Article: The demosponge genus Leptomitus and a new species from the Middle Cambrian of Spain

Forty-five specimens of Leptomitus conicus sp. nov. have been collected from the base of the Murero Formation (Caesaraugustan, Middle Cambrian) in the Murero area of Zaragoza, north-east Spain. The new species is a small obconical sponge, which has coarse oxeas forming parallel rods that run the whole length of the specimens in the manner typical of the genus. The biostratigraphy and facies of the levels with Leptomitus conicus have been analysed. Palaeoecological information derived from associated trilobites, brachiopods and ichnofossils shows that L. conicus lived in a soft substrate of a sublittoral environment of low to low/moderate energy. According to established Cambrian palaeogeographical reconstructions, a tropical distribution is inferred for the genus Leptomitus. Based on body shape, wall structure and stratigraphical distribution, a phylogenetic tree of the various Leptomitus species is proposed, with a central stock of simple cylindrical sponges branching out to other morphs.