Crepidacantha poissonii ( Audouin, 1826 )

Dick, Matthew H. & Grischenko, Andrei V., 2016, Rocky-intertidal cheilostome bryozoans from the vicinity of the Sesoko Biological Station, west-central Okinawa, Japan, Journal of Natural History 51 (3 - 4), pp. 141-266 : 233-240

Crepidacantha poissonii ( Audouin, 1826)

( Figure 32 (c, d))

Flustra poissonii Audouin, 1826, p. 240 , pl. 10, figs 5 1 and 5 2.

Crepidacantha poissonii: Harmer 1957, p. 981 (part). Brown 1954, p. 260, fig. 1(a, b). Liu et al. 2001, p. 674, pl. 71, figs 1–3. Tilbrook 2006, p. 274, pl. 61A–D.

Crepidacantha carsioseta: Tilbrook et al. 2001, p. 92 , fig. 16(a); Dick et al. 2006, p. 2239, fig. 13(f).

Not Crepidacantha carsioseta: Ryland and Hayward 1992, p. 277 , fig. 25(d); [= C. craticula Tilbrook, 2006 ].

Material examined

NSMT-Te 1100 ( MIN- 13), bleached, on SEM stub (with Parasmittina serrula ).

Measurements

AzL, 0.43–0.54 (0.483 ± 0.030); AzW, 0.32–0.43 (0.373 ± 0.036) (n = 15, 1). OrL, 0.09–0.12 (0.108 ± 0.007); OrW, 0.08–0.10 (0.090 ± 0.005) (n = 15, 1). OvL, 0.15–0.22 (0.171 ± 0.019); OvW, 0.16–0.20 (0.178 ± 0.011) (n = 13, 1). One colony observed, 8 × 6 mm.

Description

Colony forming a unilaminar, encrusting sheet. Zooids ( Figure 32 (c)) distinct, delineated by a sharp incision. Frontal wall convex, tumid but flattened on top, without pseudopores, minutely granulated; tiny, circular or slit-shaped marginal areolae present but rarely evident with light microscopy and scarcely with SEM. Orifice subterminal, with subcircular anter separated from equally broad poster by conspicuous, low, broadly rounded condyles; poster comprises two distinct lobes separated by a broad, distally flat labium. Operculum with granular surface. Orifice not immersed; proximal mucro lacking. Zooids have 11–15 (mode, 13) long, thin, straight spines around lateral and distal margins, each spine tilted against frontal wall of adjacent zooid. Frontal avicularia paired, proximolateral to orifice, both at same level along transverse line, or slightly offset; directed medially or angled slightly proximally or distally; rostrum on raised chamber, shorter than orifice length; narrow, long-triangular, tapering, with end forming trough; crossbar lacking; mandible ( Figure 32 (c)) long, setiform but not extending past opposite lateral margin of zooid. Ovicell ( Figure 32 (d)) terminal, nearly circular in outline, closed by operculum. Ooecium with smooth ectooecium; flattened on top, with broad, indistinct median ridge evident in cleaned specimens; narrow crescentic foramen of noncalcified ectooecium around frontodistal periphery exposing around 10 pseudopores in a single row. Ancestrula not observed.

Remarks

This species is characterised by the markedly trifoliate orifice; the paired avicularia situated proximolateral to the orifice and directed medially; lack of a suboral umbo; and the nearly circular ooecium with a long, narrow crescent of pseudopores towards the distal end; the ovicell is flattened proximal to the fenestra and bears a median ridge. Tilbrook (2006) indicated the presence of a median pointed projection on the distal rim of the orifice, but this is not present in our specimen. Material from Hawaii reported as C. carsioseta ( Dick et al. 2006) is actually C. poissonii ; the Hawaiian material has the distinctly trifoliate orifice characteristic of C. poissonii , lacks the suboral umbo characteristic of C. carsioseta , and shows a projection on the distal orificial rim in the form of a small, blunt transverse mucro. Crepidacantha carsioseta appears to have fewer marginal spines than C. poissonii . Winston and Heimberg (1986) reported 10 spines for the former, and although Tilbrook (2006) did not mention spine number in designating a neotype for C. poissonii from the Red Sea, our specimen from Okinawa has 11–15 spines, and Hawaiian material has around 12 spines.

