Radiella antarctica, Plotkin, Alexander S. & Janussen, Dorte, 2008

Plotkin, Alexander S. & Janussen, Dorte, 2008, Polymastiidae and Suberitidae (Porifera: Demospongiae: Hadromerida) of the deep Weddell Sea, Antarctic *, Zootaxa 1866, pp. 95-135 : 111-116

Radiella antarctica sp. nov. ( Figs. 7–9 , Table 4)

Material examined

Holotype: SMF 10558: PS67/110­2.

Paratypes: SMF 10559 (2 specimens): PS61/132­3; SMF 10560 (10 specimens), 10561 (7 specimens) and 10562 (1 specimen): PS61/135­3; SMF 10563 (66 specimens) and 10564 (1 specimen): PS67/102­11; SMF 10566 (62 specimens), 10567 (42 specimens) and 10568 (2 specimens): PS67/110­2; 10565 (1 specimen), 10569 (1 specimen) and 10570 (1 specimen): PS67/110­8.

Description

External morphology. The holotype is a lenticular, slightly irregular sponge measuring approximately 9 mm in diameter and 2 mm in thickness, without any substrate (fig. 7A). The central area of the upper surface is gently rough and has a pale colour in alcohol, with a single very low exhalant papilla of 1 mm in diameter. The periphery of the upper surface is hispid and covered with greyish sediment particles. The basal surface is nearly smooth and pale coloured. A spicule fringe of 0.7 mm in width is in the margin between the upper and basal surfaces. The cortex is hardly detachable, whitish in colour and moderately firm in consistency. The choanosome is whitish, firm but crumbly.

All paratypes share the presence of solitary exhalant papillae and the marginal fringes with the holotype. The colour of their upper surfaces is mainly determined by the hispidation pattern and the subsequent density of the soiling sediment particles. The basal surface, if present, is usually pale, and the papillae are of the same colour. The cortex is hardly detachable, whitish to grey in colour and moderately firm or slightly resilient in consistency. The choanosome is whitish to pale beige. Other external features of the paratypes vary much more. The paratype SMF 10564 is a lenticular, slightly irregular sponge without any substrate (fig. 7B). The paratype SMF 10565 is a discoid sponge attached to a very small sediment particle by the central area of its basal surface (fig. 7C). Both specimens SMF 10564 and 10565 possess uniformly hispid upper surface covered with sediments and a smooth basal surface. Another paratype SMF 10562 (fig. 7D) has a discoid upper surface with a smooth pale central area and a hispid periphery, and a conical, smooth basal surface without substrate.

Most other studied sponges are attached by the basal surface to various hard substrata including pebbles, rock pieces and volcanic concretions (fig. 7E). The shape varies from discoid to hemispherical and cushionlike. The diameter is up to 30 mm while the thickness may reach 8 mm. The upper surface is mainly smooth, velvet or gently rough though its peripheral area close to the marginal fringe may be hispid. The length of the papillae varies from 0.5 to 4 mm; the diameter is 1–2 mm.

Skeleton. The main choanosomal skeleton is constituted by the tracts of principal tylostyles radially running from the central basal area (fig. 8). The thickness of the radial tracts is 110–330 µm in the holotype and 100–280 µm in other specimens. In sponges free of substrate, or with a small substrate, the radial tracts form a smooth envelope of the basal surface (figs. 8A, B). In specimens attached to larger substrata, such an enveloping is less visible (figs. 8C, D). The additional choanosomal skeleton is composed of the variously positioned principal and small tylostyles lying singly or gathered in the thin bundles. In the upper surface the main choanosomal tracts enter the cortex, diverge into bouquets and make up the surface hispidation developed mainly in the periphery. The cortical bouquets are reinforced by the palisade of small tylostyles. Ostia are located between the bouquets. The thickness of the cortex is 250–680 µm in the holotype and 210–800 µm in other specimens. The thickness of the surface hispidation is 120–630 µm in the holotype and 260–410 µm in other specimens. The marginal fringe is made of the additional extra­long tylostyles which may also reinforce the peripheral hispidation. Papilla skeleton is constituted by the ascending main tracts surrounding the exhalant canal of 540 µm in diameter The skeleton of each papilla possesses ascending main tracts surrounding the exhalant canal, the latter measuring 540 µm in diameter (fig. 8C).

Spicules. Altogether 1307 spicules from 15 specimens were measured. Two main size categories of tylostyles are well distinguished and no intermediary class can be marked out (fig. 9A). Extra­long tylostyles of the fringe undoubtedly constituted an additional size category. But the measurements of them were very few, because most of these spicules became broken on the slides. Summarizing results of spicule measurements are given in the main text below, indicating the total number of spicules measured for each category (n). Particular results of spicule measurements for each specimen (extra­long tylostyles excluded) are given in table 4.

