Disporella ezoensis, Taylor & Grischenko, 2015

Taylor, Paul D. & Grischenko, Andrei V., 2015, Two new species of heavily calcified cyclostome bryozoans from the intertidal of Akkeshi Bay, Hokkaido, Japan, Journal of Natural History 49 (29), pp. 1763-1775 : 1766-1769

Disporella ezoensis sp. nov.

( Figures 2A and 3 )

Bimulticavea variabilis: Mawatari and Mawatari, 1974, p. 356, plate 29, figures 3–5 (non Bimulticavea variabilis d’ Orbigny, 1853, p. 983, plate 779, figures 9–13).

Material examined

Holotype: NHMUK 2014.11 .18.1 ( Figures 2A , 3A–E ), Aininkappu . Paratypes: NHMUK 2014.11 .18.2, Aininkappu; 2014.11.18.11–12 ( Figure 3F ), Aikappu; 2014.11.18.8–10, Aikappu; 2014.11.18.4–7, Aininkappu; 2014.11.18.3, Aininkappu .

Derivation of name

From Ezo, an old Japanese name for Hokkaido and smaller islands in the north of the country.

Description

Colony encrusting, multiserial, unlilamellar or multilamellar, roughly circular, oval to irregular, with undulating margins, attaining about 4 cm in maximal dimension; red in colour, amaranth or crimson when alive; surface irregularly mounded, with monticules of varying shape and size, some subcircular, others elongate. Individual layers about 1.4 mm thick. Distal fringe of basal lamina narrow (<500 µm). Skeletal organization free-walled throughout. Mural spines simple, dense at growing edge. Early astogeny unknown.

Autozooids with circular to elliptical apertures, 130–170 µm long by 100–140 µm wide, one or two stout, distally tapering, unbranched oral spines, variable in length, some> 100 µm long. Apertures often connate, sometimes in rows, occasionally separated by kenozooids. Convex, thin diaphragms, some with a median pore, developed locally.

Kenozooids (alveoli) moderately abundant, slightly outnumbering autozooids, apertures subcircular, smaller and more variable in size than those of autozooids, 60–110 µm long by 60–80 µm wide. Walls thick with a sharp median ridge. Apertures locally occluded by thin, convex diaphragms.

Gonozooid with strongly digitate to dendritic outline, indented and penetrated by single or groups of autozooids. Roof of porous interior wall, the pores large and partly occluded by fine radial spines. Brood chamber about 350 µm high, becoming overgrown by autozooids and kenozooids. Short mural spines closely spaced on vertical walls lining brood chamber close to roof. Ooeciopore not observed. Opening of fertile zooid in floor of gonozooid elliptical and about half the diameter of an autozooidal aperture.

Remarks

Notwithstanding the work of Alvarez (1995 and references therein), Disporella is a speciose genus in need of a thorough revision, beginning with the type species D. hispida ( Fleming, 1828) which has not only been variously interpreted but also lacks valid type material (see Gordon and Taylor 2001, p. 259). There can be considerable changes in skeletal morphology as colonies grow, develop additional cormidial units and become fertile with gonozooids that may subsequently be overgrown. As these changes have been documented for very few of the nominal species of Disporella , species identification is difficult.

The vivid red colour of unbleached colonies of the new species is unusual for Disporella , although a pink coloration was noted for D. wanganuiensis ( Waters, 1887) by Gordon and Taylor (2001) but this New Zealand species has autozooids arranged in well-defined radial rows 1–3 zooids wide that form distinct ridge-like fascicles, and apertural spines are wanting. The European species Disporella mamillata ( Lagaaij 1952) , considered by Hayward and Ryland (1985, p. 130) to be a form of D. hispida , has compound colonies reminiscent of D. ezoensis sp. nov. but lacks the intense red coloration seen in the Japanese species.

The checklist of Japanese cyclostome bryozoans published by Mawatari (1955) listed 11 species of lichenoporids, all assigned to the genus Lichenopora Defrance, 1823 (now Patinella Gray, 1848 ; see Gordon and Taylor 1997). Mawatari and Mawatari (1974) subsequently described six lichenoporid species from Hokkaido, five assigned to Lichenopora and one to Bimulticavea. The latter – B. variabilis d’ Orbigny, 1853 – was collected from Akkeshi and described as forming thick crusts of two or three layers encrusting stones. From the description and illustrations, it is likely that this species is D. ezoensis sp. nov. It is not conspecific with B. variabilis, which is a Late Cretaceous fossil from France (see http://www. nhm.ac.uk/research-curation/research/projects/dorbigny/dOrbgenus/Bimulticavea/ Bimulticavea.html), characterized by stellate clusters of autozooidal apertures surrounding broad maculae.

Occurrence

Colonies of D. ezoensis sp. nov. were recorded at four localities along the eastern coast of the Akkeshi Bay, showing local abundance near the tip of Aikappu Cape and at Aininkappu Cape. All colonies encrusted rock surfaces (smaller rocks and pebbles) lying beneath large stones, layered boulders, cobbles and clods. Close proximity of adjacent colonies resulted in their mutual overgrown and the formation of a continuous wrinkled cover on the substrata, attaining 12 × 4 cm in dimensions, and possessing a typically vivid red colour.

Figures

Figure 2. Intertidal cyclostome bryozoan colonies from Akkeshi Bay, Hokkaido, Japan. (A) Disporella ezoensis sp. nov., holotype, NHMUK 2014.11.18.1, bleached colony (red when alive) detached from its substrate; (B) Favosipora ainui sp. nov., paratype, 2014.11.18.23, dried but unbleached colony attached to a stone and containing numerous symbiont tubes. Scale bars: 1 cm.

Figure 3. Disporella ezoensis sp. nov. (A–E) holotype, NHMUK 2014.11.18.1: (A) surface of fertile colony; (B) large autozooidal apertures with smaller kenozooids overgrowing the roof of a dendritic gonozooid; (C) oblique view showing apertural spines; (D) thin diaphragms closing autozooidal and kenozooidal apertures; (E) partly formed gonozooid with aperture of probable fertile zooid indicated by an arrow; (F) paratype, 2014.11.18.12, vertical fracture through a gonozooid showing cylindrical autozooids passing through the brood chamber. Scale bars: A = 1 mm; B, E, F = 100 µm; C = 200 µm; D = 100 µm.