Favosipora ainui, 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 : 1769-1772

Favosipora ainui sp. nov.

( Figures 2B and 4 )

Material examined

Holotype: NHMUK 2014.11 .18.13 ( Figure 4 ), Aikappu . Paratypes: NHMUK 2014.11 .18.14–16, Aikappu; 2014.11.18.23 ( Figure 2B ), Aininkappu; 2014.11.18.17–22, Aikappu .

Derivation of name

In reference to the native people of Hokkaido, the Ainu.

Description

Colony encrusting, multiserial, unlilamellar or multilamellar, irregularly circular to oval, attaining about 3 cm across; corn or lemon when alive; surface irregularly mounded, with occasional monticules, some elongated parallel to local growth direction, and chimney-like prominences formed around tubes of symbionts. Distal fringe of basal lamina variable in width, locally extending about 1 mm beyond budding zone. Skeletal organization free-walled with the exception of fixed-walled gonozooids. Mural spines short and sparse. Early astogeny unknown.

Autozooids with elliptical apertures and bicuspate apertural rims standing slightly above the surrounding kenozooids with prolongations at opposite ends of the long axis of the aperture, diameter typically 125–138 µm by 110 µm. Apertures typically separated by kenozooids, occasionally connate.

Kenozooids abundant, outnumbering autozooids, apertures subcircular, smaller and more variable in size than those of autozooids, about 50–110 µm in diameter. Walls between kenozooids thick, with a slight median ridge.

Gonozooids frequent, subcircular in overall outline shape, about 1.50–1.65 mm in diameter, a salient wall forming the slightly digitate outer border. Roof of pseudoporous exterior wall penetrated and supported by about 30 circular autozooidal apertures having short, sharp-edged peristomes, often closed completely or partly by a terminal diaphragm and either isolated or connate and arranged in radial rows of up to five apertures. Polygonal pattern of sutures in roofs of complete gonozooids, as well as morphology of partly formed gonozooids, show calcification developing outwards from peristomes of penetrative autozooids. Ooeciopore located at centre of gonozooid, strongly elliptical in shape, the maximum width similar to that of apertures of the penetrative autozooids, 50 µm by 95 µm in diameter, a short, funnel-like, ooeciostome with a subcircular opening about 145 µm by 155 µm in diameter.

Remarks

Twelve species of Favosipora have been recognized, comprising 11 recent species from the Pacific and Indian oceans and one fossil species from the Miocene of Italy ( Gordon and Taylor 2001, 2010; Dick et al. 2006; Toscano and Taylor 2008). Favosipora ainui sp. nov. is the first species recorded from Japan. Gonozooids in species of Favosipora fall into two main morphological groups: in the majority of species, the gonozooid has a sinuous outline and the roof is not penetrated by autozooids, but in a second group, including the new species, autozooids pass through the roof and support it. Among species in this second group, Favosipora ainui sp. nov. most closely resembles F. otagoensis ( Taylor et al. 1989) , an obligate, tube-building symbiont of hermit crabs from New Zealand. However, the new species has a greater number of autozooids penetrating the roof of the gonozooid (c. 30 vs. c. 20) and their apertures are not bicuspate, unlike apertures elsewhere in colony. Furthermore, the ooeciostome is shorter and the ooeciopore appreciably smaller in F. otagoensis than in F. ainui sp. nov. Another species from New Zealand, F. marmorosa Gordon and Taylor, 2001 , also has gonozooids penetrated by autozooids but the gonozooids in F. marmorosa contrast with those of the new species in having a markedly digitate outline. In addition, colonies of F. marmorosa are strongly monticulate, with pale monticules surrounded by more heavily pigmented intermonticular areas, whereas colonies of F. ainui are corn or lemon in colour.

Occurrence

Specimens of F. ainui were detected at three localities on the eastern coast of Akkeshi Bay, being locally abundant at Aininkappu Cape. The great majority of colonies (22 of 23) formed roughly circular encrustations, up to 3 cm across, on various smaller rocks and pebbles lying beneath boulders, or occasionally on the undersides of boulders. A single colony was found encrusting a fragment of an unidentified bivalve shell. Some colonies were densely penetrated by tubes occupied by sedentary polychaetes ( Figures 2B , 4A ).

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 4. Favosipora ainui sp. nov., holotype, 2014.11.18.13: (A) colony surface showing autozooidal and kenozooidal apertures as well as the larger opening (left) of a symbiont tube; (B) two bicuspate autozooids surrounded by smaller kenozooids; (C) partly developed gonozooid with roof calcification growing centrifugally from the autozooids passing the brood chamber; (D) ooeciopore (centre), with flared ooeciostome, pseudoporous gonozooid roof and autozooidal apertures closed by pseudoporous terminal diaphragms; (E) two complete gonozooids, that on the left with some of the penetrant autozooids arranged connately. Scale bars: A, C, E = 500 µm; B, D = 200 µm.