateral margins formed by upper terminal part of distal transverse wall, with prominent shelf distally ( Fig.11A, C ); low, ill-defined rounded condyles laterally ( Fig. 11C, I, J ). Distal margin of orifice rounded, proximal margin straight with broad, low prominence having shallow median concavity and broadly rounded proximolateral corners. Pair of short, ephemeral, tubular oral spines ( Fig. 11A, C, E, M ) often present in marginal and non-ovicellate zooids and occasionally in some ovicellate zooids.

Secondary orifice ( Fig. 11D, E ) oval or quadrangular, cormidial, distolateral curvature formed by vertical walls of distal and lateral zooids, proximally restricted by thickened distal margin of frontal shield that medially incorporates cystid of suboral avicularium ( Fig. 11B, D ).

Suboral avicularian cystid very large, occupying distal one-third to half of frontal shield, bulbous to conical, strongly elevated, with roughly tuberculate surface, and with 3–7 minute frontal communication pores ( Fig. 11A–H, M ); gently tilted distally, partially overhanging orifice, covered by interareolar ridges that continue to acute conical projection on top, which is directed frontally or inclined laterally.Avicularian frontal surface (rostral/postmandibular areas) crossing zooidal midline or not, facing laterally to proximolaterally, occasionally proximally. Rostrum semioval, blunt, with acute projection at the apex of the cystid directed distolaterally upwards; palatal foramen semioval or rounded triangular, laterally bordered by narrow cryptocystal shelf, opesia oval, semiround or ellipsoid. Crossbar complete, with small ligula.

No adventitious avicularia.

Ovicells hyperstomial ( Fig. 11F–H ). Ooecium wider than long, formed by distal autozooid around shallow, arch-like concavity with communication pore at bottom, situated in proximalmost part of frontal shield just distal to distal margin of maternal primary orifice ( Fig. 11A, B, D, E ). Ectooecium smooth, sharply contrasting with shaggy, coarsely granular surface of frontal shield, with circular to slit-like sparse pseudopores. Ovicells remain prominent, with ooecium uncovered by secondary calcification.

Zooids interconnected by four mural pore chambers in each distolateral wall of zooid ( Fig. 11M ) and 1‒2 small multiporous septula in basal half of transverse walls, sometimes accompanied by individual pores.

Basal surface of zooids ( Fig. 11A, K ) fully calcified, inflated, tightly cemented to substratum.

Ancestrula and early astogeny not observed.

Remarks. The orientation of the frontal surface of the suboral avicularium varies greatly in this species. While in the majority of zooids it is situated on the lateral slope of the avicularian cystid and faces laterally, in others it is on the proximal slope, with corresponding orientation ( Fig. 11D , lowest zooid), and occasionally faces frontally ( Fig. 11A , central zooid).

Rhamphostomella aspera n. sp. most resembles R. obliqua n. sp. in the general appearance of zooids and in having: 1) a primary orifice of similar shape, 2) a bulbous to conical, strongly elevated suboral avicularian cystid tilted distally and overhanging the orifice, with a lingulate mandible; and 3) hyperstomial ovicells, with the ooecium free of secondary calcification. However, these species differ as follows: 1) the primary orifice has a broad, low, median prominence in R. aspera n. sp. and straight in R. obliqua n. sp.; 2) the suboral avicularian cystid has a pointed, conical apex that is sometimes tilted laterally in R. aspera n. sp., but a blunt apex in R. obliqua n. sp.; 3) the opesial area of the suboral avicularium faces mostly laterally to proximolaterally or occasionally proximally in R. aspera n. sp., but distolaterally to laterally in R. obliqua n. sp.; 4) the interareolar ridges are long, prominent and solid, and continue to the avicularian apex in R. aspera n. sp., but are generally shorter and lower, reaching only the sides of the avicularian cystid in the distal half of zooids in R. obliqua n. sp.; 5) the entire frontal surface is evenly coarse, giving a shaggy appearance to R. aspera n. sp., but smooth to finely granular in R. obliqua n. sp., except for the coarsely granulated surface of the avicularian cystid; 6) colonies of R. aspera n. sp. are yellow, those R. obliqua n. sp. are either saturated-brown or light-brown; 7) the orifice in R. aspera n. sp. (0.40–0.51 × 0.39–0.46 mm) is larger than that in R. obliqua n. sp. (0.34–0.41 × 0.33–0.39 mm); 8) the ooecium in R. aspera n. sp. (0.42–0.55 × 0.57–0.68 mm) is larger than that in R. obliqua n. sp. (0.33–0.39 × 0.45–0.55 mm), with non-overlapping ranges.

Ecology. The only specimen of Rhamphostomella aspera n. sp. was encrusting a sponge from 264–274 m depth.

Distribution. This species is known from only a single locality north of Iturup Island, South Kuril Islands, Sea of Okhotsk, and can be categorized as a Pacific Asian high-boreal, sublittoral species.

Figures

FIGURE 11. Rhamphostomella aspera n. sp. Holotype, ZIRAS 1/50542 (Iturup Island, Kuril Islands, Sea of Okhotsk). A. Colony margin with developing zooids. B. Lateral view of non-ovicellate zooids.C. Primary orifices of marginal zooids, showing the distal shelf, bases of oral spines and initial stage of ooecium formation (in left zooid). D. Group of non-ovicellate zooids, showing variability in opesial area of suboral avicularium. E. Zooids with early developing ooecia (arrows). F, G. Ovicellate zooids. H. Lateral view of ovicellate zooid. I. Interior of frontal shield, showing areolae and umbonuloid component. J. Internal view of orifice, showing broad proximal prominence and ill-defined condyles. 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 very large avicularian cystid, oral spines and zooid lateral wall with mural pore chambers. Scale bars: A, B, D–G, 500 μm; C, H, K, 250 μm; I, J, 100 μm; L, 50 μm; M, 200 μm.