Acarnus microxeatus, Nascimento & Pinheiro, 2023

Nascimento, Elielton & Pinheiro, Ulisses, 2023, A new species of Acarnus Gray, 1867 (Porifera, Demospongiae, Acarnidae) from NE Brazil, Zootaxa 5293 (3), pp. 521-540 : 523-529

Acarnus microxeatus sp. nov.

( Figs 2–3 , Tables 1–2 )

Type Material. Holotype. UFPEPOR 2986— Serrambi Beach (8°33’37.7”S 35°00’22.0”W, Ipojuca, Pernambuco State, Brazil), 12 august 2022, Col. Nascimento, E.F., Dias, A., Pinheiro, U., intertidal.

Paratypes. UFPEPOR 2981— Serrambi Beach (8°33’37.7”S 35°00’22.0”W, Ipojuca , Pernambuco State, Brazil) , 12 august 2022, Col. Nascimento, E.F., Dias, A., Pinheiro, U., intertidal. UFPEPOR 2987, 2988— Serrambi Beach (8°33’37.7”S 35°00’22.0”W, Ipojuca , Pernambuco State, Brazil) , 12 august 2022, Col. Nascimento, E.F., Dias, A., Pinheiro, U., intertidal. UFPEPOR 4332— Ponta do Meirim (09º32’32.22”S 35º36’49.80”W) Maceió , Alagoas State, Brazil), 30 january 2010, Col. Correia, M.D., depth 0.5 m .

Diagnosis. Acarnus with two categories of cladotylotes, tylotes, styles, three categories of toxas, acanthoxeas and smooth microxeas.

Description ( Fig. 2A ). Thickly encrusting sponge with dimensions (2.0 x 1.5 x 1.1 cm (length x width x thickness)). Compressible and easily friable consistency. Hispid surface, with subdermal gaps and rounded oscule (0.3 cm diameter). Color orange in life, but beige in alcohol.

Skeleton ( Fig. 2B ). Choanosomal skeleton plumoreticulated forming main tracts ascending to surface interconnected by renieroid isotropic tracts, both cored by choanosomal styles and tylotes; renieroid component of skeleton dominates skeletal structure; choanosomal tracts echinated by cladotylotes, particularly at nodes, microxeas found tangentially arranged in the ectosome and, other microscleres scattered in the choanosome.

Spicules ( Fig. 3 ). Tylotes, terminally microspined, 190– 211 –249/2– 3.1 –5 μm. Styles, long, lightly curved, with smooth base, 374– 395.9 –424/12– 21.1 –30 μm. Cladotylotes I, larger, smooth and straight to lightly curved shaft, base with well-defined rounded tyle, cladome with long spines, length 141– 244 –293 μm, shaft width 5– 9.8 –12 μm, cladome width 17– 33.5 –44 μm. Cladotylotes II, smaller, heavily spined with recurved spines at the base and lightly curved shaft, base with depressed (flattened), lobed tyles, length 90– 96.1 –105 μm, shaft width 2– 3.1 –5 μm, cladome width 12– 12.6 –15 μm. Palmate isochelae, 10– 10.7– 12 μm. Toxas I, accolada, 222– 435.6 –656 μm. Toxas II, thin, deeply curved, 50– 128.9 –313 μm. Toxas III, oxhorn, thick deeply curved, 35– 55.2 –80 μm. Acanthoxeas, heavily spined shafts, 61– 77.7 –98/2– 3.4 –5 μm. Microxeas, smooth, lightly curved with hastate and acerate ends, 29– 52.4 –202/5– 7.8 –12 μm.

Distribution. Alagoas and Pernambuco States, Northeast Brazil.

Etymology. The species name refers to the presence of smooth microxeas, one of the characteristic microsclere categories of this species.

Ecology. Ophiuroids were found on some specimens.

Remarks. In Acarnidae , the presence of microxea microscleres in the spicule set is observed only in Acheliderma Topsent, 1892 , where they are elongated and diamond-shaped. The presence of smooth microxea in Acarnus microxeatus sp. nov. is a new character for this genus. Both genera are similar and share tylotes, styles, acanthostyles and toxas in their spicule set. However, Acheliderma differs by the absence of cladotylotes. Additionally, Acarnus microxeatus sp. nov. presents fusiform microxea instead of the elongated diamond-shaped ones seen in Acheliderma . The presence of acanthose microscleres is observed in several genera of Acarnidae . Acheliderma , Dolichacantha Hentschel, 1914 , Megaciella Hallmann, 1920 and Paracornulum Hallmann, 1920 all have acanthostyles. Wigginsia de Laubenfels, 1953 and Zyzzya Laubenfels, 1936 have acanthostrongyles, and Acanthorhabdus Burton, 1929 has acanthorhabds. Only Cornulella Dendy, 1922 shares acanthoxea with Acarnus microxeatus sp. nov., but differs from Acarnus by the absence of cladotylotes, and the fistular habit ( Aguilar-Camacho et al. 2013, Van Soest et al. 1994, Hooper 2002).

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References. (1) van Soest, Hooper & Hiemstra, 1991; (2) Aguilar-Camacho, Carballo & Cruz-Barraza, 2013; (3) Lévi, 1998; (4) Dendy, 1896.

The new species fits best in the “souriei” group, due to the presence of acanthose spicules (here acanthoxeas) in its spicule set. We emphasize that Acarnus microxeatus sp. nov. differs from all congeners by having microxeas and acanthoxeas as microscleres ( Figs 3I and 3G , respectively). Acarnus primigenius , A. radovani , A. souriei and A. tener present only one category of cladotylotes with spined shaft and base with recurved spines, differing from A. microxeatus sp. nov. which has two categories of cladotylotes, the largest one, with a smooth shaft and rounded lobed base ( Fig. 3D ). Additionally, all these species, mentioned above, have styles with a microspined and/or rough head, in contrast to the totally smooth head of styles in A. microxeatus sp. nov. ( Table 2 ). The new species presents three categories of toxas, differing from A. caledoniensis , A. guentheri , A. levii , A. michoacanensis , A. peruanus and A. tener that have two categories, and A. primigenius , that has only one category. Furthermore, A. caledoniensis has two categories of acanthostyles and is spherical in shape, while Acarnus microxeatus sp. nov. has one category of acanthostyles and is thickly encrusting. Acarnus bicladotylotus and A. nicoleae differ from A. microxeatus sp. nov. by having larger tylotes (143–404 μm and 119–380 μm, respectively against 190– 211 –249 μm) and also for having smaller accolada toxas (150–250 μm and 140–330 μm, respectively against 222– 435.6 –656 μm) ( Tables 1 and 2 ). Additionally, none of these species of Acarnus have acanthoxea and smooth microxea as the new species do ( Table 1 , 2 , 3 and 4).

Figures

FIGURE 2. Acarnus microxeatus sp. nov. (Holotype—UFPEPOR 2986). A, in situ specimen; B, thick section showing the ectosome and choanosome. Scale, A, 1 cm; B, 300 µm.

FIGURE 3. UFPEPOR 2986. A, Style. B, Detail of the base and tip of the style. C, Tylote. D, Detail of tylotes. E, Isochelae. F, Cladotylote I. G, Detail of the base and cladome of cladotylote I. H, Cladotylote II. I, Detail of the base and cladome of cladotylote II. J, Thin deeply curved toxa. K, Oxhorn toxa. L, Accolada toxa. M, Acanthoxa. N, Microxea. Scale: A, C, 50 μm; B, D, F, H, J, K, L, M, N, 20 μm; E, 15 μm; G, I, 10 μm; L, 20 μm.