ASPECTS OF TAXONOMY AND FUNCTIONAL HISTOLOGY IN TERRESTRIAL FLATWORMS(TRICLADIDA, TERRICOLA)

The taxonomy of terrestrial flatworms is presently based upon a combin ation of external morphological characters, and internal anatomical ch aracters revealed by histological investigation. Uncertainties regardi ng the functional anatomy of Terricolan organ systems, particularly th e copulatory apparatus, have hindered the exploitation of available ch aracters for taxonomy. Considerable revision remains to be done on tax a world-wide, and provision of character-comparable taxonomic descript ions a priority. The functional histology of selected anatomical syste ms and their application in taxonomy are reviewed, and include epiderm is, subepidermal secretions, musculature and copulatory apparatus. Sec retions from the flatworm epithelium comprise at least six types, broa dly grouped on the basis of histochemical staining reactions. The secr etions are principally concerned with adhesive, locomotory, prey captu re, repugnatorial and homeostatic functions in these soil-dwelling ani mals. Structure and organisation of the body-wall musculature is impor tant in the taxonomy of the Terricola, especially at the levels of sub -family and genus. Cutaneous musculature is normally tripartite, the u ncommon simple bipartite structure probably an apomorphic condition. C haracters provided by the gonads and copulatory apparatus are importan t at the subfamily, genus and especially species level. Criteria are p rovided fur the recognition of eversible and protrusible types of peni s. Ejaculate in Terricola is similar in composition and function to th at in mammals. Spermatophores are uncommon. Functions of the atrium in clude resorption of unwanted sperm and yolk, and cocoon formation. The mechanisms of cocoon formation in the Tenicola differs from that desc ribed in the other Triclads. Vitelline cells appear not to participate in the development of the outer cocoon wall. The outer wall is a lami nate, fibrous composite, composed of at least two scleroproteins produ ced by globules and strand cells in the atrium. Accessory genital orga ns include viscid glands which are involved in cocoon deposition, copu latory bursae which receive sperm and which may also resorb copulatory products, and adenodactyli which in some species are responsible for cocoon wall formation. Seven types of adenodactyli are recognised, and the occurrence of these organs on Australian and New Zealand caenopla nids are listed.