Schizosmittina Vigneaux, 1949

Martino, Emanuela Di & Taylor, Paul D., 2017, Some Miocene cheilostome bryozoan genera of Michel Vigneaux - systematic revision and scanning electron microscopic study, Geodiversitas 39 (4), pp. 783-796 : 788-789

Genus Schizosmittina Vigneaux, 1949

TYPE SPECIES. — Schizosmittina planovicellata Vigneaux, 1949 by original designation.

EMENDED DIAGNOSIS. — Colony encrusting with zooids arranged in alternating parallel rows or bilamellar. Frontal shield evenly pseudoporous with distinct marginal areolar pores. Orifice sinuate with distinct condyles, often corrugated; lyrula absent; oral spines evanescent, present on marginal zooids only. Avicularia present or absent, adventitious or vicarious, when adventitious often suboral and associated with the peristome. Ovicells with a peripheral band of rugose calcification and a broad, flat, pseudoporous frontal area. Basal pore-chamber windows or mural septula present.

REMARKS

The genus Schizosmittina was resurrected by Gordon (1984) and subsequently recorded in both fossil and Recent material from a wide geographical area. Gordon (1994) noted that he had examined Vigneaux’s type material of S. planovicellata , scanning a few isolated zooids and using this information to rediagnose the genus. The earliest occurrence is Schizosmittina ovicellata Zágoršek & Kázmér, 2001 from the Priabonian (late Eocene) of Hungary, followed by the Rupelian (early Oligocene) S. bathydonta ( Brown, 1952) from New Zealand. Among extant species, four ( S. bicornis , S. cinctipora , S. conjuncta , S. melanobater ) are currently known from New Zealand waters ( Gordon 1984, 1989), two ( S. maplestonei and S. vitrea ) from Australia ( MacGillivray 1879), one ( S. lizzya ) from South Africa ( Florence et al. 2007), and one ( S. pedicellata ) from the eastern Pacific off USA coast ( Soule et al. 1995).

Schizosmittina planovicellata Vigneaux, 1949 ( Fig. 5 )

MATERIAL EXAMINED. — Figured syntype ( Vigneaux 1949: 104, pl. 10, fig. 5), C.B.510-1. This specimen is here designated as the lectotype of the species.

TYPE LOCALITY. — Salles, Gironde, Aquitaine, France.

AGE. — Serravallian, middle Miocene.

DESCRIPTION

Colony encrusting, multiserial, unilaminar ( Fig. 5A ). Zooids arranged in parallel rows, distinct by deep furrows, subrectangular, twice as long as wide (mean L/W = 2.05). Frontal shield slightly convex, nodular, evenly pseudoporous; pseudopores circular, large, about 20 µm in diameter ( Fig. 5A, B ). Marginal areolar pores distinct, larger than pseudopores, about 35 µm in diameter ( Fig. 5A, B, D ). Orifice longer than wide, about 100 µm long by 70 µm wide, with a narrow, deep U-shaped sinus and two, rectangular, corrugated condyles ( Fig. 5C ); oral spines absent. A raised peristome, more developed proximally and laterally, hides the primary orifice, and encloses a small, oval suboral avicularium sloping inwardly, proximally directed and with a complete crossbar ( Fig. 5D ). Vicarious avicularia absent. Ovicells large, globular, pseudoporous covered by a band of rugose calcification continuous with the frontal shield of the next distal zooid ( Fig. 5A, B, D ). Basal porechamber windows visible along distolateral zooidal margins at the colony growing edge, elliptical, about 15 µm long by 10 µm wide ( Fig. 5E ).

MEASUREMENTS

ZL 478 ± 25, 452-519 (10); ZW 234 ± 22, 204-271 (10); OvL 149 ± 10, 136-167 (10); OvW 186 ± 13, 167-203 (10).

REMARKS

Schizosmittina planovicellata differs from the fossil congeneric species, S. ovicellata and S. bathydonta , in having an encrusting rather than an erect colony-form. Recent species also differ: S. maplestonei ( MacGillivray, 1879) has a pair of frontal tubercles proximal to the orifice; S. vitrea ( MacGillivray, 1879) , S. conjuncta ( Uttley & Bullivant, 1972) and S. melanobater Gordon, 1989 have a much broader, widely rounded sinus; S. cinctipora ( Hincks, 1883) has large adventitious avicularia on the frontal shield; S. bicornis Gordon, 1989 is distinguished by a pair of prominences present on either side of the orifice; S. lizzya Florence, Hayward & Gibbons, 2007 has a subimmersed tripartite ovicell with a single, almost medial foramen. The five, stout oral spines present in S. pedicellata Soule, Soule & Chaney, 1995 link this species more with Schizomavella rather than Schizosmittina .

Figures

FIG. 5. — Schizosmittina planovicellata Vigneaux, 1949, figured syntype C.B.510-1, Serravallian, middle Miocene, Salles, Gironde, Aquitaine, France. A, group of ovicellate autozooids; B, close-up of autozooids and ovicellate zooids; C, close-up of the orifice showing the deep, narrow sinus and the corrugated condyles; D, close-up of an ovicell and suboral avicularium with complete crossbar;E, close-up of two autozooids at the colony growing edge showing basal pore-chamber windows. Scale bars: A, B, 200 μm; C, 20 μm; D, 50 μm; E, 100 μm.