Rhamphostomella curvirostrata O'Donoghue & O'Donoghue 1923

Rhamphostomella curvirostrata O’Donoghue & O’Donoghue, 1923

(Figs 14, 30F)

Rhamphostomella curvirostrata O’Donoghue & O’Donoghue, 1923, p. 44, pl. 4, fig. 34.

Rhamphostomella curvirostrata: Osburn 1952, p. 430, pl. 50, fig. 4; Androsova 1958, p. 172, fig. 103; Hayami 1973, p. 51; 1975, p. 89, pl. 17, fig.4.

Additional references. Rhamphostomella curvirostrata: Kluge et al. 1959, p. 213; Kluge 1961, p. 141; Lukin 1979, p. 37; Gontar 1979, p. 246; 1980, p. 13; 1992, p. 197; 1993b, p. 202; Sakagami et al. 1980, p. 330; Grischenko 1997, p. 175; 2002, p. 115; Denisenko 2013, p. 184.

Material examined. Lectotype: NHMUK 1964.1.2.7, single colony detached from sponge, fractured into three fragments (mounted on two SEM stubs), C.H. O’Donoghue Collection, Pacific coast of North America (presumably Vancouver Island, British Columbia).

NHMUK 2010.2.9.5, one colony fragment, KIENM Collection, Stn 152, 10 August 1992, Cape Gladkiy, coastal waters of Medny Island, Commander Islands, Bering Sea, 54°44.8ʹ N, 167°45.3ʹ E, depth 46 m, SCUBA, collector V. V. Oshurkov. NHMUK 2013.10.21.8b, 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. ZIRAS 1/50115, one colony fragment, KIENM Collection, Stn 152, 10 August 1992, Cape Gladkiy, coastal waters of Medny Island, Commander Islands, Bering Sea, 54°44.8ʹ N, 167°45.3ʹ E, depth 46 m, rock face, SCUBA, collector V.V. Oshurkov. ZIRAS 2/50116, one colony fragment, PIBOC Collection, RV Akademik Oparin, 14th Expedition, Stn 91, 10 September 1991, coastal waters of the Lesser Kuril Ridge, Pacific Ocean, 43°25.3ʹ N, 146°25.4ʹ E, depth 103 m, Sigsbee trawl, collector A.V. Smirnov. ZIRAS 4/50547, ten colony fragments, IMB Collection, RV Akademik Oparin, 41st Expedition, Stn 55/47, 26 July 2011, westward from Iturup Island, South Kuril Islands, Sea of Okhotsk, 45°01.2ʹ N, 147°00.9ʹ E – 45°01.5ʹ N, 147°01.3ʹ E, depth 150– 350 m, Sigsbee trawl, collectors A.P. Tsurpalo and A.V. Chernyshev.

Additional material. 37 specimens. IMB Collection (1972) Stn 31/93; (1973) Stns 108/284, 173/408; (2011) Stns 11/7, 16/12, 18/14, 22/17, 29/24, 31/26, 37/32, 39/34, 43/38, 48/42, 55/47, 56/48; PIBOC Collection (1991) Stn 17; KIENM Collection (1992) Stns 127, 142, 150, 152 (see Appendix 1 for details).

Measurements. NHMUK 1964.1.2.7, Pacific coast of North America (Figs 14A, F, K, 30F). ZL, 0.64–0.95 (0.81 ± 0.08). ZW, 0.35–0.56 (0.44 ± 0.06). ZD, 0.34–0.37 (n = 2). OrL, 0.17–0.25 (0.22 ± 0.02). OrW, 0.20–0.28 (0.24 ± 0.02). OeL, 0.21–0.28 (0.24 ± 0.02). OeW, 0.30–0.40 (0.36 ± 0.03). Av(s)L, 0.17–0.36 (0.27 ± 0.05). P(m)N, 11–16 (14). P(oe)N, 11–17 (15).

