Setosinella orbiculata ( Canu & Bassler, 1920 ) Canu & Bassler, 1920

Martino, Emanuela Di & Taylor, Paul D, 2012, Pyrisinellidae, a new family of anascan cheilostome bryozoans, Zootaxa 3534, pp. 1-20 : 11-13

Setosinella orbiculata ( Canu & Bassler, 1920) n. comb.

( Figs 23−30 ; Table 4 )

Amphiblestrum orbiculatum Canu & Bassler, 1920 , pp. 161–162, pl. 30, fig. 4.

Material examined. Holotype: USNM 63932, Eocene (Upper Jacksonian = Priabonian), Ocala Limestone, Old Factory, 1.5 miles above Bainbridge, Georgia, USA; NHML D34666, details as for holotype.

Description. Colony encrusting, multiserial, unilaminar. Growing edge stepped implying intrazooidal budding. Pore windows (mean L = 45 µm, mean W = 15 µm) visible in transverse vertical walls at colony growing edge, oval, facing frontally and laterally. Ancestrula not observed intact; apparent ancestrula in holotype represented by basal walls only, approximately 260 µm long and 240 µm wide, budding a distal and two distolateral zooids. Autozooids small, distinct, rounded hexagonal or oval, little elongated (mean L/W = 1.38), separated by deep furrows. Gymnocyst slight, broadest proximally. Mural rim thin, salient, together with distal rim of opesia forming a pear-shaped wall around cryptocyst and opesia. Cryptocyst shelf-like, deep, flat, granular. Opesia semicircular, limited distally by the mural rim and proximally by a transverse salient trabeculum attached to the mural rim. An indeterminate number of spine bases in non-ovicellate zooids, six in ovicellate autozooids, forming an arch close to the distal rim of the opesia. Ovicell hyperstomial, globular, prominent, slightly broader than long, smooth, the ectooecium completely calcified, resting on proximal gymnocyst of distal zooid and indenting its mural rim, opening dumbbell-shaped. Avicularia rare, interzooidal, small and triangular.

Remarks. Compared with the type species of the genus, Setosinella prolifica from the Paleocene, this Late Eocene species has larger autozooids and smaller and less frequent avicularia. Unequivocal opesiules and pores were not observed during SEM study of both holotype and topotype but the coarse preservation of the cryptocyst may account for this absence. Canu & Bassler’s solitary photograph of this species ( Canu & Bassler, 1920, pl. 30, fig. 4) shows up to about 10 pores (‘tremopores’) distributed more or less evenly over the cryptocyst, and scanning electron micrographs hint at the possible existence of pores in a few zooids ( Fig. 25 ). Like the opesia and oral spines, these structures have been inked in on top of Canu & Bassler’s photograph. Canu & Bassler (1920) noted the similarity between Amphiblestrum orbiculatum and Micropora but remarked on the difference in the ovicells, which are hyperstomial in A. orbiculatum but endozooecial in Micropora .

Canu & Bassler (1920, p. 161) assigned this species to Amphiblestrum on the grounds of the ‘interopesial avicularia’, oral spines and hyperstomial ovicell explaining that this species is a very divergent type of Amphiblestrum where the opesia is transformed into a real aperture with an operculum. We here reassign the species to Setosinella because of the combination of the following characters: zooids with a narrow gymnocyst separated from the extensive and flat cryptocyst by a thin, salient mural rim that, together with the rim of the opesia forms a pear-shaped wall, hyperstomial ovicell, and semielliptical opesia with a distal arch of oral spines. There are other species assigned to Amphiblestrum (e.g., A. willetti Brown, 1952 ) which resemble Setosinella but have an ovoidal rather pear-shaped mural rim.

Distribution. Priabonian (Late Eocene), Upper Jacksonian of Georgia, USA.

N, Number of colonies and number of zooids measured; SD, standard deviation.

Figures

FIGURES 23 − 26. Setosinella orbiculata (Canu & Bassler, 1920) n. comb., USNM 63932, holotype, Eocene, Priabonian, Ocala Limestone, Bainbridge, Georgia, USA. 23. view of part of the colony with putative ancestrula (bottom centre), scale bar = 200 µm; 24. part of the colony showing distal pore windows at the colony growing edge, scale bar = 200 µm; 25. close-up of two autozooids and interzooidal avicularium; autozooid on right shows possible pores in the cryptocyst obscured by epitaxial cement; scale bar = 100 µm; 26. close-up of an ovicellate autozooid, scale bar = 100 µm.

FIGURES 27 − 30. Setosinella orbiculata (Canu & Bassler, 1920) n. comb., NHML D 34666, Eocene, Priabonian, Ocala Limestone, Bainbridge, Georgia, USA. 27. view of part of the colony, scale bar = 200 µm; 28. ovicellate autozooids and interzooidal avicularia, scale bar = 100 µm; 29. close-up of two ovicellate autozooids and interzooidal avicularium, scale bar = 100 µm; 30. poorly preserved early astogenetic stages, scale bar = 100 µm.

Tables

TABLE 4. Measurements (in μm) of Setosinella orbiculata (Canu & Bassler, 1920) n. comb.

	N (colonies, zooids)	Mean	SD	Range
Zooid length	1, 10	391	41	327–443
Zooid width	1, 10	283	45	246–356
Orifice length	1, 10	68	4	62–73
Orifice width	1, 10	89	5	79–95
Ovicell length	1, 5	140	10	126–155
Ovicell width	1, 5	152	8	147–167
Cryptocyst length	1, 10	255	34	192–286
Cryptocyst width	1, 10	255	43	206–308
Avicularia length	1, 2	180	16	168–192
Avicularia width	1, 2	79	3	77–81