Acrobotrys tritubus Riedel

Acrobotrys tritubus Riedel, 1957, p.80, pl.1, fig.5

DESCRIPTION

Cephalis trilobate, with large subglobular [antecephalic] lobe, smaller globular [cephalic] lobe, and inflated-conical [postcephalic] lobe, lying in the same plane. [Antecephalic] lobe bears two slender cylindrical tubes, one directed apically and the other posteriorly. [Postcephalic] lobe bears a slender cylindrical tube directed anteriorly. Thorax subcylindrical, inflated, or ovate, often with somewhat constricted mouth. Shell surface smooth, perforated by numerous small circular or subcircular pores, irregularly arranged (Riedel, 1957).

DIMENSIONS

Length of cephalis plus thorax 90-125 µm, of tubes 15-120 µm. Maximum breadth of thorax 50-60 µm (Riedel, 1957).

DISTINGUISHING CHARACTERS

From the cephalis arise three long, widely divergent tubes, one from the postcephalic lobe and two from the antecephalic lobe. Early in the range of the species the tubes are not so widely divergent (Riedel and Sanfilippo, 1978a).

VARIABILITY

The ante- and post-cephalic lobes vary in size and amount of inflation. The angle between the posteriorly and anteriorly directed tubes varies from 180° to 110°. The length of the tubes and numbers of pores on the thorax are variable. Thorax may in some specimens be completely closed (Sanfilippo, unpubl. data).

DISTRIBUTION

This species occurs in tropical sediments from all oceans. It is relatively rare, but sufficiently distinctive to be identifiable from fragments. Its morphotypic first appearance occurs within the Didymocyrtis antepenultima Zone and its morphotypic last appearance is within the Stichocorys peregrina Zone.