Principal tylostyles are usually straight or rarely slightly curved, slender (fig. 9B). Most of them possess terminally located, spherical tyles. More then 60% of principal spicules have well­developed tyles and about 35% of them have weakly­developed tyles. Very infrequently, principal spicules have slightly displaced, weakly­developed tyles or even lack any tyles. In general the principal tylostyles measure: length 957­ 1599 ­ 2686 µm, tyle diameter 8­15.0­27 µm, diameter of the shaft underneath the tyle 5­11.8­26 µm, maximal diameter of the shaft 8­17.6­27 µm (n= 412).

Small tylostyles are mainly straight or rarely slightly curved and most of them are slightly fusiform (fig. 9C). The majority of small spicules have terminally located, well­developed spherical tyles. About 11% of small tylostyles are with weakly­developed tyles. The slight displacement of tyle and its absence are observed very rarely. In general the small tylostyles measure: length 125­636­1271 µm, tyle diameter 4­10.0­21 µm, diameter of the shaft underneath the tyle 2­6.0­19 µm, maximal diameter of the shaft 3­11.0­24 µm (n= 895). It should be mentioned that in three specimens (SMF 10559 and 10564), the small spicules are significantly shorter than in other sponges—125­290­829 µm (n= 209).

Extra­long tylostyles of the fringe are very slender as their diameters are similar to those of the principal tylostyles. Their minimal length is about 2500 µm while the maximal one exceeds 5600 µm. No remarkable differences in tyle location and development have been found between the fringe and principal tylostyles. Type locality: Antarctic: Northern Weddell Sea, ca. 2080–4800 m.

Etymology: The name arises from the type locality.

TABLE 4. Radiella antarctica sp. nov.: Results of spicule measurements. Measurements are given as in table 2.

Specimen no. Large tylostyles Small tylostyles

SMF 10558 (holotype) 1330­1571 ­1710 490­676­810

12.8­14.4­16 / 9.6­10.6­12 8­10.1­11.2 / 4­5.1­7.2

12.8­16­17.6 (n= 21) 8­10.8­14.4 (n= 39) SMF 10559 (specimen 1) 1014­1690 ­2686 155­275­829

9.6­15.4­23 / 4.8­11­16.2 4.1­10.6­18.9 / 2.4­6.2­11.2

8.1­19.9­27 (n= 49) 4.8­10.1­16.2 (n= 104)

SMF 10559 (specimen 2) 1064­1400 ­1710 170­320­660

12.8­14.5­17.6 / 6.4­10.4­12.8 5.6­10.2­17.6 / 2.4­5.5­12.8

16­18.8­22.4 (n= 19) 4­9.7­20.8 (n= 48)

SMF 10561 (specimen 1) 1343­1744 ­2086 557­872­1271

10.8­14­17.6 / 8.1­11.7­16.2 8.1­11.7­16.2 / 4.1­6­9.5

13.5­18.3­21.6 (n= 19) 8.1­12.1­20.3 (n= 41) SMF 10562 1064­1401 ­1710 460­702­930

8.8­10.8­13.6 / 6.4­9.3­12.8 5.6­8.7­12.8 / 2.4­6.1­9.6

12.8­15.3­17.6 (n= 60) 4.8­11.4­16 (n= 121) SMF 10563 (specimen 1) 1386­1523 ­1686 571­845­1114

13.5­16.9­21.6 / 10.8­14.1­16.2 8.1­12.3­16.2 / 4.1­7.2­13.5

16.2­19­21.6 (n= 28) 8.1­14.3­24.3 (n= 32) SMF 10563 (specimen 2) 1486­1796 ­2086 600­785­1271

9.5­13­17.6 / 8.1­11­16.2 6.8­9.5­12.2 / 4.1­6.1­8.1

13.5­17.5­20.3 (n= 30) 8.1­11.7­16.2 (n= 60) SMF 10564 1543­1864 ­2543 125­291­520

10.8­15­18.9 / 8.1­12.2­14.9 6.4­9.2­13.5 / 3.2­5.2­8.1

12.8­16.7­27 (n= 29) 5.4­8.3­13.5 (n= 57) SMF 10565 957­ 1567 ­2671 400­591­871

12.2­15.1­18.9 / 8.1­10.8­13.5 8.1­10­13.5 / 2.7­5.8­8.1

13.5­18.7­24.3 (n= 36) 8.1­11.4­16.2 (n= 54) SMF 10566 (specimen 1) 1286­1712 ­2057 510­796­1178

8­13.6­27 / 6.8­11.8­25.7 6.4­8.7­20.3 / 3.2­5.5­18.9

12.8­16.9­25.7 (n= 43) 5.4­11.1­21.6 (n= 84) SMF 10567 (specimen 1) 1102­1606 ­2090 480­684­940

11.2­14.4­17.6 / 6.4­10.4­14.4 6.4­9.9­12.8 / 2.4­5.7­8.8

12.8­15.3­18.4 (n= 20) 8­11.6­17.6 (n= 40) SMF 10568 (specimen 1) 1216­1525 ­1748 470­663­870

