Cupuladria cavernosa Cadée, 1979
Colonies are free-living (lunulitiform), attached to a minute substrate that is often totally overgrown. They are disc shaped with a convex frontal surface on which the autozooids and vibracula open, and a concave underside. Rectangular kenozooidal sectors on the underside each contain 4-10 pores. More than one layer of basal kenozooids is present, producing a thickened colony base. The diameter of colonies is up to 12 mm. In colonies originating by sexual reproduction, a triad of zooids constitutes an ancestrular complex from which subsequently budded zooids are arranged radially in alternating series. Colonies that formed from asexual reproduction through fragmentation followed by reparative growth generally lack these early generational zooids and tend to be somewhat less symmetrical in shape. The growing edge at the perimeter of the colony is stepped.
Autozooids are ovoidal to rhombic, longer than wide, on average about 0.52-0.58 mm long by 0.36-0.43 mm wide (fide Cadée 1979, table 3). Gymnocyst and spines are lacking. The cryptocyst is narrow, granular, slopes steeply inwards and lacks denticles. Most of the frontal surface of the autozooids is occupied by the longitudinally elongate opesia. Ovicells are lacking.
Vibracula are present distally of each autozooid. They are smaller than the autozooids, and have ear-shaped opesia and asymmetrical condyles. The rostrum is directed proximally, deflected either to the left or right of the associated autozooid. Vicarious vibracula rarely replace autozooids.
Two other, free-living lunulitiform species have been recorded from the Coralline Crag: Reussirella haidingeri and Lunulites conica. The first of these species, which belongs to the same family (Cupuladriidae; see Cook & Chimonides 1994) as Cupuladria cavernosa, is very similar in many respects but has a cryptocyst with denticles extending part way over the opesia. Colonies of Lunulites conica are often flat-bottomed, the concave underside being totally infilled by calcification. Frontal surfaces are badly preserved in all available specimens (see also Bishop & Hayward 1989, figs 33, 34) but lack the distinctive pairing of an autozooid with a distal avicularium that is seen in the two species of Cupuladriidae.
This species was identified by Busk (1859) in his monograph of Crag bryozoans as Cupuladria canariensis, a species he had described in the same year from the Recent of the Canary Islands. Subsequent authors, notably Lagaaij (1952, 1963), retained this name for the fossil species, interpreting C. canariensis in a broad sense. Cadée (1979) recognized that the species was in need of subdivision and introduced new subspecies, including C. canariensis cavernosa for the form found commonly as a fossil in the Miocene and Pliocene of Europe. This differs from C. canariensis canariensis principally in having more than one layer of kenozooids on the underside of the colony. Cook & Chimonides (1994) elevated Cadée’s subspecies to species rank as Cupuladria cavernosa Cadée, 1979.
Pliocene, Late Zanclean–Early Piacenzian, Coralline Crag Formation, Suffolk, UK.
Cadée (1979, pp. 452-3) also recorded this species from the Pliocene of the Low Countries (see also Bishop & Hayward 1989), France and Italy, and the Miocene of the Low Countries, France, Austria, Denmark, Germany and Poland. In view of the occurrence of numerous superficially similar species in the genus Cupuladria, these records require re-evaluation before they can all be accepted as representing C. cavernosa.