A COMPARATIVE STUDY OF GUT MUCOUS CELLS IN THIRTY-SEVEN SPECIES OF THE CLASS ECHINOIDEA (ECHINODERMATA)

¹ Division of Marine Biology, Scripps Institution of Oceanography, University of California at San Diego, La Jolla, California 92037
² Department of Zoology, University of California, Berkeley, California 94720

1. A standard terminology for echinoid gut regions is described such that one and the same name is applied to gut regions homologous among the regular echinoids, clypeasteroids and spatangoids.

2. In the regular echinoid order Aulodonta, all seven diadematid species studied lack a siphon, having instead a siphonal groove running the length of the stomach; previously, the only echinoid group known to lack a siphon was the regular echinoid order Cidaroidea.

3. All thirty-seven echinoid species investigated have gut mucous cells in the epithelium lining at least one region of the digestive tract; these cells contain sulfated acid mucus, nonsulfated acid mucus or neutral mucus.

4. Mucous cells of echinoid guts generally occur either individually as unicellular glands or collectively as secretory epithelial sheets; in addition, echinoid gut mucous cells occur (1) as intraepithelial glands in the esophageal epithelium of some species of the order Aulodonta and (2) as simple acinous glands invaginated into the connective tissue underlying the epithelium lining the distal esophagus in amphisternate species of the order Spatangoida.

5. Autoradiography of seven regular echinoid species reveals that, in mucous cells containing sulfated acid mucus, S³⁵-sulfate is incorporated in the basal-to-middle region of the cell, presumably into newly synthesized mucus; by 24 hr after administration of S³⁵-sulfate, the radioactive mucus migrates intracellularly toward the apex of the mucous cell.

6. The siphonal grooves of all cidaroids and aulodonts studied are free of mucous cells, as are the siphons of the other echinoid species studied.

7. In the regular echinoid order Cidaroidea, all four species studied have mucous cells in the pharynx, esophagus, stomach, intestine and rectum.

8. In the regular echinoid order Aulodonta, all seven species studied have mucous cells in the pharynx and esophagus; in five of these seven species, mucous cells are also found in the intestine and rectum.

9. In the regular echinoid orders Lepidocentroida, Stirodonta and Camarodonta (one, three, and fourteen species respectively studied) mucous cells are found in the pharynx and esophagus, but not in the stomach, intestine and rectum.

10. In the irregular echinoid order Clypeasteroida, all four species studied have mucous cells in the pharynx and esophagus, but not in the stomach, intestine and rectum.

11. In the irregular echinoid order Spatangoida, all four species studied have mucous cells restricted to the esophagus; these cells are in both the proximal and distal esophagus in the suborder Meridosternata, but are found only in the distal esophagus in the suborder Amphisternata.

12. The possible functions of echinoid gut mucus are discussed and the possible evolutionary history of selected features of the echinoid gut is traced from the Palaeozoic cidaroids to extant echinoids.