Proposal for a revised classification of the Demospongiae (Porifera)

Abstract

Background: Demospongiae is the largest sponge class including 81% of all living sponges with nearly 7,000 species worldwide. Systema Porifera (2002) was the result of a large international collaboration to update the Demospongiae higher taxa classification, essentially based on morphological data. Since then, an increasing number of molecular phylogenetic studies have considerably shaken this taxonomic framework, with numerous polyphyletic groups revealed or confirmed and new clades discovered. And yet, despite a few taxonomical changes, the overall framework of the Systema Porifera classification still stands and is used as it is by the scientific community. This has led to a widening phylogeny/classification gap which creates biases and inconsistencies for the many end-users of this classification and ultimately impedes our understanding of today's marine ecosystems and evolutionary processes. In an attempt to bridge this phylogeny/classification gap, we propose to officially revise the higher taxa Demospongiae classification.

Discussion: We propose a revision of the Demospongiae higher taxa classification, essentially based on molecular data of the last ten years. We recommend the use of three subclasses: Verongimorpha, Keratosa and Heteroscleromorpha. We retain seven (Agelasida, Chondrosiida, Dendroceratida, Dictyoceratida, Haplosclerida, Poecilosclerida, Verongiida) of the 13 orders from Systema Porifera. We recommend the abandonment of five order names (Hadromerida, Halichondrida, Halisarcida, lithistids, Verticillitida) and resurrect or upgrade six order names (Axinellida, Merliida, Spongillida, Sphaerocladina, Suberitida, Tetractinellida). Finally, we create seven new orders (Bubarida, Desmacellida, Polymastiida, Scopalinida, Clionaida, Tethyida, Trachycladida). These added to the recently created orders (Biemnida and Chondrillida) make a total of 22 orders in the revised classification. We propose the abandonment of the haplosclerid and poecilosclerid suborders. The family content of each order is also revised.

Summary: The deletion of polyphyletic taxa, the use of resurrected or new names for new clades and the proposal of new family groupings will improve the comparability of studies in a wide range of scientific fields using sponges as their object of study. It is envisaged that this will lead to new and more meaningful evolutionary hypotheses for the end-users of the Demospongiae classification.

Keywords: Heteroscleromorpha; Lithistids; Monophyletic; Polyphyletic; Sponges; Systematics; Taxonomy; Type taxon.

Figure 1

Demospongiae classification from orders to families, as presented in the Systema Porifera [ 1 ] . Names crossed out in red should be abandoned. Coloured names highlight taxa that should be reallocated; for their new allocation, see Figure 2.

Figure 2

Proposal for a revised classification of the Demospongiae, from subclasses to families. Relationships between the different taxa is deduced from all molecular phylogenetic studies published so far (as of November 2014). Coloured names correspond to the same colour code used in Figure 1. Only the authorships of new taxa or resurrected taxa since the publication of the Systema Porifera (2002) are given. An asterisk (*) is placed next to all order and family names suspected to be non-monophyletic, based on molecular phylogenetic results (see text for references).

Figure 3

18S tree revealing the polyphyly of the Poecilosclerida suborders. PhyML tree with branches collapsed showing the polyphyly of the poecilosclerid suborders (Microcionina, Mycalina, Myxillina), with the exception of Latrunculina; only node bootstrap support > 50 are shown. This is a subset of the data used in Redmond et al. [10].

Figure 4

18S tree revealing the polyphyly of Hadromerida. PhyML tree with branches collapsed showing polyphyly of Hadromerida (shown in red) that we propose to abandon; only nodes with > 50 b.s. are shown. This is a subset of the data used in Redmond et al. [10]. *Raspailiidae, *Suberitida, *Stelligeridae and *Tetractinellida include a mix of former ‘hadromerid’ taxa as well as taxa from other orders.

Figure 5

Pie charts showing the importance of Demospongiae subclasses and orders in terms of number of species. A. Demospongiae subclasses. B. The 22 Demospongiae orders from the revised classification, in alphabetical order. Numbers of species are estimates obtained from the World Porifera Database http://www.marinespecies.org/porifera/ (accessed on the 17th of October 2014).