Zootaxa 4466 (1): 197–204 ISSN 1175-5326 (print edition) http://www.mapress.com/j/zt/ Article ZOOTAXA Copyright © 2018 Magnolia Press ISSN 1175-5334 (online edition) https://doi.org/10.11646/zootaxa.4466.1.15 http://zoobank.org/urn:lsid:zoobank.org:pub:1BCC4BD8-A168-408A-8DFD-407DFA44C91D When is an aster not an aster? A new deep-sea Discorhabdella (Demospongiae, Poecilosclerida) with asters, from the Mozambique Channel JEAN VACELET1,3 & PACO CÁRDENAS1,2 1IMBE, CNRS, Aix Marseille Univ, Univ Avignon, IRD, Station Marine d’Endoume, 13007 Marseille, France. 2Pharmacognosy, Department of Medicinal Chemistry, Uppsala University, Uppsala 75123, Sweden. http://orcid.org/0000-0003- 4045-6718 3Corresponding author. E-mail: [email protected] Abstract Discorhabdella pseudaster n. sp. is an incrusting sponge from the upper bathyal zone of the ‘Banc du Geyser’, north of Madagascar, Mozambique Channel. This new species is described only from a single specimen but it is remarkable by the presence of spicules similar to euasters, a type of microsclere unknown in Poecilosclerida. These spicules are in fact a new example of homoplasy, being derivatives of the typical Discorhabdella pseudoastrose acanthostyles, which are here re- duced to the aster-like tyles. The isochelae with a large lamella on the shaft are also quite unique in Poeciloclerida. Key words: Porifera, new species, Madagascar, bathyal, homoplasy Introduction The Mozambique Channel is still a poorly explored area for Demospongiae, despite the works of Bösraug (1913), Lévi (1956, 1964), Vacelet & Vasseur (1965, 1971) and Vacelet et al. (1976), Vasseur & Lévi (1976) who collected extensively in W Madagascar and Europa Island. The ‘Benthédi’ 1977 campaign in the Mozambique Channel collected shallow and deep-sea sponges but they have been barely studied apart from the calcareous keratose Vaceletia crypta by Vacelet (1977, 1979), collected from shallow waters around the Glorieuses Islands. The rest of the ‘Benthédi’ material (currently stored in the collections of the ‘Muséum National d’Histoire Naturelle’, Paris, France) remains to this day undescribed. These few studies focused on shallow-water sponges, up to 70 m for Lévi (1964), so that the bathyal demosponge fauna in this region is largely unknown. The BIOMAGLO expedition (https://expeditions.mnhn.fr/campaign/biomaglo) organized by the Muséum National d’Histoire Naturelle (MNHN, Paris, France) in collaboration with the IFREMER took place in January- February 2017. The aim of BIOMAGLO was precisely to investigate the deep-sea benthos in the Mozambique Channel, with a special focus around Mayotte, Comoros and Glorieuses Islands. While sorting this large collection, a puzzling observation in an incrusting sponge attracted our attention: euasters in a poecilosclerid sponge, when asterose microscleres are unknown in this large order and currently found only in the orders Chondrosiida, Axinellida (Stelligeridae), Tetractinellida, Clionaida (Placospongiidae, Spirastrellidae) and Tethyida (Morrow & Cárdenas 2015). We show here that these “asters of a new Discorhabdella species are not true asterose microscleres, but derivatives of the pseudoastrose acanthostyles megascleres characteristic of this genus, which once more hints at the extraordinary capacity of sponges to re-invent the same spicule types through convergent evolution. Material and methods The specimen of the new species was collected by dredging on ‘Banc du Geyser’, placed between Mayotte and Glorieuses Islands. Soon after collection with a Warén dredge, a photograph was taken (Fig. 1) and the specimen was preserved in 95% ethanol. Accepted by M. Klautau: 19 Jun. 2018; published: 31 Aug. 2018 197 Due to the small size of the unique specimen, spicule preparations were made by boiling a very small piece of the sponge in a few drops of nitric acid directly on microscope slides. After rinsing in distilled water, the slides were either mounted in Araldite for light microscopy or sputter-coated with gold–palladium for scanning electron microscopy (SEM) with a Hitachi S570. A section was hand made through the sponge for examination of skeletal organization. Molecular analysis, which would have destroyed the remaining tiny specimen with uncertain chances of success, was not undertaken. The type specimen is deposited in the MNHN, at room temperature, with a slide of spicule preparation. Description Class Demospongiae Sollas, 1885 Subclass Heteroscleromorpha Cárdenas, Pérez & Boury-Esnault, 2012 Order Poecilosclerida Topsent, 1928 Family Crambeidae Lévi, 1963 Genus Discorhabdella Dendy, 1924 Discorhabdella pseudaster n. sp. Holotype. MNHN-IP-2015-1083, station DW 4788, Warén dredge, 22/01/2017, Banc du Geyser, 12°22’ S, 46°25’ E, 346–349 m depth, rocks and pebbles. Field# PMG 05, coll. C. Debitus, ethanol 95%. Description. A minute, incrusting sponge, 4 x 2.5 mm and 200 µm thick, hispid (Fig. 2 A). Color grayish white alive and in alcohol. No visible aperture. A stoloniferous calcified octocoral, possibly Scleranthellia (Gary