Specimens. BELUM.Mc 2015.284, cruise sample number NBP 1103 –DH 95 –sponge04, Sars Seamount 59 ° 43.76 ’S, 68 ° 53.93 ’W, 740–820m, Hein Dredge. BELUM.Mc 2015.329, cruise sample number NBP 1103 –TO 104 – sponge04 and BELUM.Mc 2015.335, cruise sample number NBP 1103 –TO 104 –sponge 10, both Sars Seamount 59 ° 43.43 ’S, 68 ° 45.38 ’W, 570–820m, Otter Trawl.
Comparative material examined. R. antarctica specimens from station the ANT XXIV/ 2 ( SYSTCO I) expedition (SMF 11734, 11735, 11908 –11915, 11916– 11930).
External appearance (Figure 6 A, B). The three sponges are sacciform with a basal attachment and a terminal oscule. The largest specimen is 15cm long and 9cm wide and the smallest 5cm long and 2cm wide. All were cream coloured when collected and have a veil of projecting diactins which protrude up to 1.5cm from the body. No dense velum of protruding pentactins is present in the specimens.
Spicules. Measurements are taken from BELUM.Mc 2015.284, figures are restricted to spicules of high taxonomic value.
Dermal spined pentactin: Very large spicules – tangential rays of the one specimen measures were 3750 / 117 µm. The spicules are covered with large, fairly widely spaced spines.
Rough pentactin tangential ray 90 –(122)– 184 µm, proximal ray 80 –(117)– 110 µm
Rough hexactin diameter 149 –(268)– 403 µm
Oxyhexactin diameter 89 –(115)– 142 µm
Oxyhexaster diameter 86 –(102)– 116 µm
Calycocome (Figure 6 C) diameter 85 –(99)– 109 µm, number of secondary rays 4 (5) 6 µm, Complete ray length 43 –(48)– 55 µm, Primary ray length 6 –(11)– 13 µm, Centrum length 6 –(10)– 13 µm, Secondary ray length 20 –(28)– 33 µm.
Microdiscohexaster (Figure 6 D) diameter) 22 –(33)– 36 µm
Remarks. This species differs from other Antarctic Rossella species by its distinctive spined dermal pentactins. It has relatively small (~ 100 µm) calycocomes with 3–8 secondary rays and primary and secondary rays of a similar length; this distinguishes it from many other species of Rossella which tend to have calycocomes with short primary and long secondary rays. The microdiscohexasters found in this species are characterised by the lack of a capitulum at the end of the primary rays, the secondary rays originate directly from the endings of the primary rays; this feature is shared only with R. levis (Kirkpatrick 1907). See Göcke & Janussen (2013) for a full discussion.
The spicule dimensions of our specimens are generally in good correspondence with those given by Kirkpatrick (1907) and Göcke & Janussen (2013). The dimensions of the middle piece of the calycocomes are longer (6 –(10)– 13 µm in our specimens, 2–4 in Kirkpatrick, 2.5–5.5 µm in Göcke & Janussen 2013), however, this may be due to a variation in how these were measured, proportions in images look similar.
The genus Rossella is currently in a very problematic state as many of the described species are suspected to be synonyms. Attempts to install synonymies nevertheless were so far not fully successful (see Barthel & Tendal 1994, Göcke & Janussen 2013). Rossella antarctica nonetheless is a very well defined and accepted species. The species is widely distributed all around the Southern Ocean with Antarctic records from the Amundsen/ Bellingshausen Sea, Antarctic Peninsula and South Shetland Islands, East Antarctic Dronning Maud Land, East Antarctic Enderby Land, East Antarctic Wilkes Land, the Ross Sea and the Weddell Sea. It has also been recorded from the sub-Antarctic from Kerguelen, Prince Edward Islands and South Georgia and from Namaqua (Barthel & Tendal 1994; Göcke & Janussen 2013; Van Soest et al. 2015). The Sars Seamount sites may be at the lower end of the depth range for this species, the majority of Antarctic specimens have been recorded between 90 and 600m. Göcke & Janussen (2013) note that during the SYSTCO-I expedition the deepest records of R. antarctica were in 600m with deeper stations yielding no specimens. However, Barthel & Tendal (1994) do note one record from off Patagonia in 1100m.