Class Gastropoda Cuvier, 1795
Family Rissoidae Gray, 1847
Genus Alvania Risso, 1826
Species Alvania cimicoides (Forbes, 1844)
Alvania cimicoides (Forbes, 1844)
Common in yellow sands. Surroundings of San Gimignano (Siena), Pliocene (Piacenzian).
Gastropoda Rissoidae Alvania Alvania cimicoides
Description
(O.D.) Testâ ovato-conica, albidâ, anfractibus 7 convexiusculis, sulcis longitudinalibus spiralibusque granulato-decussatis, ad suturam marginatis, crenulatis; aperturâ ovatâ, labro externo incrassato. Long. 02/12 unc.
Conchiglia formata da 6-7 giri convessi separati da suture profonde. Protoconca giri 2,5 percorsi da 9-10 file di minuscole papille a forma di punta di freccia, così disposte a partire dalla sutura anteriore: le prime 2 file sono collegate fra loro tanto da assumere l’aspetto di vere e proprie strie granulose, seguono 3-4 file di papille più distaccate in posizione più obliqua, quindi altre 2-3 file che tendono nuovamente ad unirsi e infine 1-2 file presso la sutura posteriore con papille distintamente separate.
La comparsa di una debole costicella nella metà anteriore del giro indica l’inizio della teleoconca. Il primo giro della teleoconca è ornato da 12-13 coste assiali e due forti cingoli spirali. Sul penultimo giro sono presenti tre cingoli spirali. Ultimo giro alto 2/3 dell’altezza totale, ornato da 16-17 forti coste assiali separate da intervalli più ampi e sfumate sulla base. Cingoli spirali 8-9 alti sopra le coste ma non nodulosi. Apertura ovale con labbro esterno varicoso internamente liscio. Occasionalmente sono presenti alcuni dentelli poco evidenti (Chirli, 2006).
Shell formed by 6-7 convex whorls, separated by deep suture lines. Protoconch, 2.5 whorls, with 9-10 rows of tiny papillae shaped like an arrowhead, thus arranged starting from the anterior suture: the first 2 rows are connected so as to take on the appearance of real grainy striae, followed by 3-4 rows of more detached papillae in a more oblique position, then another 2-3 rows that tend to join again and, finally, 1-2 rows near the posterior suture with distinctly separated papillae.
The appearance of a weak rib in the front half of the last whorl of protoconch, indicates the beginning of the teleoconch. First whorl of the teleoconch with 12-13 axial ribs and two strong spiral threads. On the penultimate whorl there are three spiral thrreads. Last whorl 2/3 of the total height, with 16-17 strong axial ribs separated by wider intervals and shaded on the base. 8-9 spiral threads, high above the ribs, but not nodulosis. Oval aperture with varicose external lip, internally smooth. Occasionally there are some not very noticeable teeth.
Bibliographic references and some more common synonyms
1844 Rissoa cimicoides – Forbes, p. 189
1844 Rissoa sculpta – Philippi, p. 131, pl. 23, fig. 21
1847 Rissoa intermedia – Aradas, p. 75
1867 Rissoa cimicoides v. minima – Jeffreys, p. 15
1903 Rissoa (Acinulus) dubius – Seguenza L., p. 49, fig. 14
1864 Rissoa scrabella – Doderlein, p. 25
1895 Alvania (Alvaniella) cimicoides v. scabrella – Sacco, p. 26, fig. 62
2006 Alvania cimicoides – Chirli, p. 17, pl. 7, figs 8-16
2021 Alvania cimicoides – Chirli & Forli, p. 104, pls 78, 79, 80, 81, figs B1-3, A1-19, A1-19, A1-3
Stratigraphic distribution
Miocene – Bulgaria and Italy (Montegibbio, Modena). Pliocene – Portugall, Spain and Italy, where is reported for many localities. Pleistocene – Italy (Calabria), Greece and Rodes Island. Recent – Atlanto-mediterranean species, reported until the coasts of Denmark, lives between the mud and the debris of the circalittoral zone.
References
Chirli C. (2006). Malacofauna Pliocenica Toscana – Caenogastropoda. Vol. 5, pp. 144, 46 Plates.
Forbes E. (1844). Report on the Mollusca and Radiata of the Aegean sea, and on their distribution, considered as bearing on geology. Reports of the British Association for the Advancement of Science for 1843. 130-193., available online at http://biodiversitylibrary.org/page/12920789
Acknowledgements
Si ringrazia l’amico Carlo Chirli (Tavarnelle, Firenze) per la concessione all’uso di alcuni suoi testi. see also Edizioni Danaus
