THE OLDEST MEMBERS OF PORCELLIOIDEA (GASTROPODA): A NEW LINK BETWEEN BALTICA AND PERUNICA

The strata of Gotland, Sweden, provide one of the richest records of Silurian gastropod faunas in the world. Recent re-evaluation of museum collections revealed for the first time the presence of gastropods of the superfamily Porcellioidea (Archaeogastropoda) in the Silurian strata of Gotland (Baltica). Additionally, the porcellioideans from Gotland represent the oldest record of the superfamily, members of which were an element of marine gastropod communities from Silurian to Cretaceous time, a period of more than 350 million years. The morphology of the sinistrally coiled teleoconchs in the oldest porcellioidean gastropods supports an existing hypothesis that the pseudo-bilaterally symmetrical teleoconch and the mid-whorl position of the selenizone in the post-Silurian porcelliids is a derived shell character. The occurrence of porcellioidean gastropods in the Silurian strata of Baltica also represents a new faunal link between Baltica and Perunica which corresponds well with published palaeobiogeographical and palaeogeographical models. Six taxa are described, including the Sheinwoodian (early Wenlock) Gotlandiela contraria (Lindstrom), the Gorstian (early Ludlow) Mannegaardina hedei gen. et sp. nov., the Ludfordian (late Ludlow) Gotlandiela sp. and Pernericirrus lindstroemi sp. nov., as well as two agnesiid species.