Placospongia amphinolastra sp. nov. Sandes, Moraes & Muricy

urn:lsid:zoobank.org:act: 998EB1A4-B682-45EC-9D00-9ED433024076

(Figs. 4 and 11–12; Tables 2 and 3)

Synonyms

Placospongia sp. sensu Moraes 2011: 95.

Type material. Holotype: MNRJ 7878, Ressurreta, Rata Island, Fernando de Noronha Archipelago, Pernambuco State, Brazil (3º48’46.764”S, 32º23’25.224”W), 8 m depth, coll. Eduardo Hajdu, 12 November 2003.

Etymology. The specific epithet amphinolastra refers to the presence of immature selenasters similar to amphinolasters, typical of this species.

Diagnosis. Placospongia thinly encrusting, with light brown color and orange edges. The megascleres are tylostyles in two slightly overlapping categories. Microscleres are elongated, bean- or peanut-shaped mature selenasters, immature selenasters similar to amphinolasters, small spirasters with short and rugose rays, and rare spherasters.

Description (Fig. 11a–b). Shape thinly encrusting, size 15 x 15 x 1 mm (length x width x thickness). The surface is smooth, composed by six cortical plates separated by grooves with circular openings 1–2 mm in diameter, probably oscules (Fig. 11a). Color light brown with orange edges in vivo (Fig. 11a), becoming beige in ethanol (Fig. 11b). Consistency hard, but brittle.

Skeleton (Fig. 11c–d). The cortex is 100–250 µm thick, distinct from the choanosome. The inner layer of the cortex is densely packed with selenasters and the outer layer is thin and sparse, formed by scarce spirasters. The choanosomal skeleton is composed of tylostyle tracts of 50–100 µm thick and 1000 µm apart, which run obliquely from substrate to the cortex (Fig. 11c). Immature selenasters and rare spherasters are scattered throughout the choanosome, between the tylostyle tracts (Fig. 11d).

Megascleres (Fig. 12a–b). Tylostyles in two slightly overlapping categories, with blunt or mucronate ends; few modified to styles. The tyles are ovoid, round, lobate or bi-lobate (Fig. 12a–b). Tylostyle I: 360–454–540 / 5–7–10 µm, tyle width 7–9–13 µm. Tylostyle II: 150–238–330 / 3–5–8 µm, tyle width 6–6–8 µm.

Microscleres (Fig. 12c–g). Mature selenasters are elongate, bean- or peanut-shaped: total size 40–45–53 / 15– 21–30 µm, hilum with 7–8.5–9 µm in diameter. The spines are fused and form irregular, grooved or rugose plates (Fig. 12c). Four types of immature selenasters are present: (I) straight, slender and spiny, with spines concentrated on the end of the shafts: 21–27–33 / 2–4.5–7 µm (Fig. 12d); (II) dumbbell-like shaped, with spined or lumpy shafts connecting two heads densely covered by sharp or bulbous spines, similar to amphinolasters: 29–33–36 / 13–15–19 / 9–11–13 µm (length x head width x shaft width) (Fig. 12e); (III) elongated, with short conical spines: 27–34–38 / 9–11–15 µm; (IV) elongate to oval, with spines very closely set, but still recognizable in their individuality: 47–49– 51 / 15–20–23 µm. Spirasters small and thin, with short rugose spines, bent once or twice: 5–9–14 / 1–1–2 µm (Fig. 12f). Spherasters rare, small, with short and conical rays: 11–12–13 µm in diameter (n=2) (Fig. 12g).

Habitat. The species was collected at 8 m depth, in a crevice, associated with calcareous algae.

Geographical distribution (Fig. 4; Tab. 2). Only known from Fernando de Noronha Archipelago, Pernambuco State, Northeastern Brazil (present study).

Taxonomic remarks. Placospongia amphinolastra sp. nov. is defined by the combination of tylostyles, mature selenasters elongated, bean- or peanut-shaped, immature selenasters similar to amphinolasters, small spirasters with short and rugose rays, and rare spherasters.

The immature dumbbell-shaped selenasters of Placospongia amphinolastra sp. nov. are similar to amphinolasters, which are the main cortical microscleres of the genus Onotoa (de Laubenfels 1955; Rützler & Hooper 2000). Amphinolasters have lumpy shafts connecting two heads densely covered by bulbous spines (Rützler & Hooper 2000). In the new species, it is unclear whether this is a distinct spicule type or an immature stage of development of the selenasters. In any case, we classified the new species in the genus Placospongia because it also has mature selenasters, the cortical microscleres that define the genus Placospongia and are absent in Onotoa .

Placospongia amphinolastra sp. nov. shares with the congeneric P. anthosigma (Tanita & Hoshino, 1989) from Japan and P. decorticans (Hanitsch, 1895) from the South European Atlantic Shelf the same accessory microscleres, viz., spirasters and spherasters. However, Placospongia anthosigma is distinguished from Placospongia amphinolastra sp. nov. by its larger and rounded selenasters, larger and abundant spherasters and spirasters with larger and conical spines, while Placospongia decorticans has oxyasters and selenasters larger than the new species (Tab. 3).

Placospongia amphinolastra sp. nov. shares the presence of spherasters with P. caribica, P. cristata, P. colombiensis, P. intermedia and P. soesti . Yet, it is easily distinguishable from all its congeners in the Tropical Western Atlantic: it is distinct from P. caribica by the oxyasters and acanthomicrorhabds; from P. cristata by the micro-spheroxyasters; from P. colombiensis by the two categories of spirasters; from P. intermedia by the presence of metasters and acanthomicrorhabds; and from P. soesti by the presence of amphiasters and acanthomicrorhabs. Besides the absence of spherasters, P. ruetzleri has spiny spirasters with long rays and acantomicrorhabds, and P. giseleae has only acanthomicrorhabds as accessory microscleres (Tab. 3). In addition, the immature selenasters similar to amphinolasters are exclusive of the new species.