Remarks:

Even though the PhyloCode version 4c ( is still a draft (it has not been formally implemented yet), it has already been used for several phyla, including sponges (Manuel et al., 2003; Borchiellini et al., 2004; Cárdenas et al., 2010, 2011; Gazave et al., 2010b). In our opinion, this pre-PhyloCode era is not only an opportunity to make the scientific community better acquainted with the PhyloCode but also to discuss and polish the definitions we want to give for these clades, before their formal and official acceptance.

We have defined, under the PhyloCode, five homoscleromorph clades. We have named only clades that are well supported (BP ≥70 %) in the previous phylogenetic studies mentioned in the text (Philippe et al., 2009; Gazave et al., 2010;Pick et al., 2010). To avoid a proliferation of names, we have favored the conversion of pre-existing names from the Linnaean classification.While some apomorphy-based definitionsare suggested, the majority of definitions are branch-based because in most cases taxon sampling needs to be increased before stable apomorphy-based definitions can be derived.

Homoscleromorpha PhyloCode names in hierarchical order:

HomoscleromorphaP(nomen cladi conversum ex Homoscleromorpha Lévi, 1973).

Authorship of PhyloCode name. — Borchiellini et al., 2004.

Definition.— (branch-based) the most inclusive clade of Porifera which includes Oscarella lobularis (Schmidt, 1862) and not Geodia cydonium (Jameson, 1811), Leucosolenia variabilis (Haeckel, 1870), Oopsacas minuta Topsent, 1927, Hydra circumcincta Schulze, 1914, and Beroe ovataBrugière, 1789.

Comments on definition. — Possible autapomorphies are: flagellated exopinacocytes and endopinacocytes, peculiar flagellated apopylar cells, a cinctoblastula larva, amorphous axial filament and basement membrane with type IV collagen. The original definition used Hydraviridis as a specifier (reference point) but this is a mistake since it was not part of the phylogenetic tree of Borchiellini et al. 2004: we replace it here by Hydra circumcincta.

Reference phylogeny. — Borchiellini et al., 2004; Philippe et al., 2009; Picks et al., 2010.

OscarellidaeP(nomen cladi conversum ex Oscarellidae Lendenfeld, 1887).

Authorship of PhyloCode name. — This study.

Definition.— (Branch-based) the most inclusive clade containing Oscarella lobularis

(Schmidt, 1862) and not Corticium candelabrum Schmidt, 1862.

Comments on definition. — We decided not to choose an apomorphy-based definition for this clade since it is unclear whether the absence of spicules in this group is primary (plesiomorphic) or due to secondary loss. We also decided not to use mitochondrial gene arrangement in the Oscarellidae as a possibleautapomorphy, considering it less practical for clade definition (Gazave et al., 2010a).

Reference phylogenies. — Gazave et al., 2010a.

PlakinidaeP(nomen cladi conversum ex Plakinidae Schulze, 1880).

Authorship of PhyloCode name. — This study.

Definition.— (Branch-based) the most inclusive clade containing Plakina monolopha Schulze, 1880 and not Oscarella lobularis (Schmidt, 1862).

Comments on definition. — A possible autapomorphy of this clade is a peculiar tetractine spicule (small reduced, ramified calthrops).

Reference phylogenies. — Gazave et al., 2010a.

CorticiumP(nomen cladi conversum ex Corticium Schmidt, 1862).

Authorship of PhyloCode name. — This study.

Definition.— (Apomorphy-based) the clade originating with the first species to havecandelabra spicules (heterolophose calthrop) as inherited by Corticium candelabrum Schmidt, 1862.

Reference phylogenies. — Gazave et al., 2010a.

PlakostrellaP(nomen cladi novum).

Authorship of PhyloCode name. — This study.

Origin of name. — A combination of the genus names Plakortis and Plakinastrella, both part of this clade.

Definition.— (Apomorphy-based) the clade originating with the first species to have alophose spicules as inherited by Plakortis simplex Schulze, 1880.

Reference phylogenies. — Gazave et al., 2010a.

TetralophosaP(nomen cladi novum).

Authorship of PhyloCode name. — This study.

Origin of name. — In reference to tetralophose calthrop (see below).

Definition.— (Branch-based) the most inclusive clade containing Plakina trilopha Schulze, 1880 and not Plakina monolopha Schulze, 1880 and Corticium candelabrum Schmidt, 1862.

Comments on definition. — Possible autapomorphies of this clade are a well-developed mesohyl, well-differentiated ectosome, large subectosomal cavities and tetralophose calthrops. Since the type-species of the genus Plakina (Plakina monolopha) does not pertain to this clade, the genus name Plakina cannot be converted here.

Reference phylogenies. — Gazave et al., 2010a.