Parasmittina Osburn, 1952

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 : 1106-1108

Genus Parasmittina Osburn, 1952

Parasmittina avicularissima ( Gontar, 1982)

( Figure 23 ) Parasmittina jeffreisii avicularissima Gontar 1982, p 548 , Figures 1 , 5a, b .

Material examined

ANC, colony on rock (NHM 2006.2.27.72), colony on rock (NHM 2006.2.27.73), extensive colony on rock (NHM 2006.2.27.74). Additional material: 23 specimens.

Description

Colony encrusting, coherent, unilaminar, but sporadically building up frontally budded layer of irregularly orientated zooids; irregularly circular, largest observed 3.8 cm in maximum dimension; bright yellow when alive, with lemon-yellow membranous growing edge one or two zooids deep. Zooids ( Figure 23B, C, E ) oval to irregularly hexagonal, rounded distally, 0.40–0.63 mm long (0.49¡ 0.06 mm), 0.27–0.43 mm wide (0.34¡ 0.04 mm), separated by shallow groove, with appressed adjacent vertical walls forming a thick line of calcification flanked by rows of areolar pores. Frontal wall convex, vitreous; smooth, or rugose with coarse granulation; imperforate centrally, with 7–10 conspicuous areolar pores along each lateral margin, separated by short buttresses; with large conical or nodular suboral umbo variable in size, occasionally with one to three additional protuberances scattered elsewhere on frontal surface. Primary orifice ( Figure 23B ) subcircular, typically slightly longer than broad, 0.10–0.14 mm long (0.12¡ 0.01 mm), 0.10–0.13 mm wide (0.11¡ 0.01 mm), with a low, narrow, truncate lyrula and long, pointed condyles directed proximomedially. Young zooids ( Figure 23A ) have two short, ephemeral distal spines. Peristome formed by narrow, raised lip proximally and laterally in young zooids, or rarely by two lateral lappets separated by sinus; primary orifice becomes sunken with increased secondary calcification. Zooids with or without a large avicularium ( Figure 23A–C ), about 0.12–0.15 mm long, lateral to orifice, abutting peristome, the rostrum raised distally, with an acute, slightly long-triangular mandible directed medially, approximately in line with proximal margin of orifice; cross-bar thin, complete; sometimes the lateral-oral avicularium is paired. The lateral-oral avicularium may be replaced by a larger avicularium ( Figure 23D, E ) of similar shape occupying central or proximal area of frontal wall and pointing distally, distolaterally, or sometimes proximally. Small avicularia ( Figure 23D, F ), about 0.07–0.10 mm long, pyriform or oval in shape, with semicircular mandible directed laterally or proximally, can also occur anywhere along the proximal or lateral margins proximal to the orifice, with or without the larger, acute types; sometimes an oval avicularium overlaps the margin of an ovicell. Ovicell ( Figure 23F, G ) spherical, broader than long, 0.20–0.28 mm long (0.24¡ 0.02 mm), 0.23– 0.33 mm wide (0.28¡ 0.02 mm), overhanging the orifice; smooth, flattened on top and bearing a single large, circular or transversely elliptical pore; recumbent and sunken in frontal wall of distal zooid, with contributions of ectocystal calcification from that zooid and laterally flanking zooids delineated by raised suture lines; ovicell lacking ornamentation, or with one to three conical, tuberculate processes, one per sector of secondary calcification. Interzooidal communication via uniporous septula. Ancestrula not observed; ancestrular region we observed ( Figure 23H ) appears entirely covered by a frontally budded layer of irregularly orientated zooids.

Remarks

The stable character that distinguishes this species from any other Parasmittina reported from the northwestern Pacific, including P. jeffreysii ( Norman, 1903) , P. trispinosa ( Johnston, 1838) , and P. macroavicularia ( Androsova, 1958) , is the presence of only a single, large pore in the ovicell.

Gontar (1982) described and illustrated two types of avicularia in her original description, but only briefly mentioned their arrangement, which we found to be quite variable. Most zooids located marginally or peripherally lack avicularia or have only the lateral-oral avicularium with a triangular mandible pointed medially. In contrast, zooids situated near the colony centre tend to have several different combinations of avicularia, such as: (1) a triangular lateral-oral avicularium on both sides of orifice, mandibles pointing medially; (2) an oval avicularium on each side of the orifice; (3) both triangular and oval avicularia lateral to orifice; (4) a single triangular avicularium located proximally on the frontal wall, with the mandible directed distally, laterally, or proximally; (5) a single oval avicularium lateral to orifice; (6) one or two oval avicularia in the proximal half of the frontal wall; or (7) one oval avicularium lateral to the orifice and another more proximally.

Distribution

Parasmittina avicularissima was originally described from Crabovaya Bay, Shikotan Island, southern Kuril Islands. Akkeshi Bay is the second and southernmost known locality.

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 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 23. Parasmittina avicularissima (Gontar, 1982). (A, H) NHM 2006.2.27.72; (B, C, F, G) NHM 2006.2.27.73; (D, E) NHM 2006.2.27.74. (A) Zooids differentiating at colony margin; (B) immature zooids, showing oral spinescars, lyrula, and condyles; (C) immature zooids with lateral triangular avicularia; (D) autozooids with oval proximo-lateral avicularia and large frontal avicularium directed proximally; (E) autozooids with frontal avicularia directed distally; (F) zooids with developing and completed ovicells; (G) mature zooids with ovicells possessing single pore; (H) ancestrular region. Scale bars: 0.5 mm (A, C–H); 0.4 mm (B).