title for amphipod section of A SNAIL'S ODYSSEY
   
  Predators & defenses
   
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Defenses: gastropod shells

 

Defenses in amphipods can be categorised into active and passive. Active defenses include hiding in gastropod shells, batting with the heavy gnathopods, burrowing, being active at night, and jumping, while passive defenses include chemical deterrents and warning (aposematic) coloration, and mimicry.

The present section considers Defenses: gastropod shells, with other sections on DEFENSES: GASTROPOD SHELLS, DEFENSES: CHEMICAL DETERRENTS/WARNING COLORATION, DEFENSES: MIMICRY, INVERTEBRATE PREDATORS, and VERTEBRATE PREDATORS, being dealt with elsewhere.

   
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Research study 1
 

drawing of 2 amphipods Photis conchicola suspended to a piece of alga by threadsPhotis conchicola is an amphipod that uses empty gastropod shells as a shelter, perhaps as a defense against predatory fishes.  The amphipod constructs a soft tube with a thread-like material intermixed with detrital and other material within an empty shell, and attaches the shell to algae.  The attachment device consists of a bundle of the same threads comprising the tube, fixed to the inside of the shell and extending to the alga.  Shells used are the same species of gastropods present on the algae to which the domicile-shells are attached.  Densities of P. conchicola of up to about 800 . m-2 have been recorded in intertidal areas of central and southern California.  Some shells are inhabited by one sex separately, while other shells host several of each sex.  The drawing shows a male on the Left, gripping a portion of the alga with its large gnathopod, and a female on the Right, both in their domiciles.  Note the attachment thread circled in purple) that suspends the female's shell from the alga.  The shells can be re-attached, but the author is uncertain whether translocation to new habitats is common.  The shells likely function to reduce desiccation in intertidal habitats and provide protection from predators such as fishes.  The author suggests that an amphipod in its shell domicile may appear as an unpalatable, cryptic, or disruptively coloured item to a potential visual predator.  Carter 1982 J Crust Biol 2: 328.


NOTE  in their manner of inhabiting and perhaps carrying a shell-habitat around with them,the behaviour of Photis is similar to that of hermit crabs

NOTE  commonest shells used by Photis in the San Luis Opispo area of California are Alia carinata, representing 25% of 504 domiciles surveyed
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Research study 2
 

photo/drawings showing silk-glands in amphipod Crassicorophium bonelliA recent paper published on an Atlantic species of bottom-dwelling amphipod Crassicorophium bonelli may be germane to the study on Photis presented in Research Study 1 above.  The reason is that C. bonelli uses a filamentous silk substance to bind together sand grains to form its tube (see illustrations on Left), reminiscent of the threads used by Photis to attach and line its shell domicile.  The unique discovery of silk production in an amphipod is reported by researchers at the University of Oxford, using specimens collected in Scotland.  The filamentous silk consists of mucopolysaccharides and proteins, is chemically similar to barnacle glue, and is produced in a similarly functioning gland/chamber system to that of barnacles. Its discovery leads the authors to some interesting speculation on past phylogenetic relationships between the two crustacean groups. 

The secretory glands are located in the large schematic showing secretory parts in walking legsegments of walking legs 3 and 4. Other products are received from protein-secreting rosette glands. Ducts carry the secretions to the tips of the legs where they are released as silk (see drawing on Right).  The silk's properties include adhesion, durability, and seawater resistance.  Like barnacle glue, it cures underwater and, like spider silk, it is fibrous and “extrusion-spun”. Also, just as spiders pull silk from their spigots using their legs, the amphipod attaches a bit of silk to the substratum, then pulls its limbs away. Whether the shell-inhabiting P. conchicola produces its threads in a similar way is of course not known, and will need to be researched.  Kronenberger et al. 2011 Naturwissenschafte 98: XXX.
  
NOTE  the species is actually “trans-polar”, being found from the north Atlantic to Chile.  It is thought likely to inhabit the northeastern Pacific region, although is not yet formally recorded as being here

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