Astrotoma agassizii is a large brittle star that has a circumpolar Antarctic/subantarctic distribution and occurs throughout the southern part of South America, at depths of 80 to 1200 meters. This species is reportedly viviparous, with brooding occurring in the bursae at the base of the arms. Studies of geographic variation in mitochondrial DNA have revealed that individuals of this species from the Antarctic Peninsula belong to a lineage that is distinct from two South American lineages, although within lineages there is striking genetic continuity across a large geographic range (>500 km), a somewhat surprising finding. (Hunter and Halanych 2008 and references therein)

Heimeier et al. (2010) proposed a possible explanation for the genetic homogeneity of this species in the Antarctic Peninsula. Using mtDNA sequence analysis, they found that a variety of early developmental stages collected from plankton samples in the Ross Sea matched sequences of A. agassizii from the Antarctic Peninsula and that these A. agassizii developmental stages occurred regularly in plankton samples. They proposed that that the Antarctic lineage of this species has a planktonic dispersive stage (explaining the sequence homogeneity over great distances), with brooding restricted to the South American lineages, and that these lineages may represent two or more cryptic species.

Balleny Islands, Terra Nova Bay, Victoria Land

Astrotoma agassizii is found throughout the Southern Ocean in depths of 70-1000 m (Bernasconi & D?Agostino, 1977) and occurs irregularly on the shelves of sub-Antarctic islands and the Antarctic continent (Ferrari & Dearborn, 1989). Along the Chilean margin between Chiloe (42° S) and the Strait of Magellan. On the South Atlantic to North (39°) off Argentina Coast; Tierra del Fuego; Falklands, South Georgia and Shag Rocks Islands; Antarctic region (Tierra de Graham, Ross Sea, Haakon VII Sea; Tierra Adelia, Reina María, Mac Robertson and Enderby) (Castro Manso, 2010).

Astrotoma agassizii, the large brittle star belonging to the suborder Euryalina, has long, flexible, and mobile arms that use to capture the prey from the water column.

Depth range based on 24 specimens in 1 taxon.
Water temperature and chemistry ranges based on 16 samples.

Environmental ranges
  Depth range (m): 0 - 786
  Temperature range (°C): -1.698 - -0.018
  Nitrate (umol/L): 27.050 - 32.629
  Salinity (PPS): 34.119 - 34.630
  Oxygen (ml/l): 5.338 - 7.339
  Phosphate (umol/l): 1.797 - 2.247
  Silicate (umol/l): 74.724 - 102.460

Graphical representation

Depth range (m): 0 - 786

Temperature range (°C): -1.698 - -0.018

Nitrate (umol/L): 27.050 - 32.629

Salinity (PPS): 34.119 - 34.630

Oxygen (ml/l): 5.338 - 7.339

Phosphate (umol/l): 1.797 - 2.247

Silicate (umol/l): 74.724 - 102.460
 
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The analysis of the stomach contents showed that the diet consisted of members of only two major taxa, Crustacea and Chaetognatha. Copepods occurred in 75.6% of brittle stars containing food and were the dominant prey group, followed by mysids (34.6%), chaetognaths (10.2%), and euphausiids (8.9%). Other prey included unidentified crustacean and organic remains, ostracodes, and amphipods. Euchaeta antarctica and Calanoides acutus constituted about 80% of the stomach content copepods (Dearborn et al. 1986).

The genetic diversity of the brittle star Astrotoma agassizii, distributed widely throughout Antarctica and southern South America, was studied by Hunter & Halanych (2008). This species is a brooder and, therefore, was expected to have a limited dispersal capacity. The authors hypothesized isolating barriers in the Southern Ocean, such as depth, geographic distance, and the polar front. They compared populations from the South American and Antarctic continental shelves. A. agassizii resulted to be genetically discontinuous across the polar front. In fact, populations previously assumed to be panmictic instead represent 3 separate lineages that lack morphological distinction. However, within lineages, genetic continuity was displayed across a large geographic range (500 km). Therefore, despite lacking a pelagic larval stage, A. agassizii can disperse across substantial geographic distance within continental shelf regions. These results indicate that geographic distance alone may not be a barrier to dispersal, but rather the combined effects of distance, depth, and the polar front act to prevent gene flow between A. agassizii populations in the Southern Ocean (Hunter & Halanych, 2008).

Genomic DNA is available from 2 specimens with morphological vouchers housed at Research Collection of Slava Ivanenko

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Species: 76
Species With Barcodes: 1

From the brittle star A. agassizii was isolated the sterol Polihidroxiesterols witch has an inhibiting action to HSV-2, JV y PV-3 (Márquez F. et al., 2004).