By Jean Bouillon, Cinzia Gravili, Francesc Pagès, Josep-Maria Gili, Ferdinando Boero
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Extra resources for An introduction to Hydrozoa
When experimentally removed, and under certain conditions, the interstitial cells can be regenerated from the epithelial tissues. An introduction to Hydrozoa FIG. 21. Histology of the hydroids, photography of a longitudinal histological section of an expanded hydranth of Halecium halecinum (Leptomedusae) showing the two endodermic regions of the column characteristic of the Haleciidae (after Bouillon, original). D = desmocyte; Di = diaphragm; GC = gastric cavity; GD = digestive part of the column; H = hypostome; Ht = hydrotheca; ND = non digestive part of the column; Te = tentacle; Th = hydrocladium perisarc.
Boero tentacles The tentacles are generally inserted on the umbrellar rim, but in the Narcomedusae, for instance, they are on the latero-dorsal exumbrellar face. The ectoderm of tentacles is formed by very flattened epithelio-muscular cells, and provided with longitudinal smooth muscular fibers, whose contraction leads to tentacle shortening. Solid tentacles are devoid of digestive or excretory inclusions, they present a «chordal» aspect, and they elongate by contraction of their smooth circular musculature.
Hypostomial spherulous gland cells: elongated cells containing numerous, small, regular, vacuoles each occupied by a well defined droplet of secretion formed by various enzymes, namely: leucine amminopeptidases, proteinases of trypsic type, amylases and sometimes acid and alkaline phosphatases. An introduction to Hydrozoa FIG. 22. Histology of the hydroids, photography of a longitudinal histological section of a contracted hydranth of Sertularella polyzonias, Leptomedusae, showing the abcauline gastric caecum, the ectodermal mantle and its roof (after Bouillon, original).