Occurrence

We found a single colony at the MIN site. This is an Indo-West Pacific species known from the Red Sea, South China Sea, Vanuatu, the Solomon Islands ( Tilbrook 2006) and Hawaii ( Dick et al. 2006). While Hirose (2010) reported it from Sagami Bay, Japan, that material might instead represent Crepidacantha craticula Tilbrook, 2006 , as the convex proximal border (labium) of the orifice seems to be lower and more rounded than in C. poissonii .

Superfamily CELLEPOROIDEA Johnston, 1838 Family TORQUATELLIDAE Tilbrook, 2006

Genus Torquatella Tilbrook, Hayward, and Gordon, 2001

Torquatella duolamellata (Scholz, 1991)

( Figure 33 (a, b))

Osthimosia duolamellata Scholz, 1991, p. 302 , pl. 11, figs 1–6.

Torquatella duolamellata: Tilbrook et al. 2001, p. 79 , fig. 11(a, b). Tilbrook 2006, p. 286, pl. 43A, B.

Material examined

NSMT-Te 1172 ( SES- 30), bleached, on SEM stub; NSMT-Te 1173, dried specimen, SES site; NHMUK 2016.5.13.72, dried specimen, SES site (with Calyptotheca reniformis ).

Measurements

AzL, 0.28–0.39 (0.324 ± 0.035); AzW, 0.22–0.32 (0.267 ± 0.025) (n = 15, 1). OrL, 0.096 – 0.099 (0.098); OrW, 0.95–0.100 (0.098) (n = 2, 1). OvL, 0.11–0.15 (0.140 ± 0.016); OvW, 0.21–0.25 (0.238 ± 0.020) (n = 5, 1). Ancestrula L, 0.271; ancestrula W, 0.166 (n = 1). Ancestrula OrL, 0.066; ancestrula OrW, 0.083 (n = 1). Largest of three colonies 4 × 3 mm.

Description

Colony ( Figure 33 (a)) forming a unilaminar, encrusting sheet. Zooidal boundaries indistinct ( Figure 33 (b)); zooids delineated by large marginal openings in layer of secondary calcification. Cylindrical, somewhat flared peristome occupies about half of frontal zooidal area; secondary orifice transversely oval. Primary orifice ( Figure 33 (b)) as broad as long; anter semicircular, separated from deep, broadly U-shaped poster by pair of small, rounded condyles. Except for ancestrula, zooids lack spines. Small avicularium proximal to orifice, situated deep in peristome, difficult to observe except in some marginal zooids; raised rostral end forms blunt knob; directed frontolaterally. Ovicell ( Figure 33 (b)) hyperstomial. Ooecium with a transversely oval or elliptical foramen on top, exposing entooecium in cleaned specimens; peristome usually extends around proximofrontal surface. Ancestrula (left centre in Figure 33 (a)) produces a triplet of daughter zooids distally and distolaterally.

Remarks

Scholz (1991) and Tilbrook et al. (2001) have described and discussed this species in detail. The morphology of the ancestrula is not clear in the specimen we illustrate, but the other accounts report it to be schizoporelloid, with a D-shaped orifice flanked by three pairs of spines. Although frontal budding can occur, our small colony comprised only a single layer. Our specimen is heavily secondarily calcified; previous descriptions of less heavily calcified specimens indicate the primary frontal wall to have small marginal areolae and a few scattered frontal pseudopores.

Occurrence

We found three small colonies at the SES site. This is a subtropical to tropical, western Pacific species. Scholz (1991) found it to be fairly common on the east-central coast of Cebu Island, Philippines, and it has been reported from Vanuatu ( Tilbrook et al. 2001) and the Solomon Islands ( Tilbrook 2006).

Family PHIDOLOPORIDAE Gabb and Horn, 1862

Genus Metacleidochasma Soule, Soule, and Chaney, 1991

Metacleidochasma planulata ( Canu and Bassler, 1929)

( Figure 33 (c–f))

Hippoporina planulata Canu and Bassler, 1929, p. 321 , pl. 37, fig. 6.

Metacleidochasma planulata: Tilbrook et al. 2001, p. 97 , fig. 21(c–e).

Metacleidochasma ovale Soule, Soule, and Chaney 1991, p. 480 , pl. 1, fig. 7, pl. 4, figs 1 and 2.

