Microxina benedeni (Topsent, 1901)

Göcke, Christian & Janussen, Dorte, 2013, Demospongiae of ANT XXIV / 2 (SYSTCO I) Expedition — Antarctic Eastern Weddell Sea, Zootaxa 3692 (1), pp. 28-101 : 78-80

Microxina benedeni (Topsent, 1901)

( Fig. 18 , Tab. 14)

Microxina benedeni (Topsent, 1901) : Koltun 1964: 107, pl. 15, fig. 14–16, 1976: 196. Desqueyroux-Faúndez & Valentine 2002: 885–886, fig. 7d.

Synonymy:

Gelliodes benedeni Topsent, 1901:16 , pl. 2, fig. 3, pl. 3, fig. 5. Gellius benedeni (Topsent, 1901) : Burton 1929: 423, 1932: 271, pl. 50, fig. 1, text-fig. 10.

Material. 1 specimen from station 048-1 (SMF 11836), 602.1 m, 70° 23.94' S, 8° 19.14' W, 12.01.2008. Material examined for comparison: BMNH 1928.2.15.112, “Discovery” Investigations, Antarctic, 1925–1928, stn. 149, R.N. XLII. i., wet specimen.

Description. Complete specimen ( Fig. 18 A–B) growing on a bryozoan colony. Basis very narrow, growing on bryozoan, and widening towards top. Body form club-shaped with slightly rounded top. Specimen 40 mm long and up to 20 mm wide. Surface distinctive; bearing many thin conules made up of skeletal fibres, running longitudinally throughout epidermis. These hair-like conules reaching a length of about 5 mm with a diameter of about 0.5 mm, occuring quite densely and regularly distributed, about 2 mm apart. On top side, two large oscules present ( Fig. 18 B), several additional oscules/pores occuring scattered all over the surface. Inside the sponge a rather large cavity. Colour in ethanol dirty yellowish white, texture very firm and hard.

Skeleton: Skeleton ( Fig. 18 C–D) plumose with thick solid tracts of oxeas, running mainly towards surface, branching off not very regularly. Tracts piercing the normal surface level and forming erect long conules. Tissue including large numbers of sigmas and sand grains.

Spiculation ( Tab. 14): Main spicules almost straight oxeas ( Fig. 18 E) with sharp ends and a relatively characteristic shape, tapering straightly from thick centres to the ends. Oxeas 760 to 980 µm long and 35 to 42.5 µm in diameter. Microscleres exclusively c-shaped sigmas ( Fig. 18 F–G), 47.5 to 62.5 µm in length and 22.5 to 27.5 µm in width.

parameter SMF 11836 Topsent (1901) Burton (1929) Koltun (1964) Oxea

length 760–854.5–980 (30) 750 500 500–900

diameter 35–39.2–42.5 (30) 35–40 24 24–46 Sigma

length 47.5–54.2–62.5 (30) 45–50 39 39–63

max. width 22.5–24.5–27.5 (30)

Microxea

length 67–125

diameter 3–4 Raphide

length 90–140 Remarks. Koltun (1964) reported microxea and raphides in addition to the common spicules of M. benedeni (as shown by Topsent 1901). This is caused by the fact that Koltun (1964) followed Burtons’ (1932) synonymisation of Gelliodes benedeni Topsent, 1901 and Microxina charcoti Topsent, 1916 , two species which mainly differ in their microsclere complements: G. benedeni possesses sigmas, while M. charcoti has microxeas. The synonymy was based on the high similarity in growth, skeleton and megascleres. Nevertheless, Koltun (1964) distinguished between two distinct varieties, differing by their microscleres: forma benedeni and forma charcoti . He reported that microxea and sigmas never co-occur, thus his measurements as cited in the table are sure to summarize spicule sizes of different specimens, which is not very useful. In our opinion, the differentiation between the species M. benedeni and M. charcoti seems distinct enough to consider them as different species. This raises the question, whether the assignment of G. benedeni to Microxina is legitimate. The great similarity between the species’ characters, as pointed out by Burton (1932), might speak for a close relationship between these species, thus justifying the assignment to Microxina , although on the other hand the species fits quite well with the definition of Gelliodes as given by Desqueyroux-Faúndez and Valentine (2002). A solution to this question can only be found through a close look at the holotype. Still, it must be mentioned that if this species is to be assigned to Microxina , the definition of this genus, as given in Desqueyroux-Faúndez and Valentine (2002), has to be emended in the way that not only microxea, but also sigmas are present in Microxina .

Figures

FIGURE 18. Microxina benedeni (Topsent, 1901), SMF 11836. A, habit in lateral view, B, habit in top-view. C, skeletal arrangement beneath the epidermal surface with echinating spicule bundles to the right, D, choanosomal skeleton. E, oxea. F – G. sigmas. Scale bars: A – B: 10 mm, C – D: 1 mm, E: 100 µm, F – G: 10 µm.