Deep phylogeny and evolution of sponges (phylum Porifera)

Area of Science:

• * Marine Biology
• * Evolutionary Biology
• * Systematics

Background:

• * Sponges (phylum Porifera) are ecologically, commercially, and biopharmaceutically significant benthic animals.
• * As early-branching metazoans, sponges are crucial for reconstructing early metazoan evolution.
• * The deep phylogeny and systematics of sponges remain debated, particularly their relationships with other non-bilaterian animals.

Purpose of the Study:

• * To review the current state of deep sponge phylogeny.
• * To evaluate the monophyly versus paraphyly of the phylum Porifera.
• * To detail the molecular phylogenies of the four main sponge classes: Demospongiae, Hexactinellida, Calcarea, and Homoscleromorpha.

Main Methods:

• * Review of recent phylogenomic analyses.
• * Analysis of mitochondrial genes and genomes in sponge phylogenetics.
• * Comparison of molecular phylogenies with classical systematic systems and morphological data.

Main Results:

• * Recent phylogenomic analyses support the monophyly of the phylum Porifera, contrasting with some previous studies suggesting paraphyly.
• * Molecular phylogenies show congruence with classical systems in Hexactinellida, Demospongiae, and Homoscleromorpha, but highlight challenges in Calcarea.
• * Sponge larvae exhibit traits suggesting complexity shared with eumetazoans, implying a secondary simplification of the adult sedentary lifestyle.

Conclusions:

• * The phylum Porifera is likely monophyletic, with significant implications for interpreting early animal evolution and developmental traits.
• * Further research is needed to resolve incongruences, especially within the class Calcarea, and to achieve a comprehensive understanding of sponge relationships.
• * Sponge evolution is characterized by complex larval stages and a secondarily simplified adult form, underscoring their unique position in metazoan phylogeny.