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polarization of pallial oviduct structures i s difficult, as there is no elear homology of these structures with those of the examined outgroups.

Observing the disposition of the species in the tree, and their pallial oviducts, it was possible to notę that the basie plan of this organ is the following. A deep open glandular furrow with a smali chamber in each lamina (bursa and receptacle) as in M. modulus and other species. Although each smali chamber disappeared or duplicated in species of different groups. In generał, however, the pallial oviduct variation tums around that basal standard.

Johansson (1953) provides additional discussion of pallial oviduct possible evoIution.

114.    Ovopositor: 0= absent; 1= present (Doryssa macapa, Pachychilus sp, Turritella hookeri, M. modulus, cerithids, Alaba incerta, Cerithidea costata) (CI- 14, RI= 14).

Several female cerithioideans present an obvious ovopositor in the right side of the head-foot, at the anterior extremity of a eiliated furrow that originates in the anterior extrcmity of the pallial oriduct. Other cerithioideans have the furrow but no elear ovopositor; this condition indicating an absence of this structure, or that this structure is present but not anatomically defined. In these cases the taxon is considered having the plesiomorphic State. In single genera (e.g., Doryssa) some species have an ovopositor while others do not. The ovopositor is regarded as apomorphic due its absence in all examined outgroups, including higher caenogastropods. However, at least in Littorina ziczac (Gmelin, 1791) an ovopositor is apparently present (Marcus & Marcus, 1963). Observing the tree, the ovopositor is one of the cerithioidean synapomorphy, however, it disappeared orbecoming anatomically undefined in some taxa.

115.    Ciliated furrow in right side of head: 0= absent; 1= present (all cerithioideans) (CI= 100, R1= 100).

116.    Aperture on right side for a inner brood pouch: 0= absent; 1= present (thiarids, Supplanaxis nucleus) (CI- 100, RI= 100).

117.    Deve!opment of an epithelial chamber within haemocoel-foot muscles: 0= absent; 1 =

present (thiarids, Supplanaxis nucleus) (CI-100, RI= 100).

118.    Brood pouch: 0-absent; l = dorsaland single

(thiarids); 2= ventral and double (Supplanaxis nucleus) (CI= 100, RI= 100, not additive).

119.    Number of embryos in brood pouch: ?= inapplicable (brood pouch absent); 1= up to 20 {Aylacostoma spp); 2= about 100 (Melanoides tuberculatus)\ 3= about 1000 (Supplanaxis nucleus) (CI= 100, RI= 100, not additive).

In the case of planaxids and thiarids, the ciliated groove that commences at the anterior extremity of the oviduct does not finish in at an ovopositor, but at the aperture of an inner brood pouch. Except for this feature, no other similarity is found upon examination of the brood pouch of both groups. In planaxids, the brood pouch is double, runs ventral to the esophagus, and stays in the dorsal region of the foot, and contains about a thousand embryos at the same level of development (see also Houbrick. 1987a, 1990). In contrast, the brood pouch of thiarids is single, runs dorsal to the esophagus, stays free in the posterior region of the haemocoel, and contains up to a hundred (in case of Melanoides or less than 20 in Aylacostoma spp.) young specimens in different growth stages (from one to five whorls). Scott (1953: 443) found only about 3 young specimens in the brood pouch of Aylacostoma guaratinica. Beny and Kadry (1974) found an average of 29 - 48 in different samples of M. tuberculatus. In the present analysis, the character brood pouch was divided into 2, an entrance in right side of head, at the end of ciliated furrow, and the remainder of the brood pouch. Even with this supposed non-homology, the proximity of the planaxid and thiarids in the obtained tree suggests that these structures may be homologue.

120.    Pallial sperm groove: 0= non-glandular; 1= glandular (prostatę) (all cerithioideans, except thiarids, with no małe examined); 2= which a chamber in inner lamina (pleurocerids) (CI= 100, Ri= 100, additive).

The aphalate condition of cerithioidean males is controversial. This had been regarded as secondary, i.e., originating from lost of a pre-existent penis (Fretter, 1951:584; Houbrick 1988),