Taxonomy, ecology and zoogeography of the Recent species of Rhamphostomella Lorenz, 1886 and Mixtoscutella n. gen. (Bryozoa, Cheilostomata) Author Grischenko, Andrei V. gat1971@mail.ru Author Gordon, Dennis P. dennis.gordon@niwa.co.nz Author Taylor, Paul D. p.taylor@nhm.ac.uk Author Kuklinski, Piotr kuki@iopan.gda.pl Author Denisenko, Nina V. ndenisenko@zin.ru Author Spencer-Jones, Mary E. m.spencer-jones@nhm.ac.uk Author Ostrovsky, Andrew N. andrei.ostrovsky@univie.ac.at text Zootaxa 2022 2022-05-02 5131 1 1 115 http://dx.doi.org/10.11646/zootaxa.5131.1.1 journal article 54924 10.11646/zootaxa.5131.1.1 1daf4875-bf0f-4fb9-b648-459a83357801 1175-5326 6521113 CF550031-D6A9-48A3-A953-A1BD40C72F5E Rhamphostomella commandorica n. sp. ( Figs 2 , 30B ) Diagnosis. Colony encrusting,multiserial.Zooids large, hexagonal to oval.Frontal shield convex, pustulose.Marginal areolae large, separated by high interareolar ridges connected with cystid of suboral avicularium. Umbonuloid component extensive. Primary orifice sunken, broadly semicircular to bell-shaped, with blunt condyles; proximal margin with low, wide median prominence. No oral spines. Secondary orifice irregularly oval, cormidial. Suboral avicularian cystid large, bulging, occupying most of frontal shield, finely granulated. Avicularian frontal surface situated asymmetrically in respect to zooidal orifice, crossing zooidal midline, facing distolaterally and slightly overhanging proximal margin of primary orifice. Rostrum semicircular, blunt. Palate short, broadly triangular to semiround. Crossbar complete. Large adventitious avicularia also present, often associated with ooecia. Rostrum elongate-oval or elongate-triangular, blunt. Palate elongate-triangular or spatulate. Palatal foramen heart-shaped. Crossbar complete, with small ligula. Ovicells hyperstomial, rapidly subimmersed by secondary calcification. Ectooecium smooth, with pseudopores arranged in arch around a few central pseudopores. Two mural pore chambers in distolateral wall, and 1‒3 multiporous septula in transverse walls. Basal surface of zooids fully calcified with some tubular protuberances. FIGURE 2. Rhamphostomella commandorica n. sp. Holotype , ZIRAS 1/50125 (Medny Island, Commander Islands, Pacific Ocean). A. Colony margin with developing zooids. B. Distolateral view of young zooids, showing details of primary orifice and suboral avicularium. C. Non-ovicellate zooids in young part of colony (arrow, communication pore of future ooecium). D. Lateral view of autozooids in young part of colony, showing details of suboral avicularia. E. Ovicellate zooids in older part of colony with suboral and adventitious avicularia. F. Ooecium overgrown by secondary calcification, showing arrangement of pseudopores. G. Group of ovicellate zooids in older part of colony. H. Distolateral view of frontal shield, showing comparative size and shape of suboral and adventitious avicularia. I. Interior of frontal shield, showing ring scar, areolae and ooecial communication pore (arrow). J. Internal view of primary orifice. K. Basal colony surface, showing small protuberances. L. Interior of frontal shield, showing ring scar and exterior wall microstructure of umbonuloid component. M. Lateral view of zooidal row, showing ooecia (some covered by secondary calcification) and adventitious avicularia on frontal surface, tubular processes on basal surface, and lateral wall with mural pore chambers. Scale bars: A, G, K, 500 μm; B, H, M, 200 μm; C–E, 250 μm; F, I, J, 100 μm; L, 50 μm. Material examined. Holotype : ZIRAS 1 /50125, single colony fragment, IMB Collection , Stn 224/582, 2 October 1973 , Poludennaya Bight , coastal waters of Medny Island , Commander Islands , Pacific Ocean , 54°36.8ʹ N , 167°21.5ʹ E , depth 130–250 m , rock dredge, collector S.D. Vavilin. Paratype : NHMUK 2013.10 .21.1, one colony , RV Norseman , Stn AS –1, 17 July 2011 , coastal waters of Adak Island , Andreanof Islands , Aleutian Islands , Pacific Ocean , 51°46.2ʹ N , 176°25.6ʹ W , depth 10 m , SCUBA , collector P. Kuklinski. Etymology. The species name alludes to the type locality in the Commander Islands (in Russian, “Komandorskie ostrova”). Type locality. Poludennaya Bight , coastal waters of Medny Island , Commander Islands , Pacific Ocean , 54°36.8ʹ N , 167°21.5ʹ E , depth 130–250 m . Measurements. ZIRAS 1/50125, Medny Island, Commander Islands, Pacific Ocean ( Figs 2A–M , 30B ). ZL, 0.77–1.28 (1.03 ± 0.12). ZW, 0.47–0.75 (0.59 ± 0.07). ZD, 0.62–0.67 ( n = 2). OrL, 0.22–0.30 (0.26 ± 0.02). OrW, 0.22–0.35 (0.28 ± 0.03). OeL, 0.32–0.45 (0.39 ± 0.03). OeW, 0.42–0.58 (0.51 ± 0.04). Av(s)L, 0.15–0.28 (0.20 ± 0.03). Av(ad)L, 0.37–0.53 (0.44 ± 0.04). P(m)N, 12–18 (14). P(oe)N, 11–16 (15) ( n = 10). NHMUK 2013.10.21.1, Adak Island, Aleutian Islands, Pacific Ocean. ZL, 0.59–1.08 (0.85 ± 0.09). ZW, 0.34– 0.57 (0.45 ± 0.06). ZD, 0.55–0.61 ( n = 2). OrL, 0.16–0.24 (0.20 ± 0.02) ( n = 25). OrW, 0.18–0.28 (0.23 ± 0.02) ( n = 25). Av(s)L, 0.12–0.17 (0.14 ± 0.01) ( n = 14). P(m)N, 14–24 (19) ( n = 10). Description. Colonies encrusting, multiserial, unilaminar ( Fig. 2A ), more or less circular, attaining 12 × 15 mm in size, pink when dry. Zooids large, hexagonal to oval, arranged in regular rows in checkered pattern, demarcated by fine sutures between lateral and transverse walls ( Fig. 2A–D ); sutures occluded by secondary calcification in older parts of colony. Frontal shield umbonuloid ( Fig. 2A–D, I ), thick, convex, pustulose, with numerous, large, elongate areolae along zooidal margins, separated by narrow, high interareolar ridges connected with cystid of suboral avicularium. Some proximal ridges fusing with each other. Thickening of frontal shield resulting in smaller areolae. Umbonuloid component extensive, occupying about 70% of length of frontal shield (72% in one measured zooid), with fine parallel lineation and accretionary banding ( Fig. 2I, L ). Ring scar forming boundary between umbonuloid exterior wall microstructure and extra-umbonuloid calcification clearly visible but not as single discrete line ( Fig. 2L ). Primary orifice ( Fig. 2A, B, J ) broadly semicircular to bell-shaped or oval; its distal and lateral margins formed by upper terminal part of distal transverse wall ( Fig. 2A, B, E ) and bearing low blunt condyles proximolaterally ( Fig. 2J ). Distal margin of orifice round, proximal margin with low, wide median prominence and broadly rounded proximolateral corners. No oral spines. Secondary orifice ( Fig. 2A–E, G ) irregularly oval, cormidial, formed proximally by avicularian cystid connected with thin vertical wall surrounding primary orifice ( Fig. 2A–D ). Distally and distolaterally, secondary orifice restricted by vertical walls of distal and lateral zooids. With increasing secondary calcification, outline of secondary orifice often changing, acquiring trapezoidal shape ( Fig. 2E, G ) in ovicellate zooids. Suboral avicularium with cystid large, bulging, broad, occupying most of frontal shield, with 6–9 communication pores connecting avicularian and hypostegal coelomic cavities ( Fig. 2A, C, D ); surface finely granulated when young, pustulose in older zooids. Avicularian frontal surface (rostral/postmandibular areas) situated asymmetrically with respect to zooidal orifice, on right or left slope of avicularian cystid, normally crossed by zooidal midline, facing distolaterally or laterally, tilted frontodistally at angle of 60–90°. Rostrum semicircular, blunt, directed proximomedially upwards. Palate short, semicircular to rounded-triangular. Palatal foramen repeating shape of palate, opesia oval or semielliptical, surrounded by cryptocystal shelf. Crossbar complete. Large adventitious avicularia developing by frontal budding in older parts of colony, often associated with ooecia. Zooidal orifices deeply immersed in areas where avicularia are numerous. Avicularian cystid broad, with finely granulated surface ( Fig. 2E, G, H ). Frontal surface of avicularium facing