Rhamphostomella echinata, 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 : 78-81

Rhamphostomella echinata n. sp.

( Fig. 24 )

Rhamphostomella sp. : Grischenko 1997, p. 176; 2002, p. 115.

Diagnosis. Colony encrusting, multiserial. Zooids small, hexagonal. Frontal shield moderately convex, uniformly tessellated, with a few marginal areolae. No interareolar ridges. Umbonuloid component small. Suboral mucro absent. Primary orifice irregularly oval to quadrangular; proximal margin bisinuate, with median bifurcated to multiply branched lyrula and small, lateral, triangular processes. Condyles absent. Secondary orifice irregularly oval, cormidial, just slightly above primary orifice. 2‒3 pairs of very long tubular, articulated oral spines with massive bases on lateral margins of secondary orifice, conferring spinose appearance to colony. Suboral avicularian cystid very small, with finely dimpled surface. Rostrum short, oval, slightly elevated. Mandible spatulate, with rounded distal end. Crossbar incomplete. No adventitious avicularia. Ovicell hyperstomial. Ectooecium with small scattered pseudopores, no secondary calcification. 2–3 pore chambers in distolateral wall, and 1–2 multiporous septula in transverse walls. Basal surface of zooids fully calcified, with tubular protuberances.

Material examined. Holotype: ZIRAS 1 /50126, one colony fragment, IMB Collection , Stn 158/393, 18 September 1973, Kitolovnaya Bank , Medny Island , coastal waters of Medny Island , Commander Islands, Bering Sea, 55°02.2ʹ N, 167°10.9ʹ E, depth 60 m, rock dredge, collector S.D. Vavilin. Paratype: NHMUK 2013.10 .21.3, one colony encrusting oyster shell , RV Norseman, Stn LT –2, 3 July 2011, Longshot , East of Square Bay , coastal waters of Amchitka Island , Rat Islands , western Aleutian Islands, Bering Sea, 51°26.6ʹ N, 179°12.2ʹ E, depth 10 m , SCUBA, collector P. Kuklinski.

NHMUK 2013.10 .21.4, one colony , RV Norseman, Stn LT –1, 4 July 2011, Longshot , South of Crown Reefer Point , coastal waters of Amchitka Island , Rat Islands , western Aleutian Islands, Bering Sea, 51°27.3ʹ N, 179°11.4ʹ E, depth 13 m , SCUBA, collector P. Kuklinski.

Additional material. 14 specimens. IMB Collection (1973) Stns 108/284, 150/385, 151/386, 160/395, 173/408; KIENM Collection (1992) Stns 5, 39, 140 (see Appendix 1 for details).

Etymology. The specific name echinata alludes to the spinose appearance of the colony, with numerous oral spines.

Type locality. Kitolovnaya Bank , coastal waters of Medny Island , Commander Islands, Bering Sea, 55°02.2ʹ N, 167°10.9ʹ E, depth 60 m.

Measurements. ZIRAS 1/50126, Medny Island, Commander Islands, Bering Sea ( Fig. 24A–L ). ZL, 0.52–0.78 (0.64 ± 0.06). ZW, 0.32–0.45 (0.39 ± 0.04). ZD, 0.28–0.35 (n = 2). OrL, 0.18–0.25 (0.23 ± 0.02). OrW, 0.20–0.25 (0.22 ± 0.02). OeL, 0.27–0.33 (0.30 ± 0.02) (n = 20). OeW, 0.27–0.33 (0.31 ± 0.02) (n = 20). Av(s)L, 0.06–0.11 (0.08 ± 0.01) (n = 20). Sp(or)L, 0.39–1.05 (0.77 ± 0.14). P(m)N, 5–10 (7) (n = 12). P(oe)N, 18–22 (20) (n = 5).

NHMUK 2013.10.21.3, Amchitka Island, Aleutian Islands, Bering Sea. ZL, 0.49–0.80 (0.61 ± 0.07). ZW, 0.25–0.48 (0.35 ± 0.05). ZD, 0.27–0.32 (n = 2). OrL, 0.18–0.27 (0.23 ± 0.02). OrW, 0.18–0.27 (0.22 ± 0.02). OeL, 0.21–0.31 (0.26 ± 0.02). OeW, 0.21–0.35 (0.31 ± 0.03). Av(s)L, 0.05–0.10 (0.08 ± 0.01). Sp(or)L, 0.16–0.69 (0.37 ± 0.11). P(m)N, 3–8 (6) (n = 20). P(oe)N, 6–21 (15).

Description. Colonies encrusting, multiserial, unilaminar ( Fig. 24A ), irregular in form, small, attaining 5 mm in maximal dimension, bright brown when alive, light brown or pink when dry. Zooids small, oval, rectangular or hexagonal, arranged in checkered pattern, demarcated by fine undulating sutures between lateral and transverse walls; sutures recognisable in all parts of colony.

Frontal shield moderately convex in distal half, flattened proximally, uniformly tessellated, with a few circular to oval areolae along zooidal margins. Interareolar ridges absent. Interior of frontal shield ( Fig. 24I ) with thin discrete ring scar ( Fig. 24K ). Umbonuloid component small, occupying 15‒26% of length of frontal shield.

