Myriozoella plana ( Dawson, 1859 )

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 : 1120-1122

Myriozoella plana ( Dawson, 1859)

( Figure 29 )

Lepralia plana Dawson 1859, p 256 .

Myriozoella plana: Osburn 1952, p 516 , Plate 64, Figures 1 , 2 ; Kluge 1952, p 154; Mawatari and Mawatari 1981b, p 51; Dick and Ross 1988, p 91, Plate 6J.

Myriozoella planum: Mawatari 1956, p 135 .

Myriozoum crustaceum Smitt 1868, p 114 , Plate 25, Figures 88–91.

Myriozoum crustaceum: Robertson 1908, p 295 , Plate 21, Figure 54; Kluge 1929, p 19; Okada 1933, p 216.

Myriozoella crustacea: Androsova 1958, p 144 , Figure 70; Gontar 1980, p 11; Kubanin 1997, p 124; Grischenko 1997, p 186; 2004, p 40.

Schizoporella crustacea: Okada 1929, p 20 , Plate 1, Figure 6 , Plate 4, Figure 5 ; Kluge 1962, p 478, Figure 321; 1975, p 580, Figure 321.

Material examined

ANC, colony on rock (NHM 2006.2.27.66), two colonies on rock (NHM 2006.2.27.79), ancestrular colony on rock (NHM 2006.2.27.82); DIN, five colonies on rock (NHM 2006.2.27.80), colony on rock (NHM 2006.2.27.81). Additional material: 105 specimens.

Description

Colony encrusting, coherent, unilaminar at first but bilaminar or multilaminar with age, forming characteristic circular layers of zooids, with each successive layer forming a smaller concentric circle over previous one; up to 5.5 cm across; white, yellowish, or greyish when alive. Zooids ( Figure 29A ) oval or hexagonal, 0.42–0.60 mm long (0.51¡ 0.04 mm), 0.35– 0.43 mm wide (0.39¡ 0.03 mm), with indistinct boundaries even in early stages. Frontal wall well calcified, convex in young zooids, sparsely perforated by tubular alveoli with small pores at the bottom, giving a reticulate appearance; with age, pore openings enlarged, some occluded; frontal surface becomes thick, regular; zooidal boundaries completely obscured ( Figure 29B, C ). Some zooids have one or two frontal umbones. Orifice ( Figure 29A–C ) semicircular, 0.09–0.13 mm long (0.10¡ 0.01 mm), 0.10–0.15 mm wide (0.12¡ 0.01 mm), with straight proximal margin bisected by deep, narrow median sinus. With developing calcification, orifice becomes submerged and surrounded by shallow, sloping peristome. Operculum a rich brown colour, in sharp contrast to lighter frontal walls of zooid. On each side of orifice is a slightly raised chamber bearing an avicularium ( Figure 29B ) on distal side; semicircular mandible orientated at angle to colony surface and pointing proximally or laterally. Vicarious avicularia ( Figure 29D ) scattered throughout colony; mandible semicircular to subspatulate, larger than operculum of autozooids and orientated in any direction. Ovicell ( Figure 29C, E ) hyperstomial, 0.22–0.30 mm long (0.27¡ 0.02 mm), 0.25–0.32 mm wide (0.29¡ 0.02 mm), convex, imperforate, deeply immersed, covered with thick radial to reticulate calcification from surrounding zooids. Zooids communicate via numerous uniporous septula along basal wall. Ancestrula tatiform, nearly circular, 0.35 mm long, 0.33 mm wide, with uncalcified basal wall; opesia oval, 0.18 mm long, 0.14 mm wide, with nine spines around margin. Ancestrula ( Figure 29F ) buds triplet of small zooids distally and distolaterally.

Remarks

This species has appeared in the northern literature under the names M. plana and M. crustacea . Osburn (1952) discussed the controversy surrounding the names, noting that some authors had preferred M. crustacea Smitt, 1868 because of the inadequacy of Dawson’s (1859) original description of M. plana . Osburn argued convincingly that there is little doubt that M. plana represents the same species as M. crustacea , and that the former thus has priority.

Distribution

This is a circumpolar, Arctic-Boreal species widely distributed in the northern Pacific; Kluge (1962, 1975) and Gontar and Denisenko (1989) gave many distributional records. It has been reported from Alaska from the Pribilof Islands ( Osburn 1952), Unalaska Island ( Kluge 1961), Kodiak Island ( Dick and Ross 1988), Orca, Yakutat, and Juneau ( Robertson 1900). On the Asian side, records exist from the Commander Islands, eastern Kamchatka, Shantar Archipelago, Sakhalin Island, Kuril Islands, and Primorye ( Kluge 1961; Gontar 1980; Grischenko 1997; Kubanin 1997). In Japan, it has previously been reported only from Shirikishinai, Pacific coast of Hokkaido ( Mawatari and Mawatari 1981b).

Figures

Figure 1. Map of Akkeshi Bay showing the 10 sampling stations (filled squares); 5, 10, and 20 m depth contours are indicated. Inset shows the location of Akkeshi Bay on Hokkaido Island, northern Japan.

Figure 2. Dendrogram (below) showing similarity of sampling localities based on species presence/absence, and a map (above) showing the geographical distribution of three groups of sampling localities (circled) that are less than 70% similar in species composition between groups.

Figure 5. Electra asiatica n. sp. (A, G) NHM 2006.2.27.19; (B) NHM 2006.2.27.20; (C, D) NHM 2006.2.27.21; (E, F) NHM 2006.2.27.24. Colony from Ptichiy Island, Sea of Okhotsk (H). (A, B) Colonies radiating in coherent, fan-shaped lobes from the point of origin, unbleached; (C) colony margin with developing zooids, unbleached; (D) astogenetically mature zooids, unbleached; (E) astogenetically mature zooids, bleached; (F) astogenetically mature zooids with a small interzooidal kenozooid (lower right quadrant), bleached; (G) ancestrula and periancestrular zooids; enlargement of ancestrular area seen in panel (A), unbleached; (H) astogenetically mature zooids, bleached. Scale bars: 2 mm (A, B); 0.5 mm (C–H).

Figure 6. Conopeum nakanosum n. sp. (A, F) NHM 2006.2.27.26; (B, D) NHM 2006.2.27.27; (C, E) NHM 2006.2.27.25; (G, H) NHM 2006.2.27.28. (A) Colony margin with differentiating zooids, bleached; (B) zooids with developing angular cone-shaped kenozooids, bleached; (C) mature zooids with erect and curved spines, unbleached; (D) group of mature zooids with granulated cryptocyst, bleached; (E) distally facing triangular avicularia replacing kenozooids, unbleached; (F) distal view of kenozooids, bleached; (G) lateral view of zooids showing multiporous septula, bleached; (H) interior of distal zooidal wall showing developing angular kenozooids and also multiporous septula, bleached. Scale bars: 0.5 mm (A, G); 1 mm (B–D); 0.2 mm (E, F, H).

Figure 29. Myriozoella plana (Dawson, 1859). (A) NHM 2006.2.27.79; (B–E) NHM 2006.2.27.81; (F) NHM 2006.2.27.82. (A) Differentiating zooids near colony margin; (B) immature zooids; (C) two zooids with developing ovicells; (D) zooids with almost completed ovicell flanked distally by three vicarious avicularia; (E) mature zooids with deeply immersed ovicells; (F) ancestrula and periancestrular zooids. Scale bars: 0.5 mm.