Leucetta delicata

Rapp, Hans Tore, Göcke, Christian, Tendal, Ole Secher & Janussen, Dorte, 2013, Two new species of calcareous sponges (Porifera: Calcarea) from the deep Antarctic Eckström Shelf and a revised list of species found in Antarctic waters, Zootaxa 3692 (1), pp. 149-159 : 154-156

Leucetta delicata sp nov.

( Figure 3 , Table 3 )

Type locality: Eckström Shelf, Eastern Weddell Sea, Antarctica . SYSTCO station 71/48-1 at 70° 23.94' S, 8° 19.14' W, 602.1 m depth to 70° 23.89' S, 8° 18.67' W, 595.2 m depth.

Type material: Holotype SMF 11868, from the type locality.

Etymology: Named from the easily compressible and delicate structure of this species of Leucetta .

Additional material examined: BMNH25.11.1.35a. Pericharax carteri var. homorrhaphis (Polejaeff, 1883) . Challenger collection. Tristan da Cunha. Antarctic. Discovery Collection. BMNH 10.2.7.1a. Leucandra microrhaphis Haeckel, 1872 . Antarctic Belgica Expedition. BMNH07.8.6.65a. Leucandra primigenia var. leptoraphis (Jenkin, 1908) (now defined as Leucascus leptoraphis (Cavalcanti et al. 2013)) . SMF 10359. Leucetta weddelliana Rapp et al., 2011 . ANDEEP II Expedition. Weddell Sea. Leucetta antarctica . EASIZ Expedition. Weddell Sea, st. nr ps 39/29, 22.02.1996., 17°S31.7’W, 503–518 m depth (Identified as Pericharax pyriformis in Barthel et al. 1997).

Description: The holotype is an ovoid and massive tube reaching 2.2 cm in height and 1.2 cm in width. Colour in life and in alcohol is beige ( Figure 3 A). Surface is smooth. Consistence is soft and compressible. The single apical osculum is naked. Below the osculum there is a small atrial cavity, smooth to slightly echinated because of single actines of choanosomal triactines piercing the atrial wall (may be an artefact due to collection or fixation). Numerous exhalant canals are dispersed in the atrium. The aquiferous system is leuconoid and the skeleton is disorganized, as typical in the genus. The cortex and the atrial walls are thin ( Figure 3 D–E), while the choanosome is thick. Triactines are the dominating spicules while very rare tetractines are found sparsely scattered in the choanosome. Sub-cortical spaces are present but poorly developed.

Spicules: Triactines: They are regular, equiradiate and equiangular. Actines are conical, with gradually tapering and sharply pointed tips. The size is variable, but the majority of the bigger spicules are tangentially arranged in the cortex. Some larger triactines can also be found in the choanosome (299-392-505 µm x 23.4 µm) ( Table 3 , Figure 3 ).

Tetractines: The basal system of these spicules is similar to those of the triactines. Apical actines are very short and irregular (134-213-309 µm x 13.1 µm, apical actine up to 15 µm long) ( Table 3 , Figure 3 ).

Molecular identification: A ITS1-5.8S-ITS2 sequence of the holotype has been deposited in GenBank under the accession number KC874654 . BLAST search confirmed the poriferan origin of the sequence, with Leucetta chagosensis Dendy, 1913 as the closest match.

Distribution: Weddell Sea, known only from the type locality.

Remarks: Five species of Leucetta are at present known from Antarctic waters, namely L. antarctica Dendy, 1918 ; L. apicalis Brøndsted, 1931 ; L. gelatinosa (Jenkin, 1908) ; L. pyriformis (Burton, 1932) and L. weddelliana Rapp et al., 2011 . Recent work on Leucetta , including the status of L. microrhaphis and L. primigenia has resulted in more limited distribution of these species and they are no longer considered part of the Antarctic fauna (Valderrama et al. 2009). Material representing species previously published as Leucetta spp or species potentially representing Leucetta from adjacent waters were studied to avoid confusion with L. delicata sp. nov. (listed under “additional material examined”). Our L. delicata sp. nov. bears the strongest similarities to L. antarctica and L. weddelliana . L. weddelliana and L. delicata sp. nov. both have triactines of very variable size, and the spicules cannot be divided into specific size classes. However, the triactines in L. delicata sp. nov are almost two times bigger than in L. weddelliana . In addition L. delicata sp. nov. presents rare tetractines dispersed in its choanoskeleton. Leucetta antarctica and L. delicata sp. nov. have triactines that are similar. However, the maximum size of triactines in L. antarctica is around 360 x 35 µm (Dendy 1918), while the average size is around 390 x 23 µm in L. delicata sp. nov. No tetractines have been found in L. antarctica , and while the tips of the actines are sharply pointed in L. delicata sp. nov they are slightly blunt in L. antarctica . In ongoing molecular phylogenetic analyses based on the D2 region of 28S as well as the entire region comprising the two spacers (ITS1 and ITS2) and the 5.8S ribosomal DNA, comprising a high number of clathrinid taxa, Leucetta delicata sp. nov. clusters within a well-defined group also containing L. chagosensis and with an unidentified Antarctic species of Leucetta as the most closely related species (Klautau et al. in preparation).

Figures

FIGURE 3. Leucetta delicata sp. nov. A. Preserved Holotype (SMF 11868). os = osculum. B. Spicules from L. delicata sp. nov. Bottom left: rte = regular tetractine with very short apical actine. Remaining spicules: rtri = regular triactines of variable size. C. Cross section of the body wall. cx = cortex. ca = canal. atr = atrium. D. Cross section of the cortical region. cx = cortex. cch and arrow = choanocyte chamber (scale bar as in E). E. Cross section of the atrial region. atr = atrium.

Tables

TABLE 3. Spicule measurements of holotype of Leucetta delicata sp. nov. Measurements are given as minimum, mean and maximum values. σ = standard deviation. n = number of spicules measured.

Spicule	Length (Μ m)			Width (Μ m)
	min max	mean	s	mean s	n
Triactines	299 505	392	±42.6	23.4 ±3.9	50
Tetractines	134 309	213	±62.5	13.1 ±1.7	9
Apical actine	- 15	-	-	- -	2