Material examined

NSMT-Te 1174 ( MIN- 11), bleached, on SEM stub; NSMT-Te 1175 ( SES- 24), bleached, on SEM stub; NSMT-Te 1176 ( SES- 9), bleached, on SEM stub; NSMT-Te 1177, SES site, dried colony.

Measurements

AzL, 0.31–0.40 (0.353 ± 0.023); AzW, 0.25–0.38 (0.295 ± 0.036) (n = 15, 1). OrL, 0.11–0.13 (0.122 ± 0.007); OrW, 0.08–0.09 (0.087 ± 0.004) (n = 15, 1). Largest colony observed 5 mm in diameter.

Description

Colony forming a unilaminar, encrusting sheet; cream coloured. Zooids small, boundaries often indistinct ( Figure 33 (c, d)). Frontal wall slightly convex, smooth, with only two pseudopores ( Figure 33 (d)), one inset from margin on each side at approximately widest part of zooid. Orifice ( Figure 33 (e)) conspicuously keyhole shaped; broader, circular anter separated from narrower, proximally rounded poster by blunt, proximomedially directed condyles; distal margin of orifice beaded below smooth surface rim. Frontal wall lateral to orifice on each side is raised as a thick, low umbo. Marginal zooids bear two or three small, ephemeral spines. Ovicell endozooidal, sometimes evident as a swelling (arrowheads, Figure 33 (c, d)) in frontal wall of distal zooid; totally covered by smooth secondary calcification, except for small, curved membranous window near proximal edge. Ancestrula ( Figure 33 (f)) tatiform, with spines, though these are often obscured by surrounding zooids.

Remarks

Tilbrook et al. (2001) considered M. ovale , originally described from Hawaii ( Soule et al. 1991), to be a junior synonym of M. planulata ( Canu and Bassler 1929) , originally described from the Philippines. We have accepted this synonymy but note that it needs confirmation, as the characters of the ovicell are not clear in the original description and illustration of Philippine M. planulata . Marginal zooids in our specimens have only two or three oral spines, compared to four in Hawaiian material ( Soule et al. 1991) and usually four (range, three to five) in specimens from Vanuatu ( Tilbrook et al. 2001). Frontal avicularia occur rarely in Hawaiian populations, but were not reported at Vanuatu or observed in our study.

Occurrence

We found six colonies, at the SES and MIN sites. This species is broadly distributed in the Indo-West Pacific, with previous records from the Philippines ( Canu and Bassler 1929); Hawaii (Maui and Kauai islands), Bora Bora, Tonga, Thailand and the Maldives ( Soule et al. 1991); and Vanuatu ( Tilbrook et al. 2001).

Genus Rhynchozoon Hincks, 1895

Rhynchozoon ferocula Hayward, 1988

( Figure 34)

Rhynchozoon ferocula Hayward, 1988, p. 332 , pl. 13a–c.

Rhynchozoon ferocula: Tilbrook et al. 2001, p. 100 , fig. 22(c–e). Tilbrook 2006, p. 297, fig. 65(e, f). Dick et al. 2006, p. 2242, fig. 14(d–f).

Rhynchozoon globosum: Scholz 1991, p. 320 , pl. 17, figs 4 and 6.

Material examined

NSMT-Te 1178 (REEF-6), two colonies, bleached, on SEM stub; NSMT-Te 1179 ( SES- 50), bleached, on SEM stub; NSMT-Te 1180 ( SES- 17), ancestrula, bleached, on SEM stub; NSMT-Te 1181, three dried specimens, SES site.

Measurements

AzL, 0.27–0.42 (0.355 ± 0.038); AzW, 0.24–0.31 (0.273 ± 0.019) (n = 15, 1). OrL, 0.09–0.11 (0.101 ± 0.007); OrW, 0.08–0.10 (0.089 ± 0.004) (n = 10, 1). OvL, 0.13–0.18 (0.150 ± 0.017); OvW, 0.13–0.20 (0.166 ± 0.020) (n = 11, 1). Largest colony observed 4 × 2 mm.

