Rhamphostomella microavicularia, 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 : 26-29

publication ID	https://doi.org/ 10.11646/zootaxa.5131.1.1
publication LSID	lsid:zoobank.org:pub:CF550031-D6A9-48A3-A953-A1BD40C72F5E
DOI	https://doi.org/10.5281/zenodo.7626595
persistent identifier	https://treatment.plazi.org/id/03892374-0B2E-3321-FF73-AA8F18E5FBA5
treatment provided by	Plazi
scientific name	Rhamphostomella microavicularia
status	sp. nov.

Treatment

Rhamphostomella microavicularia n. sp.

( Fig. 6 View FIGURE 6 )

Diagnosis. Colony encrusting, multiserial. Zooids large, hexagonal. Frontal shield flattened, covered with fine pointed tubercles. Marginal areolae small, deeply submerged. Interareolar ridges short, mostly not reaching cystid of suboral avicularium. Umbonuloid component extensive. Primary orifice proportionally large, occupying over 30% of zooid length, roughly quadrangular, with large lateral condyles. No oral spines. Secondary orifice identical in form to primary orifice, cormidial. Suboral avicularian cystid small, slightly elevated, narrow, forming crescentic lip around proximolateral edge of primary orifice. Rostrum semioval, blunt. Crossbar complete, thickened in the middle or with very small ligula. Multiple adventitious frontal avicularia, 2–5 per zooid, of equal size and form, situated along lateral margins. Ovicells hyperstomial, rapidly subimmersed by peripheral secondary calcification. Ectooecium smooth, with scattered pseudopores. 3‒5 pore chambers in distolateral wall and two multiporous septula in transverse walls. Basal wall of zooids fully calcified, with protuberances of irregular form.

? Rhamphostomella scabra: Androsova 1958, p. 169 View in CoL , fig. 100.

Material examined. Holotype: ZIRAS 1/50543 , colony encrusting cirripede plate, IMB Collection, RV Akademik Oparin , 41st Expedition, Stn 39/34, 19 July 2011, southeastward from Chiproy Island, middle Kuril Islands , Pacific Ocean , 46°20.7ʹ N, 150°58.7ʹ E – 46°21.3ʹ N, 150°58.8ʹ E, depth 436– 480 m, Sigsbee trawl, collectors A.P. Tsurpalo and A.V. Chernyshev. GoogleMaps Paratype: ZIRAS 2/50544 , two fragments of single colony originally growing on 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 GoogleMaps .

Etymology. The species name alludes to the numerous small adventitious avicularia developing along zooidal margins.

Type locality. Southeastward from Chiproy Islands , middle Kuril Islands, Northwestern Pacific, 46°20.7ʹ N, 150°58.7ʹ E – 46°21.3ʹ N, 150°58.8ʹ E, depth 436–480 m. GoogleMaps

Measurements. ZIRAS 1/50543, Chiproy Island, Kuril Islands, Pacific Ocean ( Fig. 6A–M View FIGURE 6 ). ZL, 1.07–1.68 (1.34 ± 0.17). ZW, 0.77–1.13 (0.96 ± 0.10). ZD, 0.77–0.87 (n = 2). OrL, 0.42–0.53 (0.46 ± 0.03). OrW, 0.36–0.45 (0.40 ± 0.02). OeL, 0.52–0.55 (n = 2). OeW, 0.55–0.58 (n = 2). Av(s)L, 0.10–0.17 (0.14 ± 0.02). Av(ad)L, 0.11–0.19 (0.15 ± 0.02). P(m)N, 15–26 (20). P(oe)N, 26 (n = 1).

Description. Colonies encrusting, multiserial, unilaminar ( Fig. 6A View FIGURE 6 ), irregular in outline, up to about 19 × 8 mm in size, light-yellow to beige when dry. Zooids large, hexagonal to irregularly oval, arranged in a checkered pattern, demarcated by fine undulating sutures between lateral and transverse walls ( Fig. 6A, B, D–H View FIGURE 6 ).

Frontal shield umbonuloid ( Fig. 6A, D, I View FIGURE 6 ), initially convex but becoming flattened with age, entirely covered with fine, pointed tubercles, with small, deeply submerged circular to oval areolae along zooidal margins, separated by narrow, short interareolar ridges, mostly not reaching cystid of suboral avicularium. Thickening of frontal shield in older parts of colony resulting in some reduction of areolae in size and number. While boundaries between zooids visible in all parts of colony, some sutures between vertical walls disappearing along with some interareolar ridges. Umbonuloid component extensive, occupying about 75% of length of frontal shield (77% in one measured zooid), with fine parallel lineation and accretionary banding ( Fig. 6I View FIGURE 6 ). Ring scar discrete but fainter than typical ( Fig. 6L View FIGURE 6 ), forming regular boundary between umbonuloid exterior wall and extra-umbonuloid interior wall microstructure.

