Setosella fragilis Rosso & Martino & Gerovasileiou, 2020

Rosso, A., Martino, E. Di & Gerovasileiou, V., 2020, Revision of the genus Setosella (Bryozoa: Cheilostomata) with description of new species from deep-waters and submarine caves of the Mediterranean Sea, Zootaxa 4728 (4), pp. 401-442 : 434-435

Andreella ? fragilis ( Canu, 1907) n. comb.

( Fig. 22 )

Setosella fragilis Canu, 1907: p. 140 , pl. 19, fig. 15.

Setosella fragilis: Buge, 1946: p. 433 ; Balavoine, 1957: p. 192; Cheetham, 1966: p. 37, text-figs 15, 16.

Examined material. NHM D48468, single fragment from Villers-Saint-Fréderic, Lutetian, Paris Basin, listed in Balavoine (1957) and figured in Cheetham (1966).

Description. Colony erect with cylindrical branches, about 1 mm in diameter. Autozooids distinct by thin grooves and laterally raised margins, arranged in alternating longitudinal rows, rounded rhomboidal, 730–865 µm long by 430–540 µm wide (mean L/ W 1.58). Gymnocyst absent; cryptocyst smooth, raised laterally and proximally to the opesia, sloping inwards and depressed centrally between opesiules. Opesiules slit-like, paired, asymmetrical, 300–320 µm and 160–200 µm long respectively, parallel to the zooidal sides, placed at a short distance below the opesia. Opesia semielliptical with concave proximal margin, 130 µm long by 150 µm wide. Distal vibracula absent. Avicularia and ovicells not observed.

Remarks. Cheetham (1963) described Poropeltarion for Calpensia -like species with erect colony-form and tentatively allocated Setosella fragilis Canu into this new genus. Subsequently, after examining the same specimen illustrated here in Fig. 22 , Cheetham (1966) confirmed Canu’s original attribution to Setosella , despite the lack of distal vibracula associated with autozooids, a diagnostic feature of the genus. However, this species differs from Poropeltarion in having an imperforate cryptocyst and slit-like opesiules but based on its general aspect, it fits better in Microporidae rather than in Setosellidae . Here, it is provisionally placed in Andreella for its similarity with Andreella dubia Gordon & Taylor, 2015 (p. 1024, fig. 31a) from the Eocene of the Chatham Island ( New Zealand). The two species share the general aspect of the zooids distinct by grooves and raised margins, the presence of a pair of opesiules unequal in size, and the imperforate cryptocyst sunken between the opesiules. However, Andreella is characterized by the presence of basal pore chambers, a feature not observed in this species or in A. dubia . Andreella ? fragilis also differs from A. dubia in having an erect colony form. It is very likely that A.? fragilis belongs to a new microporid genus but the scarcity of available material currently prevents its introduction.

Specimens from the late Oligocene site 117 in the North Atlantic Ocean identified as Setosella fragilis by Cheetham & Håkanson (1972, pl.15, figs 11, 12) likely belong to a species of Vincularia Defrance, 1829 . Although poorly preserved, the two fragments illustrated show subrectangular autozooids, which also give the idea of quadriserial branches, subquadrangular in cross-section, and with zooids placed back to back.

Distribution. Paleogene to Eocene of France and England.

Figures

FIGURE 22. Andreella? fragilis (Canu, 1907) n. comb., NHM D48468, figured by Cheetham (1966), Villers-Saint-Fréderic, Paris Basin. a, b. Two different lateral views of the only available fragment. c. Close-up of some zooids. d. Close-up of an orifice. Scale bars: a–c = 500 μm; d = 100 μm.