Ascandra arenaria sp. nov. urn:lsid:zoobank.org:act: 9C6C8B9A-3972-4523-A558-65FAE77FA311 (Figs. 4, 5; Table 4) Etymology: From the Latin arenarius, meaning “sandy”, referring to the large amount of sediment accumulated among the sponge tubes. Type locality: Saco do Poço, São Sebastião Island, Ilhabela, São Paulo State, Brazil. Type material: Holotype — MNRJ757, Saco do Poço, São Sebastião Island, Ilhabela, São Paulo State, Brazil, depth 8 m, coll. E. Hajdu, 09/I/1996. Diagnosis: Ascandra with branching tubes connected only at the base, where they are loosely anastomosed. Skeleton composed of predominantly lanceolate diactines, one category of triactines and one of tetractines. The triactines are the most abundant spicules. Colour: White in life and in ethanol (Fig. 4A). Morphology and anatomy: Cormus formed by elongated, erect, branching tubes, connected and loosely anastomosed at the base (Fig. 4A). Each tube ends in a simple osculum (Fig. 4A). The external surface of the tubes is slightly hispid, as well as their lumen. Aquiferous system asconoid. The skeleton is composed of triactines and tetractines arranged without organisation, and diactines that lie perpendicular or obliquely to the tubes (Fig. 4B–D). The triactines are the most abundant spicules. Spicules (Table 4): Diactines: Often curved, with the proximal tip sharp and thicker than the distal one, which is predominantly lanceolate, but can also be sharp (Fig. 5A). Size: 214.5 (±38.3)/11.3 (±1.9) µm. Triactines: Regular to subregular, rarely sagittal with the unpaired actine shorter than the paired ones. Actines are conical to slightly conical, with sharp tips (Fig. 5B, C). Size: 132.0 (±17.1)/11.5 (±1.3) µm. Tetractines: Regular to subregular. Basal actines are conical to slightly conical and sharp (Fig. 5D). The apical actine is smooth, curved and conical, occasionally undulated near the tip and sharply pointed. It varies greatly in length, being sometimes longer than the basal actines (Fig. 5D, E). Size: basal—135.6 (±24.4)/13.6 (±2.8) µm; apical—53.3 (±27.5)/8.7 (±2.6) µm. Ecology: The specimen had sediment accumulated among the tubes at the base of the body, with associated bryozoans, bivalve molluscs, and polychaete tubes (Fig. 4A). Geographic distribution: Southeastern Brazil ecoregion—São Sebastião Island (Ilhabela), São Paulo State (provisionally endemic), Brazil. Remarks: The genus Ascandra currently comprises 19 species (De Voogd et al. 2025), of which only two have lanceolate diactines in the skeleton: A. mascarenica Klautau, Lopes, Tavares & Pérez, 2021 (from Réunion Island, Indian Ocean), and A. polejaeffi Lopes, Padua, Azevedo & Klautau, 2025 (from Espírito Santo, Brazil). Ascandra arenaria sp. nov. can be readily distinguished from both by the presence of a single category of tetractines, whereas A. mascarenica and A. polejaeffi exhibit two size categories. In addition, A. mascarenica differs from the new species by its more anastomosed cormus with a large water-collecting tube and the predominance of tetractines in the skeleton. We also compared A. arenaria sp. nov. with specimens from the Brazilian coast previously identified by Borojević & Peixinho (1976) as A. atlantica, due to the shared presence of lanceolate diactines. As noted by Klautau & Valentine (2003), these specimens do not correspond to Ascandra atlantica (Thacker, 1908) from Cape Verde, as they exhibit a clathroid body and lanceolate diactines. A taxonomic revision of these specimens is needed, as they may correspond to A. polejaeffi, or possibly represent an undescribed species. However, like A. mascarenica and A. polejaeffi, these specimens have two size categories of tetractines, which distinguishes them from the new species described herein. As the presence of diactines has not been fully validated as a reliable diagnostic character in Ascandra, although it has often been used for species distinction, we compared our new species with two Ascandra species that have a single category of triactines and tetractines but lack diactines: A. brandtae (Rapp, Göcke, Tendal & Janussen, 2013), from Antarctica, and A. spalatensis Klautau, Imešek, Azevedo, Pleše, Nikolić & Ćetković, 2016, from the Adriatic Sea. The former differs from A. arenaria sp. nov. by having spicules with cylindrical actines and a higher abundance of tetractines. The latter differs in having smaller triactines [90.5 (±17.2)/8.0 (±0.8) µm] and tetractines [basal actine: 99.4 (±16.9)/12.0 (±1.6) µm], and a longer and thicker apical actine in the tetractines [74.3 (±1.9)/10.8 (±0.0) µm] compared to our new species [triactines—132.0 (±17.1)/11.5 (±1.3) µm; tetractines—basal actine: 135.6 (±24.4)/13.6 (±2.8) µm, apical actine: 53.3 (±27.5)/8.7 (±2.6) µm].

Published as part of Pereira, Sara Emilly, Azevedo, Fernanda, Hajdu, Eduardo, Cavalcanti, Fernanda F. & Klautau, Michelle, 2025, Calcareous sponges (Porifera, Calcarea) from São Sebastião, São Paulo: new species and new records in two marine protected areas of Southeastern Brazil Ecoregion, pp. 1-107 in Zootaxa 5688 (1) on pages 14-15, DOI: 10.11646/zootaxa.5688.1.1, http://zenodo.org/record/17017479