Abstract
This paper reports the discovery of a small population of sponges in the Pigeon River of eastern Tennessee, USA, which were morphologically distinct from Spongillida of North America. A morphological comparative analysis resulted in the first Nearctic record of the genus Heterorotula with the description of a new species Heterorotulalucasi sp. nov. diverging from all other known species by its unique combinations of diagnostic morphotraits of spicules and gemmules. The new record enlarges the geographic range of the genus which has been known until now only from Australia, New Zealand, New Caledonia, Japan (as an alien species), and from subequatorial Brazil (as subfossil remains). The discovery of a biogeographic enclave of Heterorotula in the southeastern United States contributes to the understanding of Porifera inland water biodiversity, biogeographic patterns, and adaptive morphotraits in the Nearctic and globally. Data confirm that the Appalachian region (Ordovician-Permian origin) of Tennessee and, in general, of North America have high levels of diversity and endemicity.