ZIRAS 1/50115, Medny Island, Commander Islands, Bering Sea (Fig. 14D, E, I). ZL, 0.87–1.38 (1.11 ± 0.14). ZW, 0.37–0.63 (0.50 ± 0.07). ZD, 0.35–0.39 (n = 2). OrL, 0.18–0.32 (0.24 ± 0.05). OrW, 0.20–0.35 (0.27 ± 0.04). OeL, 0.23–0.32 (0.28 ± 0.03). OeW, 0.27–0.42 (0.33 ± 0.03). Av(s)L, 0.29–0.55 (0.43 ± 0.07). P(m)N, 12–20 (16). P(oe)N, 9–16 (15) (n = 10).

ZIRAS 4/50547, Iturup Island, Kuril Islands, Sea of Okhotsk (Fig. 14B, C, G, H, J, L, M). ZL, 1.05–1.58 (1.30 ± 0.15). ZW, 0.52–0.70 (0.60 ± 0.05). ZD, 0.46–0.52 (n = 2). OrL, 0.24–0.31 (0.27 ± 0.02) (n = 20). OrW, 0.24–0.29 (0.26 ± 0.01) (n = 20). OeL, 0.31–0.38 (0.35 ± 0.02). OeW, 0.35–0.44 (0.40 ± 0.02). Av(s)L, 0.39–0.53 (0.46 ± 0.03). P(m)N, 18–26 (22). P(oe), 13–20 (18) (n = 10).

Description. Colonies encrusting, multiserial, unilaminar (Fig. 14A), more or less circular, attaining 25 mm in maximal dimension; red, bright-orange to yellow when alive, light-orange or beige when dry. Zooids oblong, hexagonal to pyriform or irregular in shape, arranged in checkered pattern and demarcated by fine sutures between lateral walls in both young and old parts of colony.

Frontal shield umbonuloid (Fig. 14A, D, I), thin, slightly convex, with either dimpled (Fig. 14A, D, F) or finely granulated (Fig. 14B, C, G, H) surface and angular areolae along zooidal margins, separated by short and relatively narrow interareolar ridges. In older zooids, areolae can be very large with thick, elongate interareolar ridges that sometimes fuse along zooidal midline, giving a costate appearance to zooids (Fig. 14E). Umbonuloid component extensive, occupying about 70% of length of frontal shield (67% in one measured zooid), with distinct parallel lineation and accretionary banding (Fig. 14I, L). Ring scar (Fig. 14L) discrete, forming regular boundary between umbonuloid exterior wall and extra-umbonuloid interior wall microstructure.

Primary orifice (Fig. 14A, B, J) submersed, quadrangular; distal and lateral margins formed by upper terminal part of distal transverse wall bearing prominent shelf (Fig. 14B–D) and forming very low, blunt condyles laterally (Fig. 14B, J). Distal margin of orifice shallowly rounded, proximal margin with central anvil-shaped lyrula with acute tips directed distolaterally, laterally or proximally, and distinct triangular, round-tipped process on each side (Fig. 14B, J, I). In some colonies, marginal zooids and those from the zone of astogenetic change bearing pair of short, hollow, ephemeral oral spines at distolateral corners of orifice.

Secondary orifice transversely oval to irregularly triangular, cormidial, distally and distolaterally restricted by arch-like extensions of vertical walls of distal and distolateral zooids forming subcircular or semioval “collar” (Fig. 14D); proximal part of secondary orifice formed by asymmetrically placed cystid of suboral avicularium and narrow lappet derived from frontal shield. In ovicellate zooids, extensions of lateral walls of distolateral zooids grow as narrow lobes towards each other over central part of ectooecium and above avicularian cystid, forming peristome of two symmetrical arches (Fig. 14E–H), conferring to secondary orifice a circular, transversely oval to irregularly triangular outline with large suboral slit between frontal shield and avicularian rostrum.

Cystid of suboral avicularium of moderate to large size, elevated, situated proximolateral to zooidal orifice on left or right side, with dimpled or granulated surface having gymnocystal rim and 1–2 communication pores (Fig. 14A–H). Rostrum long, curved or straight, elongate triangular, sometimes with short hooked tip (Fig. 14C), reaching or sometimes fusing with peristomial lappet on opposite side of peristome, directed distolaterally and angled so as to conceal most of palate. Avicularian frontal surface (rostral/postmandibular areas) crossing zooidal midline, facing obliquely proximally and frontally. Palate elongate triangular, with pointed distal end and rounded tip, foramen elongate oval, bordered by narrow cryptocystal shelf; opesia semicircular. Crossbar complete.

