[The structure of the cercarian tegument of microphallid trematodes]

The tegument of mature cercariae of Microphallus sp. Podlipajev, 1979, M. claviformis, Levinseniella brachysoma and Maritrema subdolum consists of the outer syncytial layer filled with several types of secretory inclusions. Cytons and subtegumental cell ducts are absent. Covers of Microphallus cercariae have structure typical of larvae of trematodes. The tegument surface of L. brachysoma cercariae carries lamelli, spines are divided into two parts: short massive body sharpened at fore end and long thin stalk connected with basal membrane. The tegument surface of M. subdolum larvae forms tongue-like protrusions, modified spines serve as their frame. The development of tegument of the above species during cercaria morphogenesis has been traced. It is shown that at first in embryos syncytial lamina of the tegument is formed. Within it rudiments of spines have been detected as narrow transversal columns of mediate electron density. Henceforward syncytial layer has thickened, provisional spines have become conical, their matrix has become fibrous. Then the joining of protrusions of subtegumental glandular cells to outer syncytium has begun. These cells have been arranged into three types depending on the character of secret produced. The spines have acquired the species-specific structure. In members of the genus Microphallus they have become massive, and both in L. brachysoma and M. subdolum they have lengthened and subdivided into body and stalk. Spines of M. subdolum have flattened appreciably, their bodies have been found within tegumental tongue-like protrusions.