Rhamphostomella morozovi, 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 : 29-32

Rhamphostomella morozovi n. sp.

( Fig. 7 )

Diagnosis. Colonies initially encrusting, multiserial, unilaminar, rapidly rising into bilamellar, fan-like expansions. Zooids very large, hexagonal.Frontal shield relatively flat, finely granulated. Marginal areolae initially large, reduced in size with age. Interareolar ridges short, not reaching cystid of suboral avicularium. Umbonuloid component medium-sized. Primary orifice wider than long, broadly semicircular, with small lateral condyles; proximal margin straight or with low median prominence. Oral spines lacking. Secondary orifice irregularly quadrangular to semicircular, cormidial, with lateral peristomial lappets in ovicellate zooids. Suboral avicularian cystid large, subconical, occupying one-third to half of frontal shield, less prominent in older zooids; frontal surface across zooidal axis, facing distolaterally. Rostrum broadly triangular or semielliptical, with blunt hooked tip. Crossbar complete. Adventitious avicularia small, central to proximal, facing frontalwards to slightly angled. Rostrum and palate broadly triangular to semielliptical, with a blunt hooked tip. Crossbar complete. Ovicells hyperstomial, rapidly subimmersed by secondary calcification. Ectooecium with few radially arranged slit-like proximal pseudopores. 1–3 pore chambers in distolateral wall and two multiporous septula in transverse walls. Basal surface of zooids fully calcified, with small prominences.

Material examined. Holotype: ZIRAS 1 /50570, one colony fragment, KamchatNIRO Collection, RV Professor Probatov, Stn 62, 16 August 2013, coastal waters of western Kamchatka, Sea of Okhotsk , 57°14.9ʹ N, 155°37.7ʹ E, depth 116 m, bottom-grab “Ocean–50”, collector T. B. Morozov . Paratype: ZIRAS 2 /50571, two fragments from same colony, KamchatNIRO Collection , RV Professor Probatov, Stn 82, 11 August 2013, coastal waters of western Kamchatka, Sea of Okhotsk , 58°09.0ʹ N, 156°03.0ʹ E, depth 146 m, bottom-grab “Ocean–50”, collector T. B. Morozov .

Etymology. The specific name honours Mr Taras B. Morozov (KamchatNIRO, Petropavlovsk-Kamchatsky, Russia), who collected and donated the type material.

Type locality. Western Kamchatka shelf, Sea of Okhotsk , 57°14.9ʹ N, 155°37.7ʹ E, depth 116 m.

Measurements. ZIRAS 1/50570, western Kamchatka, Sea of Okhotsk ( Fig. 7A–M ). ZL, 1.11–2.03 (1.50 ± 0.26). ZW, 0.57–0.83 (0.68 ± 0.07). ZD, 0.90–1.03 (n = 2). OrL, 0.25–0.31 (0.28 ± 0.02). OrW, 0.30–0.38 (0.33 ± 0.02). OeL, 0.39–0.51 (0.45 ± 0.03). OeW, 0.46–0.60 (0.55 ± 0.03). Av(s)L, 0.15–0.31 (0.22 ± 0.04). Av(ad)L, 0.13–0.33 (0.21 ± 0.05). P(m)N, 11–18 (16). P(oe)N, 2–6 (5) (n = 10).

Description. Colonies initially encrusting, unilaminar ( Fig. 7A ), later rising into bilamellar ( Fig. 7M ), fan-like, ruffled expansions, about 80 × 50 mm in size. Dried colonies greyish to dark yellow. Bilaminate parts of colony up to 2.03 mm thick, adjoining layers of zooids closely adpressed ( Fig. 7M ). Directions of development of zooids in adjoining layers not fully coinciding, with angles of 5–10° between main axes of zooid rows in opposing layers. Zooids very large, hexagonal ( Fig. 7D ) to irregularly oval or tapering proximally ( Fig. 7E–G ), arranged in straight, regular rows in a checkered pattern in colony lobes, or arranged irregularly in older regions of colony. Autozooids demarcated by fine undulating sutures between lateral and transverse walls ( Fig. 7A, F–H ). Boundaries between zooids in older parts of colony often becoming occluded with increasing secondary calcification ( Fig. 7E, G ).

