26. The development of Diplozoon Nordmann 



The development of the common parasite of carp fishes, D. 

 paradoxum Nordm.ann(Fig. 231) was studied by Zeller (Zeller, 1872b) and 

 by us; however, one must indicate that the existing data concerning the 

 structure of the larva are insufficient and need to be supplemented. 

 According to our data, the larvae emerge from the eggs on the 9th to the 

 10th day and according to Zeller on the 12th - 17th. The free -swimming larva 

 (Fig. 232) has an elongated form with a small band at the level of the 

 anterior end of the pharynx with a weakly expressed attaching disc and a 

 cap-shaped growth behind the latter. According to Zeller, the length of 



the larva is about 0. 26 

 mm and, according to our 

 data, about 0. 23 mm. The 

 ciliary covering of 



0.}m» 



Fig. 231. Diplozoon paradoxum Nordmann, 

 pair of adult wornns from the gills of 

 Abramis brama from the Bay of Finland 

 near Peterhof. 



Fig. 232. Diplozoon 

 paradoxum Nor dmann , 

 free -swimming larva. 



p. 202 



the larva is strongly developed and is represented by five groups of cells. 

 The first two groups lie along the sides of the anterior part of the body 

 somewhat away from the anterior end and reach back to the above-mentioned 

 band. The two next groups also occupy the sides of the body starting a 

 little below the band and reach posteriorly to the level of the anterior edge 

 of the attaching disc. Finally, the fifth group lies beyond the disc on the 

 posterior growth of the body. Two small buccal suckers are located on 

 the cephalic end somewhat lower than the buccal opening; a little below 

 them are located 2 bean-shaped, pigmented eyes drawn close together so 

 that their convex sides touch or even merge. The digestive system of ths 

 larva is strongly developed. The above-mentioned suckers, which are 

 characteristic for the entire group of Oligonchoinea, are located on each 



219 



