Microporella trigonellata Suwa and Mawatari, 1998

Grischenko, Andrei V., Dick, Matthew H. & Mawatari, Shunsuke F., 2007, Diversity and taxonomy of intertidal Bryozoa (Cheilostomata) at Akkeshi Bay, Hokkaido, Japan, Journal of Natural History 41 (17 - 20), pp. 1047-1161 : 1134-1136

Microporella trigonellata Suwa and Mawatari, 1998

( Figure 35 )

Microporella trigonellata Suwa and Mawatari 1998, p 913 , Figure 7A–M .

Material examined

KAI, colony on rock (NHM 2006.2.27.41); BAC, ancestrular colony on bivalve shell (NHM 2006.2.27.52), two colonies on bivalve shell (NHM 2006.2.27.95), intact colony (NHM 2006.2.27.96). Additional material: 262 specimens .

Description

Colony encrusting, unilaminar, coherent, irregularly circular, up to 2.5 cm across, light beige when alive. Zooids ( Figure 35A, B ) hexagonal to oval, 0.48–0.75 mm long (0.62¡ 0.07 mm), 0.33–0.47 mm wide (0.39¡ 0.04 mm), delineated by a deep groove and fine suture. Frontal wall markedly convex when young, slightly convex with age, finely granulated, evenly perforated with small, round pores over entire surface, except for suboral area. Orifice ( Figure 35C ) semicircular, broader than long, 0.09–0.12 mm long (0.11¡ 0.01 mm), 0.12–0.15 mm wide (0.14¡ 0.01 mm), with straight proximal margin and rounded proximolateral corners; condyles lacking. Four (rarely, three) to six hollow oral spines ( Figure 35A–C ) located along curvature of orifice in immature zooids; most proximal pair, with enlarged, cylindrical bases, is retained close to proximolateral corners of ovicell in reproductive zooids. Ascopore ( Figure 35C ) separated from proximal border of orifice by a distance slightly greater than ascopore width; crescentic, with a crisply denticulate margin, raised on an oval or circular prominence; proximal to ascopore is a sharp, smooth, conical umbo. Avicularium ( Figure 35B, C ) single, located lateral or proximolateral to ascopore, the chamber with smooth surface; rostrum raised from frontal wall, directed distally or distolaterally, with a narrow channel at the tip; cross-bar complete; mandible elongate-triangular, acute, with setiform tip. Zooids occasionally have two avicularia, or lack them altogether. Ovicell ( Figure 35D, E ) hemispherical, prominent, broad, 0.20–0.27 mm long (0.24¡ 0.02 mm), 0.25–0.34 mm wide (0.30¡ 0.03 mm), finely granulated, often umbonate, radially ribbed, with pores of varying size around margin, some occluded; indented proximal margin with a smooth rim. Zooids interconnect by three distal and two distolateral basal pore chambers. Ancestrula ( Figure 35F ) tatiform, oval, 0.37 mm long, 0.28 mm wide, with large oval opesia 0.25 mm long, 0.16 mm wide, surrounded by nine spines. Ancestrula buds two daughter zooids distolaterally, each with five or six tubular oral spines.

Remarks

Our material generally agrees with the original description, except that in contrast to Suwa and Mawatari (1998), we did not observe blunt condyles occasionally present at the proximolateral corners of the orifice. Also, ancestrulae of M. trigonellata from Akkeshi Bay are larger than indicated for the type material .

Distribution

Suwa and Mawatari (1998) recently described this species from Deshin-Hama, Muroran, on the Pacific coast of Hokkaido; Akkeshi Bay is the second known locality .

Superfamily CELLEPOROIDEA Johnston, 1838

Figures

Figure 7. Callopora craticula (Alder, 1856). NHM 2006.2.27.29. (A) General view of colony fragment, unbleached; (B) immature zooids near colony margin, unbleached; (C) mature zooids showing ovicells and associated avicularia, unbleached; (D) group of immature zooids and vicarious avicularium on right, unbleached. Scale bars: 0.5 mm (A); 0.2 mm (B–D).

Figure 35. Microporella trigonellata Suwa and Mawatari, 1998. (A, E) NHM 2006.2.27.96; (B–D) NHM 2006.2.27.95; (F) NHM 2006.2.27.52. (A) Colony margin with developing zooids; (B) immature zooids; (C) distal half of immature zooid, showing orifice, ascopore, and avicularium; (D) mature zooids; (E) heavily calcified, abraded mature zooids; (F) ancestrula and periancestrular zooids. Scale bars: 0.5 mm (A, B, D–F); 0.2 mm (C).