Acarnus hooperi Ozga, Santos & Menegola, 2024, sp. nov.
Creators: name: Ozga, Aline Vasum
name: Santos, George Garcia
name: Menegola, Carla
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Porifera
Demospongiae
Poecilosclerida
Acarnidae
Acarnus
Acarnus hooperi

description: Acarnus hooperi sp. nov. Santos & Menegola
(Fig. 4A–K; Table 2)
Material examined. Holotype: MNRJ 3942, Brazil, Rio de Janeiro State, Vermelha Beach, 22°57’15”S 43°09’49”W, 2.5 m depth, Coll. E. Hajdu, free diving, 30.XII.2000, Det. G. Santos & C. Menegola. Paratype: MNRJ 6460, 6464, 6466, 6491, 6577, 6580, Brazil, Rio de Janeiro State, #y1, 22°11’48.1”S 40°29’36.2”W, 60 m depth, coll. R. V. “Astro Garoupa”, through dredging, 11. VI.2002, Det. G. Santos & C. Menegola.
Diagnosis. Acarnus with a combination of blunt spines over acanthostyles, longer and thicker megascleres (style 505/13 µm; tylote 425/8 µm), cladotylotes with less clads (3–4) and larger chelae (~40 µm).
Description. Thinly encrusting sponge (1 mm thick) growing on dead coral fragments (MNRJ 3942). Surface varying from smooth to rough, with spicules protruding externally. Fragile consistency, MNRJ 3942 had a “soft cheese” consistency in life. Color in life red, pale in preservation. The fragments in general are quite damaged, in which oscules and pores are not visible. Acarnus hooperi sp. nov. was found in two distinct forms: encrusting in algae thallus (most specimens) and homogeneously amalgamated in sand grains (one specimen).
Skeleton. Ectosome with tangential tylotes. Choanosome with scarce spongin, but echinated plumose tracts are nevertheless formed, ascending from the substrate; echinating spicules (acanthostyles) singly erect on the substrate.
Spicules (Fig. 4A–K). Megascleres: styles (Fig. 4A and B) with rugose spines (319–442.8–505/ 7.9–10– 13.3 µm). Microspined tylotes (Fig. 4C and D) with well-developed heads, shaft thoroughly smooth and slightly curved (266–345–425/ 5.3–6.0–7.9 µm). Acanthostyles (Fig. 4G and H) slightly curved and spiny on their entire surface, but density of spines varying along the length, base with rounded spines (66.5–97.7–109/ 2.9–3.4–4.8 µm). Cladotylotes I (Fig. 4E and F) sparsely spined shaft, stout and strongly hooked, with a cladome more developed than the other, with three to four clads (172–210.7–260/ 8–8.9–10.6 µm). Cladotylotes II (Fig. 4E) with the same morphology as cladotylotes I (79–97.8–122/ 2.6–3.3–5.3 µm). Microscleres: toxas in two categories: toxa I (Fig. 4J) elongated, with a slight curvature in the middle (accolada-like) (133–209.5–532 µm); toxa II (Fig. 4I) thin and slightly curved (34.5–109.6–218.1 µm). Oxhorn toxa not observed. Palmate isochelae (Fig. 4K) with the alae fused to the shaft (29.2–34.4–39.9 µm).
Distribution. Southwest Atlantic, Brazil. Recorded from Southeast Brazil in the Rio de Janeiro State.
Etymology. Named “ hooperi ”. This species is named in honor of Dr. John N.A. Hooper, from the Queensland Museum, Brisbane, Australia, for his remarkable contribution to the progress of sponge taxonomy, especially of the Acarnus genus.
Remarks. Concerning the spicule set, Acarnus hooperi sp. nov. belongs to the “souriei ” group due the possession of acanthostyles. Currently, there are twelve species described worldwide (Table 4) belonging to the “souriei group”. Acarnus hooperi sp. nov. is morphologically similar to A. nicoleae. However, A. nicoleae has toxas in three categories and smaller chelae, while Acarnus hooperi sp. nov. has two categories of toxas and larger chelae, about twice in size (14.4–21 µm against 29–39.9 µm) (Tab. 2). Other similar species are the Mediterranean Acarnus levii (Vacelet, 1960), the Pacific Acarnus peruanus van Soest et al. 1991 and Indo-Pacific A. bicladotylotus Hoshino, 1981. Acarnus bicladotylotus has three categories of toxas, megascleres and chelae smaller, while Acarnus hooperi sp. nov. has two categories of toxas and very larger chelae (Tab. 4). The differences between A. levii, A. peruanus and Acarnus hooperi sp. nov. are minimal and reduced to spicular dimensions of the megascleres, toxas and chelae (Tab. 4). However, due to the vast geographic distances between all species (western Mediterranean, eastern Central Pacific, Indo-Pacific and the southern Atlantic) they are unlikely to be the same species.
From the “souriei ” species group, six species have cladotylotes in one category: Acarnus souriei, A. radovani, Acarnus tener Tanita, 1963, Acarnus michoacanensis Aguilar-Camacho, Carballo &Cruz-Barraza, 2013, A. guentheri (Dendy, 1896) and Acarnus primigenius Hiemstra & Hooper, 1991. Furthermore, A. souriei and A. radovani have two categories of acanthostyles and toxas in three sizes. Acarnus tener is an encrusting to massive sponge with a plumose skeleton formed by ascending tracts. Acarnus michoacanensis has smaller megascleres and chelae (Tab. 4). Finally, A. primigenius has only one category of toxas.
Acarnus caledoniensis Hooper & Lévi, 1993 has two categories of acanthostyles and is spherical in shape. In comparison to other three species known to Brazil, A. innominatus, A. toxeata and A. microxeatus differs from Acarnus hooperi sp. nov. in not having acanthostyles.
description: Published as part of Ozga, Aline Vasum, Santos, George Garcia & Menegola, Carla, 2024, Taxonomic and geographic novelties of Acarnus (Porifera: Demospongiae) from the Brazilian coast, with description of two new species, pp. 401-422 in Zootaxa 5523 (4) on pages 407-409, DOI: 10.11646/zootaxa.5523.4.1, http://zenodo.org/record/13949596