Porella belli ( 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 : 1101-1103

Porella belli ( Dawson, 1859)

( Figure 21 )

Lepralia belli Dawson 1859, p 256 .

Porella concinna var. a (Belli, Dawson): Hincks 1880, p 324, Plate 46, Figure 2 .

Porella concinna var. belli: Kluge 1952, p 158 ; Gontar and Denisenko 1989, p 353. Smittina concinna var. belli: Androsova 1958, p 155 , Figure 84; Kluge 1962, p 432, Figure 283. Porella concinna belli: Gontar 1980, p 10 ; 1992, p 146; Grischenko 1997, p 179.

Porella belli: Hayward 1994, p 188 , Figure 4c, d ; Kubanin 1997, p 123.

Material examined

ANC, eight colony fragments ( NHM 2006.2.27.9) and two colonies on rocks ( NHM 2006.2 .27.10, NHM 2006.2.27.66). Additional material: 85 specimens .

Description

Colony encrusting, unilaminar, coherent, tightly attached to substratum, irregularly circular, up to 2.5 cm across; yellowish, greyish, or off-white when alive. Zooids ( Figure 21B–E ) hexagonal or rectangular, sometimes tapering proximally, 0.35–0.60 mm long (0.48¡ 0.07 mm), 0.23–0.38 mm wide (0.31¡ 0.04 mm), delineated by a deep groove with a suture line when young, and by deep, undulating lateral groove with age; transverse boundaries indistinct. Frontal wall imperforate centrally, coarsely granulated, with four to seven circular areolar pores along each lateral margin; inflated and convex in young zooids; increasingly thick with age, quite convex, roughly granulose, sometimes with a prominent umbo in suboral or proximolateral region. Primary orifice semicircular, deeply submerged, difficult to measure, but about 0.10–0.13 mm long by 0.12–0.15 mm wide; lyrula low and broad, occasionally lacking in some zooids, which have a slightly convex proximal border; condyles low, tapering distally, located near proximal corners of orifice. Peristome deep, secondary orifice pyriform in outline, 0.11–0.16 mm long (0.14¡ 0.02 mm), 0.12–0.16 mm wide (0.15¡ 0.01 mm), cormidial, its distal half formed by indented proximal margin of succeeding zooid; this is confluent with thick, rounded lateral flanges that meet proximally with sides of suboral avicularian chamber; in ovicellate zooids lateral flanges connect with proximolateral corners of ovicell; suture lines separate contributions of secondary calcification from a zooid and its neighbour that make up the secondary orifice. A large, oval median suboral avicularium lies within peristome, below secondary orifice, orientated vertically or tilted slightly proximally; mandible semicircular, cross-bar complete; avicularian chamber broader than long, lunate, occupying frontal surface from margin to margin, with two to five small pores around chamber margin or in chamber itself; in young zooids chamber is convex, inflated, finely granulated, but with age it becomes immersed and rugose. Ovicell ( Figure 21C–E ) hyperstomial, spherical, 0.16–0.21 mm long (0.19¡ 0.01 mm), 0.20–0.25 mm wide (0.23¡ 0.02 mm), initially finely granulated, rapidly immersed with thick, roughly granulose calcification from surrounding zooids, becoming flush with colony surface. Oral spines lacking. Two multiporous septula in transverse wall and four circular multiporous septula in each lateral wall. Ancestrular complex ( Figure 21F ) comprises five zooids radiating from common centre; in the specimen illustrated, the ancestrula proper is completely obscured by periancestrular zooids.

Remarks

The structure of the frontal wall varies considerably in P. belli according to substratum. In general, the frontal wall is inflated in young zooids and becomes gradually mucronate with age. Colonies on flat surfaces tend to retain the inflated appearance of the frontal wall, without an umbo, whereas those on irregular substrata may comprise entirely heavily calcified zooids with a strongly mucronate frontal wall.

Distribution

This is a circumpolar, Arctic-Boreal, species. Kluge (1962, 1975) and Gontar and Denisenko (1989) gave many distributional records for the Arctic. In the northern Pacific, P. belli has been reported from the Commander Islands ( Grischenko 1997; Kubanin 1997), eastern Kamchatka ( Kluge 1961), the Kuril Islands ( Gontar 1980), Sakhalin Island, and Primorye ( Androsova 1958). Akkeshi Bay is the southernmost known locality of P. belli in the Asian Pacific.

Figures

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 4. Electra arctica Borg, 1931. ZIRAS 36/50535. Colony on rock collected by A. V. Grischenko, 12 September 1992, Sea of Okhotsk, western Kamchatka shelf (57°36.039N, 156°9.009E), depth 78–81 m. (A) Portion of colony showing anastomosing, narrowly multiserial branches; (B) autozooids and kenozooids; (C) enlargement of autozooids and kenozooids; (D) autozooids with operculum in place and kenozooids with nearly completely closed aperture. Specimen lightly bleached. Scale bars: 2 mm (A); 1 mm (B); 0.5 mm (C, D).

Figure 21. Porella belli (Dawson, 1859). (A, F) NHM 2006.2.27.10; (B, D, E) NHM 2006.2.27.9; (C) NHM 2006.2.27.66. (A) Distal view of colony margin with differentiating zooids; (B) immature zooids; (C) zooids with developing and complete ovicells; (D) mature zooids with inflated immersed ovicells; (E) mature zooids with granulose and umbonate frontal walls; (F) ancestrular region. Scale bars: 0.5 mm.