Ascoleucetta compressa Dendy & Frederick, 1924

Cavalcanti, Fernanda F., Rapp, Hans Tore & Klautau, Michelle, 2013, Taxonomic revision of Leucascus Dendy, 1892 (Porifera: Calcarea) with revalidation of Ascoleucetta Dendy & Frederick, 1924 and description of three new species, Zootaxa 3619 (3), pp. 275-314 : 299-302

Ascoleucetta compressa Dendy & Frederick, 1924 (type species)

(type species, by original designation)

Diagnosis: Cortex with conspicuous inhalant apertures, with beehive appearance. Trichoxeas projected into the lumen of these apertures.

Synonymies: Ascoleucetta compressa: Dendy & Frederick 1924: 481; Burton 1963: 243; Ascaltis compressa: Borojevic 1968: 205 ; Leucascus compressus: Borojevic & Klautau 2000: 192 ; Rapp 2004: 124. Type material: BMNH 1924.9.1.3 (Holotype; Wooded Isle, Australia; RN. III 12; Dendy collection). Type locality: Abrolhos Islands, Australia

Additional analysed material: WAM Z31421 (Jurien Bay, North Essex, Western Australia. 3021.13’S 11500.15’E; coll. J. Fromont, M.A. Titelius, C.S. Whisson, and G. Moore; 27/IV/2005; depth: 3–4.5 m).

Description: The fragment of the holotype analysed here measures 1.0 cm in its length and 0.8 cm in its thickness. The body has a compressible, soft consistency. It is formed by tightly anastomosed tubes in the external region and loosely anastomosed tubes in the inner part ( Figure 16 A). The solenoid aquiferous system is not so evident in the specimen from WAM because there are several tubes going directly from the cortex to the atrium ( Figure 16 B). A very well developed cortex covers the entire body ( Figure 16 B). It has numerous conspicuous inhalant apertures and some oscula surrounded by membrane. The inhalant apertures are spherical (about 200 µm in diameter) and regularly distributed ( Figure 16 C).

The skeleton is composed of trichoxeas, two size categories of triactines, and tetractines. The trichoxeas are present inside the inhalant apertures, laying perpendicularly to them and being projected into the lumen ( Figure 16 D). Large triactines delimit the inhalant apertures and give the surface of the sponge a beehive appearance ( Figure 16 C). Abundant tangentially arranged tetractines and rare triactines of small size are also included in the cortical skeleton. The skeleton of the choanocyte tubes consists of the same kind of small tetractines and triactines found on the cortex. The tubes are hispid because of the presence of the apical actine of the tetractines, which are more numerous ( Figure 16 E). The atrial skeleton is formed mainly by tetractines ( Figure 16 F).

Spicules ( Table 10 ):

(i) Trichoxeas: Short, straight and thin;

(ii) Large cortical triactines ( Figure 17 A): Equiangular and equiradiate or with actines of different lengths. Actines are conical with blunt tips;

(iii) Triactines ( Figure 17 B): Frequently regular, but occasionally with actines of different sizes. Actines are conical with blunt tips;

(iv) Tetractines ( Figure 17 B): Similar to the small triactines. They are regular, but one of the actines can be slightly shorter. The apical actine is long, very thin, smooth, and slightly curved near the tip.

Remarks: Ascoleucetta compressa was originally described as the type species of the genus Ascoleucetta . According to Dendy and Frederick (1924), Ascoleucetta consisted of sponges of the family Leucascidae with a well-developed cortex formed by large and small triactines and pierced by well-defined inhalant apertures ornamented by a fringe of trichoxeas that are oriented into the aperture. The genus was originally composed only of A. compressa and was invalidated when this species was transferred to Ascaltis (Borojevic 1968) . Later on, Borojevic and Klautau (2000) proposed to transfer the species to Leucascus .

In the present work we propose to revalidate Ascoleucetta (see discussion) as three species of Leucascus ( A. amitsba , A. compressa , and A. ventricosa ) show the very distinctive morphological characteristics of Ascoleucetta : a well developed cortex composed of large spicules and absence of spines in the apical actines of the tetractines. We consider that these three species evolved from a common ancestor with these characteristics and that Ascoleucetta consists of a monophyletic group different from Leucascus .

The skeleton of A. compressa is composed of the same spicule categories mentioned in the original description. Nevertheless, we observed that the tetractines are also present in the cortical region, and are more abundant than the small triactines. Moreover, Dendy and Frederick (1924) mentioned three categories of small triactines, while we are considering only one, which becomes sagittal and curved if positioned around the tubes or which can be folded and curved only due to bad formation.

The species most similar to A. compressa is A. ventricosa . Both species present a cortex with conspicuous inhalant apertures and large triactines, tightly anastomosed external tubes, loosely anastomosed internal tubes, and a skeleton composed mainly of two size categories of triactines and one of tetractines. However, in A. compressa the diactines are trichoxeas and the length of the small triactines is also different [87.0 µm (18.2) in A. compressa and 146.4 µm (11.8) in A. ventricosa ; Tables 10 , 11].

Distribution: Indian Ocean. Abrolhos Islands, Australia (Dendy & Frederick 1924). Spalding et al. (2007) corresponding ecoregion: Shark Bay.

Figures

FIGURE 16. Ascoleucetta compressa. A, C – F, BMNH 1924.9. 1.3, holotype; B, WAM Z 31421. A, Preserved specimen; B, Transverse section showing the cortex (ct), choanocyte tubes and atrium (at); C, Tangential section showing the cortical skeleton with large triactines around the inhalant apertures; D, Trichoxeas (arrow) protruding into the lumen of an inhalant aperture; E, Apical actine projected into the lumen of a tube; F, Atrial membrane.

FIGURE 17. Ascoleucetta compressa (BMNH 1924.9. 1.3, holotype). A, Cortical triactine; B, Choanosomal triactine (left) and tetractine (right).

Tables

TABLE 10. Spicules measurements (µm) of the holotype of Ascoleucetta compressa.

Spicules			Length (µm)		Width (µm)
	Actine	Min	Mean SD Max	Min	Mean SD Max	N
Cortical triactine		120.0	204.4 46.9 306.0	24.0	36.5 8.7 54.0	30
Choanosomal triactine		45.0	87.0 18.2 120.0	10.5	14.4 2.2 18.0	30
Tetractine	Basal	75.0	97.5 13.5 132.0	13.5	16.5 1.5 18.0	30
	Apical	27.0	46.3 8.2 60.0	4.5	5.7 0.6 6.0	30