Ryan Photographic - Ophiuroidea - Brittle stars, snake stars and basket stars


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Class Ophiuroidea

There are around 1900 species of ophiuroids in 230 genera. Although common in shallow water many species are found in the abyssal depths. The snakestars and brittle stars have five arms, strongly demarcated from their central disk which contains all of their organs. In the basket stars multiple divisons of the arms (rather like feather stars) leads to multiple branching. As the name suggests, the strongly nocturnal basket stars open their arms (which may be mucus covered) and filter food from the water. Brittle stars and basket stars range from relaively immobile species which tend to stay on their host, sometimes stealing food from it to those which can move quickly, either for escape or for predation.

The ophiuroids lack an anus, one of the facts my marine biology students can remember about the class.

The brittle stars, as the name suggests, readily autotomize (break off) arms when threatened. They do grow them back. The snake stars are so quick that they can usually reach cover and this ability to autotomize is, as far as I know, lacking. Some of the nsake stars can undergo marked color change between day and night. The New Zealand snake star Pectinura maculata detects the light of an underwater torch and will actively try and avoid it. As far as I know the light receptors of P. maculata have not been studied, however research has been done on Ophiocoma wendtii which has optically advanced calcite lenses. When I watched P. maculata changing color and avoiding my torch beam I didn't realize this wasn't common knowledge ...

In New Zealand's Fiordland (yes, that is spelled correctly) black coral grow to within 5m of the surface in some places, part of a phenomenon known as deepwater emergence. The area is prone to regular tree slides, a function of the incredibly heavy rainfall and steep terrain. These tree slides put large amounts of sediment into the water which settles out on the black corals. The corals expend significant energy freeing themselves of this pollution. A study has shown that those black corals with symbiotic snake stars Astrobrachion constrictum grow better than those without. Their snake star(s) usually steals food from them but this is a small price to pay for being freed of silt when the inevitable disaster occurs.

 

Astroboa nuda Giant basket star

Astroboa nuda, Kri, Raja Ampat, West Papua

OPHI 0479 Astroboa nuda, Giant basket star, Raja Ampat, West Papua.

Astrobrachion constrictum Black coral snake star

rAstrobrachion constrictum on black coral, Fiordland, New Zealand

OPHI 223 Astrobrachion constrictum Black coral snake star, Fiordland, New Zealand.

Astrodictyon panamense Panamic basket star

Astrodictyon panamense, Panamic basket star, Sea of Cortez

OPHI 5576 Astrodictyon panamense, Panamic basket star, Sea of Cortez,

Ophiarachna affinis Marbled brittlestar

Ophiarachna affinis marbled brittlestar Raja Ampat

OPHI 9786 Ophiarachna affinis marbled brittlestar Raja Ampat.

Ophiothrix purpurea Dark red-spined brittle star,

Ophiothrix pupurea dark red-spined brittle star, Fiji

OPHI 235 Ophiothrix purpurea Dark red-spined brittle star, Fiji.

Ophiothrix purpurea Brittle star on soft coral Taveuni,  Fiji

OPHI 4406 Ophiothrix purpurea Brittle star on soft coral Taveuni, Fiji.

Ophiothrix purpurea Brittle star, Fiji

OPHI 314 Ophiothrix purpurea, Fiji

Ophiothrix purpurea Brittle star, Fiji

OPHI 253 Ophiothrix purpurea Brittle star on sea fan, Fiji

Ophiothrix suensonii Sponge brittle star

Ophiothrix suensonii, Glover's Reef,  Belize

OPHI 3417 Ophiothrix suensonii Sponge brittle star, Glover's Reef, Belize.

Ophiothrix variabilis Variable brittle star

Ophiothrix variabilis Variable brittle star Kri Eco, Raja Ampat

OPHI 8556 Ophiothrix variabilis Variable brittle star Kri Eco, Raja Ampat (or at least two arms of it anyway!).

Pectinura maculata Red snake star

Pectinura maculata Snake star

OPHI 300 Pectinura maculata, Fiordland, New Zealand.

Pectinura maculata Snake star

OPHI 301 Pectinura maculata, Fiordland, New Zealand.

Pectinura maculata feeding on dead fish, Fiordland, New Zealand

OPHI 302 Pectinura maculata feeding on dead fish, Fiordland, New Zealand.

 

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