Electra asiatica, 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 : 1065-1067

Electra asiatica new species

( Figure 5 ) Electra crustulenta var. baltica: Kubanin 1976, p 31 . Electra baltica: Kubanin 1997, p 121 ; Grischenko 2002, p 113 (part). Electra arctica: Nikulina 2006, p 28 , Figure 5A–C .

Diagnosis

Colony coherent; opesia large; gymnocyst well developed; cryptocyst moderately well developed, the entire rim crenulate; chitinous spine well developed; base of spine variable in size; chitinized operculum contrasting sharply in colour with the transparent frontal membrane; colony uniserial only near ancestrula, rapidly giving rise to fan-shaped coherent sheets.

Etymology

The species name refers to this species’ distribution in the northwestern (Asiatic) Pacific.

Material examined

Holotype: BAC, colony on bivalve shell (NHM 2006.2.27.19) . Paratypes: BAC, colony on bivalve shell (NHM 2006.2.27.20) ; BAC, colony on bivalve shell (NHM 2006.2.27.21); KAI, colony on rock (NHM 2006.2.27.22); MIN, colony on rock (NHM 2006.2.27.23), colony on rock (NHM 2006.2.27.24). Additional material: 84 specimens from Akkeshi and one colony on a barnacle ( Balanus sp. ) fragment, Ptichiy Island (57 ° 109N, 156 ° 359E), western Kamchatka shelf, Sea of Okhotsk , lower intertidal, collected by A. V. Grischenko , 6 September 1992 .

Description

Colony encrusting, unilaminar, radiating in coherent, fan-shaped lobes ( Figure 5A, B ) from point of origin, forming circular patches up to 2.8 cm across, whitish or light-yellowish when alive. Zooids oblong hexagonal, barrel-shaped, oval, or subrectangular, rounded distally, 0.45–0.80 mm long (0.56¡ 0.07 mm), 0.21–0.35 mm wide (0.30¡ 0.03 mm), arranged in linear series with almost parallel lateral walls, separated by deep grooves; boundaries between transverse walls indistinct; proximal frontal wall transversely convex. Mural rim raised, sharp. Cryptocyst ( Figures 5E, F, H ) narrower and nearly vertical distally and laterally, wider and gradually sloping proximally, granulated just inside mural rim, smooth around opesial margin. Basal wall calcified. Opesia oval, elliptical, or roundedquadrate in outline, 0.25–0.48 mm long (0.36¡ 0.05 mm), 0.16–0.25 mm wide (0.20¡ 0.02 mm), occupying 60–80% of zooidal length. Frontal membrane thin, transparent; operculum strongly chitinized, semicircular, a sharply contrasting bright brown in colour. Gymnocyst ( Figures 5C–F ) smooth, relatively narrow distally and laterally, usually elongate and tapering proximally, often with minute transverse striations. In most zooids, the gymnocyst proximal to opesia rises to a conspicuous boss bearing a pointed chitinous spine ( Figure 5D ). Zooids interconnect by three to five circular multiporous septula in each lateral wall and by numerous small pores in basal half of distal wall. Avicularia, lateral spines, ovicells, and hibernacules absent. Small kenozooids ( Figure 5F ) of irregular shape and size occur sparsely among autozooids; these are completely ringed by a granular cryptocyst and have a small, roughly circular opesia. Ancestrula ( Figure 5G ) tatiform, small, oval, about 0.40 mm long, 0.28 mm wide; opesia oval, 0.21 mm long, 0.18 mm wide. Ancestrula buds one ( Figure 5B ) or two ( Figure 5A, G ) small zooids distally and another proximally ( Figure 5A, G ) or proximolaterally.

Remarks

Among congeners, E. asiatica most closely resembles E. baltica ( Borg, 1931) in having a similarly coherent colony, a large opesia, and a chitinized operculum contrasting sharply in colour with the transparent frontal membrane. Both species commonly have, proximal to the opesia, a knob terminating in a pointed chitinous spine. However, unlike E. baltica , chains of zooids of E. asiatica radiate and anastomose only close to the ancestrula, and subsequently form only fan-shaped multiserial sheets that do not diverge again into uniserial chains. In E. asiatica , the proximal gymnocyst is more extensive and the opesia is proportionately smaller than in E. baltica . Owing to the general similarity between these two species, previous investigators have likely interpreted the differences in zooid size and colony form as intraspecific variation in a single species, E. baltica . The records of E. baltica by Kubanin (1976, 1997) from numerous localities in the Far Eastern seas appear to be misidentifications of E. asiatica ; a specimen from the intertidal zone of Ptichiy Island ( Figure 5H ) proved to be this species.

At Akkeshi, E. asiatica is often found growing close to E. korobokkura on the same substratum, particularly on dead bivalve shells. Electra asiatica has larger zooids than E. korobokkura (compare Figure 5C–E, H with Figure 3D at the same scale), a difference readily apparent in specimens close to one another. Nikulina (2006) illustrated and discussed this size difference, but identified the species with larger zooids as E. arctica .

Distribution

We consider Kubanin’s (1976, 1997) E. baltica to be synonymous with E. asiatica . To the extent that all of Kubanin’s records represent correct identifications of the latter, E. asiatica is widely distributed in the northwestern Pacific: southeastern Kamchatka (Kamchatsky, Kronotsky, and Avacha Gulfs); northern and northeastern coast of the Sea of Okhotsk (southwestern Kamchatka; Penzhinskaya, Gizhiginskaya, Yamskaya, and Taujskaya Inlets; Okhotsk; Ayan; Zavyalov Island); southern and southeastern coast of Sakhalin Island (Terpeniya and Aniva Gulfs); northern Sea of Japan (southwestern coast of Sakhalin Island and Moneron Island). Akkeshi Bay is the southernmost known locality.

Figures

Figure 3. Electra korobokkura Nikulina, 2006. (A–C) NHM 2006.2.27.1; (D) NHM 2006.2.27.2. (A) Colony fragment with uniserial branches; (B) colony fragment with anastomosing, multiserial branches; (C) zooids without spinous processes; (D) zooids with spinous processes. All unbleached. Scale bars: 2 mm (A, B); 1 mm (C); 0.5 mm (D).

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).