(Bernasconi 1973a). This is a brooding sea star with an aboral nidamental
chamber, where fifty embryos can be brooded. The size of embryos ranges
between 1.5 and 7 mm. Inside the nidamental chamber, embryos are located in
specific areas: eggs and smallest embryos are among the paxillae, close to the
osculum; the intermediate embryos are, following the edge of the arms, between
paxillae and resting on the actinolateral membrane; and the largest embryos
(radius = 4–6 mm) are located between paxillae in the interradii. When embryonic development is completed, the juveniles leave the aboral chamber by
breaking the suture between the supradorsal and actinolateral membranes. The
estimated brooding season is between September and May, from spring until
autumn (Bernasconi 1937).
Ophiuroidea
Few publications focus exclusively on this group in Argentina. Bernasconi (1965b,
c), Tommasi (1968), and Bernasconi and D’Agostino (1971, 1974, 1975, 1977)
published a taxonomic revision for the Argentine region. Bartsch (1982) analyzed
benthic samples from the Patagonian shelf and described external and internal
characters of 11 species of brittle stars. The first reports of Argentinian brittle stars
were provided by Bernasconi (1926, 1934). She documented the presence of
Gorgonocephalus chilensis and Amphipholis squamata in the region.
Zaixso and Lizarralde (2000) examined the distribution of the most frequent
echinoderm species of the SJG and southern SMG, referring to four brittle star
species. They analyzed species densities by using a point kriging method, and
related them to environmental parameters (depth, substrata granulometry, currents
and bottom temperature). Amphiura crassipes (1–25 ind m
-2 ) was found close to
80 m depth on substrates with high percentages of silt and clay. The increase of
abundance was associated with an increase of fine sand substrates and no correlation was found with temperature and currents. Ophiactis asperula was the most
abundant ophiuroid (25–3,125 ind m
-2 ) in the study area. The density of this
species was not related to any particular depth, but the density decreased with
increasing summer temperatures and the increase of silt–clay and fine sand substrates. Higher densities were correlated with faster surface currents. Amphiura
magellanica (5–125 ind m
-2 ) was associated with coarse sand substrates. The
abundance was not related to any particular depth or temperature. However,
abundance was positively related to faster surface currents. The abundance of
Ophioplocus januarii (5–125 ind.m
-2 ) was highest at shallow depths and on
coarse sand substrates, and increased with summer temperature.
Several aspects of the biology of the brittle star Ophioplocus januarii
(Fig. 11.3c) in a shallow water population from SJG were studied. Arribas et al.
(2008) analyzed presence and abundance of the fauna associated with this ophiuroid species throughout two years. The authors observed that the fauna associated, mainly mollusks, arthropods and annelids, remained stable over the study
period (2005–2007). The number of species did not show annual variation. This is
374
M. I. Brogger et al.
chamber, where fifty embryos can be brooded. The size of embryos ranges
between 1.5 and 7 mm. Inside the nidamental chamber, embryos are located in
specific areas: eggs and smallest embryos are among the paxillae, close to the
osculum; the intermediate embryos are, following the edge of the arms, between
paxillae and resting on the actinolateral membrane; and the largest embryos
(radius = 4–6 mm) are located between paxillae in the interradii. When embryonic development is completed, the juveniles leave the aboral chamber by
breaking the suture between the supradorsal and actinolateral membranes. The
estimated brooding season is between September and May, from spring until
autumn (Bernasconi 1937).
Ophiuroidea
Few publications focus exclusively on this group in Argentina. Bernasconi (1965b,
c), Tommasi (1968), and Bernasconi and D’Agostino (1971, 1974, 1975, 1977)
published a taxonomic revision for the Argentine region. Bartsch (1982) analyzed
benthic samples from the Patagonian shelf and described external and internal
characters of 11 species of brittle stars. The first reports of Argentinian brittle stars
were provided by Bernasconi (1926, 1934). She documented the presence of
Gorgonocephalus chilensis and Amphipholis squamata in the region.
Zaixso and Lizarralde (2000) examined the distribution of the most frequent
echinoderm species of the SJG and southern SMG, referring to four brittle star
species. They analyzed species densities by using a point kriging method, and
related them to environmental parameters (depth, substrata granulometry, currents
and bottom temperature). Amphiura crassipes (1–25 ind m
-2 ) was found close to
80 m depth on substrates with high percentages of silt and clay. The increase of
abundance was associated with an increase of fine sand substrates and no correlation was found with temperature and currents. Ophiactis asperula was the most
abundant ophiuroid (25–3,125 ind m
-2 ) in the study area. The density of this
species was not related to any particular depth, but the density decreased with
increasing summer temperatures and the increase of silt–clay and fine sand substrates. Higher densities were correlated with faster surface currents. Amphiura
magellanica (5–125 ind m
-2 ) was associated with coarse sand substrates. The
abundance was not related to any particular depth or temperature. However,
abundance was positively related to faster surface currents. The abundance of
Ophioplocus januarii (5–125 ind.m
-2 ) was highest at shallow depths and on
coarse sand substrates, and increased with summer temperature.
Several aspects of the biology of the brittle star Ophioplocus januarii
(Fig. 11.3c) in a shallow water population from SJG were studied. Arribas et al.
(2008) analyzed presence and abundance of the fauna associated with this ophiuroid species throughout two years. The authors observed that the fauna associated, mainly mollusks, arthropods and annelids, remained stable over the study
period (2005–2007). The number of species did not show annual variation. This is
374
M. I. Brogger et al.