A NEW SPECIES OF STRATIODRILUS ( POLYCHAETA , HISTRIOBDELLIDAE ) FROM FRESHWATER CRAYFISHES OF SOUTHERN BRAZIL 1

A new species of polychaete, Stratiodrilus vilae, epizoic on Parastacus brasiliensis (von Martens, 1869) and P. defossus Faxon, 1898, is described from the State of Rio Grande do Sul, southern Brazil. The new species has one pair of long, anal, conical ventral lobes, one on each side of the anus, claspers in the males, and one pair of tubercles in each of the posterior locomotor appendages; and the jaw apparatus not reaching the limit between the head and the first segment.


INTRODUCTION
Histriobdella van Beneden, 1858, found on eggs of lobsters in Europe and in North America, Stratiodrilus Haswell, 1900, found in the branchial chamber of freshwater crayfishes in Australia, Madagascar and South America, and Dayus Steiner & Amaral, 1999, collected from the pleopods of a marine isopod in South Africa are the three genera of epizoic, ectocommensal polychaetes in Histriobdellidae.
A new species of Stratiodrilus has been found on two species of freshwater crayfish Parastacus brasiliensis and P. defossus in the State of Rio Grande do Sul, southern Brazil, which is described.

MATERIAL AND METHODS
Specimens of P. brasiliensis were collected from a tributary of the Mineiro creek, Taquara, State of Rio Grande do Sul (RS), Brazil (50º 47'W, 29º 37'S), in November 1997 and September 1998 and from an unidentified creek of Mariana Pimentel (RS) (30º 21'S, 51º 35'W), in January of 1998.One specimen of P. defossus was collected from a swampy area in Mariana Pimentel in March 1998.The annelids were collected after immersion of the crayfish in water with menthol, to prevent body contraction, and were fixed in A. F. A. (70% ethanol, formalin 37%, glacial acetic acid).Some specimens were cleared in Amann's lacto-phenol (HUMASON, 1972) and beech wood creosote; others were stained in Delafield's hematoxylin; all specimens were mounted in Canada balsam.Photomicrographs were taken using Kodak Gold 100 ISO film.Measurements are in micrometers (µm), unless otherwise indicated; the range for each character is followed between parentheses by the arithmetic mean the indication of sample size, when the number measured is different from that stated at the beginning of the description, and the standard deviation.
Female (n = 10) (figs.2, 5-9, 15-18): 0.89 -1 Diagnosis.Stratiodrilus vilae sp.nov.has one pair of long, anal, conical, ventral lobes (AcvLb); the cirrus 4 single, adjacent to a long conical ventral lobe (CvLb); claps in the males; one pair of tubercles in each of the posterior locomotor appendages; and the jaw apparatus not reaching the limit between the head and the first segment.According to the pictorial keys given by MOYANO et al. (1993) and by AMARAL & MORGADO (1997), it is possible to see that S. tasmanicus and S. novaehollandiae lack the pair of anal, conical, ventral lobes (AcvLb) called cirrus C5 by some authors, including STEINER & AMARAL (1997).To treat the conical lobes present in the posterior locomotor appendages, both the CvLb and the AcvLb as cirri is an unwarranted action as the nature of these structures is completely different, as can be seen in figs.7, 9. Using this approach none of the species of Stratiodrilus presents a cirrus denominated C5 by these authors.Using the same reasoning C4 cannot be "double".It might, in some species, be associated with an adjacent conical, ventral lobe CvLb.There are species in which C4 lacks the adjacent conical, ventral lobe (CvLb).This character is shared by S. haswelli, S. aeglaphilus, and S. arreliai.
Type host: Parastacus brasiliensis (von Martens, 1869) and Parastacus defossus Faxon, 1898.In the branchial chamber.Type locality, Taquara, RS, Brazil.Etymology.The specific epithet vilae was given in honor of Dr. Irma Vila, of the Universidad de Santiago, Chile, who has described the first species of Stratiodrilus from Chile.Discussion.Stratiodrilus vilae differs from all species of Stratiodrilus, except S. pugnaxi for having one pair of long, anal, conical, ventral lobes (AcvLb), which STEINER & AMARAL (1997) called C5. Stratiodrilus pugnaxi has a double pair of long, anal, conical, ventral lobes (AcvLb).Stratiodrilus sp. has one pair of AcvLb as S. vilae.Stratiodrilus vilae differs from all species of Stratiodrilus known to date, except S. circensis and Stratiodrilus sp. of MOYANO et al. (1993), for having one pair of tubercles in each of the posterior locomotor appendages.The tubercles are absent in S. tasmanicus, S. novaehollandiae, S. platensis, and S. robustus, while they are single in S. haswelli, S. aeglaphilus, S. pugnaxi, and S. arreliai, and two pairs in S. circensis and Stratiodrilus sp. of MOYANO et al. (1993).
made the first revision of Histriobdellidae, proposing the genus Dayus to accomodate Stratiodrilus cirolanae described by FÜHR (1971), from South Africa and described two species of Stratiodrilus, S. robustus epizoic on Trichodactylus sp., from São Paulo and S. circensis on Aegla sp.(probably A. schmitti Hobbs III) from the State of Paraná.DIONI (1972) recorded S. platensis on undetermined specimens of Aegla and Parastacus from Argentina while MOYANO et al. (1993) recorded the same species in Chile on Aegla bahamondei