Exidmonea zagorseki, Ramalho, Muricy & Taylor, 2009

Ramalho, L. V., Muricy, G. & Taylor, P. D., 2009, Cyclostomata (Bryozoa, Stenolaemata) from Rio de Janeiro State, Brazil, Zootaxa 2057, pp. 32-52 : 39-41

Exidmonea zagorseki sp. nov.

( Figs 3B–C, 5A–F)

Material examined. Type material. MNRJ-183 (holotype), MNRJ-238 (paratype), Região dos Lagos, Rio de Janeiro State, 23°47.629’S, 041°42.514’W, 20 July 2004, collector D.C. Savi, depth 341 m.

Diagnosis. Colony arborescent, dichotomously branched, autozooidal apertures isolated or grouped into pairs or threes, alternating on each side of branch midline; peristome elongate, slightly curved; branch dorsal side flattened with small pseudopores and arcuate growth bands; gonozooid on frontal side, forked at branch bifurcation; ooeciostome short, unicuspate, with circular ooeciopore.

Description. Colony arborescent, dichotomously branched, in some parts with branches twisted around their longitudinal axes, strongly calcified, originating from well-developed and wide base ( Fig. 5A, B). Sterile branch diameter (average 441 µm) usually slightly smaller than distance between autozooidal series (average 588 µm). Flattened dorsal side of branches with arcuate growth bands, lacking kenozooidal overgrowth. White in colour. Autozooids tubular with long (at least 200 µm) well-developed peristomes, these slightly curved outwards and upwards ( Fig. 5C–D); frontal wall transversely wrinkled; apertures disposed alternately in connate series comprising 2–3 apertures, sometimes solitary, opening on frontal side of colony ( Fig. 5B–E), zooidal boundaries marked by fissures; aperture circular ( Fig. 5C). Basal, frontal and dorsal walls perforated by small pseudopores, rounded or slightly longitudinally elongate (10–(11)–12.5 µm long x 5–(6.75)–10 µm wide) ( Fig. 5E–F). Gonozooid located on branch frontal side, extending between autozooidal apertures; originating proximal to bifurcation and extending into both daughter branches as far as 2nd or 3rd autozooidal series. Gonozooid large (2370 µm long x 437 µm wide), diffuse; frontal wall densely pseudopores ( Fig. 3B); ooeciostome short, ending in a circular, unicuspate ooeciopore ( Fig. 3C).

Etymology. In honour of Dr Kamil Zagorsek, bryozoan specialist at the Narodni Museum, Prague.

Remarks. The genus Exidmonea contains a large number of species, the majority of which are Cretaceous or Cenozoic fossils. There are, however, many recent species known from, for example, the Mediterranean, the Philippines and the Antarctic.

Of the Exidmonea species described previously from Brazil, E. foresti ( Buge, 1979) has one to three autozooids per series and a gonozooid located close to the branch bifurcation, as in E. zagorseki sp. nov. The width of the branch (140–200 µm), however, and the distance between fascicles (200–320 µm) are appreciably larger than in E. zagorseki sp. nov. Exidmonea atlantica (Forbes in Johnston, 1847) differs from E. zagorseki in having three to five autozooids per series, wider branches (280–350 µm), and gonozooids not associated with branch bifurcations.

The presence of secondary calcification at the colony base, obscuring the older autozooids and the general form of the colony, recalls E. hula ( Borg, 1944) , which normally has, however, up to four autozooids in each series and shorter peristomes.

The Antarctic species E. arcuata Ostrovsky & Taylor, 1996 is similar to E. zagorseki but differs in having a weakly calcified colony, branches that bend strongly backwards (dorsally), and two to five autozooidal apertures per series (normally three to four). According to Ostrovsky and Taylor (1996), the colony begins from a Stomatopora -like base, followed by a supporting disc from which two or three new branches originate. This is not observed in E. zagorseki where the base produces a single erect stem.

Another Antarctic species, E. curvata ( Borg, 1944) , resembles E. zagorseki in having a well-developed colony base and branches that are slightly curved backwards. Exidmonea curvata differs, however, in having three to five autozooids per series, a long, ooeciostome with bilabiate ooeciopore that is almost slit-like, and gonozooids that do not fork at branch bifurcations.

Ecology. Colonies were found on calcareous rocks in deeper waters (341 m).

Geographic distribution. Região dos Lagos (23°47.629’S, 41°42.514’W), Rio de Janeiro State .