PHENETIC ANALYSIS OF MICROPHALLOIDEA (TREMATODA) ACCORDING TO THE CHAETOTAXY OF CERCARIA

The main interest of digenean cercarial chaetotaxy lies in its close a ssociation with the nervous system, which is very stable and evolves v ery slowly. A phenetic analysis of the chaetotaxy was completed for th e following: (i) 12 microphallids, including five Maritrema spp., five Microphallus spp., one Megalophallus sp. and one Gynaecotyla sp.; (ii ) three lecithodendriids, including one Pseudocephalotrema sp., one Pr osotocus sp. and one Pleurogenoides sp.; (iii) three renicolids, Renic ola sp., Cercaria sp. 7 and Cercaria sp. 8 of Richard (1971). The cerc arial sensilla were stained using a silver nitrate impregnation techni que. It was assumed that, when one or several sensilla are observed in the same locus in different cercariae, they are homologous, and that, during the course of evolution, chaetotaxy becomes more complicated. At each locus, the presence or absence and the number of sensilla were listed. This allowed a classification of the,cercariae from the simpl est to the most complex, firstly within each genus and subsequently wi thin the same family. The families themselves were then compared. The total number of sensilla, C + A(I)D + P + U, was 36-47 in Maritrema, 4 0-52 in Microphallus, 51-52 in Megalophallus and 57-58 in Gynaecotyla. These cercariae have no acetabulum or S sensilla. The total number of sensilla, C + A(I)D + P + U, was 56-64 in Pseudocephalotrema, 60-68 i n Prosotocus, 66-72 in Pleurogenoides and 67-79 in Renicola. These cer cariae have an acetabulum and the number of the S sensilla must be add ed to the total. These data suggest that, within the sample analysed, the genus Maritrema is the most primitive and the genus Renicola the m ost evolved. The authors assume that the three families studied here h ave a common origin and may be grouped together in the superfamily Mic rophalloidea. The cercarial chaetotaxy of the Plagiorchioidea is known for Cephalogonimus, Plagiorchis, Astiotrema, Leptophallus, Opisthiogl yphe, Haplometra, Haematoloechus, Skrjabinoeces, Macrodera and Omphalo metra. All of these cercariae exhibit more than 80 C + A(I)D + P + U s ensilla and display a relative homogeneity; for these reasons, only th e chaetotaxy of Omphalometra is compared with those of the 16 micropha lloids. This comparison allows us to reject the hypothesis for the ori gin of the Microphalloidea within the Plagiorchioidea. In the suborder Plagiorchiata, the superfamily Microphalloidea appears to be the most primitive.