Rhamphostomella multirostrata n. sp.

(Figs 22, 30I)

Diagnosis. Colony encrusting, multiserial, partly forming small free-growing frills. Zooids large, oblong-hexagonal. Frontal shield moderately convex, very finely granular. Interareolar ridges reaching avicularian cystid in distal part of zooid. Umbonuloid component extensive. Primary orifice submerged, broadly circular, with very broad median lyrula-like prominence. No condyles. Secondary orifice transversely oval, cormidial; proximolateral curvature incorporating large mucro with two thin-walled symmetrical lateral lappets. 1‒2 pairs of long, tubular, basally articulated oral spines around distal curvature of orifice. Suboral aviculiferous mucro very tall, conical to bulbous, finely granular, bearing 3–5 spirally arranged avicularia decreasing in size towards apex. Basalmost main avicularium budding 2–4 smaller avicularia. No adventitious avicularia. Ovicells hyperstomial. Ectooecium smooth, with numerous scattered pseudopores, mostly with no secondary calcification. 4–5 pore chambers in distolateral wall and two multiporous septula in transverse walls. Basal surface of zooids fully calcified, with numerous tubular protuberances.

Material examined. Holotype: ZIRAS 1/50545, single large colony detached from sponge, IMB Collection, RV Akademik Oparin, 41st Expedition, Stn 19/15, 13 July 2011, westward from Urup Island, middle Kuril Islands, Sea of Okhotsk, 45°54.2ʹ N, 149°40.4ʹ E – 45°54.2ʹ N, 149°40.0ʹ E, depth 183– 213 m, Sigsbee trawl, collectors A.P. Tsurpalo and A.V. Chernyshev . Paratype: ZIRAS 2/50546, single colony encrusting sponge. IMB Collection, RV Akademik Oparin, 41st Expedition, Stn 41/36, 19 July 2011, southeastward from Chiproy Island, middle Kuril Islands, Pacific Ocean, 46°20.5ʹ N 150°58.0ʹ E – 46°21.0ʹ N 150°58.4ʹ E, depth 438– 567 m, Sigsbee trawl, collectors A.P. Tsurpalo and A.V. Chernyshev.

Etymology. This specific name multirostrata refers to the multiple avicularian rostra spirally arranged on the aviculiferous suboral mucro.

Type locality. Westward from Urup Island, middle Kuril Islands, Sea of Okhotsk, 45°54.2ʹ N, 149°40.4ʹ E – 45°54.2ʹ N, 149°40.0ʹ E, depth 183– 213 m.

Measurements. ZIRAS 1/50545, Urup Island, Kuril Islands, Sea of Okhotsk (Figs 22A–M, 30I). ZL, 0.93–1.78 (1.22 ± 0.20). ZW, 0.50–0.83 (0.66 ± 0.08). ZD, 0.51–0.74 (n = 2). OrL, 0.21–0.29 (0.24 ± 0.02). OrW, 0.26–0.35 (0.30 ± 0.02). OeL, 0.47–0.73 (0.58 ± 0.06). OeW, 0.37–0.55 (0.47 ± 0.05). Av(s)L, 0.35–0.64 (0.51 ± 0.08). Av(s)2L, 0.21–0.28 (0.24 ± 0.02) (n = 10). Av(s)3L, 0.19–0.25 (0.22 ± 0.02) (n = 10). Av(s)4L, 0.18–0.25 (0.21 ± 0.03) (n = 10). Av(s)5L, 0.14–0.18 (0.16 ± 0.02) (n = 6). Sp(or)L, 0.70–1.05 (0.89 ± 0.15) (n = 4). P(m)N, 18–31 (25). P(oe)N, 42–52 (43) (n = 7).

Description. Colonies encrusting, multiserial, unilaminar (Fig. 22A), forming extensive muff-like encrustations on sponges, attaining 35 × 22 mm in size, partly developing small, free-growing frills, light-brown when dry. Zooids large, oblong-hexagonal to irregularly oval, tapering proximally, arranged in checkered pattern, demarcated by fine sutures between lateral and transverse walls; sutures less visible in older parts of colony (Fig. 22F).

Frontal shield umbonuloid (Fig. 22A, I), thin, flattened in young zooids, moderately convex in older zooids, with very fine surface granulation. Areolae circular to oval, separated by interareolar ridges; ridges elongate and reaching avicularian cystid in distal part of zooid, shorter proximally (Fig. 22A, D). Umbonuloid component extensive, occupying about 70% of length of frontal shield (76% in one measured zooid), with characteristic lineation and accretionary banding (Fig. 22I, J, L). Ring scar discrete (Fig. 22L).

Primary orifice submerged (Fig. 22A, C, J) broadly circular to oval; distal and lateral margins formed by upper part of distal transverse wall, with narrow or distinct shelf distally (Fig. 22A). Distal margin of orifice rounded, proximal margin straight, with low, very broad, median lyrula-like prominence and rounded proximolateral corners. No condyles.

