Rossella nuda Topsent, 1901

Göcke, Christian & Janussen, Dorte, 2013, Hexactinellida of the genus Rossella, of ANT XXIV / 2 (SYSTCO I) Expedition — Antarctic Eastern Weddell Sea, Zootaxa 3692 (1), pp. 102-122 : 114-116

Rossella nuda Topsent, 1901

( Figs. 2 E, 6, Tab. 5)

Synonymy:

Rossella nuda Topsent, 1901a: 4 –5; 1901b: 32–33, pl. 1, fig. 7, pl. 4, figs. 8–13. Burton 1929 (pars): 409–412, figs. 1–2, pl. 2; 1932: 255–256, figs. 1–2; 1934: 7. Koltun 1976 (pars): 165, pl. 1–3. Barthel & Tendal 1994: 99–101, fig. 39–40, pl. 9– 10.

Hyalyscus hodgsoni Kirkpatrick, 1907: 3–5, pl. 3, fig. 1, pl. 4, fig. 1. Burton 1929: 411.

Material examined. 2 specimens from SYSTCO-station 48-1, one was sampled alive (SMF 11715), one was dead (SMF 11901). Other material examined: IRSNB POR. 0 0 3 (type), BMNH 1928.11.15.2, BMNH 1928.11.15.6, BMNH 1928.11.15.7.

Description. The description given in here is concentrated on the one specimen still alive when captured ( Fig. 2 E). This specimen was 40 cm high. It has a very tight tissue with a smooth surface, which is absolutely bare of any conules or protruding spicules. A basal tuft of spicules could not be documented, as the basis of the specimen was torn off. The body wall is up to 3 cm thick. Within the tissue, some larger cavities can be found, which do not open up to visible pores, neither on the inner nor on the outer surface. The specimen was barrel-shaped with a large osculum on the top, it has collapsed while dredging. The color is light brown when living and preserved in ethanol.

The most typical spicule of this species is its calycocome ( Fig. 6 F–G). It is relatively large, up to 350 µm in diameter, probably even up to 400 µm, when estimating from the length of separated rays ( Tab. 5). The most characteristic aspect of this calycocome is the number of its secondary rays, which are usually not more than 4. Microdiscohexasters ( Fig. 6 A–B) have secondary rays of two different lengths. They are relatively large, with mean diameters of 63 µm and a maximum of 75 µm. Mesodiscohexasters ( Fig. 6 C–D) are 120 µm in diameter. Oxyhexactins are 115 µm, they are rather rare. Oxyhexasters ( Fig. 6 E) are on average 130 µm in diameter, with a maximum diameter of 200 µm.

maximum (number of spicules measured). For comparison, values from Topsent (1901b) and Barthel & Tendal (1994)

are given.

parameter SMF 11715 Topsent (1901b) Barthel & Tendal (1994)

rough Pentactin

tangential ray (L) 100–130.5–170 (30) 500–800 proximal ray (L) 120–125–130 (2)

rough Hexactin (D) 150–533–1675 (30)

Stauractin ray (L)

Oxyhexactin (D) 90–115–140 (2)

Oxyhexaster (D) 90–128.1–200 (35) 120 120

Heterodiactin (L)

Discohexactin (D) 130 (1)

Microdiscohexaster (D) 37.5–63.3–75 (30) 40–50 40–75

Mesodiscohexaster (D) 62.5–121.4–155 (30) 100 100

Calycocome

(D) 330–340–350 (2) 250 250 complete ray (L) 140–172.7–200 (30)

primary ray (L) 7.5–13.4–20 (30) 15 15 middle piece (L) 15–27.7–50 (30) 25 25 secondary ray (L) 97.5–128.3–162.5 (30)

number of sec. rays 2–3.6–4 (30) 2–3 2–4 Curvature S: 25

S-C: 5

C: 0

Our spicule measurements correspond to those reported by Barthel and Tendal (1994), but extend our knowledge of the character variations of most spicules in this species. For calycocomes, Barthel and Tendal reported sizes of 250 µm and more in diameter (thus simply following the description in Topsent (1901b)). We can now state, that they reach up to 400 µm and are therefore amongst the largest calycocomes known from the genus Rossella . The very large microdiscohexasters, also the largest known from any Rossella species, are well within the spectrum previously known. Mesodiscohexasters however, up to 155 µm in diameter, are much larger than previously documented (up to 100 µm, Barthel & Tendal (1994)). This corresponds to the observation, that many sponges from this station have spicules significantly larger than known elsewhere, especially discohexasters, oxyhexasters and oxyhexactins. Nonetheless, this finding complicates the differentiation between R. nuda and R. vanhoeffeni , as the latter was formerly reported to have mesodiscohexasters reaching more than 150 µm, while R. nuda was considered only to possess specimens of 100 µm or less. Consequently a reliable differentiation between R. nuda and R. vanhoeffeni can now only be reached on the basis of their calycocomes, as described above.

Remarks. Burton (1929) synonymized several species with R. nuda , including R. vanhoeffeni and R. levis . These particular species can in fact be differentiated clearly from R. nuda . R. vanhoeffeni has a similar shape, but calycocomes usually have more than 4 secondary rays on each primary ray. It therefore shows much more similarities with R. racovitzae , from which it is often difficult or even impossible to distinguish (see below for R. racovitzae ). R. levis (see above) can be easily distinguished as it has microdiscohexasters with secondary rays of only one length as opposed to two lengths in R. nuda .

Figures

FIGURE 2. Habitus-pictures of Rossella spp. A – B, Rossella antarctica, A lateral view (SMF 11913) with spicular fringe visible at the top, B, section (SMF 11921). C, Rossella fibulata, SMF 11906. D, Rossella levis (SMF 11728) photographed ex situ on board RV Polarstern. E, Rossella nuda (SMF 11715) photographed ex situ on board RV Polarstern. F, Rossella racovitzae (SMF 11871) with specimen of Tetilla leptoderma attached, photographed ex situ on board RV Polarstern. G, Rossella vanhoeffeni armata (ZMH S 2932).

FIGURE 6. Spicules of Rossella nuda Topsent, 1901 (SMF 11715). A, microdiscohexaster, B, isolated ray of microdiscohexaster, C – D, mesodiscohexasters, E, oxyhexaster, F – G, complete rays of calycocomes.