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Arquivos de Zoologia

Introduction

The Cerithioidea is an enigmatic group abundant in species, with representatives in almost all aquatic habitats. This taxon had been regarded as the stem group of the order Caenogastropoda (Haszprunar, 1988). The comprehension of this group is, then, extremely important for understanding the order.

Being such an important group, sonie studies on the entire superfamily, or part of it, are found in the literaturę (e.g., Morrison, 1954), introducing an systematic order and looking for its relationship among the Prosobranchia. Although, a mark of the cerithioidean knowledge is the paper of Houbrick (1988). In that paper, the author undertaken a fuli historie; analysis on each character interesting for systematics of 14 of the 17 families considered within the superfamily; summarized the data firom his own papers and of other authors; finalizing with eladistie and phenetic analyses of the group. Ponder (1991) madę a reanalysis of the Houbrick *s results, and inserted some new data and other outgroups. Haszprunar (1988: 416), on the other hand, noted that no synapomorphic character unites the Cerithioidea, remaining grouping taxons by shared plesiomorphies, such as lack of penis, opened pallial oviduct, spiral operculum, etc. This point was also noted by Ponder & Lindberg (1997:226), in a recent phylogenetic analysis of the Gastropoda. The cerithiids, in particular, occupies a position in the consensus tree (fig. 2, p. 182 of that paper) among the caenogastropods, just between the architaenioglossans and the remainder

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The human interest by Cerithioidea is not only for systematics, it contains some species of medical importance, being hosts of some human disease etiologie agents, such as Paragonimus western ani and Clonorchis sinensis (Abbott, 1948; 1952;Davis, 1971; Brandt, 1974). Some thiaridsare used as probable competitors of Planorbidae (Pulmonata), host of schistossomiasis (Pointier, Toffart et al., 1991; Pointier, Fredich et al., 1991; Freitas & Santos, 1995). By detrivory, they are important agents in drainage and marinę ecosystems.

As part of a laiger project on comparative morphology of Caenogastropoda, 19 species belonging to 12 cerithioidean families were selected for analysis.

Most of the analyzed species come firom Western Atlantic (when marinę) and Neotropical (when freshwater) regions. In Neotropical region two families of Cerithioidea are represented, the Thiaridae (genus Aylacostoma) and the Pleuroceridae (genus Doryssa). In the area west of the Andes, 83 nominał species of these families occur, although the systematic organization is too obscure which rendering any study impractical. The present paper is a step in direction of a better systematic organization of the Neotropical cerithioideans. It provides anatomical comparative dcscriptions and systematic analysis of 7 species, which may be the base for futurę revisions. Practically all systematic papers on Neotropical cerithioideans only inelude species descriptions (e.g., Scott, 1954). From those, only Ihering (1902; 1909) and Morrison (1954) have some comprehensive revision aspects, the last concemed about worldwide melanians. Except for some brief data found in Scott (1953), Morrison (1954) and Martinez-Escarbassiere & Royero (1995), and with some detail in Abbott (1955), no other anatomical data on Neotropical cerithioidean has been published.

The main objective of this paper is to providc a new phylogenetic analysis based on comparative morphology, of the 19 species of 12 cerithioidean families. The analysis involves characters never before examined, such as the heart site, mantle border, intrinsic odontophore muscles, etc. Also a comparison with non-caenogastropod outgroups, i.e., species of the archaeogastropod grade, is provided and commented (see outgroup choice section for specific groups utilized). The concem is to test the cerithioidean monophyly, and if other groups such as Campaniloidea and Vcrmetoidea are actually separated taxa.

Materiał and Methods

A detailed list of the specimens examined follows each species description. lnstitutional abbreviations are: AMNH, American Museum of Natural History, New York; ANSP, Acadcmy of Natural Sciences of Philadelphia; MZSP, Museu de Zoologia da Universidade de Sao Paulo; USNM, National Museum of Natural History, Smithsonian lnstitution.

All dissected specimens were preserved in