| Home> Cenozoic> Miocene>

List species

Theocalyptra tetracantha Bjørklund and Kellogg, 1972

Description - Add description

Test thin-walled, smooth-surfaced, divided into three segments. Cephalis small, hemispherical, bearing two stout, three-bladed horns, a vertical horn in a lateral-oblique position, and a longer apical horn with a highly distinctive structure. About halfway between its base and its tip, the apical horn branches out into four thornlike spines, one spine an extension of the horn along its vertical axis, the remaining three spines laterally and slightly upward-directed extensions of each of the three blades. There is also a rare five-spined form. Cephalic pores small, circular and shallow-set. Collar stricture indistinct. Thorax campanulate, with large, circular to oblong pores increasing in size toward the abdomen. In some of the better-preserved individuals, the thoracic pores contain a delicate meshwork, and the thorax bears a thin dorsal spine. Lumbar stricture a distinct hyaline ring. Abdomen attatched to proximal margin of lumbar ring so that ring forms an internal collar around open mouth. Abdomen variable, in some cases absent, often broken, generally containing two rows of circular to oblong pores, somewhat larger than those of thorax, set in a thin, delicate lattice which is expanded and flattened like the brim of a hat.
Dimensions of holotype:
Length of cephalis and thorax 104 microns. Width of thorax at widest point 104 microns. Width of abdomen at widest point 174 microns. Diameter of largest thoracic pore 15 microns. Diameter of largest abdominal pore 17 microns. Abdomen and vertical horn are broken.
Dimensions of ohter specimens:
Length of cephalis and thorax 90-119 microns. Width of thorax at widest point 86-122 microns. Width of abdomen at widest point 119-180 microns. Length of abdomen 18-43 microns. Length of apical horn 29-54 microns. Length of vertical horn 18-29 microns. Diameter of thoracic pores 14-21 microns. Diameter of abdominal pores 14-29 microns.
Bjørklund and Kellogg 1972
Cycladophora tetracantha
Conical thorax having little or no upper-thorax/lower-thorax differentiation, medium-sized subspherical cephalis having small partially filled circular pores. Thorax moderately flared; regular-to-flat, uninflated outline; pores rounded, hexagonal; bars thin, circular. Tho­rax termination ragged in incomplete specimens, marked by strongly flared basal spines in some specimens. Two apical horns, three-bladed, one more axially located, larger, and with apical thorns in most speci­mens. Second apical horn smaller, projects at angle from near cephalic suture.
In the recent revision of cycladophorids by Lombari and Lazarus (1988), the scope of Theocalyptra is restricted to only those forms hav­ing extremely flat, flared thoracic architecture. C. tetracantha clearly does not possess this type of thorax. Instead, it possess all diagnostic characteristics of Cycladophora (Lombari and Lazarus, 1988) and thus is transferred to this latter genus.
Occurrence: Rare to few, Oligocene to early Miocene.
Lazarus and Pallant 1989











Discussion / Comments


Web links