Inversaria von Hagenow, 1851

Taylor, Paul D., Martha, Silviu O. & Gordon, Dennis P., 2018, Synopsis of ‘ onychocellid’ cheilostome bryozoan genera, Journal of Natural History (J. Nat. Hist.) 52 (25 - 26), pp. 1657-1721 : 1684-1685

Genus Inversaria von Hagenow, 1851

( Figure 15 )

Type species

Ceriopora tubiporacea Goldfuss, 1826 , by subsequent designation ( Gregory 1899, p. 35). Late Cretaceous, Maastrichtian, Maastricht, Netherlands.

Diagnosis

Colony erect, thick-branched ramose with inner endozone comprising zooids oriented parallel to branch axis surrounded by an outer, multizonal exozone comprising zooids oriented perpendicular to branch axis ( Figure 15 (a)); in section, zooids long and tubular with regularly spaced, collar-like transverse constrictions ( Figure 15 (b)). Zooidal boundaries narrowly grooved, inconspicuous ( Figure 15 (d)). Cryptocyst granular. Gymnocyst lacking. Opesia subterminal to central, occupying more than half of frontal surface; subelliptical, proximal edge straight to concave, lacking opesiular indentations or constrictions; opercula calcified, with a conical process on the exterior side and a pair of long antler-like spines on their interior side ( Figure 15 (c)). Ovicells unknown. Avicularia vicarious, symmetrical ( Figure 15 (d,f)), small, located on edges of branch distolaterally of the autozooids; opesia longitudinally elliptical; rostrum very short.

Remarks

Originally attributed to the Cyclostomata , Inversaria is an unusual cheilostome with tubular, thickly calcified zooids and typically vincularian colonies with robust branches that have endozonal and exozonal components ( Figure 15 (a)), like many ramose stenolaemate bryozoans. Voigt and Williams (1973) published a comprehensive revision of the genus and established its true affinity as a cheilostome. Peculiar plug-like calcified opercula were described by Voigt (1974) in the type species ( Figure 15 (c)).

The affinity of Inversaria and the closely related genus Solenonychocella Voigt and Williams, 1973 (see below) to Onychocellidae was questioned by Voigt and Williams (1973). However, the two genera can be envisaged to have evolved from bilamellar, eschariform onychocellid ancestors ( Voigt and Williams 1973, p. 169) and might therefore be accommodated in Onychocellidae in the broad sense of the family.

A questionable colony of Inversaria from the late Campanian Simsima Formation of the United Arab Emirates has encrusting colonies ( Di Martino and Taylor 2013). Along with the youngest known species of Inversaria , I. gondwanae Gordon and Taylor, 1999 from the Late Paleocene or Early Eocene Red Bluff Tuff of the Chatham Islands, New Zealand, this is the only species of the genus known from beyond Europe.

Range

Cretaceous (Campanian) to Paleocene (?Thanetian) or Eocene (?Ypresian).

Figures

Figure 15. (a–c) Inversaria tubiporacea (Goldfuss); NHMUK D35836; Cretaceous, Maastrichtian, Valkenberg, east of Maastricht, Netherlands; (a) transversely fractured branch showing endozone (lower centre) surrounded by multizonal exozone; (b) detail of exozone showing regularly constricted autozooids;(c) operculum in an autozooidal chamber (arrowed).(d,e) Inversaria tuber Voigt and Williams; holotype, SMF 24524; late Maatrichtian, Kunrade, Limburg, Netherlands; (d) autozooids surrounding an avicularium; (e) new layer of growth developing on the colony surface. (f) Inversaria flabellula (von Hagenow); Cretaceous, early Maastrichtian, Rügen, Mecklenburg-Vorpommern, Germany; SMF 24478; avicularium surrounded by autozooids. Scale bars: a = 2 mm; b, d, e = 1 mm; c = 200 µm.