Kamptosoma asterias A. Agassiz 1881

Kamptosoma asterias (A. Agassiz, 1881)

( Figures 22–25)

Material examined. 97 specimens from 6 records (all NIWA).

Tasman Basin: 3 specimens (71 mm TD), 41° 37 S, 165° 11´E, 4439 m, NIWA45130; 1 specimen (75 mm TD), 41° 39.1 S, 165° 13.6´E, 4405 m, NIWA45132; 2 specimens (52, 47 mm TD), 35° 29.7 S, 157° 28´E, 4570 m, NIWA45133; 8 specimens (28, 45, 47, 54, 54, 54, 55 mm TD), 35° 33.2 S, 159° 5.8´E, 4744 m, NIWA45030; 79 specimens (37, 38, 38, 41, 41, 43, 43, 44, 45, 45, 46 mm TD), 36° 55.7 S, 159° 31.5´E, 4954 m, NIWA45135; 4 specimens (50, 50, 54 mm TD), 37° 39.7 S, 162° 15.5´E, 4077 m, NIWA45131. Unless stated, all stored in 80% ethanol.

Size range. The 25 specimens measured range in size from 28 mm to 75 mm TD, with an average of 48 mm TD.

Remarks. This species is distinctive due to the presence of five enlarged plates on the peristome similar to the buccal plates of acroechinoids, the lack of buccal sacs, series of large crenulate tubercles in the adambital oral interambulacra, and reduction of the secondary plates along with their exclusion from the edges of the ambulacraeven close to the apical system. The ocular plates are also unusual; long and narrow, they extend the apical system down into the corona in a way more usually exhibited by the genital plates of many other echinothurioid genera, especially Araeosoma. The test is very thin and delicate—with a faint red colouration visible in places, as noted in the Challenger specimens examined by Mortensen (1935), and clearly seen in the living animal (Figure 23). Oral primary spines are similar to those of Phormosoma, i.e. skin-clad, rather than bearing a hoof.

A second species in the genus, K. abyssale Mironov 1971, differentiated from K. asterias based on characters of the globiferous pedicellariae, is taken here to be synonymous with K. asterias. The validity of K. abyssale remains uncertain as the number of valves in these pedicellariae (two in K. abyssale, three in K. asterias) has not been clearly determined for all the type specimens of K. asterias, and this difference is the sole character by which the two species can be distinguished (Mooi et al. 2004, Mironov 2015).

Three kinds of pedicellariae are present in this genus: globiferous (considered by Mironov (2015) to be better described as claviform due to their rudimentary, non-functional valves), tridentate, and triphyllous (Figure 24). Pedicellariae were extracted from several of the Tasman Basin specimens. Tridentate and triphyllous forms were found to be abundant over the test, as noted also for K. abyssale (Mironov et al. 2015), especially on the oral side. Bidentate pedicellariae, observed in some specimens of K. abyssale, were not found. Claviform (globiferous) pedicellariae were readily found, but not common; they have 2 valves as described for K. abyssale (Mironov 1971, Mironov et al. 2015).

The presence of the buccal-like peristomial plates, crenulated tubercles, and other unusual characters of the test plates have led to doubts about the place of Kamptosoma in the Order Echinothurioida, with some authors suggesting a closer relationship with the diadematoids (e.g Fell 1966). But others (e.g. Mironov 1972) and recent phylogenetic analyses based on morphological features show it to be a true echinothurioid in a separate family most closely related to Phormosoma, Paraphormosoma, and Hemiphormosoma (Mooi et al 2004), or basal to all other echinothurioids (Kroh & Smith 2010).

Occurrence. This is the deepest-living of all the known echinothurioids; the six new records were all from 4077–4954 m in the Tasman Basin (Figure 25), collected with either an epibenthic sled or a Menzies trawl. A further (unconfirmed) record is available from a photograph taken of the seafloor near the Scott seamounts, Antarctica, at a latitude of about 67.6° S (Figure 23). There are only two physical records reported from the Antarctic region, collected by the Marion Dufresne expedition of 1974 (De Ridder et al. 1992, David et al. 2005) and cruise PS-61 of the R/V Polarstern in 2002 (Mooi et al. 2004). These records (from about 55.8° S near the Kerguelan and Crozet Islands, and about 65.3° S in the western Weddell Sea, respectively) along with the photographic record, confirm the presence of K. asterias in Antarctica, and this is the only echinothurioid to have been recorded in the region. Other records of the species are from the central Pacific Ocean, the Tasman Sea, Chile, and the southern Indian Ocean (Agassiz 1881, Mironov 1971, Schulz 2011) in 3890–6235 m.