The spermatozeugmata of Tubifex tubifex (Annelida, Clitellata, Tubificinae) studied by different technical approaches

Oligochaete annelids belonging to the subfamilies Tubificinae and Limnodriloidinae are characterized, inter alia, by the production of two different spcnn types, named eusperm and paraspenn [I]. In Tubifex tuhifex the two sperm types differ in nearly all their characters,like nuclear size [(about 30 ~ in the euspenn, but 3 11m in the paraspeml); the amount of nuclear o A (about eight times more in the eusperm than in the parasperm); the extreme reduction of the acrosome in the parasperm; the size of the mitochondria (about double in the paraspeml with respect to the eusperm); and the tail (the cell membrane is separated from the axoneme by a consistent space in the parasperm, and the space is filled by y glycogen, whereas in the euspcrm the space is reduced and has pglycogen granules)]. We have studied the production of the two speml types, and we found that, starting from similar spermatocytes, euspermatooza are produced through a regular meiotic process, whereas the paraspermatozoa are produced through a peculiar process of nuclear fragmentation which, produces a very high number of aneuploid parasperm [2]. When fully mature, the two types of spenn are transmitted to the partner during copulation, and both reach the spemlathecae. There, the two sperm types are grouped to fonn typical bundles, called spennatozeugmata, rod-shaped structures, up to 2 mm long, already known since 1861 [3]. The spennatozeugmata have an outer layer, the cortex, formed by tightly packed parasperm, and an inner core, the axial cylinder, formed by paralelly arranged euspcnn. The spennatozeugmata are stored in the spermathccae up to the moment of fertilization, when they move towards the spennathccal duct at the edge of which they are broken, thus delivering the eusperm [3]. Thus, the spermatozeugmata perfonn different functions, accompanied by particular features: they hold together a certain number of fertilizing sperm "ready for use". This is probably accomplished by an impressive complex of cell junctions fonned mainly by septate junctions, followed by scalarifonn junctions connecting paraspenn tails [3] they are able to move with a metachronal wave fomled by the distal extremities of the paraspenn, thus carrying the fertilizing eusperm [3]. We have studied T. whifex spermatozeugmata using different techniques: TEM, SEM, freeze fracture, high speed video microscopy. confocal microscopy and immunogold labeling. We were able to show the metachronal wave produced by the paraspenn tails and measure its beat frequency (10 Herz). For the first time using CLSM we have documented by a TRITC phalloidin labeling the presence of a large amount of F-actin inside the cytoplasm of the paraspenn tails. Actin was also localized by means of immunogold staining under TEM. It remains to be established to what extent actin is cOJUlected to the septate junctions.