At right there are SEM micrographs showing three coenecia of the hemichordate Rhabdopleura compacta collected alive by A.R.D. Stebbing in 1967 while dredging off Stoke Point (depth 21-24 m), South Devon, England. The colonies were attached to the concave surfaces of disarticulated shells of the bivalve Glycymeris glycymeris. For SEM study, they were etched intact from the shell with a weak solution of acetic acid.
The colonies are about 0,8-2.9 mm in diameter and form irregular, compact and encrusting mats of adhering repent tubes, from which arise 2, 3, or up to 10 erect tubes. A frayed marginal membrane runs around the periphery of the attached part of each coenecium.
According to P.N. Dilly (1971), colonies of Rh. compacta are rarely more than 4 mm across, although some colonies may have diameters of about 1 cm.
Explanations:
A. Young coenecium composed of a sicula and two zooidal tubes.
B. Adult coenecium consisting of a sicula and a dozen or so zooidal tubes.
C. Young coenecium built of a sicula and three zooidal tubes.
Source:
Mierzejewski, P. and Kulicki, C. 2003. Cortical fibrils and secondary deposits in periderm of the hemichordate Rhabdopleura (Graptolithoidea). - Acta Palaeontologica Polonica 48, 1, 99-111. |