Frontal shield umbonuloid ( Fig. 7A, B, D, I ) initially relatively flat, gradually becoming more convex with age, finely granulated, granulation becoming coarser in older zooids. Relatively large oval to circular areolae along zooidal margins, separated by narrow short interareolar ridges not reaching cystid of suboral avicularium. With age, areolae reduced in size to small marginal holes separated by flat, broad areas of calcification (former interareolar ridges) ( Fig. 7E, G, H ). Umbonuloid component occupying about 50% of length of frontal shield (49% in one measured zooid), with fine parallel lineation and accretionary banding ( Fig. 7I ). Ring scar discrete ( Fig. 7L ), forming regular boundary between umbonuloid exterior wall and extra-umbonuloid interior wall microstructure.

Primary orifice ( Fig. 7A, C, J ) broadly semicircular to bell-shaped (wider than long) and transversely oval; distal and lateral margins formed by upper terminal part of distal transverse wall bearing distinct shelf distally ( Fig. 7A–E ) and forming small, low triangular condyles with acute tips laterally ( Fig. 7J ). Distal margin of orifice round, proximal margin more or less straight or with low, ill-defined median prominence and broadly rounded proximolateral corners ( Fig. 7C, J ). Oral spines lacking.

Secondary orifice ( Fig. 7B–H ) irregularly quadrangular, oval to semicircular, cormidial, proximally formed by thickened frontal shield incorporating avicularian cystid medially, and laterally by two symmetrical, oblique, low triangular lappets that are outgrowths of frontal shield. Distally, distolaterally and sometimes laterally, secondary orifice restricted by vertical walls of distal and lateral zooids. In ovicellate (maternal) zooids, lateral outgrowths of frontal shields form peristomial lappets connecting with proximal corners of ooecium distally and with lappets formed by frontal shield of neighbouring zooid proximally ( Fig. 7G, H ).

Suboral avicularium with cystid large, broad, subconical, occupying from one-third to about half of frontal shield, strongly elevated in young zooids ( Fig. 7A–D ), becoming less prominent in older zooids ( Fig. 7E–H ) owing to immersion into thickening frontal shield; surface finely granulated, with 2–4 tiny communication pores on surface ( Fig. 7A–D ). Frontal surface of avicularium (rostral/postmandibular areas) situated on left or right slope of cystid, across zooidal axis, facing distolaterally. Rostrum broadly triangular or semielliptical, directed medially, laterally or proximolaterally upwards, blunt, with terminal hook. Palate and foramen conforming to shape of rostrum, with blunt distal end; opesia oval, surrounded by narrow cryptocyst. Crossbar complete.

Adventitious avicularia small, central to proximal on zooidal frontal shield in older parts of colony ( Fig. 7F–H ), with relatively narrow cystid, slightly elevated, with finely granulated surface; avicularian frontal surface facing frontally or slightly angled. Rostrum broadly triangular or semielliptical, directed laterally or proximally, with hooked tip, palate and palatal foramen conforming shape of rostrum, opesia oval or elliptical. Crossbar complete. Cystids of these avicularia frequently situated close to ooecia of neighbouring zooids ( Fig. 7G ).

Ovicells hyperstomial, rapidly becoming subimmersed, with ooecium peripherally overgrown by secondary calcification from neighbouring zooids in older parts of colony ( Fig. 7F, G ). In some ovicells, two-thirds of ooecium covered by secondary calcification ( Fig. 7H ). Ooecium formed by distal autozooid around small, shallow arch-like concavity with communication pore at bottom, situated in proximalmost part of frontal shield just immediate to distal margin of maternal primary orifice ( Fig. 7B–D ). Ectooecium with radial growth lines and a few radially arranged slit-like pseudopores near proximal margin. Finely granulated secondary calcification, produced by neighbouring zooids, overgrowing peripheral parts of ooecium, also forming two convex lateral lobes that fuse with lateral lappets of frontal shield to produce low peristome around orifice ( Fig. 7F–H ).

Zooids interconnected by 1–3 mural pore chambers in each distolateral wall ( Fig. 7M ). Communication pores usually form two multiporous septula in basal half of transverse walls. In some zooids, septulum single, as horizontal “band”. ( Fig 7A, D ).

