Feeding & growth
  Ophiuroids suspension-feed from the plankton, eating a variety of small invertebrates and perhaps detrital particles. No studies on growth appear to have been done on west-coast species.
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  Brittle stars
  This section deals with brittle stars, while a comparable section on BASKET STARS is located elsewhere.
 

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Research study 1

 

photograph of brittle star Ophiopholis aculeata courtesy Bill Austin, Khoyotan Marine Laboratory, Victora, BCphotograph of a mass of feeding brittle starsRemoval of food particles from suspension by brittle stars is thought to be by means other than simple sieving.  Experiments on Ophiopholis aculeata at Friday Harbor Laboratories, Washington suggest that the mechanism may involve adhesion of particles to the tube feet through the presence of fixed charged groups on the surface of the particles.  During feeding the brittle stars extend their arms perpendicular to the current flow and particles adhere to the mucus-covered tube feet.  Periodically, an arm bends inwards and its terminal tube feet are wiped by more proximally located tube feet.  This process continues down the arm and in the process a bolus of particles embedded in mucus is formed.  In past studies there has been no indication of particle selection by the tube feet.  On reaching the mouth each bolus seems to be accepted or rejected in its entirety by the oral tube feet. 

graph showing percentage of plastic "food" particles caught by brittle stars vs. diameter of the plastic bead particlesIn experiments to test the null hypothesis that there is no size selection by Ophiopholis, Sephadex beads of different sizes (30-340µm) are used as a suspended “food” material.  The bead suspension is sampled before and after the brittle star is allowed to feed.  After a time, and just before a food bolus approaches the base of the arm en route to the mouth, it is sucked up into a pipette and stored for later size analysis of contained particles.  Results are shown in the graph on the Left.  The coloured lines represent the size distributions of the before and after samplings of Sephadex beads in the water flowing past the feeding brittle star, as well as in the food bolus.  Note the larger size distribution of particles in the food bolus as compared with that of the other samplings, indicating that the brittle star has selectively removed particles of larger size.  Additionally, note that the brittle star has removed particles from the complete range available, namely, 30-340µm, which should not be possible if it were using a simple filtering method because the tube feet are spaced >400µm apart, a distance that is larger than the particle diameters provided.  To explain this, the author proposes that a direct interception-type mechanism of filtration is being used, with opposite-charged particles impinging on the tube feet and becoming stuck to the negatively charged mucous coating. LaBarbera 1978 Science 4361: 1147. Photo of O. aculeata courtesy Bill Austin, Khoyotan Mar Laboratory, Victoria.

NOTE  the size distributions of the particles differ slightly in the before and after samplings owing to settlement of some of the larger particles between the 2 samplings

NOTE  direct interception is only one of several types of filtration theoretically possible for suspension-feeding animals.  Other possible methods are filtering, inertial impaction, gravitational deposition, diffusive deposition, and electrostatic attraction. In a separate, unrelated study the same author measures oxygen uptake in a brittle star Ophiopholis aculeata, basket star Gorgonocephalus eucnemis, and crinoid Florometra serratissima in a special flow tank where current speeds are carefully regulated to mimick natural rates. Values obtained are one-third to one-half the magnitude of those reported previously for other suspension-feeding echinoderms where current regimes are not carefully controlled. LaBarbera 1982 Comp Biochem Physiol 71A: 303.

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photograph of brittle stars feeding (still shot from video)

CLICK HERE to see a video of a mass of brittle stars feeding.

NOTE the video replays automatically

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Research study 2
 

Laboratory culture of larvae of several species of echinoderms at Friday Harbor Laboratories, Washington, including brittle stars Ophiopholis aculeata, reveals a common pattern of suspension feeding.  The studies involve videotaping larvae as they capture 20µm diameter plastic spheres, while simultaneously recording elapsed time, and later measuring lengths of ciliated bands and arm lengths.  The view on the right shows an 8-armed Ophiopholis larva of about 1mm diameter capturing a single sphere over a time span of 0.9sec. The sphere is first captured on one of the arms then directed towards ciliary tracts leading to the mouth.  Hart 1991 Biol Bull 180: 12.

NOTE  the ciliated bands of the larva are shown by the black lines

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