13. The development of Tetraonchoides Bychowsky 



The curious species, T. paradoxus (Fig. 29) was described by p. 174 

 us recently from Uranoscopus scaber L. It is characterized by a pipe- 

 shaped intestine and a complex attaching apparatus with four supplementary 

 sucker-shaped growths on the dorsal surface of the attaching disc. The 

 armature of the latter participates in attachment but the main role is played 

 by the powerful attaching disc itself. In 1935 at the Sebastopol Biological 

 Station we obtained free-swimming larvae of this species, but unfortunately 

 the drawings of these larvae were lost. From the notes and indications in 

 our work (Bychowsky, 1937) it is apparent that the larva is devoid of eyes 

 just as are the adult individuals. It has a sac -shaped intestine and only 16 

 edge hooks on the well-developed attaching disc. Thus the formation of the 

 remaining attaching armature in this species takes place in the postembry- 

 onic period. 



14. The development of Nitzschia Baer 



The representatives of the genus Nitzschia (Fig. 17) have two 

 attaching grooves on the head end and a powerfully developed sucker-shaped 

 disc at the posterior end. The armature of the disc consists of 14 edge and 

 3 pair of middle hooks; there are no septa on the interior surface of the 

 sucker-shaped disc. The sex system is strongly developed and the testes 

 are very numerous. The sex oriface opens on the ventral side of the body 

 almost along its middle line. They parasitize sturgeons. 



We studied the development of N. sturionis Abildgaard in July, 

 1932 during our work on the Caspian Sea (Island of Sara). The larvae 

 were obtained from eggs deposited by individuals collected from the great 

 sturgeon- -Huso huso (L. ). The Nitzschia larva which has just hatched 

 from the eggs has an elongated cylindrical body, but with slightly thickened 

 ends and a slightly inflated middle and three zones of ciliary epithelium 

 (Fig. 193). Its length is about 0. 35 mm and the width is 0. 1 mm. The 

 anterior end of the larva has two clearly expressed thickenings equipped 

 with a number of glands corresponding to the head growths of Dactylogyrus 

 and the attaching organs of the head ends of Epibdella and Benedenia . 

 Directly behind these thickenings are located 2 pairs of large eyes under 

 which, closer to the ventral side of the body, lie 2 large head ganglia of 

 the nervous system. The ciliary covering of the head end of the larva 

 starts from the anterior edge and terminates at a level with the posterior 

 end of the anterior pair of eyes. The pharynx of rounded shape and 

 relatively large dimensions is located somewhat away from the eyes; a 

 small ring-shaped intestine emerges from the pharynx. The second zone 

 of ciliary epithelium starts at the level of the middle of the intestine. It 

 is located nnainly along the sides of the body and terminates near the be- 

 ginning of the attaching disc. The excretory system is easily noticeable; 



188 