Description

Colony ( Figure 34 (a)) small, forming a unilaminar, encrusting sheet; white in colour. Zooids distinct at colony margin ( Figure 34 (b)), delineated by a fine incision, but boundaries increasingly indistinct towards centre of colony. Zooids typically with one to three (up to six) conspicuous circular areolae ( Figure 34 (c)) along each lateral margin. Frontal wall convex, smooth, without pseudopores; with two to five coarse, blunt or sharp, umbonate processes around raised, thickened rim proximal to orifice ( Figure 34 (b)). With age, frontal wall becomes thickened by secondary calcification ( Figure 34 (e)) and primary orifice becomes immersed in sunken peristome. Primary orifice ( Figure 34 (d)) slightly longer (including sinus) than broad; anter nearly circular, or broader than long; sinus deep, U-shaped, flanked but not constricted by pair of raised, triangular processes, which are in turn flanked by blunt condyles. Periphery of anter is beaded with 14 to 19 rounded denticles. Marginal zooids have two to four (usually four) low, blunt oral spines ( Figure 34 (b)); these remain but are obscured within the peristome in older zooids ( Figure 34 (c–e)). Suboral avicularia lacking. Frontal avicularia uncommon; some zooids have one or two located close to zooidal margin ( Figure 34 (b)); mandible short-triangular, pointing laterally, proximolaterally or proximally; crossbar complete. Ovicell ( Figure 34 (e)) initially subimmersed, eventually becoming endozooidal. Ooecium broader than long, covered by layer of secondary calcification originating from adjacent zooids and often bearing one or two coarse umbonate processes on top. Proximal face of ooecium with small, subcircular to transversely elliptical zone of membranous (non-calcified) ectooecium that, in cleaned specimens, becomes a window ( Figure 34 (e), arrowhead) exposing the entooecium; labellum (band of calcified ectooecium along proximal margin of ovicell ( Figure 34 (e), arrow) wide, complete. Colony precocious, with fully developed ovicells starting in second daughter-zooid generation from ancestrula. Ancestrula ( Figure 34 (f)) oval in outline; initially giving rise to triplet of zooids distally and distolaterally. Ancestrular orifice with straight proximal margin lacking a sinus; surrounded by eight spines.

Remarks

Rhynchozoon ferocula was originally described from Mauritius ( Hayward 1988). Our specimens differ from that population in the following characters. The orificial sinus in our material is deeper, broader and more U-shaped, with the opening not constricted by medially curved projections. We observed no zooids to have a lateralsuboral avicularium, whereas this is variably present among zooids in Mauritian R. ferocula . The proximal peristomial rim usually bears several prominent projections, whereas Mauritian zooids generally have few. Finally, frontal avicularia are rare in our specimens and have a short-triangular mandible, whereas Mauritian material bears numerous avicularia with a long-triangular mandible, clustered around the zooidal secondary orifices.

There are several Pacific records for Rhynchozoon ferocula . Among these, Hawaiian specimens ( Dick et al. 2006) are virtually indistinguishable from the Okinawa specimens we describe here. Zooids in R. ferocula reported from Vanuatu ( Tilbrook et al. 2001) show several characters more like those in Mauritian material, including a shallow orificial sinus flanked by medially curved processes, and avicularia having a long-triangular mandible commonly present; however, suboral avicularia appear to be entirely lacking. Specimens of R. ferocula from the Solomon Islands ( Tilbrook 2006) likewise share many characters with Mauritian material: zooids often have more than one frontal avicularium each; the mandible is long-triangular; the orificial sinus is dropshaped, flanked by medially curved projections; and a suboral avicularium is variably present.

Based on the differences mentioned above, the Hawaiian and Okinawan populations might be considered a distinct species from the Mauritian and other Pacific specimens . However , examination of SEM images of nominal R . ferocula from Sagafa Bay, Red Sea ( Andrew Ostrovsky , unpublished data); argued against this, as one Red Sea specimen shows intracolony variation in the shape of the primary orifice and sinus, with some zooids having a shallow, drop-shaped sinus bordered by medially curved processes, and others a deeper, U-shaped sinus not constricted at the opening, as is characteristic at Hawaii and Okinawa . In addition, the ancestrula is indistinguishable between the Okinawa and Solomon populations, although mature zooids in the latter population are more similar to those in the Mauritian than in the Okinawan population .

Occurrence

We found seven colonies, at the SES and REEF sites. This species is broadly distributed in nearshore habitats in the subtropical to tropical Indo-West Pacific, with previous records from Mauritius, the Red Sea, Vanuatu, the Solomons, the Philippines and Hawaii.