Rhamphostomella bilaminata

Rhamphostomella bilaminata (Hincks, 1877)

(Figs 12, 32F, G)

? Cellepora plicata: Smitt 1868a, p. 30, 31 (part), pl. 28, fig. 191.

Cellepora bilaminata Hincks, 1877, p. 111, pl. 11, figs 6, 7.

Rhamphostomella bilaminata: Lorenz 1886, p. 13, pl. 7, fig. 10 (mentioned as fig. 11 in the text); Nordgaard 1906, p. 33, 41, pl. 4, fig. 57; Kluge 1962, p. 545, fig. 382; 1975, p. 663, fig. 382; Osburn 1912a, p. 244, pl. 26, fig. 61; 1952, p. 427, pl. 52, fig. 10; Gostilovskaya 1978, p. 231, fig. 147; Winston & Hayward 2012, p. 120, fig. 76.

Discopora bilaminata: Nordgaard 1918, p. 79.

Rhamphostomella porosa: O’Donoghue & O’Donoghue 1923, p. 45, pl. 4, fig. 35.

Additional references. Rhamphostomella bilaminata: Kluge 1908a, p. 533; 1928, p. 257; 1964, p. 190; Osburn 1936, p. 542; 1955, p. 38; MacGinitie 1955, p. 130; Gostilovskaya 1957, p. 454; 1968, p. 70; Hansen 1962, p. 39; Powell 1968a, p. 2311; 1968b, p. 257; Denisenko 1988, p. 13; 1990, p. 39; 2008, p. 187; 2011, p. 14; 2013, p. 184; Gontar 1989, p. 113; 1990, p. 133; 2010, p. 153; Gontar & Denisenko 1989, p. 359; Gontar et al. 2001, p. 194; Grishankov 1995, p. 48; Grischenko et al. 1999, p. 112; Grischenko 2001, p. 46; 2002, p. 115; 2014, p. 19; Shunatova & Ostrovsky 2001, p. 115, 118; Kuklinski 2002a, p. 181; 2002b, p. 203; 2009, p. 228; Shunatova & Nielsen 2002, p. 263, figs. 5a, c; Denisenko & Kuklinski 2008, p. 48; Ostrovsky 2009, p. 26; 2013, p. 8; Foster 2010, p. 57.

Material examined. Neotype: NHMUK 1911.10.1.1580A, one colony, A.M. Norman Collection, Gaspe, Gulf of St Lawrence, Atlantic Ocean, collector J. Whiteaves.

NHMW 92533 (=1884.II.49), one colony, L. Lorenz Collection, II Austro-Hungarian Polar Expedition, 1882– 1883, Jan Mayen, depth 20–130 m, collector F. Fischer. NHMW 72989, one colony fragment, L. Lorenz Collection, II Austro-Hungarian Polar Expedition, 1882–1883, Jan Mayen, depth 20–130 m, collector F. Fischer. NHMUK 1911.10.1.1579A, five colony fragments encrusting hydroids, A.M. Norman Collection, Gaspe, Gulf of St Lawrence, Atlantic Ocean, collector J. Whiteaves. ZIRAS 23 /50121, three colony fragments, detached from broken shells of bivalve mollusc Chlamys sp., MFRT Rodino, 12 September 1992, about 32 km from Cape Hayryuzova, western Kamchatka shelf, Sea of Okhotsk, 57°36.2ʹ N, 156°09.0ʹ E, depth 78–81 m, crab trap, collector A. V. Grischenko. ZIRAS 24 /50122, one colony encrusting branch of bryozoan colony Dendrobeania sp., KIENM Collection, RV Nazarovsk, Stn 182, 11 May 1988, Avacha Gulf, eastern Kamchatka Peninsula, Pacific Ocean, 53°36.0ʹ N, 160°07.0ʹ E, depth 100 m, rock dredge, collector A. V. Rzhavsky. ZIRAS 32 /50549, nineteen colonies encrusting a colony of the ctenostome bryozoan Flustrellidra filispina, 15 July 2003, Nakanoze Bank, Akkeshi Bay, Pacific coastal waters of Hokkaido Island, 43°00.4ʹ N, 144°46.6ʹ E, depth 4–6 m, rock dredge, collector A. V. Grischenko.

Additional material. Four specimens. PIBOC Collection (1991) Stn 19; IMB Collection (2011) Stns 3/1, 63/53, 64/54 (see Appendix 1 for details).

Measurements. NHMUK 1911.10.1.1579A, Gulf of St Lawrence, Atlantic Ocean (Fig. 12B–D, G–I). ZL, 0.47–0.75 (0.59 ± 0.07). ZW, 0.32–0.53 (0.43 ± 0.05). ZD, 0.43–0.49 (n = 2). OrL, 0.17–0.25 (0.22 ± 0.02). OrW, 0.20–0.30 (0.25 ± 0.02). OeL, 0.22–0.32 (0.27 ± 0.03). OeW, 0.27–0.43 (0.34 ± 0.03). Av(s)L, 0.12–0.20 (0.15 ± 0.02). P(m)N, 4–8 (6). P(oe)N, 5–11 (7).