Secondary orifice (Fig. 22B–D) transversely oval, cormidial; distolateral curvature restricted by proximal and lateral vertical walls of daughter and adjacent lateral zooids; proximolateral curvature represented by low peristome incorporating mucro with avicularia medially and forming two symmetrical, thin-walled lappets laterally. One or two pairs of elongate, tubular, basally articulated oral spines around distal curvature of orifice in non-ovicellate zooids (Fig. 22A–D); one pair of spines near proximolateral corners of ooecium in some ovicellate zooids (Fig. 22G–H). Spines long, fragile, easy detached, slightly tilted distally, with strong bases. Situated proximal to orifice, a conical to bulbous, aviculiferous mucro up to 1.34 mm tall; surface finely granular, with 6–9 scattered minute communication pores. Mucro incorporating 3–5 spirally arranged avicularia that decrease in size toward apex; main, most basal avicularium budding 2–4 smaller avicularia.

Cystid of main (basal) avicularium positioned symmetrically relative to proximal margin of zooidal orifice (Fig. 22A), frontal surface (rostral/postmandibular areas) facing distolaterally, crossing zooidal midline; rostrum elongate triangular to elongate oval, pointed, slightly narrowing in middle, with prominent hooked tip, directed distolaterally and frontally (Fig. 22B, D, G, H). Palatal foramen triangular, acute or rounded distally, cryptocystal shelf occupying one-third to half of rostrum; opesia oval or ellipsoid, bordered by cryptocyst. Crossbar complete, sometimes with small ligula. Mandible elongate triangular (Fig. 22D). Frontal surface of second suboral avicularium (Fig. 22B, D–H) facing distolaterally, obliquely downwards, rostrum acute, tip sometimes hooked; overall positioned at nearly right angle to rostrum of main avicularium, overhanging zooidal orifice; palatal foramen triangular, restricted distally by cryptocystal shelf; opesia oval or ellipsoidal, bordered by cryptocyst. Crossbar complete. Postmandibular area in main and second suboral avicularia located at more or less similar level relative to zooidal surface. Third and fourth avicularia, when present, almost identical in form and size to one another (Fig. 22G); situated higher, in different positions closer to apex of mucro; frontal surface facing laterally to proximolaterally, occasionally proximally or distolaterally. Rostrum elongate triangular, often with hooked tip, directed frontally or tilted slightly basally. Palatal foramen triangular, restricted distally by cryptocystal shelf; opesia circular, reduced to small, elongate pore, bordered by extensive cryptocyst (Fig. 22G). Crossbar complete, sometimes with small ligula. Fifth avicularium (when present) small, variable in shape (Fig. 22E–G), usually located on side of mucro, with frontal surface facing laterally, elongate triangular rostrum directed frontally; palate triangular. Crossbar complete. Sometimes avicularium located at apex of mucro and facing frontally, with nearly circular to oval rostrum and palate. While most zooids have first to third avicularia, fourth to fifth avicularia frequently absent, particularly in young zooids.

No adventitious avicularia.

Ovicells hyperstomial (Fig. 22F–H); only basal part overgrown by secondary calcification in some instances (Fig. 22F). Ooecium formed by distal autozooid around small, shallow concavity with oval communication pore at bottom, situated in proximalmost part of frontal shield just immediate to distal margin of maternal orifice (Fig. 22A). Ooecium compressed proximally, with straight to slightly concave proximal margin. Ectooecium smooth, with numerous circular, oval to slit-like pseudopores.

Zooids interconnected by 4–5 mural pore chambers (Fig. 22M) in each distolateral wall and two multiporous septula (sometimes with individual pores in between) in basal half of transverse walls (Fig. 22A). In some zooids, transverse walls distally with two recesses separated by medial buttress.

Basal surface of zooids (Figs22K, 30I) fully calcified, convex, smooth, thin, with numerous tubular protuberances (0.09–0.25 mm in diameter), surface covered with fine, parallel to centripetal lineation. Numerous white spots (presumably less-calcified areas) visible in semitransparent basal wall by light microscopy. Boundaries between zooids recognizable basally by fine sutures.

Ancestrula and early astogeny not observed.

Remarks. The presence of large a suboral mucro bearing 3–5 avicularia distinguishes R. multirostrata n. sp. from all congeners, making it a unique member of the genus. The suboral aviculiferous mucro and highly pseudoporous ooecium closely resemble similar structures in the lepralioid-shielded genus Bitectipora (Gordon 1994) . Bitectipora species lack a lyrula, having instead a sinusoidal orifice.

Ecology. Rhamphostomella multirostrata n. sp. was collected from depths of 183–567 m, encrusting glass sponges on gravelly bottoms.

Distribution. Presently known from the Pacific and Sea of Okhotsk coasts of the middle Kuril Islands (Chiproy to Urup), R. multrostrata n. sp. is a Pacific Asian high-boreal, sublittoral to upper bathyal species.