title for amphipod section of A SNAIL'S ODYSSEY
  Foods & feeding
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Corophiids & ampithoids


drawing of gammarid amphipod courtesy Eugene Kozloff, University of WashingtonThe general features of a corophiid amphipod (SubOrder Gammaridae) are shown in the accompanying drawing. This may help with the interpretation of feeding methods in the Research Study below. Drawing courtesy of Kozloff 1974 Marine Invertebrates of the Pacific Northwest Univ Wash Press, Seattle.



In burrow-inhabiting corophiids, the main morphological
adaptations for feeding include a greatly enlarged
peduncles of the 2nd antennae, used for raking up edible
deposits from the sediment surface, and extensively
bristled 2nd gnathopods, used for filter-feeding

  Studies on corophiids & ampithoids are considered here, while ones on TALITRIDS and CAPRELLIDS are dealt with in their own sections.
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Research study 1

drawings comparing modes of suspension- and deposit-feeding in corophiid amphipodsdrawing of a corophiid amphipod deposit-feeding from its tubeBurrow-inhabiting Corophium species feed on organic particles that they stir up from the sediment surface or filter-feed from the plankton. A study on food-capture mechanics in 3 species at Friday Harbor Laboratories, Washington using small sections of glass tubing or "sandwich aquaria" reveals that oscillatory motions of mouthparts are employed to ingest selected particles.  Experiments on particle size-selection, done in a recirculating flume device, show that particles of a range 5-53µm are sorted and eaten, while 60µm particles are too large. Particles of 9µm diameter are ingested at a rate of >20 . sec-1.   

An individual within its tube feeds either by suspension-mode or deposit-mode, often somersaulting and rotating about to change position.  Suspension feeding is done as follows: currents generated by beating of the pleopods carry suspended particles into a sieve formed by the double row of plumose setae of the 2nd gnathopods (see Left blue drawing above).  From time to time the 1st gnathopods brush these particles into the maxillipeds and maxillae around the mouth. Experiments with dye show that almost all of the pleopodal-generated water stream passes through these sieves.  Scissor-like movements of the maxillipeds and maxillae sort the particles, some being moved into the mouth and others being moved anteriorly in a rejection stream.

In deposit-feeding, the amphipod emerges from its tube and uses its 2nd antennae in a scraping motion to collect and form particles into a bolus from the substratum surface (see drawing far Left). The 2nd antennae are greatly extended through large pedunclular expansion. The amphipod then backs into its tube with the food bolus held in its 2nd antennae and sorts the contained particles in the same manner as described for suspension feeding (see Right part of drawing above).  The author notes that particle selectivity differs for the 3 species, but is uncertain of the reasons for it.  Miller 1984 J Exp Mar Biol Ecol 82: 59. Drawing upper Left courtesy Meadows & Read 1966 J Zool 150: 387.

NOTE  the species are spinicorne, insidiosum, and salmonis.  They inhabit shallow U- or semicircular-shaped tubes in the sediment

NOTE  the particles are spherical polystyrene beads of different diameters.  After a feeding experiment, test animals are dissected, and the beads counted and measured from the gut contents

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Research study 2

drawing of flower (inflorescence) structure of eelgrass Zostera marinaAmpithoe valida is a non-indigenous species introduced to San Francisco Bay in the early 1940s from the Atlantic coast that now occupies eelgrass habitats from Newport Bay, California north to Puget Sound, Washington. Ampithoe is a tube-dwelling species that in its native areas eats mainly algae such as membranous green Ulva spp., but that in San Francisco Bay prefers eelgrass Zostera marina. Researchers at San Francisco State University, Tiburon find that it prefers reproductive structures (spathes) over vegetative shoots, with special preference for later-stage fruits and seeds. The authors consider possible nutritional benefits to explain these preferences, but laboratory analyses do not support this idea. The spathes are morphologically complex and may provide roosting spots and physical protection from predators. Reynolds et al. 2012 Mar Ecol Progr Ser 451: 107. Drawings courtesy A.W.A.M. De Cock 1980 Aquat Bot 9: 201.

NOTE actually the sheathing bracts that surrounds the flower (inflorescence) structures, but here referring to the entire inflorescence structure (see drawings)

NOTE the nutritional investigation, comprising comparative spectrophotometric analyses of carbon and nitrogen contents of preferred and non-preferred parts of the plant, could never be convincing owing to the generality of the “nutrients” selected. Without a knowlege of Ampithoe’s specific nutritional requirements which, in all fairness, exists only for a scant handful of invertebrates, relative contents of basic building-block components, such as carbon and nitrogen, are likely to be much less informative than certain other finer-scale analyses. The eelgrass fruits and seeds may be packed with all manner of nutrients useful to the amphipod, including amino acids, fatty acids, and a host of minor elements, not known to us at this time. If not already done, the researchers should begin by comparing growth and fecundity of Ampithoe on different algal and eelgrass diets, separating vegetative and reproductive parts of the latter