Rissoa decorata Philippi, 1846
Mediterranean.
Grazer and detritus feeder in the infralittoral.
 
« Testa turrita, undato-costata, sulcis profundis, transversis, regularibus exarata, alba, interstitiis costarum striga fusca exaratis; anfractibus convexiusculis; apertura vix dimidiam spiram aequante, ovata; peristomate continuo; labro incrassato. » – R. A. Philippi: “Diagnoses testaceorum quorundam novorum”, Zeitschrift für Malakozoologie, Hannover 1846, p.97.

Cap ras, Llançà, Girona, Catalunya, NE. Spain. 4,3mm.
 
The species is so close to some members of the polymorphic R. guerinii Récluz that « it would not be surprising if further studies show that » this species is an ecophenotype of the latter (Criscione & al., 2009).
The species in H. C. Weinkauff: “Die Gattungen Rissoina und Rissoa”, Systematisches Conchylien-Cabinet Bd.1:Abt.22, Nürnberg 1855, plate VI.
 
« Testa […] costis 12 robustis elevatis et rotundatis, striis transversalibus subtilissimis punctis impressis dense notata; […] Color albo vitreus, glaberrimus, apex violaceus, inter costas lineae longitudinales fuscae… »Ibid. p.133.
One of the very few species of Rissoa to be white and not translucent when fresh.
12m deep, in Posidonia bush, Vignola bay, Marina di Davia, Corbara, NW. Corsica. 5,5mm.
Same spot. 4,4mm.
Original pictures provided by S. Clanzig (FR) – (CC BY-NC-SA).

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