ZIRAS 23/50121, western Kamchatka, Sea of Okhotsk (Fig. 12A, E, F). ZL, 0.50–0.93 (0.69 ± 0.10). ZW, 0.32–0.57 (0.45 ± 0.08). ZD, 0.40–0.48 (n = 2). OrL, 0.17–0.30 (0.25 ± 0.04). OrW, 0.20–0.31 (0.25 ± 0.04). OeL, 0.19–0.32 (0.27 ± 0.03). OeW, 0.30–0.45 (0.36 ± 0.04). Av(s)L, 0.11–0.27 (0.19 ± 0.04). P(m)N, 7–13 (9). P(oe)N, 12–23 (18) (n = 10).

ZIRAS 24/50122, Avacha Gulf, eastern Kamchatka, Pacific Ocean (Fig. 12 J–L). ZL, 0.47–0.68 (0.55 ± 0.05). ZW, 0.35–0.50 (0.42 ± 0.04). ZD, 0.48–0.53 (n = 2). OrL, 0.18–0.28 (0.22 ± 0.02). OrW, 0.18–0.25 (0.22 ± 0.02). OeL, 0.20–0.28 (0.24 ± 0.02). OeW, 0.27–0.38 (0.32 ± 0.03). Av(s)L, 0.13–0.24 (0.19 ± 0.03). P(m)N, 4–9 (6). P(oe)N, 7–13 (9).

Description. Colonies encrusting, multiserial, unilaminar (Fig. 12A), more or less circular in outline, small, attaining 16 mm in maximal dimension; bright brown to orange when alive, light brown to pink when dry. Freegrowing bilaminate folds can be present in some colonies. Zooids small, rectangular to hexagonal (Fig. 12A, D, H) or irregular in form, arranged in checkered pattern, demarcated by irregular sutures between lateral and transverse walls; boundaries indistinct at all parts of colony.

Frontal shield (Fig. 12A, D–F, I), thin, moderately to strongly convex, smooth, with deep areolae along strongly raised zooidal margins that occasionally expand above proximal half of frontal shield to form additional layer of calcification (Fig. 12D). Areolae separated by short, thin or thick interareolar ridges arranged radially and connected to lobe of peristomal lappet on one side and to avicularian cystid on the other (Fig. 12E–H). Umbonuloid component small, occupying about 35% of length of frontal shield, with fine parallel lineation and accretionary banding (Fig. 12I, L). Ring scar discrete, forming clear boundary between umbonuloid exterior wall and extra-umbonuloid interior wall microstructure (Fig. 12L).

Primary orifice submerged, circular; distal and lateral margins formed by upper terminal part of distal transverse wall (Fig.12A). Distal margin of orifice rounded, proximal margin bisinuate, with small trapezoidal or bifurcate lyrula in midline, lateral margins normally with short processes, blunt or pointed (Fig. 12B, C, I, K, L). Condyles absent. No oral spines.

Secondary orifice (Fig. 12D, G) rounded to asymmetrically oval or irregular, cormidial, distally and distolaterally restricted by strongly elevated vertical walls of distal and lateral zooids (Fig. 12D); laterally and proximally, formed by thin-walled and strongly elevated peristome, comprising two triangular or rounded flared lappets formed from frontal shield (one incorporating cystid of suboral avicularium and substituted by latter almost completely) with deep V- to U-shaped median pseudosinus between them (Fig. 12D–H). Peristomial lappets not fusing with proximolateral corners of ooecium in ovicellate zooids.

Cystid of suboral avicularium (Fig. 12A–H) not large but very distinct, elevated, situated asymmetrically with respect to zooidal orifice and associated with left or right peristomial lappet; surface smooth; one communication pore connecting avicularian and hypostegal coeloms. Frontal surface (rostral/postmandibular areas) of avicularium weakly concave, normally to one side of zooidal midline but sometimes crossing it, facing proximally to proximolaterally (Fig. 12C, F–H). Rostrum elongate oval, directed distolaterally, obliquely to vertically upwards, fusing with peristomial lappet distally. Shape of palate lingulate, palatal foramen elongate oval, with narrow cryptocystal shelf laterally, opesia semicircular. Crossbar complete. Avicularia lacking in some zooids, with paired peristomial lappets forming flared tubular peristome in this instance (Fig. 12D).

No adventitious avicularia.

Ovicells hyperstomial, cleithral (Fig. 12F–H). Ooecium formed by distal autozooid; ooecial fold forming at distal margin of primary orifice concurrently with formation of frontal shield of distal zooid (Fig. 12A). Ooecial and visceral coelomic cavities connected via communication canal opening on underside of frontal shield as small curved slit-like pore at some distance from transverse wall (Fig. 12I). Ectooecium smooth, with straight or slightly concave proximal margin and scattered circular to elongate pseudopores. Basal part of ooecium slightly overgrown by thin secondary calcification proceeding from frontal shields of neighbouring zooids (Fig. 12G, H); this calcification additionally forming thin vertical walls between distal margin of peristomial lappets and proximal corners of ooecia (Fig. 12G, H), adding to secondary orifice.