No adventitious avicularia.

Ovicells initially prominent, later becoming subimmersed, with ooecium peripherally overgrown by secondary calcification proceeding from daughter and neighbouring lateral zooids (Fig. 14B, E, F, G, H, M). Ooecium formed by distal autozooid at colony periphery (Fig. 14A, B), its coelomic cavity connected with visceral coelom via communication canal that opens on underside of proximal part of frontal shield of distal zooid as straight slit-like communication pore about mid-distance between transverse wall and ring scar. Ooecium with straight or concave proximal margin and circular to oval or slit-like pseudopores, some occluded by secondary calcification.

Zooids interconnected by three mural pore chambers in each distolateral wall (Fig. 14M) and two multiporous septula (sometimes with individual pores inbetween) in basal half of transverse walls (Fig. 14B).

Basal wall of zooids (Figs 14K, 30F) fully calcified, smooth, slightly convex, often with elongate tubular protuberances (up to 0.65 mm long, 0.12–0.45 mm in diameter). Occasionally basal protuberances strongly elongate (up to 1.55 mm long), with multiply divaricated, terminal “rootlets”. Boundaries between zooids indicated by sinuous sutures.

Ancestrula and early astogeny not observed.

Remarks. Rhamphostomella curvirostrata clearly differs from congeners in the large suboral avicularium with curved or straight rostrum overhanging the proximal half of the orifice. Osburn (1952, p. 430) mentioned that “occasionally the avicularium is wanting and two lateral lappets extend towards each other across the aperture”.

A specimen from the South Kuril Islands (ZIRAS 4/50547), while similar in zooid morphology and size to the other colonies studied, differs in having a finely granulated surface of the frontal shield and avicularian cystid, and smaller and more rounded areolae with relatively short interareolar ridges. In this specimen, the avicularian rostrum is normally straight, differing from the more or less curved shape in other colonies examined. The proximal margin of the ooecium is also straight, with a slightly raised edge. The overgrowth and subsequent immersion of ooecia by secondary calcification are less prominent in this specimen. The proximal margin of the primary orifice is bisinuate, with a lyrula having the tips directed distolaterally or laterally. In contrast, they are directed proximally in a colony from the Commander Islands (ZIRAS 1/50115). These various differences may indicate either considerable phenotypic variability or a sibling species. More specimens need to be studied to determine which is the case.

The Canadian Museum of Nature contains a dried specimen of R. curvirostrata from British Columbia (Cat. No. – CMNI 1988-0131). Unfortunately, there are no images, and the specimen is not mentioned as a type in the On-line Collection Data of the Museum. Accordingly, we selected a lectotype from C.H. O’Donoghue Collection deposited in the Natural History Museum, London. This colony likely came from the waters around Vancouver Island, British Columbia.

Ecology. Rhamphostomella curvirostrata occurs predominantly on rocky bottoms at 10–566 m depth. Colonies encrust pebbles, polychaete tubes, shells of gastropod and bivalve molluscs and sponges.

Distribution. This is a Pacific boreal, sublittoral to upper bathyal species, widely distributed across the North Pacific Rim. In the western Pacific, it has been recorded from the Commander Islands in the Bering Sea (Grischenko 1997, 2002; our data); along the shelf and slope of the Kuril Islands, Sea of Okhotsk (Lukin 1979; Gontar 1979, 1980, 1993b; our data); Sea of Japan, including the western shore of southern Sakhalin Island (Androsova 1958; Kluge et al. 1959) and Moneron Island (Kluge 1961); along the Pacific side of northern Honshu Island, Japan (Sakagami et al. 1980). In the eastern Pacific it has been documented from the coastal waters of Adak Island, Andreanof Islands, Aleutian Islands (our data), and the Gulf of Alaska near Kodiak Island (our data), and Northumberland Channel, Vancouver Island, British Columbia (O’Donoghue & O’Donoghue 1923), and southwards to southern California (Osburn 1952).

Hayami (1973, 1975) reported R. curvirostrata from Neogene deposits in northern Japan.