Microxina lanceolata, Calcinai & Pansini, 2000

Calcinai, Barbara & Pansini, Maurizio, 2000, Four new demosponge species from Terra Nova Bay (Ross Sea, Antarctica), Zoosystema 22 (2), pp. 369-381 : 376-378

Genus Microxina Topsent, 1916 Microxina lanceolata n. sp.

( Figs 6 ; 7 )

MATERIAL EXAMINED. — Holotype: stn F2, rock, 70 m, 27.XII.1989, POR64 (MNA No 3); paratypes:

stn MM78, sand, gravel, 235 m, 25.I.1990, POR28 (MSNG). — Stn D4D, 100 m, 3.I.1990, POR65. — Stn Adelie Cove, 10.I.1994, POR273, POR274. — Stn F2bis, 67 m, POR24; 13.I.1988, POR91; haul 24, 20.I.1988, POR92, POR96; 70 m, 13.I.1990, POR157; 1987- 1988 campaign, POR 272.

ETYMOLOGY. — The name is suggested by the shape of one oxea extremities which resembles a spear.

TYPE LOCALITY. — Terra Nova Bay, 74°42’20S, 164°10’90E.

DESCRIPTION

The sponge is erect and forms numerous cylindrical branches (1-2 cm in diameter), which arise from a common base and divide dichotomically ( Fig. 6A ). Some specimens may attain a height of 30-40 cm and look bushy. The colour of alcoholpreserved specimens is pale yellow, beige, grey or brown. The consistency is soft and fragile. The surface is areolate; most areolae bear pore sieves and some oscules; both are supported by an erect series of oxeas forming a rim ( Fig. 6D, E ). Only well-preserved specimens retain this ectosomal specialization which is easily lost.

Skeleton

The ectosome includes perpendicular tufts of oxea surrounding the areolae and is supported by extensions of the choanosomal spicule tracts ( Fig. 6B, C ). Tangential spicules are absent even between the areolae.

The rather loose choanosomal skeleton is made up by ascending paucispicular (three to eight) tracts (50-180 µm thick) which are parallel or slightly plumose and connected by transverse spicules (two to three) ( Fig. 6F ). The spicule tracts diverge towards the sponge surface and merge with the ectosomal oxea layer. Interstitial spicules and dispersed microscleres (sigmas) are rare. Several yellow-brown embryos with a diameter of about 200 µm are incubated within the choanosome.

Spicules

Oxeas are mostly straight or seldom slightly curved ( Fig. 7A ), their ends are generally acerate although abruptly bent tips and lanceolate extremities are common ( Figs 6G ; 7C ). Oxea measure 390-525 (450) × 11-20 (16.3) µm. Straight, slender and much thinner oxeas (8 µm) are considered developmental stages ( Fig. 7A ).

Sigmas are always present but not abundant ( Figs 6H ; 7B ); they measure 25-60 (42.6) × 2-4 µm.

REMARKS

A remarkable number of Haplosclerida with sigmas and microxeas were recorded from continental Antarctic and circum Antarctic islands (Sarà et al. 1992) and attributed to the genera Gellius, Haliclona and Microxina . However, as Boury- Esnault & Van Beveren (1982) pointed out, there is confusion in the taxonomy of this group and a worldwide revision is needed. Boury-Esnault & Van Beveren (1982) decided to use the genus Gellius in a broad sense in their study of the demosponges of the Kerguelen and Heard Islands. More recently, Wiedenmayer (1989: 105) synonymized Hemigellius Burton, 1932 with Microxina Topsent, 1916 , two genera that are nearly identical except for the microscleres, sigmas in the former and microxeas in the latter (see Van Soest 1980: 109). This decision seems justified because Microxina species which have

A

B

both sigmas and microxeas as microscleres actually exist (e.g. M. benedeni (Topsent, 1901)) . Wiedenmayer (1989) stated that “toxa also occur in some species of Niphatidae (Microxina) of which Hemigellius is here considered a synonym” emending de facto the definition of the genus Microxina to receive also species bearing toxas. This allowed Hooper & Wiedenmayer (1994) to attribute to Microxina several species of Haplosclerida with toxas, such as M. phakelloides (Kirkpatrick, 1907) and M. spongiosa (Topsent, 1916) , and “ Microxina ” flagellifer (Ridley & Dendy, 1886). We agree with the proposed synonymy but, for the moment, will restrict its use to species that being devoid of toxas would have previously been placed in Hemigellius.

The new species is attributed to Microxina on account of its skeletal structure. It is well separated from other species by its shape, spear-shaped oxea extremities, peculiar cribrose appearance of its surface, and absence of tangentially arranged ectosomal spicules.

Based on the skeleton structure, the closest species is Microxina (Hemigellius) pachydermata Burton, 1932 which too has a dermal palisade of oxeas but differs from M. lanceolata by its even surface (with regularly distributed pores), by shape and size of oxeas, and by absence of sigmas. Microxina rudis sensu Topsent, 1901 (see Boury- Esnault & Van Beveren 1982: 117 regarding the genotype of Hemigellius) differs from the new species by its massive shape, by having thin, often centrotylote sigmas, and by an ectosomal reticulation of tangentially arranged oxeas. Finally, Microxina (Hemigellius) pilosa (Kirkpatrick, 1907) is erect and ramified like M. lanceolata but has flattened branches, a slightly conulose surface with large, round oscules, a different shape of oxeas, and smaller sigmas. Both M. rudis and M. pilosa were recorded from Terra Nova Bay.

Figures

FIG. 6. — Microxina lanceolata n. sp.; A, paratype; B, C, ectosomal oxeas which form tufts supporting the pore sieve membrane (arrow); D, areolate surface showing the inhalant sieves supported by the oxeas; E, oscule; F, choanosomal skeleton; G, lanceolate extremity of an oxea; H, sigma. Scale bars: A, 1 cm; B, 50 µm; C, 20 µm; D, E, 1.5 mm; F, 400 µm; G, H, 10 µm.

FIG. 7. — Microxina lanceolata n. sp.; A, straight oxeas; B, sigmas; C, oxea extremities. Scale bars: A, 100 µm; B, C, 50 µm.