Zooids interconnected by one mural pore chamber in each distolateral wall (Fig. 12L) and two multiporous septula in basal half of transverse walls.

Basal walls of zooids fully calcified, smooth, inflated to moderately convex. Sparse white spots (presumably less-calcified areas) visible in semitransparent basal wall by light microscopy. Tubular protuberances of basal wall (0.06–0.19 mm in diameter) complex in shape, depending on substratum; textured by fine parallel lineation (Fig. 12J). Boundaries between zooids recognizable basally as slightly sinuous incisions.

Ancestrula and early astogeny not observed.

Remarks. Although Hincks (1877) described and illustrated R. bilaminata (as Cellepora) as distinct species, which was further confirmed by Lorenz (1886), it is still possible that it was first illustrated by Smitt (1868a) in his fig. 191 (pl. 28) under the name Cellepora plicata. Because we were unable to locate Hincks’ (1877) specimen, we have selected as a neotype for this species a specimen from the Gulf of St Lawrence, North Atlantic, collected by J. Whiteaves and deposited in the Natural History Museum, London.

O’Donoghue & O’Donoghue (1923) described a new species, Rhamphostomella porosa, from British Columbia. Osburn (1952, p. 427) synonymised R. porosa with R. bilaminata, arguing for the latter that “It has not been reported south of Alaska, except for O’Donoghue’s record of R. porosa at Cape Ebenshaw, British Columbia. O’Donoghue recognized the similarity to bilaminata, but the distinguishing characters he indicates for porosa (viz., “the far larger size of the rostrum and peristome”) are within the range of variation of bilaminata ”.

While most of the colonies examined were flat and encrusting, some from the shelf and slope of the southern Kuril Islands encircled hydroid stems, forming free-growing bilaminate folds and frills.

Ecology. Rhamphostomella bilaminata is known from 4–435 m depth, generally on mixed bottoms, including silt, sand, gravel and mollusc shells, encrusting hydroid stems, ascidians, molluscs and other bryozoans (Alcyonidium sp., Flustrellidra filispina, Dendrobeania sp.). Several colonies were detected on carapaces of the red king crab Paralithodes camtshaticus, caught at 78–81 m in the western Kamchatka shelf, Sea of Okhotsk (Grischenko 2001).

Distribution. This is a boreal-Arctic, circumpolar, sublittoral to upper bathyal species. Arctic records include Barents Sea (Bidenkap 1900a; Andersson 1902; Kluge 1915, 1962, 1975; Nordgaard 1918, 1923; Kuznetsov 1941; Denisenko 1988, 1990), White Sea (Kluge 1908 a, 1928; Gostilovskaya 1957, 1978; Grishankov 1995; Shunatova & Ostrovsky 2001; Shunatova & Nielsen 2002; Ostrovsky 2009, 2013), Kara Sea (Nordgaard 1923; Kluge 1962, 1975), Laptev Sea (Kluge 1962, 1975; Gontar 1990), East Siberian Sea (Denisenko 2011); Chukchi Sea (Osburn 1923; Kluge 1962, 1975; Denisenko 2008; Denisenko & Kuklinski 2008; Gontar 2010), Point Barrow, Alaska, Beaufort Sea (Osburn 1955; MacGinitie 1955), Canadian Arctic Archipelago (Nordgaard 1906, 1929; Osburn 1936), Baffin Bay (Hansen 1962), Davis Strait (Kluge 1962, 1975; Hansen 1962), Hudson Bay (Osburn 1932), Labrador (Hincks 1877), western Greenland (Levinsen 1914; Osburn 1936; Denisenko & Blicher 2021), eastern Greenland (Gontar & Denisenko 1989; Denisenko & Blicher 2021), Greenland Sea (Gontar & Denisenko 1989), Spitsbergen (Gontar et al. 2001; Kuklinski 2002a, 2002b, 2009), Jan Mayen Island (Lorenz 1886; Nordgaard 1907b), northern Norway (Nordgaard 1918), Finmark (Smitt 1868a). In the northeastern Atlantic it has been reported from St Lawrence Gulf (Whiteaves 1901) southwards to Cape Cod (Osburn 1912b; Powell 1968b; Winston & Hayward 2012). In the northwestern Pacific it has been documented in Bering Strait (Gontar & Denisenko 1989), Avacha Gulf (our data) and Avacha Inlet off eastern Kamchatka Peninsula (Gontar 1989; Grischenko 2002); in the Sea of Okhotsk from Koni Peninsula, Tauyskaya Inlet (Grischenko 2014), along western Kamchatka (Grischenko et al. 1999; Grischenko 2001; our data), around Iturup and Kunashir Islands, south Kuril Islands (our data); in Japan it is known from Akkeshi Bay, Hokkaido, Japan (our data). In the northeastern Pacific it occurs in Cook Inlet (Foster 2010) and near Kodiak Island, Gulf of Alaska (our data) south to British Columbia (O’Donoghue & O’Donoghue 1923).