Sessile marine invertebrates living on hard substrata usually present strategies such as size variations, longer life spans, fragmentation and fusion to occupy and compete for space. Calcareous sponges are usually small and short-lived, and some species are known to undergo frequent fragmentation and fusion events. However, whether fusion occurs only between genetically identical individuals remains unclear. We investigated the occurrence of chimaeras in the calcareous sponge Clathrina aurea by following the dynamics of fragmentation and fusion of 66 individuals in the field for up to 18 months and determined size variations and the life span of each individual. Microsatellites were used to determine whether fusion events occur among genetically different individuals. Growth and shrinkage of individuals were frequently observed, showing that size cannot be associated with age in C. aurea. The life span of the species ranged from 1 to 16 months (mean: 4.7 months). Short life spans and variable growth rates have been observed in other species of the class Calcarea. Fragmentation and fusion events were observed, but fusion events always occurred between genetically identical individuals, as has been suggested by graft experiments in adult Demospongiae and other Calcarea. These results suggest that at least C. aurea adults may have some mechanism to avoid chimaerism.

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Clathrina aurea was considered endemic to Brazil before being recorded from the Pacific (Peru) and the Caribbean Sea. We assessed the morphological variability, phylogeographic pattern and population genetic structure of the species across its geographic range to understand how habitat fragmentation/reduction can affect a widely distributed species with supposedly low dispersal capability. Samples from 15 localities in the Caribbean Sea (n = 8), Brazil (n = 5), and Peru (n = 2) were studied. Morphological analyses included characterisation of external morphology, skeleton composition, and spicules morphometry. Phylogenetic trees and haplotype network were constructed using rDNA sequences. Population structure was assessed using microsatellite loci (F ST fixation index and Discriminant Analysis of Principal Components). Morphological traits were consistent with C. aurea, although certain differences have been found, possibly due to environmental factors (temperature and pH). Phylogenetic analyses corroborated the conspecificity of the individuals and indicated higher genetic variability in individuals from Brazil and Caribbean, compared to Peru. Phylogeographic analyses indicated that Brazil had the oldest population of C. aurea, suggesting the expansion of this species across the Amazon River to the Caribbean and its connectivity through intermediate populations (e.g., Abrolhos). Population structure analyses also revealed high levels of genetic connectivity between the Caribbean and Northeast Brazil and among Southeast Brazilian localities. All analyses indicated isolation or restricted gene flow between Pacific and Atlantic populations. This, combined with the reduced genetic diversity in Peru and the supposedly limited larval dispersal capability, suggest a possible non-natural dispersion; however, we cannot exclude other hypotheses.

This paper reports four new Leucettidae (Porifera, Calcarea) from Western Australia, with two representatives of Leucetta and two of Pericharax: L. foliata sp. nov., L. purpurea sp. nov., Pericharax crypta sp. nov., and P. vallii sp. nov. This is the first time tripods have been described within Pericharax. In addition, one species (L. foliata sp. nov.) has an external morphology not previously reported for Leucetta, and for the first time tetractines of the inhalant and exhalant canals have been distinguished. Leucettidae now comprises 28 species, eight of them occur in Western Australia, which means this Australian State has the highest species richness for this family in Australia. The WA coastline has been largely unexplored for Calcarea so it is likely that further collecting will yield additional species. Leucetta microraphis is the most widespread species of Leucettidae in Australia, occurring in all States except the Northern Territory and Tasmania. We highlight the importance of a revision of the Leucettidae using molecular and morphological characters to determine which morphological characters have a phylogenetic signal.