Basal surface of zooids ( Fig. 7K ) fully calcified, roughly lineated, with small prominences. Boundaries between zooids recognizable basally by deep, meandering incisions.

Ancestrula and early astogeny not observed.

Remarks. Apart from the striated appearance of young parts of the colony of R. cristata , R. morozovi n. sp. resembles this species in the following characters: 1) the elevated, conical suboral avicularian cystid with a hooked tip; 2) the primary orifice is commonly bell-shaped, occasionally with a weak median convexity in the proximal margin; and 3) the secondary orifice has two symmetrical, obliquely directed triangular lateral lappets. The quadrangular primary orifices that are rather common in R. cristata and the quadrangular secondary orifices in R. morozovi n. sp. add to this similarity. These two species differ, however, in the following characters: 1) the rostrum and palate of the suboral and adventitious avicularia in R. morozovi n. sp. are broadly triangular to semielliptical, with a blunt tip, but are elongate-triangular with an acute tip in R. cristata ; 2) the suboral and adventitious avicularia are proportionally smaller relative to zooid size in R. morozovi n. sp. than in R. cristata ; 3) fully formed ooecia of R. cristata have 11–32 circular to slit-like pseudopores scattered over the entire frontal surface ( Fig. 4F–H ), whereas ooecia have only 2–6 slit-like pseudopores near the proximal margin in R. morozovi n. sp. ( Fig. 7G, H ).

Ecology. Rhamphostomella morozovi n. sp. was recorded from a depth of 116–146 m on a mixed seafloor, including pebbles and gravel overlying sand and silt. Substrata unknown.

Distribution. Currently known from two nearby localities in the western Kamchatka shelf, Sea of Okhotsk, this is a Pacific Asian high-boreal, sublittoral species, possibly endemic to the Sea of Okhotsk.

Figures

FIGURE 4. Rhamphostomella cristata (Hincks, 1889). ZIRAS 2/50110 (Medny Island, Commander Islands, Pacific Ocean).A. Colony margin with developing zooids. B. Distal view of non-ovicellate zooids, showing primary orifices and suboral avicularia. C. Suboral avicularium. D. Lateral view of non-ovicellate zooids, showing suboral avicularium and lobes of peristome. E. Group of non-ovicellate zooids in young part of colony (arrows, communication pores of future ooecia). F. Ovicellate zooid with ooecium, suboral and adventitious avicularia. G. Group of ovicellate zooids in older part of colony. H. Distal view of ovicellate zooids, showing suboral and adventitious avicularia. I. Interior of frontal shield, showing ring scar and areolae. J. Internal view of orifice, showing slightly curved proximal margin and hardly recognisible condyles. K. Lateral view of basal colony surface with numerous protuberances. L. Frontal shield interior, showing ring scar and exterior wall microstructure of umbonuloid component. M. Zooidal lateral wall with mural pore chambers. Scale bars: A, K, 500 μm; B, D, E, G, 250 μm; C, F, I, J, 100 μm; H, M, 200 μm; L, 50 μm.

FIGURE 7. Rhamphostomella morozovi n. sp. Holotype, ZIRAS 1/50570 (western Kamchatka, Sea of Okhotsk). A. Growing margin of bilaminate colony, showing only one layer of developing zooids. B. Lateral view of zooids in young part of colony. C. Zooidal orifice with suboral avicularium (communication pore of future ooecium visible near distal margin of orifice). D. Group of non-ovicellate zooids in young part of colony (arrows, communication pores of future ooecia). E. Zooids with developing ooecia. F. Zooids with developing and nearly completed ooecia and small adventitious avicularia. G. Zooids with developing and nearly complete ooecia and small (central to proximal) adventitious avicularia. H. Lateral view of ovicellate zooid, showing ooecium embedded into secondary calcification and having slit-like proximal pseudopores; notice nearly identical size of suboral and adventitious avicularia. I. Interior of frontal shield showing ring-scar, areolae and communication pores of adventitious avicularium. J. Internal view of orifice, showing straight proximal margin and strongly reduced, pointed condyles. K. Basal surface of encrusting part of colony (some zooids damaged). L. Close-up of frontal shield interior, showing ring scar and exterior wall microstructure of umbonuloid component. M. Lateral walls of zooids in bilaminate colony, showing 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.