12.8­15.2­22.4 / 9.6­12.8­16 8­10.8­12.8 / 4.8­5.9­8

12.8­17.6­22.4 (n= 21) 8­10­12.8 (n= 43)

SMF 10568 (specimen 2) 1330­1594 ­2014 490­707­900

13.6­15.8­17.6 / 10.4­12.2­14.4 8­10.2­12.8 / 4.8­6.1­8

14.4­16.6­19.2 (n= 20) 7.2­10­12.8 (n= 40) SMF 10569 1330­1568 ­1786 460­649­850

14.4­17.7­22.4 / 12.8­14.1­17.6 6.4­10.1­14.4 / 1.6­5.4­8

16­18.4­22.4 (n= 26) 4­10.2­16 (n= 41)

SMF 10570 1026­1429 ­1634 420­641­950

12.8­19.1­22.4 / 6.4­14.8­17.6 6.4­9.2­12.8 / 2.4­5.4­9.6

16­19.3­20.8 (n= 28) 3.2­9.4­16 (n= 54) Remarks. No species of Radiella has previously been reported from the Antarctic, although two species were described from other regions of the Southern Hemisphere, namely R. irregularis ( Ridley & Dendy, 1886) from the Chilean Coast, and R. sarsi ( Ridley & Dendy, 1886) from Australia. Both species are from the deep sea. In contrast to the Antarctic sponges, the choanosomal skeleton of R. irregularis and R. sarsi consists of a confused mass of small tylostyles, while the upper cortical skeleton is formed by intermediary spicules, and long spicules constitute the basal envelope and the marginal fringe. Radiella irregularis is also distinguished by the presence of several papillae. The status of R. sarsi is somewhat controversial because its type locality simultaneously includes Australia and the Azores. Meanwhile later findings of this species have been made exclusively in the Northern Hemisphere (Boury­Esnault et al. 1994; Plotkin 2004). Another similar deep­water species, R. straticulata ( Wilson, 1925) from the Philippines, is distinguished from other Radiella spp. by the three­layered cortex.

The status of R. sol Schmidt, 1870 , the type species of the genus, is rather confused. Schmidt (1870) described it from Cuba. His illustration of the sponge habit resembles R. sarsi and also some of our Antarctic sponges, but the description is very brief and gives no information about the skeleton architecture. Boury­ Esnault (2002) discovered a specimen collected by the ‘Blake’ expedition 1878–1879 from the Western Central Atlantic deep waters and identified by Schmidt as R. sol . She considered this specimen as the holotype but made a question mark and emphasized that the discovered specimen differs from the original illustration of Schmidt (1870). The differences are not listed but the comparison of Schmidt’s drawing and Boury­Esnault’s description and photo reveals that the former sponge had a single papilla and a hispid upper surface whereas the latter specimen possessed 15 papillae and a velvety surface. Additionally, Schmidt’s drawing indicates a very long marginal fringe whereas Boury­Esnault’s photo shows a considerably damaged or probably just weakly­developed fringe; although in her description the fringe is alleged to be very long. Meanwhile, the possession of several papillae, the smooth or velvety upper surface and the moderately­developed fringe are typical of R. hemisphaerica (Sars, 1872) , widely distributed in the North Atlantic and Arctic deep and shallow waters ( Koltun 1966; Plotkin 2004). Boury­Esnault writes (2002, p.213): “…Presently it is impossible to ascertain if this specimen from the West central Atlantic is a synonym of ‘ hemisphaericum ’ from the Arctic and North Atlantic…”

Albeit a detailed revision of Radiella being necessary, it appears quite clear that the materials dealt with here belong to a new species. We should just mark out high variability of external morphology of R. antarctica sp. nov. Sponges free of substrate, or attached to very small substrata, have lenticular or discoid shape with a prominent basal surface enveloped by main spicule tracts, which is typical of other Radiella spp. On the contrary, specimens attached to larger substrata are hemispherical or cushion­shaped and the enveloping of their basal surface is reduced. However, in both cases a marginal fringe of additional spicules is developed to a greater or lesser extent.

Figures

FIGURE 7. Radiella antarctica sp. nov.: external morphology. A – holotype SMF 10558. B – paratype SMF 10564. C – paratype SMF 10565. D – paratype SMF 10562. E – a paratype from series SMF 10563 on a rock piece. Scale bars: 10 mm.

FIGURE 8. Radiella antarctica sp. nov.: skeleton architecture. A—holotype SMF 10558, manual section. B—the same as A, histological section. C—a paratype from series SMF 10563, manual section. D – the same as C, histological section. Scale bars: 2 mm.

FIGURE 9. Radiella antarctica sp. nov.: spicules. A—frequency distribution of length (extra­long spicules of the fringe excluded). B—principal tylostyles. C—small tylostyles. Scale bars for B – C: 0.1 mm.