Primary orifice ( Fig. 6A–C, I, J View FIGURE 6 ) quadrangular with broadly rounded angles to oval; distal and lateral margins formed by upper terminal part of distal transverse wall bearing distinct shelf distally and forming large condyles with blunt or pointed tips laterally ( Fig. 6A–C, G, I, J View FIGURE 6 ). Distal margin of orifice round, proximal margin slightly concave or straight, with broadly rounded proximolateral corners. No oral spines.

Secondary orifice with the same outline as primary orifice; cormidial, formed proximally by finely granulated slope of avicularian cystid; distally and distolaterally restricted to vertical walls of distal and lateral zooids.

Suboral avicularium with cystid forming crescentic lip around proximolateral edge of primary orifice; relatively small, only slightly elevated above frontal shield, with finely granulated surface and 1–3 communication pores connecting avicularian and hypostegal coelomic cavities; frontal surface (rostral/postmandibular areas) normally crossed by zooidal midline and facing to right or left of it ( Fig. 6A–H View FIGURE 6 ). Small rostral face of avicularium angled frontally at about 45° to frontal shield. Rostrum semioval, blunt, with serrated distal margin, directed medially upwards. Palate and palatal foramen conforming to shape of rostrum, opesia oval. Crossbar complete, thickened in middle or with very small ligula.

From one to five small adventitious avicularia of equal size and form present on lateral, proximolateral or proximal surface of zooidal frontal shield close to margins ( Fig. 6A–H View FIGURE 6 ), more numerous in older parts of colony. Avicularian cystid low, with finely granulated surface, frontal surface (rostral/postmandibular areas) facing frontally. Rostrum semicircular to broadly oval, blunt, with serrated distal margin, directed outwards. Palate and palatal foramen conforming to shape of rostrum, short, semicircular to semioval, opesia oval or round, surrounded by cryptocyst. Crossbar complete, thickened in middle or with very small, low ligula. Orifices of non-ovicellate zooids surrounded by 3 adventitious avicularia (including suboral) in young areas of colony ( Fig. 6B–D View FIGURE 6 ) and by 4–6 avicularia in older areas ( Fig. 6E–H View FIGURE 6 ). Each ovicell surrounded by two to four avicularia ( Fig. 6F–G View FIGURE 6 ).

Ovicells initially prominent, later becoming subimmersed due to peripheral overgrowth of ooecium by secondary calcification proceeding from daughter and neighbouring lateral zooids ( Fig. 6F, G View FIGURE 6 ). Ooecium formed by distal autozooid around small, shallow concavity with communication pore at bottom, situated in proximalmost part of frontal shield just immediate to distal margin of maternal primary orifice ( Fig. 6C, D View FIGURE 6 ). Ooecium with concave proximal margin, with smooth ectooecium and numerous rounded to elongate pseudopores.

Zooids interconnected by 3‒5 mural pore chambers in each distolateral wall ( Fig. 6M View FIGURE 6 ). Two lateral or one central multiporous septula in basal half of transverse walls.

Basal wall of zooids ( Fig. 6K, M View FIGURE 6 ) fully calcified, slightly convex, smooth, with some protuberances of irregular form (0.21–0.39 mm in diameter), and with fine, parallel folds on surface. Boundaries between zooids recognizable basally by deep undulating incisions. Numerous white spots (presumably less-calcified areas) visible in semitransparent basal wall under light microscope.

Ancestrula and early astogeny not observed.

Remarks. The following character combination clearly distinguishes R. microavicularia from congeners: 1) proportionally large orifice, occupying more than 30% of zooid length; 2) cystid of suboral avicularium around proximolateral edge of primary orifice narrow, crescentic; 3) interareolar ridges short, most not meeting suboral avicularian cystid except for those lateral to cystid; and 4) numerous, small, peripheral adventitious avicularia.

Androsova (1958) reported what might be this species as R. scabra from the northern part of the Sea of Japan, including Moneron Island (46°18.0ʹ N, 141°13.0ʹ E), and from three localities along the southwestern coast of Sakhalin Island, i.e., near the settlements of Kholmsk, Krasnogorsk and Uglegorsk (47°03.0ʹ N, 142°00.0ʹ E to 49°05.0ʹ N, 142°01.0ʹ E), at depths of 10–117 m on rocks and shells. She mentioned the unusually large orifice, comprising one-quarter to half of zooidal length, associated with numerous (3–5) adventitious avicularia arranged irregularly on the frontal shield. Hence, Androsova’s material might have been R. microavicularia n. sp.. At the same time, she described and illustrated strongly enlarged marginal areolae separated by long interareolar ridges connected to a well-developed, elevated suboral avicularian cystid. It thus remains unclear whether our specimens and those of Androsova are conspecific.

Ecology. Rhamphostomella microavicularia n. sp. was found at 264–480 m depth on a barnacle shell plate and a sponge.

Distribution. Our two specimens were collected from two northwestern Pacific localities along the middle to southern Kuril Islands, including the Pacific slope between Urup and Chiproy Islands, and at one site northward of Iturup Island, Sea of Okhotsk. Accordingly, R. microavicularia n. sp. is a Pacific Asian high-boreal, sublittoral to upper-bathyal species.