Eurystomella foraminigera, (Hincks, 1883)

Gordon, Dennis P., Mawatari, Shunsuke F. & Kajihara, Hiroshi, 2002, New taxa of Japanese and New Zealand Eurystomellidae (Phylum Bryozoa) and their phylogenetic relationships, Zoological Journal of the Linnean Society 136 (2), pp. 199-216 : 201-203

EURYSTOMELLA FORAMINIGERA ( HINCKS, 1883)

( FIG. 1A, B )

Lepralia foraminigera Hincks, 1883: 200 , pl. 7, fig. 1; not Waters 1887: 62; Hincks 1893: 180; Hamilton 1898: 195, 198; Waters 1925: 542, pl. 28, fig. 12.

Eurystomella foraminigera: Levinsen 1909: 36 , 41, 314, pl. 18, fig. 14a-c; Canu & Bassler 1923: 141, fig. 26D-F; Brown 1952: 286 (part), fig. 215 (not fig. 216); Macken 1958: 105; Powell 1967: 310 (part), not fig. 66a-b; Gordon 1967: 59, fig. 33; Gordon 1970: 315; Whitten 1979: 159, pl. 7, fig. 12; Cook & Chimonides 1981: 113, fig. 5E, F; Gordon 1984: 65 (part), not pl. 21F; 1989: 17 (part), not pl. 4 A-C; Stevens et al. 1996: 324, pl. 4C.

Material examined

Colonies from Goat Island Bay , Leigh ; Auckland Harbour ; Greta Point, Wellington Harbour, New Zealand (unregistered, all DPG Collection); NZOI Stns Z 9669, Z9670, Z9677, Z9684, Z9685, Z9687, Z9700, Z9701, Z9710 .

Description

Colony encrusting, multiserial, unilaminar, circular on clean substrata, attaining c. 38 mm diameter. Self-overgrowth not usual, but possible from loci of damaged zooids through reparative budding, or on small pebbles where lateral expansion is restricted. Colony pink in newly forming zooids to red in fully formed and ephebic zooids, the pigment residing in epithelial tissues in foramina, under the operculum, and in the cells of the pharynx and oesophagus, thus imparting colour to the introvert, whereas the tentacles are colourless. Polypide with 14–17 tentacles. Autozooids contiguous, quincuncially arranged, 0.39–0.68 mm long (0.51 ± 0.08 mm), 0.22–0.47 mm wide (0.37 ± 0.07 mm). Gymnocystal frontal shield scarcely elevated, perforated by 3–7, rarely only 2, large oval to circular foramina; these with inwardly sloping sides, inner diameters of each foramen smaller than outer diameters; foramina covered in life with an epitheca. Orifice having a somewhat hatshaped outline, the anter high-arched and rounded with the proximal corners somewhat condyle-like; poster wider than anter, the proximal rim nearly straight though tending to sinuous, extended at the corners where there are lateral indentations. No peristome, umbones, spines, or avicularia. Maternal zooids with internal brooding of embryos, the distal zooidal wall strongly convex, overarched by a distal kenozooidal chamber whose extensive frontal wall resembles an ovicell; this perforated by a relatively large circular foramen with inwardly sloping walls, the foramen covered in life with an epitheca. Maternal orifice slightly broader (0.24–0.26 mm wide at the proximal margin) than that of autozooids (0.15–0.22 mm). Zooids communicating by 1–2 distal and 2–3 basolateral pore-chambers. Ancestrula subcircular with entire frontal area membranous, 0.40–0.42 ¥ 0.32–0.38 mm, larger than immediate daughter zooids; no spines; operculum with narrow subperipheral sclerite; ancestrular polypide with 13–15 tentacles. First daughter zooid budded mid-distally.

Remarks

As originally described, autozooids of E. foraminigera sensu stricto have several frontal foramina — Hincks (1883) illustrated 3–5. Very rarely, zooids may have only two, especially if they are constrained in their growth. At least one other New Zealand species ( E. biperforata sp.nov.) has been consistently confused with E. foraminigera . Its zooids have only a pair of oval to circular foramina (rarely one) (see Brown, 1952; Powell, 1967; Gordon, 1984, 1989). A rarer, second new biperforate species ( E. aupouria sp. nov.) has narrowly crescentic foramina. These three species also share a feature first noted, and illustrated, by Brown (1952), namely a median triradiate suture in the proximal rim of the orifice. His observations are germane to the phylogenetic relationships of eurystomellids: “the proximal lip of the orifice closely resembles the ‘apertural bar’ of Figularia ... for it appears to be formed by the coalescence of a pair of lateral, spiny processes, and, as in that genus, often shows a tiny median notch where the primitive spines have joined”. Scanning electron microscopy has allowed close examination of this feature, lending strong support for Brown’s interpretation. Gordon (1989), for example, interpreted the triradiate suture as indicating the boundaries between contiguous vestigial costae, noting similar features in the orificial rims of some catenicellids.

Ryland (1975) gave parameters of the lophophore in E. foraminigera from Goat Island Bay, Leigh, on the north-east coast of North Island (36°16¢S, specimens collected November 1971). The number of tentacles varied from 14 to 16 (mean 15.17). Mean tentacle length was 0.504 mm ( SD 0.053 mm) and mean funnel diameter 0.530 mm ( SD 0.028 mm). These figures accord with specimens freshly collected (February 2001) from Greta Point, Wellington (41°18¢S) which have the same range in tentacle number. Tentacle length and lophophore diameter can attain 0.566 mm and introvert length (measured from the plane of the orifice to the base of the lophophore) 0.415 mm. Faecal pellets measure 0.134 ¥ 0.068 mm, are circular in cross section, and rounded at each end.

Distribution

Eurystomella foraminigera is endemic to New Zealand. Its exact geographical and depth distributions are uncertain owing to previous confusion of this species with E. biperforata . It certainly occurs from Spirits Bay at the far north of North Island, along the north-east coast of Northland, and from Wellington Harbour, at depths of 0– 76 m. Whitten (1979) reported living colonies from the intertidal to 21 m depth, and transported colonies to 82 m depth in the vicinity of the outer Hauraki Gulf. Eurystomella foraminigera is among the more commonly encountered bryozoans of the middle to lower shore around New Zealand, encrusting shells, plastic, broken glass, brown algal holdfasts ( Carpophyllum maschalocarpum (Turner) Grev. , Ecklonia radiata (C.Agardh) J.Agardh , and the undersides of boulders ( Gordon, 1967; Stevens et al., 1996). The reddish coloration of the colonies makes them conspicuous.

Figures

Figure 1. A, B, Eurystomella foraminigera. Greta Point, Wellington, intertidal. A, group of zooids, ¥65. B, suboral rim, showing triradiate suture, ¥803. C-E, Eurystomella biperforata sp. nov. C,E, NZOI Stn Z9700. C, group of autozooids, ¥53. D, NZOI Stn Z9677, maternal zooid with distal foraminate kenozooid, ¥95. E, rare zooid with a single foramen, ¥163. F, Eurystomella aupouria sp. nov. NZOI Stn Z9716, ¥63.