Family PENETRANTIIDAE Silén, 1946

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• Penetrantiidae Silén, L. 1946. On two new groups of Bryozoa living in the shells of molluscs. Arkiv för Zoologi 38B: 1-7 [2].

Introduction

This family was defined by Silén (1946) for Penetrantia densa Silén (1946), from South Africa. Other Recent species of Penetrantia have been described from New Zealand, Sweden, Mexico, Hawaii and the Spanish coast of the Mediterranean Sea. The autozooids extend nearly vertically into the substratum object, a short distance from the stolon; and are connected to the stolon by a peduncle, which joins the zooid in the distal ('upper') half. The orifice is slightly offset from the main stolon branches. The zooids usually have an operculum in the orifice. In the genus Penetrantia, an additional cavity at the side of the zooid cavity is presumably a brood chamber, and has been called an ovicell. The autozooids in various species may range from 0.36 to 0.7 mm long, and 0.10 to 0.18 mm wide. Two genera are defined, with the monospecific Mesozoic fossil genus Haimeina distinguished simply by the absence of ovicells (Pohowsky 1978).

In some species of the genus Penetrantia the orifice is not round, but has a projection from the proximal edge, which was considered, by Soule & Soule (1969), to be analogous to the lyrula of ascophorans such as the smittinids. The presence of the operculum, and of ovicells, led to their suggestion that the Penetrantiidae should be assigned to the Cheilostomata. This interpretation was discounted by Pohowsky (1978). The presence of penetrantiids in Australia is based upon the occurrence of borings showing the characteristic orifice shape. These have been observed in several samples from southeastern Australia, but the preliminary identifications have not been followed by detailed study.

Diagnosis

Colony boring. Zooids pedunculate, vaneless, essentially vertical in the substratum. Peduncle inserted in distal half of zooid. Ovicelled gonozooids typically present. Closing apparatus an operculum.

General References

Pohowsky, R.A. 1978. The boring Ctenostomate Bryozoa: taxonomy and paleobiology based on cavities in calcareous substrata. Bulletin of American Paleontology 73: 1-192

Silén, L. 1946. On two new groups of Bryozoa living in the shells of molluscs. Arkiv för Zoologi 38B: 1-7

Soule, J.D., & Soule, D.F. 1969. Systematics and biogeography of burrowing bryozoans. American Zoologist 9: 791-802

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