THE SYSTEMATIC POSITION OF ALECTONA (PORIFERA, DEMOSPONGIAE): A TETRACTINELLID SPONGE

Abstract

The affinities of the genus Alectona Carter and of Spiroxya levispira (Topsent) have been investigated using 28S rDNA sequences and SEM study of their boring pattern. The close relationships of Alectona millari with the tetractinellids are strongly supported by molecular data, although its affinities with the orders Astrophorida or Spirophorida remain unresolved. Spiroxya levispira has no relationship with the tetractinellids. These results imply modifications of the conventional classification of Alectona within Hadromerida. In the Systema Porifera, Alectona and Spiroxya were classified in the family Alectonidae, whereas Thoosa was placed in the Clionaidae. We propose maintaining Spiroxya in the Clionaidae, and Alectona and Thoosa, which share a unique hoplitomella larva, in the family Thoosidae of the tetractinellids. Morphological evidence suggests the placing, possibly temporary, of Thoosidae in the order Astrophorida. However, the molecular data, and the uniqueness of the reproduction pattern and of spiculation suggest that the family could represent a special order of Tetractinomorpha.