Leucascus leptoraphis (Jenkin, 1908)

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 : 283-285

Leucascus leptoraphis (Jenkin, 1908)

Diagnosis: Cortical membrane with tripods. Atrial skeleton composed of triactines and tetractines with cylindrical actines. Tetractines are very rare.

Synonymies: Leucandra primigenia var. leptoraphis: Jenkin 1908: 14 ; Leucetta leptoraphis: Burton 1929: 404 ; Gappa & Landoni 2005: 219.

Type material: BMNH 1907.8.6.65 (Holotype, McMurdo Bay, Antarctica ; Discovery Antarctic Expedition).

Type locality: McMurdo Bay, Antarctica .

Additional analysed material: ZMAPOR 13265 (Turtle Rock, McMurdo Sound, Antarctica ; coll. B. Baker; 1997).

Description: There is no information about the colour of the holotype in vivo, but the specimen from the ZMA was white. After fixation, both specimens became beige ( Figure 5 A). The cormus is digitiform and formed by tightly anastomosed tubes covered by a smooth and thin membrane. The consistency is soft. Only a fragment of the holotype was analysed, but the specimen from the ZMA measures 9.5 x 5.5 x 2.0 cm ( Figure 5 A). At the end of each digitiform projection of the cormus there is an apical osculum (diameter of 0.1 to 1.0 cm) surrounded by a delicate membrane. It was not possible to recognize the oscula in the fragment of the holotype. The atrial cavity is wide in the ZMA specimen, but Jenkin (1908) mentioned that in the holotype it was small, however, he did not give measurements.

The skeleton is composed of tripods, triactines, and very rare tetractines. The cortical membrane has only tripods ( Figures 5 B, C) while the tubes and the atrial membrane have only triactines ( Figure 5 D). Consequently, the tubes and the atrium are smooth. Tetractines were not observed in the skeleton preparations of the holotype, and were not mentioned in the original description of the species, however some rare tetractines were found in the spicule slides. Two tetractines were found in the atrial skeleton of the specimen ZMAPOR 13265.

Spicules/ Specimens Length (µm) Width (µm)

Min Mean SD Max Min Mean SD Max N

Tripod

BMNH 1907.8.6.65 (H) 80.2 114.4 25.0 157.9 6.1 7.9 1.5 10.9 12

ZMAPOR 13265 89.9 123.8 14.9 153.1 4.9 7.5 1.6 12.1 30

All specimens 80.2 119.1 4.7 157.9 4.9 7.7 0.2 12.1 –

Triactine

BMNH 1907.8.6.65 (H) 128.8 176.3 20.0 206.5 3.6 4.3 0.6 6.0 30

ZMAPOR 13265 97.2 160.6 23.9 189.5 3.6 5.4 0.8 7.3 30

All specimens 97.2 168.4 7.8 206.5 3.6 4.8 0.5 7.3 – Spicules ( Table 3):

(i) Tripods ( Figure 5 E): Regular or irregular with an elevated centre. Actines are the same length or not. They are conical, curved, with blunt tips. However, they are not stout as typical tripods;

(ii) Triactines ( Figure 5 F): Regular. Actines are cylindrical, very long and thin, with blunt tips;

(iii) Tetractines: Very rare. They are similar to the triactines. The apical actine could not be observed.

Remarks: Jenkin (1908) described Leucascus leptoraphis as Leucandra primigenia var. leptoraphis , after transferring Leucetta primigenia Haeckel, 1872 to the genus Leucandra . Haeckel (1872) described Leucetta primigenia comprising three varieties: microraphis, isoraphis and megaraphis. Jenkin (1908) added the new variety leptoraphis that, according to him, was similar to isoraphis except for the size of the spicules that were more slender in his variety. He also mentioned the presence of “alate triradiates”, which we understand as being the tripods.

In 1929, Burton elevated Leucandra primigenia var. leptoraphis to the species rank and transferred it to the genus Leucetta . He also synonymized L. leptoraphis with Leucetta antarctica Dendy, 1918 but without justifying his action. Nevertheless, according to its original description, in L. antarctica the cortical and choanosomal triactines are similar, while in L. leptoraphis the cortical skeleton is composed of tripods. Years later, Burton (1963) also synonymized “ Leucetta ” leptoraphis with Leucetta isoraphis var. apicalis Brøndsted, 1931 . However, they are very different species, being the former currently accepted as Soleneiscus apicalis (Borojevic et al., 2002) . Leucandra primigenia var. leptoraphis is indeed a species of Leucascus , as it is formed by anastomosed tubes and has cortical and atrial membranes. It should be noted that the spicule composition and organisation as well as general morphology is quite similar to what is found in Ascaltis abyssus described from the Weddell Sea, Antarctica (Rapp et al. 2011). However, the spicules are generally smaller in L. leptoraphis and the true atrial membrane characteristic for Leucascus is absent in A. abyssus .

Distribution: Antarctic Ocean: McMurdo Bay (Jenkin 1908), and Turtle Rock, McMurdo Sound—Antarctica; Argentina (Gappa & Landoni 2005). Spalding et al. (2007) corresponding ecoregions: Ross Sea and Malvinas / Falklands.

Figures

FIGURE 5: Leucascus leptoraphis. A – E, ZMAPOR 13265; F, BMNH 1907.8. 6.65, Holotype. A, Preserved specimen; B, Cortical membrane; C, Transverse section showing the cortex (ct), choanocyte tubes, and atrium (at); D, Atrial membrane; E, Tripods (SEM); F, Choanosomal triactine.