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Arquivos de Zoologia

degrees of development, siphonal canal in the shell aperture. This character is absent in archaeogastropods and basal caenogastropods. The canal of the cerithioideans does not correspond with a great development of a muscular siphon of the mantle edge, like those of the higher caenogastropods (see discussion on mantle), and so appears to have been acquired independently. Among the cerithioideans the canal is absent only in turritellids and vermetids. In the prescnt analysis the canal was separated into two characters, its presence (#3) and if greatly differentiated in the shell aperture (#2). This last State revealed to be developed in several taxa independently.

4.    Determinate growth: 0= absent; 1= present (Ali

taxa except Turritella hookeri, Campanile symbolicum, Serpulorbis decussatus); 2= periodical determinate growth (Cerithidea costata, Bittium varium, Finella dubia, Alaba incerta (CI= 50, RI= 80).

Determinate growth, i.e., development of a differentiated aperture in the adult form, appears to be the rule among the cerithioideans (see also Vermeij & Signor, 1992), and is practically absent among archaeogastropods and basal caenogastropods. This charactcr may be convcrgent with determinate growth of higher caenogastropods, and other gastropods (e g., Pulmonata). This character, among cerithioideans, is absent only in turritellids, vermetids and Campanile, appeared in the tree as a reversion. Periodical determinate growth, i.e., presence of several differentiable lips, marked in the shell by axial varices, is found in cerithideids and also in the miniaturized forms examined, such as Bittium, Finella and Alaba.

5.    Periostracum: 0= chitinous; 1= calcified

{Campanile symbolicum) (CI= 100,Rl= 100).

This character is a Campanile symbolicum autapomorphy, also pointed out by Houbrick (1981 a).

6.    Inner chitinous layer: 0= absent; 1= present

(Bittium varium, Finella dubia) (CI= 100, RI= 100).

A developed inner chitinous layer, resembling those of hydrobioid Barleeidae (Simone, 1995a), is easily found in both taxa when the shell is decalcified or broken.

7.    Size: 0= medium/largc; 1= miniaturized (adult

form smaller than 8 mm) (Bittium varium, Finella dubia, Alaba incerta) (Cl= 50, RI= 66).

8.    Autotomy of protoconch: 0= absent; 1= present

(.Aylacostoma spp, Doryssa spp.) (Cl= 50; RJ- 80).

Snout

9.    Typc: 0= cylindrical, deep ventral-anterior

furrow; 1= flattened, bilobed anterior mouth (Thiarids, Supplanaxis nucleus, pleurocerids, cerithids, Finella dubia, Alaba incerta, Batillaria minima, Cerithidea costata) (Cl= 100, RI= 100).

Two types of snout occur in the cerithioideans, most of them present a dorso-ventrally flattened snout, with the buccal mass partly or even completely within it. In this type, the mouth is almost terminal and is approximately in the same piane of the integument. In contTast, the other type is cylindrical, the buccal mass is only partly or completely outside, posterior to it, and the mouth is in the posterior region of a longitudi-nal, ventral-anterior furrow. This last type is also found in archaeogastropods and basal caenogastropods, and is regarded as piesiomorphic. Species of some genera such as Supplanaxis, Bittium, Finella and Alaba, the snout is not clearly dorso-ventrally flattened, but the inner organization is morę similar to that of flattened type and is regarded as this type in present analysis. The explanation of the flattened type of snout is the apomorphic lack of peri-buccal muscular rod. Some cerithioidean species have very extensible snout, as scaliolids (Ponder, 1994).

10.    Size: 0= normal (about 1/4 whorl); 1= large

and flattened (Cerithium atratum); 2= smali and flattened (Bittium varium. Finella dubia, Alaba incerta); 3= large and cylindrical (iSerpulorbis decussatus) (CI= 100, RI- 100, not additive).

Foot

11.    Size: 0= normal (about 1/3 whorl); 1=very large

{Turritella hookeri, Bittium varium.