Williams, pers. com.), is growing on the same rock. Skeleton. The skeleton is made of long styles with a barely inflated head bearing low, round tubercles. These styles are disposed vertically on the substratum and give the long hispidation. They are surrounded by smaller tylostyles irregularly arranged, sometimes forming poorly defined bouquets. Pseudoastrose acanthostyles are arranged vertically, with the head on the substratum. Pseudoasters and isochelae are dispersed in the whole choanosome. Spicules. (1) Subtylostyles (Fig. 2 B), straight or slightly curved, with a barely tuberculated head, all broken in the spicule or skeleton slides. Axial canal ending in a small vesicle in the head (not divided), although faint, radiating darker lines could be seen (Fig. 3 A). Maximum length of the broken spicules: 600 µm, diameter 40–56 µm near the base.(2) Tylostyles (Fig. 2 C), straight or slightly curved, with a well-marked oval head, 240– 370 x 9–10 µm.(3) Pseudoastrose acanthostyles (Fig. 2 D–F). Spine-like rays of the head obtuse, those of the end of the shaft generally more acute. Total length 35–45 µm, diameter of the head 35–40 µm, shaft 20-25 x 12 µm with spines at the extremity. Axial canal barely visible by transparency (not divided in the head), although faint, radiating darker lines could be seen in the head (Fig. 3 B). Some rare spicules, likely juvenile, are a little smaller (e.g. 28 µm in length), and have more acute spines.(4) Pseudoasters (Fig. 2 G–I), similar to spherasters, very abundant, 12.5–18 µm in diameter, with conical, sharp spine-like rays, 2.5–4 µm long. No visible axial canals in the spines.(5) Unguiferous cleistochelae (Fig. 2 J), small, 12–15 µm. Shaft straight, 4 or 5 teeth nearly in contact, often with the end on one side blunt and the other slightly indented. The shaft bears a conspicuous lamella, attached by a part of its length, similar to a hatchet. The free part of the hatchet is most often directed towards the non- indented teeth, but the opposite case has also been observed. Etymology. From Latin pseudo (meaning false) and aster. Remarks. The presence of chelae makes this sponge a Poecilosclerida. This minute sponge clearly belongs to the genus Discorhabdella by its shape, skeleton and especially the diagnostic club-shaped pseudoastrose acanthostyles. Unfortunately, the unique specimen is too small to allow obtaining sequences, so the affinities between Discorhabdella and Crambe remain likely (Maldonado & Uriz 1996), but not formerly demonstrated. It is rather puzzling to find “aster” spicules in a poecilosclerid, which moreover have the same position in the skeleton as true asters in non-poecilosclerid encrusting sponges (e.g. Spirastrellidae, Chondrillida or Tethyida). The 198 · Zootaxa 4466 (1) © 2018 Magnolia Press VACEL ET & CÁRDENAS true nature of these asters is questionable. It is essential in taxonomy and phylogeny to use homologous morphological characters, and that is not always obvious as clearly shown by Fromont & Bergquist (1990) with the example of sigma microscleres or acanthose megascleres. Here, the most likely explanation is that the “asters” derive from the pseudoastrose acanthostyles with reduced shaft typical of Discorhabdella by complete loss of the shaft. The presence of “asteroid” corpuscules somewhat similar to asters have been described in two other members of the family Crambeidae, Crambe tuberosa Maldonado & Benito, 1991, and Crambe chilensis Esteves et al., 2007; these spicules, which in C. tuberosa have axial filaments in the actines, were interpreted as developmental stages of desmas, otherwise present in Crambe spp. (Maldonado & Benito 1991; Uriz & Maldonado 1995; Maldonado & Uriz 1996). FIGURE 1. On-deck picture of the piece of rock bearing the specimen (arrow). Square = 25 mm. NEW DISCORHABDELLA WITH ASTERS Zootaxa 4466 (1) © 2018 Magnolia Press · 199 FIGURE 2. Discorhabdella pseudaster n. sp., A, habitus of holotype (arrow). B, large subtylostyle. C, tylostyle. D, pseudoastrose acanthotyle. E, immature pseudoastrose acanthotyle. F, pseudoastrose acanthotyle seen from the tip. G, H & I, pseudoasters. J, unguiferous cleistochelae. 200 · Zootaxa 4466 (1) © 2018 Magnolia Press VACEL ET & CÁRDENAS NEW DISCORHABDELLA TABLE 1. Comparative table of world Discorhabdella species showing spicule measurements (in μm). Discorhabdella species Region and depth Tuberculated Tylostyles Pseudoastrose Pseudoasters Isochelae Other microscleres range subtylostyles acanthostyles WITH ASTERS D. hindei Alboran Sea 855–1556 x 34–52 276–445 x 5.2 43–57 x 8–10, ––– 22–27 Sigmas 11–16 x 534–604 m head 36–39 1–1.3 D. incrustans New Zealand 1700/50 540/12 52/40 ––– 48 Oxydiscorhabds 183 m 900–1700 x 28–61 * 357–592 x 10–15 * 36–53* 33–51* 28 x 1.3 26–34* D. littoralis Panama (Pacific) 117–300 x 5–10 130–180 x 2.5–4 26–40 ––– ––– Sigmas 13–15 10–30 m D. tuberosocapitatum Azores 650 x 28 330 130 ––– 25 ––– 736 m D. urizae Panama (Pacific) 380–750 x 19–42 180–220 x 5–7 23–37 ––– 26–29 Acanthomicroxea 55–73 m 19–26 & sigmas 13–16 Zootaxa D.