Relevance of an integrative approach for taxonomic revision in sponge taxa: case study of the shallow-water Atlanto-Mediterranean Hexadella species (Porifera:Ianthellidae:Verongida)

Abstract

The identification of sponges that lack a mineral skeleton is always highly challenging, especially for Hexadella species, which are also fibreless. Recently, the yellow species Hexadella pruvoti Topsent was identified as a cryptic species complex while the pink coloured Hexadella racovitzai Topsent showed two highly divergent lineages. We performed a COI phylogenetic reconstruction using 27 new Mediterranean Hexadella samples in order to confirm the presence of divergent lineages within both shallow-water species. Specimens were described with an integrative approach combining morphological and cytological investigations, biochemical profiling and assessment of natural toxicity in order to identify diagnostic characters for each taxon. H. topsenti, sp. nov. is distinguished from H. racovitzai by its colour, its surface network shape, divergent secondary metabolite patterns and toxicity values. H. crypta, sp. nov. differs from H. pruvoti by a different encrusting growth form when alive, and by distinctively colouring the ethanol fixative solution. In addition, H. pruvoti and H. crypta show different types of cells with inclusions as well as distinct metabolic fingerprints. Natural toxicity values, however, do not permit the separation of H. pruvoti and H. crypta. Our work shows that only the use of a combination of complementary tools can provide relevant descriptions for some problematic taxa.

Host-specificity among abundant and rare taxa in the sponge microbiome

“…Similarly, the recently identified shallow-water species H. pruvoti, H. crypta, H. topsenti and H. racovitzai showed divergent associated bacterial communities. Differential metabolic patterns occur within each of these four shallow-water sponge groups (Reveillaud et al, 2012), and although no direct inference can be made concerning the actual producers of secondary metabolic compounds in these sponge-microbe associations, divergent bacterial communities could explain different secondary metabolites profiles for the different Hexadella species.…”

“…Their phylogenetic relationships inferred from comparisons of mitochondrial and nuclear genes were previously reported (Reveillaud et al, 2010). The taxonomy for shallow-water species Hexadella pruvoti, Hexadella crypta, Hexadella racovitzai and Hexadella topsenti were also previously analyzed using molecular data, morphology, toxicity and biochemistry (Reveillaud et al, 2012).…”

Vansoestia caribensis gen. nov., sp. nov.: first report of the family Ianthellidae (Verongida, Demospongiae) in the Caribbean

“…Sample P12x402 (from Redmond et al, 2013) preserved in glutaraldehyde 2.5%, was processed using a standard protocol for cytology and transmission electron microscopy (Reveillaud et al, 2012). Ultrastructural details could be clearly observed, such as various cells containing inclusions, choanocytes, collagen fibril strands, archaeocytes, and bacteria.…”

“…There is a striking similarity between V. caribensis gen nov. sp. nov. and the external appearance of Hexadella pruvoti Topsent, 1896 (Reveillaud et al, 2012), particularly with respect to the abundant subdermal canals converging in a wide oscule, and its yellowish coloration. However, 18S and 28S gene sequence analyses confirmed the very distinct nature of these two species.…”

“…Species of Verongida are conspicuous components of the benthic fauna on both exposed and cryptic hard substrates on coral reefs, reef walls, and other rocky substrates (Díaz et al, 2013;Bergquist and Cook, 2002 a, b, c, d). All verongid sponges produce complex brominated tyrosine-derived compounds, which have generated interest in the pharmaceutical industry and promoted several scientific investigations (Wu et al, 1986;Erwin and Thacker, 2007;Erpenbeck and van Soest, 2007;Reveillaud et al, 2012).…”