Conopeum nakanosum, Grischenko & Dick & Mawatari, 2007

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 : 1067-1070

Conopeum nakanosum new species

( Figure 6 )? Conopeum reticulum: Mawatari 1956, p 115 , Figure 1e ; 1974, p 33, Figure 5 .

Diagnosis

Zooids large; opesia about 70–80% of zooidal length; cryptocyst widest proximally, finely tuberculate; gymnocyst hidden; all zooids with a triangular, cone-shaped kenozooid at each distal corner; kenozooids with small, distally facing opesial opening in central depression, sometimes transformed into an avicularium with triangular, vertically orientated mandible; two to three spines occasionally present around mural rim. Ovicells absent. Multiporous septula in lateral and transverse wall.

Etymology

The species name refers to Nakanose Bank in Akkeshi Bay, where the holotype specimen was collected subtidally .

Material examined

Holotype: NB, intact colony (NHM 2006.2.27.25). Paratypes: ANC, young intact colony (NHM 2006.2.27.26); NB, five pieces of a single colony (NHM 2006.2.27.27); NB, five pieces of a single colony (NHM 2006.2.27.28). Additional material: one specimen.

Description

Colony encrusting, multiserial, sheet-like, up to 3.5 cm across, greyish when alive, with purple to reddish marginal zone one or two developing zooids deep. Zooids ( Figure 6A, B, D ) oval, hexagonal, or subquadrangular, widest in middle, 0.67–0.95 mm long (0.81¡ 0.09 mm), 0.40–0.50 mm wide (0.45¡ 0.02 mm), separated by fine sutures between raised lateral walls. Opesia oval, elliptical, or rounded-rectangular; 0.55– 0.73 mm long (0.63¡ 0.04 mm), 0.30–0.43 mm wide (0.36¡ 0.03 mm); occupying 70– 80% of zooidal length. Cryptocyst ( Figure 6A, F ) extending around entire opesia; steep and narrow laterally, flatter and wider proximally, reduced distally, finely tuberculate below mural rim. Lateral and proximal gymnocyst hidden between adjacent zooids. Distal gymnocystal wall raised slightly above level of lateral wall into a smooth, narrow, sharpedged crescentic lip separated from cryptocyst by a transverse, slit-like cavity. At each distal corner is a raised, cone-shaped, subtriangular kenozooid ( Figure 6F, H ); sharp or blunt on top, smooth except for depressed, finely granulated cryptocystal area distolaterally, surrounding a small, circular to oval opesial opening. Kenozooids at first have this cryptocystal area covered with transparent membrane, but later often become closed to form a pair of knobs, rarely vestigial or lacking. Sometimes kenozooids are transformed into avicularia ( Figure 6E ) with a distolateral rostral face; mandible triangular with sharp, hooked, vertically orientated tip; such avicularia are rare, developing only in mature regions of the colony. Mural rim often with two or three spines ( Figure 6C ): a straight, blunt hollow tubular spine on one or both sides of orifice, in line with proximal orificial margin, jointed at base; another finer, curved, acute spine more proximally on one side, slightly arching over opesia. Like the avicularia, the spines tend to appear in mature regions of the colony; many young zooids lack them altogether. Ovicells lacking, but raised mural rim distally with transverse, slit-like cavity below ( Figure 6F ) may represent kenozooidal ooecium. Four oval multiporous septula ( Figure 6G ) in each lateral wall and two septula in transverse wall. Ancestrula not observed.

Remarks

In zooidal characters, C. nakanosum is very similar to Conopeum reticulum (L., 1767), the type species of the genus, especially in having triangular kenozooids at the distal angles of autozooids. However, these two species differ in several characters. In C. reticulum , the kenozooids develop predominantly on older zooids, whereas in C. nakanosum they occur on all zooids, at all astogenetic stages. With increasing calcification in C. reticulum , the pair of kenozooids occasionally comes into contact along the entire distal end of the zooid, forming a single, dumbbell-shaped unit. The kenozooids of C. nakanosum are always separated by a raised, crescentic gymnocystal lip. The opesial opening in the central depression of the kenozooids is terminal on the knob and facing upward in C. reticulum , whereas it always faces distally or distolaterally in C. nakanosum . Finally, zooid size in C. nakanosum exceeds that of C. reticulum , and the ranges do not overlap: zooids are 0.67–0.95 mm long by 0.40– 0.50 mm wide in the former, compared to 0.4–0.6 mm long by 0.2–0.3 mm wide in the latter ( Hayward and Ryland 1998).

There has been some confusion over the nature of the distal kenozooids in Conopeum , and both Osburn (1950) and Mawatari (1974) were sceptical that these represented vestigial avicularia or ever formed true avicualaria. However, there is no doubt that in C. nakanosum the distolateral kenozooids can be replaced by avicularia. This does not occur on every zooid, but usually only among a few zooids in a mature region of a colony. It remains unclear whether the possible occurrence of avicularia in place of the kenozooids should be incorporated into the generic diagnosis of Conopeum . Another anascan, Crassimarginatella leucocypha Marcus, 1937 , described from Brazil and subsequently reported by Mawatari (1952) from the Kii Peninsula, Sea of Japan, is morphologically similar to C. nakanosum in having angular kenozooids that can transform into an avicularium (see Marcus 1937, p 46, Plate 8, Figure 20A ). The apparent lack of ovicells in the former suggests Conopeum rather than the calloporid Crassimarginatella . The kenozooids in this species are more extensive than in C. nakanosum , with a more central opesial opening, and there has been no mention of spines.

Distribution

Akkeshi Bay is the only known locality for C. nakanosum . Mawatari’s (1956) short description and illustration of C. reticulum from the Kuril Islands (Alaid and Paramushir) and from Hokkaido (Akkeshi Bay and Kushiro) suggest he might have had C. nakanosum instead.

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 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 20. Porella acutirostris Smitt, 1868. (A, C, D) NHM 2006.2.27.62; (B) NHM 2006.2.27.64; (E) NHM 2006.2.27.63; (F) NHM 2006.2.27.65. (A) Immature zooids; (B) group of non-ovicellate zooids; (C) enlargement of orifice and suboral avicularium; (D) group of zooids with developing ovicells; (E) group of non-ovicellate zooids and zooids with umbonate ovicells; (F) ancestrula and periancestrular zooids. Scale bars: 0.5mm (A, B, D, E); 0.1mm (C); 0.2 mm (F).