obliquely upwards. Rostrum elongate-oval or elongate-triangular, blunt, oriented distolaterally to proximolaterally. Palate elongate-triangular or spatulate. Palatal foramen heart-shaped, with extensive distal cryptocystal shelf. Opesia oval or semielliptical, cryptocyst narrow. Crossbar complete, with small ligula. In older parts of colony, adventitious avicularia cover most of free space, together with thick secondary calcification, strongly changing appearance of colony (compare Fig. 2A, C, D with Fig. 2E, G ). Ovicells initially hyperstomial, rapidly becoming subimmersed as ooecium is covered by thick secondary calcification proceeding from daughter and neighbouring zooids; surface finely granular, often with 1–2 sutures demarcating calcification (often bearing interareolar ridges) from different zooids ( Fig. 2E, F, G ). In older parts of colony, secondary calcification covering half to two-thirds of ooecium; ovicell appearing endozooidal when only proximal triangular or semicircular area of ectooecium with pseudopores is visible ( Fig. 2G ). Ooecium formed by distal autozooid around distinctive curved slit ( Fig. 2A, C, D ) in slope of proximal vertical wall of distal zooid contributing to secondary orifice, immediately distal to margin of primary orifice of maternal zooid; this slit leading to communication canal connecting ooecial and visceral coeloms, opening on underside of frontal shield of distal zooid as small, straight, slit-like communication pore at mid-distance between transverse wall and ring-scar ( Fig. 2I ). Ooecium spherical, with straight or slightly concave proximal margin often bearing very low, central convexity ( Fig. 2F ). Ectooecium smooth, with oval, irregular or often slit-like pseudopores arranged in compressed arch around оne large or several small central pseudopores, oval or irregular. Ooecial base surrounded by oval to elongate areolae separated by short, narrow ridges ( Fig. 2F, G ). Zooids interconnected by two mural pore chambers ( Fig. 2M ) in each distolateral wall, and by one wide, horizontal or 2‒3 (usually 2) compact multiporous septula in basal half of transverse wall. Distally transverse wall can bear up to three buttressed recesses (each with multiporous septula) resembling basal pore chambers ( Fig. 2A ). Basal surface of zooids ( Figs 2K, M , 30B ) fully calcified, convex, smooth, with numerous tubular protuberances ( 0.04–0.27 mm in diameter) having fine parallel folds on surface. Boundaries between zooids recognizable basally by deep undulating incisions. Sparse white spots (presumably weakly calcified areas) visible in semitransparent basal wall under light microscope. Ancestrula and early astogeny not observed. Remarks. In the general appearance of the zooids, as well as in having: 1) a bulging, broad oval suboral avicularium with semicircular palate, and 2) ooecia with a narrow arch of slit-like pseudopores, R . commandorica n. sp. resembles R . pacifica (see below), but differs from the latter as follows: 1) the primary orifice is submerged in zooids of R . commandorica n. sp. at all stages of zooidal development, whereas it is clearly visible in non-ovicellate zooids and surrounded by a tubular peristome in ovicellate zooids of R . pacifica ; 2) the palatal foramen of the adventitious avicularia is heart-shaped in R . commandorica n. sp. , but Y-shaped in R . pacifica ; 3) the two known colonies of R . commandorica n. sp. are both encrusting, whereas colonies of R . pacifica are encrusting only initially, but rapidly grow into erect bilamellar ruffled expansions. Ecology. Rhamphostomella commandorica n. sp. has been found at depths of 10–250 m , on mixed bottoms (silt, pebbles, boulders). The original substrata for our specimens are unknown. Distribution. Presently known only from Poludennaya Bight off Medny Island, Commander Islands, and Adak Island, Andreanof Islands, Aleutian Islands, R . commandorica n. sp. can be categorized as a Pacific high-boreal, sublittoral species.