Primary orifice ( Fig. 24A, C, D ) irregularly oval to quadrangular with broadly rounded angles; distal and lateral margins formed by upper part of distal transverse wall. Distal wall of orifice shallowly rounded or nearly straight, proximal margin bisinuate, with prominent, median, bifurcate, trifid or multiply branched lyrula and small, lateral, triangular processes, often looking like acute spinules, 1–4 in number on each side ( Fig. 24A, B ). Condyles absent.

Secondary orifice ( Fig. 24D–H ) irregularly oval to quadrangular, cormidial; distolateral curvature just slightly above primary orifice, formed by upper terminal part of distal transverse wall ( Fig. 24C, D ); proximally restricted by asymmetrically placed cystid of suboral avicularium. Usually, two or three pairs of tubular, articulated oral spines along lateral margins of secondary orifice, two (less frequently three) pairs in ovicellate zooids ( Fig. 24A–H ); spines very long, sometimes exceeding length of zooid, with thick bases, weakly bent ( Fig. 24E, F ), giving distinctive spinose appearance to colony.

Cystid of suboral avicularium ( Fig. 24B–D, F–H ) very small, flattened, surface finely dimpled, with single minute communication pore situated proximally, on left or right side relative to orifice. Frontal surface (rostral/ postmandibular areas) of avicularium curved to one side, out of zooidal midline, facing obliquely proximolaterally. Rostrum short, oval, slightly elevated, directed distolaterally and frontally. Mandible spatulate, with rounded distal end ( Fig. 24B, F ), palate of similar shape, forming blunt angle with postmandibular area; opesia semioval. Crossbar incomplete, visible as two indictinst denticles.

No adventitious avicularia.

Ovicells hyperstomial ( Fig. 24G, H ), ooecium not overgrown by secondary calcification. Ooecium formed by distal autozooid, ooecial fold developing at colony periphery, concurrently with frontal shield of distal zooid ( Fig. 24D ). Ooecium flattened laterally, proximal margin weakly concave with minor wrinkles. Ectooecium with numerous small, circular uniformly scattered pseudopores. Bases of distalmost oral spines appressed to sides of ooecium.

Zooids interconnected by 2–3 mural pore chambers ( Fig. 24L ) in each distolateral wall and 1‒2 multiporous septula (sometimes with individual pores in between) or line of individual pores in basal half of transverse walls.

Basal surface of zooids ( Fig.24J ) fully calcified, flattened to moderately convex, with long, tubular protuberances (up to 0.24 mm long, 0.11–0.27 mm in diameter) ( Fig. 24J ). Boundaries between zooids indicated basally by irregular undulation and sutures.

Ancestrula and early astogeny not observed.

Remarks. Rhamphostomella echinata n. sp. clearly differs from congeners in the following combination of characters: 1) small zooid size; 2) two or three pairs of very long, basally articulated oral spines, frequently exceeding zooid length and conferring a distinctive spiny appearance to the colony; 3) wide, massive spine bases; 4) a bisinuate proximal orificial margin, with a bifurcate or multi-pronged median process and irregular lateral processes; and 5) a very small, frontally curved suboral avicularium.

Rhamphostomella spinigera has a generally similar proximal margin of the primary orifice and distolateral oral spines with large bases, but in R. spinigera , the spines are straight and situated along the distal curvature of the orifice, whereas in R. echinata n. sp. they are slightly curved, and their bases are arranged laterally along the orifice. Among other differences, the frontal shield is tuberculate in R. spinigera but tesselated in R. echinata n. sp., and the suboral avicularium differ in morphology between the two species.

Ecology. This species has been collected from from depths of 10–100 m on hard bottoms, including rock, boulders and pebbles. Colonies encrust serpulid tubes, oyster shells, hydroid stolons, articulated red algae, other bryozoans ( Tricellaria beringia and lichenoporid cyclostomes) and crab carapaces.

Distribution. Based on known records, which include several localities from the shelf zone of the Commander Islands ( Grischenko 1997, 2002; and our data) and Beringian coastal waters of Amchitka Island, Rat Islands, and the western Aleutian Islands, R. echinata n. sp. is a Pacific high-boreal, sublittoral species.

Figures

FIGURE 24. Rhamphostomella echinata n. sp. Holotype, ZIRAS 1/50126 (Medny Island, Commander Islands, Bering Sea). A. Colony margin with developing and fully formed young zooids. B. Lateral view of orifice, showing branching lyrula, four spinules, suboral avicularium and bases of oral spines; non-bleached colony. C. Orifice of non-ovicellate zooid showing lyrula, lateral denticles and bases of oral spines. D. Group of non-ovicellate zooids, showing dimpled frontal shields and early stages of ooecial formation. E. Non-ovicellate zooids with long oral spines; unbleached colony. F. Close-up of non-ovicellate zooid, unbleached. G. Group of zooids with broken and completed ooecia. H. Single ovicellate zooid, showing details of orifice, spine bases and ooecium. I. Interior of frontal shield, showing lyrula, lateral denticles, umbo, ring scar and areolae. J. Basal surface of colony, showing protuberances. K. Interior of frontal shield, showing ring scar and umbonuloid component with lyrula and lateral denticles. L. Lateral view of zooid, showing frontal shield, oral spines and lateral wall with mural pore chambers. Scale bars: A, D, E, G, 250 μm; B, K, 50 μm; C, F, H, I, 100 μm; J, 500 μm; L, 200 μm.