Abstract
Keratose (horny) sponges constitute a very difficult group of Porifera in terms of taxonomy due to their paucity of diagnostic morphological features. (Most) keratose sponges possess no mineral skeletal elements, but an arrangement of organic (spongin) fibers, with little taxonomic or phylogenetic information. Molecular phylogenetics have targeted this evolutionary and biochemically important lineage numerous times, but the conservative nature of popular markers combined with ambiguous identification of the sponge material has so far prevented any robust phylogeny. In the following study, we provide a phylogenetic hypothesis of the keratose order Dictyoceratida based on nuclear markers of higher resolution potential (ITS and 28S C-region), and particularly aim for the inclusion of type specimens as reference material. Our results are compared with previously published data of CO1, 18S, and 28S (D3-D5) data, and indicate the paraphyly of the largest dictyoceratid family, the Thorectidae, due to a sister group relationship of its subfamily Phyllospongiinae with Family Spongiidae. Irciniidae can be recovered as monophyletic. Results on genus level and implications on phylogenetic signals of the most frequently described morphological characters are discussed.
Highlights
In the last couple of decades, our knowledge on phylogenetic relationships of sponges, demosponges, experienced major turmoil when molecular data demonstrated serious pitfalls in the classical, morphology-based classification
A difficult order of sponges is the Dictyoceratida (Subclass Keratosa), which possess a skeleton of organic material only and lack mineral skeletal elements
The dictyoceratid taxa fall into clades differently supported by the individual fragments. These molecular analyses, as currently the most comprehensive to unravel the phylogenetic relationships of dictyoceratid sponges including type material, demonstrate that family Thorectidae sensu Cook and Bergquist (2002d) cannot be upheld
Summary
In the last couple of decades, our knowledge on phylogenetic relationships of sponges, demosponges, experienced major turmoil when molecular data demonstrated serious pitfalls in the classical, morphology-based classification (see, e.g., BouryEsnault, 2006; Cárdenas, Pérez, & Boury-Esnault, 2012; Erpenbeck & Wörheide, 2007; Redmond et al, 2013; Wörheide et al, 2012). A difficult order of sponges is the Dictyoceratida (Subclass Keratosa), which possess a skeleton of organic material (spongin) only and lack mineral skeletal elements (with the exception of Vaceletia, which possesses a hypercalcified secondary limestone skeleton instead of spongin fibers, see Wörheide, 2008). These sponges were historically assigned to the "horny" sponges. Internal relationships are still insufficiently understood, are mandatory for a variety of downstream research (Boufridi et al, 2017; Chianese et al, 2017; see e.g., Erpenbeck, Hooper, et al, 2012)
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