An unusual Silurian erratic astylospongiid (Porifera) from Gotland, Sweden

Astylospongia gothlandica Schlüter, 1884 was considered by Rauff (1893) and later authors as synonymous with Caryospongia diadema (Klöden, 1834). However, recent examination of the holotype and of several identical specimens found as erratics has revealed an internal skeletal and canal structure basically different from that of both the genus Astylospongia, and other genera of the family. Therefore, the new genus Caryoconus is introduced. Caryoconus gothlandicus (Schlüter, 1884) differs from all of the other transported sponge pebbles in its very restricted distribution, in that this species was found only on Gotland. A Silurian age was established on microfossils that occur with some of the sponges. This contrasts to all of the other numerous erratic sponge species, which originated from Late Ordovician beds. Because of this, it is concluded that representatives of Caryoconus gothlandicus came from an unknown, most probably restricted source area different from the source area of the numerous erratic sponge species from older strata