Desma-bearing sponges, also known as lithistids or rock sponges, are a group typical of bathyal environments throughout tropical and warm-temperate regions. In this study the lithistids collected in the course of the Harbor Branch Oceanographic Institute eastern Atlantic 1991 campaign to Madeira, Selvagens and the Canary Islands were identified and assigned to eight species, representing eight genera and five families. Several constitute new records for these islands and one is a new species of Isabella, a genus thus far only known from the Norfolk Ridge in New Caledonia, that is here described and illustrated. Some considerations are made in regards to the diversity and biogeographical affinities of the Atlanto-Mediterranean lithistid sponges.

Background Lithistid demosponges, also known as rock sponges, are a polyphyletic group of sponges which are widely distributed. In the Northeast Atlantic (NEA), 17 species are known and the current knowledge on their distribution is mainly restricted to the Macaronesian islands. In the Mediterranean Sea, 14 species are recorded and generally found in marine caves. Methods Lithistids were sampled in nine NEA seamounts during the scientific expeditions Seamount 1 (1987) and Seamount 2 (1993) organized by the MNHN of Paris. Collected specimens were identified through the analyses of external and internal morphological characters using light and scanning electron microscopy, and compared with material from various museum collections as well as literature records. Results A total of 68 specimens were analysed and attributed to 17 species across two orders, seven families, and seven genera, representing new records of distribution. Ten of these species are new to science, viz. Neoschrammeniella inaequalis sp. nov., N. piserai sp. nov., N. pomponiae sp. nov., Discodermia arbor sp. nov., D. kellyae sp. nov., Macandrewia schusterae sp. nov., M. minima sp. nov., Exsuperantia levii sp. nov., Leiodermatium tuba sp. nov. and Siphonidium elongatus sp. nov., and are here described and illustrated. New bathymetric records were also found for D. ramifera, D. verrucosa and M. robusta. The Meteor seamount group has a higher species richness (15 species) compared to the Lusitanian seamount group (six species). The majority of the species had their distribution restricted to one seamount, and ten are only known from a single locality, but this can be a result of sample bias. Discussion The number of species shared between the seamounts and the Macaronesian islands is very reduced. The same pattern repeats between the NEA and Mediterranean Sea. This study demonstrates that NEA seamounts are ecosystems with a higher diversity of lithistids than previously thought, increasing the number of lithistids known to occur in the NEA and Mediterranean Sea from 26 to 36 species.

Phymaraphiniidae Schrammen 1924 (Porifera: Astrophorina) is a family of lithistid demosponges that has received little attention in the past decades. The systematic problems within this family have not been addressed for a long time due to the absence of new records and material. The genus Exsuperantia Özdikmen 2009 was first described by Schmidt (1879) as Rimella to allocate the species Rimella clava, found in the Caribbean. In 1892, Topsent found what he thought to be the same species described by Schmidt in the Azores, and synonymized it with Racodiscula clava, as he thought this species belonged to the family Theonellidae Lendenfeld 1903. However, Rimella and Racodiscula belong to distinct families: Rimella to Phymaraphiniidae, and Racodiscula to Theonellidae. Due to the fact that the genus Rimella was already preoccupied by a gastropod, it was renamed as Exsuperantia. In result of the poor preservation of Schmidt’s material and the absence of new specimens, the attribution of Topsent’s specimens to the family level remained obscure. Here, we review the genus Exsuperantia based on the analysis of new material recently collected during various research expeditions in the northeast Atlantic Ocean. The comparison of these new specimens with Schmidt’s and Topsent’s type material, allowed us to assign Topsent’s specimens to a new species, Exsuperantia archipelagus sp. nov., and confirm its attribution to the family Phymaraphiniidae (not Theonellidae). Phylogenetic reconstructions using newly generated sequences of the cytochrome subunit (COI) marker also support the assignment of the new species to the family Phymaraphiniidae (not Theonellidae).

Deep-sea sponge-dominated communities are complex habitats considered hotspots of biodiversity and ecosystem functioning. They are classified as Vulnerable Marine Ecosystem and are listed as threatened or declining as a result of anthropogenic activities. Yet, studies into the distribution, community structure and composition of these habitats are scarce, hampering the development of appropriate management measures to ensure their conservation. In this study we describe a diverse benthic community, dominated by a lithistid sponge, found in two geomorphological features of important conservation status -Le Danois Bank and El Corbiro Canyon-of the Cantabrian Sea. Based on the analyses of visual transects using a photogrammetric towed vehicle and samples collected by rock dredge, we characterize the habitat and the associated community in detail. This deep-sea sponge aggregation was found on bedrock. It is dominated by one lithistid sponge, Neoschrammeniella aff. bowerbankii (0.2 ind./m 2 ) and further composed of various sponge species as well as of other benthic invertebrates such as cnidarians, bryozoans and crustaceans. Using a non-invasive methodology (SfM -Structure from Motion) and empirical relationships of individuals size and biomass/volume obtained in laboratory for N. aff. bowerbankii, we were able to estimate a total biomass of 41 kg and volume of 39 l of this species in the surveyed area. This approach allows a fine tune methodology for estimating biomass and volume by image-based-observed area avoiding destructive techniques for this species.

Lithistid sponges are globally distributed in temperate and sub-tropical areas, constituting an important component of deep-sea benthic communities where they form structurally complex and vulnerable marine ecosystems (VMEs). In this study, we assess the diversity and investigate the spatial and bathymetric distribution of the lithistid sponges of the Azores archipelago (North Atlantic) based on historical records and examination of samples accidentally collected during deep-sea longline fishing operations in the region. Eleven lithistid species are recognized to occur in the Azores, including Leiodermatium tuba, recently described from material collected in several Northeast Atlantic seamounts that is hereby reported for the first time to the archipelago. We provide molecular barcodes (mtDNA COI and rRNA 28S) for seven of these species, including Discodermia ramifera, Macandrewia azorica, and Exsuperantia archipelagus, for which the Azores constitutes the type locality. We further discuss the phylogenetic and biogeographic affinities of the Azorean lithistids in the context of the Porifera classification, and the wider Northeast Atlantic upper bathyal fauna. Our study also warrants the addition of some lithistid species to the list of VME indicators for the Northeast Atlantic in support of the sustainable management and conservation of these species and habitats, as well as the ecological functions they deliver.