TWO NEW SPECIES OF ASTEROCHERIDS (COPEPODA: SIPHONOSTOMATOIDA) ASSOCIATED WITH A SPONGE FROM THE STRAIT OF MESSINA, ITALY: TAXONOMIC AND ECOLOGICAL TRAITS.

Two new species of asterocherid associated with sponges are described from the Mediterranean Sea. They are Psilomyzon laetitiae sp. nov. and Psilomyzon sarcotragusicola sp. nov. The genus Psilomyzon consists of only one known species, P. pauciseta. The two new species can be easily distinguished from the cogenus species by reduction of the endopod of leg 4. In P. pauciseta leg 4 endopod is 3-segmented, with the third segment reduced; in both two new species it is 2-segmented, with the second segment carrying an inner projection, possibly homologous to the third segment of the leg 4 endopod of P. pauciseta. In the new two species, the bifid outer process on male leg 4 second endopodal segment seem to be serial homologous of the similar processes on the same segment in leg 1 to 3, whereas the inner projection may represent a vestigial element of the third endopodal segment of leg 4.