Polymastiidae

Abstract: Phylogeny of the sponge family Polymastiidae was reconstructed based on 25 morphological characters. Twenty-one polymastiid species and three suberitid species, Suberites domuncula as outgroup, Aaptos aaptos and A. papillata as sister groups, were included in the analyses. The reconstructions were done in PAUP* running heuristic search with the parsimony criterion. We analysed three possible evolutionary scenarios based on three alternative interpretations of the body plan of Quasillina brevis and Ridleia oviformis: first—Ridleia possesses aquiferous papillae whereas Quasillina lacks them, second—both genera lack papillae and third—the body in both genera is a single hyper-developed papilla. All three scenarios excluded the secondary loss of the papillae in the polymastiid evolution. Scenario 2 also excluded the secondary loss of the regular choanosomal skeleton, while scenario 1 assumed its loss in Ridleia and scenario 3 admitted its loss in both Ridleia and Quasillina. We prioritised scenario 2 due to its maximal parsimony and rescaled consistency index and subsequently favoured the clustering of Ridleia and Quasillina separately from the monophyletic polymastiid clade. In all three scenarios Pseudotrachya hystrix clustered separately from other polymastiids in agreement with the molecular evidence, and thus the exclusion of Pseudotrachya from Polymastiidae was proposed. The relationships between A. papillata, Tentorium semisuberites, Polymastia uberrima, the clade Weberella bursa + Polymastia boletiformis and the main polymastiid clade were ambiguous. Meanwhile, all scenarios showed the non-monophyly of Polymastia and Aaptos. Our hypotheses should be tested by reconstructions based on larger taxon sampling of hadromerid species and larger sets of morphological and molecular characters before any ultimate taxonomic decisions are taken.