Antho (Plocamia) bremecae, Barbara, 2017

Barbara, Calcinai, 2017, Description of Antho (Plocamia) bremecae sp. nov. and checklist of Microcionidae (Demospongiae: Poecilosclerida) from Burdwood Bank and neighboring areas, SW Atlantic Ocean, Zootaxa 4312 (3), pp. 580-594 : 582-584

Antho (Plocamia) bremecae sp. nov.

Figures 2 and 3

Material examined. Holotype and 2 paratypes. The holotype was deposited at the Museo di Storia Naturale di Genova ( MSNG), Italy ( MSNG n° 59505), while two paratypes were deposited at the Museo Argentino de Ciencias Naturales “ Bernardino Rivadavia ” ( MACN), Buenos Aires, Argentina (MACN-In 41003). Samples were labeled together as NBP 05/08 TB 4 #30 during the cruise; this was the station 4 (54° 44.02’S and 62° 12.98’ W); 804 m. Collection date: April 2008. Collector: Laura Schejter

Type locality. West slope of Burdwood Bank, SW Atlantic Ocean (54° 44.02’S and 62° 12.98’ W); 804 m ( Figure 1 ).

Diagnosis. Flabellate Antho (Plocamia) species characterized by long choanosomal styles, ectosomal subtylostyles and long toxas. The main skeleton is reticulated, made by dumbbell-shaped diactines and by choanosomal styles supporting the ascending tracts.

Description. Flabellate, foliate sponge arising from a short peduncle and from an encrusting base ( Figure 2 A); the holotype is 4.5 cm long in total; the peduncle is about 3 mm thick, and it was detached from the substrate. The two paratypes are flat and flabellate; one is about 4 cm long and the other is slightly broken, about 3 cm long. Both present small peduncles attached to dead scleractinian corals ( Figure 2 A). The lamellae are about 3 mm thick. The preserved specimens are light brown colored and full of sediments. The consistency is hard. The sponge surface is microhispid due to the styles extending through it.

Ectosome: Subtylostyles tangentially arranged and forming bundles protruding through the ectosome ( Figure 2 B – D).

Choanosome: Regular renieroid, isodictyal skeleton ( Figure 2 E) of dumbbell-shaped diactines and of ascending, paucispicular tracts of choanosomal styles (two or three styles in the tracts), with little visible spongin. The meshes are made of one, two, up to four dumbbell-shaped diactines and are about 300 µm wide ( Figure 2 F). Choanosomal styles pierce the ectosomal layer protruding through the surface ( Figure 2 D).

Spicules: slightly curved choanosomal styles with smooth or slightly microspined heads and hastate tips ( Figure 3 A); thin ectosomal subtylostyles, straight or sometimes curved, or flexuous, with spined heads and hastate tips ( Figure 3 B); dumbbell-shaped diactines, sometimes anisotylote ( Figure 3 C); they are always with microspined, slightly enlarged heads, and scattered spines along the shaft. Smooth toxas in a large size range and variable in shape, U- and wing-shaped, with intermediate forms ( Figure 3 D); palmate isochelae ( Figure 3 E). Measurements are shown in Table 1.

Distribution and habit. The species is currently known only from its type locality, in the slope of Burdwood Bank. The habit registered in the studied specimens is epibiotic, on dead corals.

Etymology. The species is named in honor of Dr. Claudia Bremec, mentor of Dr. Laura Schejter. She also promoted the participation of Dr. Schejter onboard the R/V “Nathaniel B. Palmer” during the 2008 Expedition.

Remarks. According to the World Porifera Database (WPD) (van Soest et al. 2016), species of the genus Antho are numerous (59). Recently, van Soest et al. (2013) resurrected the subgenus Plocamia Schmidt for Antho species having peculiar dumbbell spicules making the basal reticulation. Eleven species belong to this subgenus, but none of these are present in the Magellanic Province or in biogeographic regions nearby ( Spalding et al. 2007). One species of subgenus Acarnia (previously considered a senior synonym of Plocamia ) was described as A. (A.) inconspicua Desqueyroux for Central Chile. It differs from this new species in having an encrusting habit and different spicule features: it is characterized by large styles (403‒ 1020 x 21 µm), smooth tylostrongyles, and small styles (388 x 15 µm), and by palmate isochelae (22 µm) as microscleres.

A species close to the new one here described is Antho (Plocamia) erecta (Ferrer Hernandez) . This species is lamellate and has similar spicule features, with ectosomal subtylostyles, large styles, dumbbell-shaped spicules, toxas, and palmate isochelae; however, the shape of the spicules is different with the large styles being smooth, whereas toxas are oxhorn in form. Also, spicules are smaller than those of the new species.

All the other species of subgenus Plocamia differ in shape and spicule features. Antho (P.) anisotyla (Lévi) described from Senegal, A. (P.) karykina (de Laubenfels) from Northern California, A. (P.) karyoka (Dickinson) from Mexican Tropical Pacific and A. (P.) manaarensis (Carter) from the Indian Ocean are characterized by shorter spicules: styles are 130–275 x 5–11 µm long and tylotes 125–185 x 7–8 µm long in A. (P.) anisotyla ; choanosomal tylostyles are 165 x 20 µm, and toxas 45 µm in A. (P.) karykina ; subtylostyles and strongyles are 340 x 18 and 175– 200 x 16–22 µm long respectively, tylostyles 160–200 x 3–12 µm, twisted palmate isochelae are 10–17 µm and toxas 18–80 µm long in A. (P.) karyoka ; finally, styles are 600 x 21 µm, hair-like styles are 238 µm, tylotes 238 µm, toxas 50 µm and isochelae are 16.8 µm long in A. (P.) manaarensis . Antho (P.) arbuscula (Burton) , from Yemen, has a small category of acanthostyles (50– 70 x 5–7 µm, and shorter spicules); A. (P.) gymnazusa (Schmidt) from Florida has larger spicules (smooth styles 2130–2480 x 44 µm, dumbbell-shaped spicules 470 x 63 µm, Ridley & Duncan 1881); A. (P.) hallezi (Topsent) from Western North Africa, has smaller spicules and contort isochelae. Antho (P.) lambei (Burton) was described for the North East Pacific Ocean, but unfortunately Burton gave only a short description of the species without spicules measurements. Given the unlikelihood of there being any shared species between the Magellanic and the Cold Temperate Northeast Pacific Provinces, Burton’s species is also deemed distinct from A. (P.) bremecae sp. nov.

Figures

FIGURE 1. Localization of Burdwood Bank in the Sw Atlantic Ocean. Diamonds indicate the research stations.

FIGURE 2. Antho (Plocamia) bremecae sp. nov. A. Macroscopic view of the Holotype (1) and paratypes (2, 3). B. SEM image of a cross section showing the choanosomal skeleton and subtylostyles tangentially arranged and forming bundles in the ectosome. C. SEM image of the ectosomal subtylostyles. D. Magnification of the peripheral part with subtylostyles tangentially arranged and choanosomal styles piercing the ectosomal layer. E Renieroid, isodictyal skeleton. F SEM image of the regular renieroid choanosomal skeleton.

FIGURE 3. Antho (Plocamia) bremecae sp. nov. Spicules of the holotype. A. Choanosomal styles with smooth and slightly microspined heads and hastate tip; B. thin, flexuous and straight ectosomal subtylostyles with magnification of the spined heads and hastate tip; C. dumbbell-shaped diactines, slightly anisotylote (on the left) and magnification of the microspined head. D. Smooth toxas in large size range and variable in shape from U-, wing-shaped and intermediate forms. E. palmate isochelae.