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  Habitats, behaviour, & ecology
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  "True" or caridean shrimps
  Much has been written on the habitats, behaviour, and ecology of west-coast mud- and ghost-shrimps, but much less on “true” or caridean shrimps.  Considered here are "true" shrimps, while MUD SHRIMPS and GHOST SHRIMPS are dealt with in other sections.
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Research study 1

photograph of coonstripe shrimp Pandalus danae courtesy Dave Cowles, Walla Walla University, Washingtondrawing of caridean shrimp Pandalus danae showing a few of the appendages used in groomingGrooming is a common behaviour of all crustaceans, and is an especially noticeable behaviour in shrimps.  It functions to clean the exoskeleton of fouling organisms, including various phytoplankters, and settling invertebrate larvae and possibly plant spores.  Grooming of sensory appendages, such as eyes, and antennae and antennules is especially important.  A detailed study of grooming in coonstripe shrimps Pandalus danae at Friday Harbor Laboratories, Washington reveals that several appendages are involved in brushing, nipping, and preening of the body parts to keep them tidy (see drawings).  Perhaps the most important are the 3rd maxillipeds, whose setal brushes clean the antennal and antennular flagellae (see photograph of setae below Left), followed possibly by the chelae (representing the larger set of the double 2nd pair of periopods or walking legs).  Note that the smaller pair of these is also chelate, with primary function of general picking and crushing of attaching organisms. Eyes are tended by the large chelae, and the general body area by the 5th pair of walking legs. The 3 drawings below illustrate the functioning of selected limb-pairs in grooming.  The author provides detailed descriptions of all grooming behaviours in Pandalus and includes several scanning e-microscopical views of the various setal brush-bundles involved.  How effective is this grooming?  The author tests this by removing certain appendage pairs and assesses the condition of the test individuals after 10d.  Results show that general exoskeleton surfaces become rapidly fouled with suctorial protists, and antennae and antennules become coated with diatoms and other debris.  Bauer 1975 Zool J Linn Soc 56: 45. Photograph courtesy Dave Cowles, Walla Walla University, Washington

NOTE  there are basically 5 pairs of periopods or walking legs in a shrimp. The 2nd pair, however, are split into 2 pairs of chelate appendages, one small; the other large. The latter are the ones termed chelae or chelipeds. In most shrimps the 1st pair of walking legs is also chelate, but not apparently in P. danae. In this species there are setal brushes on either side of the bending part of the distal segment. These are used to brush clean the long antennae

NOTE  the grooming appendages all have other functions, including locomotory, feeding, sensory, and gas exchange

drawing of shrimp Pandalus danae cleaning its antennule with the paired 3rd maxillipeds
Antennules are cleaned by pulling them upwards between the juxtaposed 3rd maxillipeds
drawing of shrimp Pandalus danae cleaning its antennule with the paired 3rd maxillipeds
Antennae are cleaned by drawing them upwards between the setal brushes of the 1st pereopods
drawing of shrimp Pandalus danae cleaning its general body surfaces with the setal brushes with its 5th pereopods
General body surfaces are cleaned by setal brushes on the 5th pereopods
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Research study 2

photograph of shrimp Heptacarpus sitchensis courtesy Gary McDonald and CALPHOTOSdrawing of shrimp Heptacarpus sitchensis cleaning its antennaIn later research done at the Scripps Institution of Oceanography, La Jolla the same author provides more details on grooming in caridean shrimps, this time with an emphasis on involvement of chelipeds and walking legs in 5 families of west-coast species.  Overall, general body grooming is done by the chelipeds and, in some species, by the last pair of walking legs, as described in Research Study 1 above.  In species that groom with one of the doubled 2nd pair of chelated pereopods, such as Pandalus danae in Research Study 1 above, the appendage used is usually the more slender of the pair.  This appendage  drawing of shrimp Palaemon ritterialso has extra segments, thus increasing distal flexibility for more effective grooming.  The larger of the chelated appendages in such species tend to function in agonistic behaviour and prey capture.  A general feature in  most of the families surveyed (87%) is the use of chelated appendages in cleaning the long, chemotactile antennae. This is shown for Heptacarpus sitchensis (formerly H. pictus) in the drawing upper Right.

The author describes Palaemon ritteri (not a west-coast species) as being the most acrobatic of the caridean shrimps in its grooming behaviour, balancing on its extended tail and walking legs while grooming with several appendages (see drawing middle Right). Once again, the author shows that if cleaning appendages are removed, as done in an experiment with the broken-back shrimp Heptacarpus sitchensis, body parts become quickly fouled with epizoites and particulate debris. Bauer 1978 Mar Biol 49: 69; Bauer 1977 Mar Biol 40: 261. Photograph of H. sitchensis courtesy Gary McDonald, Long Marine Laboratory, Santa Cruz, California and CALPHOTOS.

drawing showing a shrimp Heptacarpus sitchensis cleaning its gillsphotograph of preening setae from shrimp Heptacarpus NOTE  a further 10 families are included in the form of a review. In another review paper on the same subject, the author provides a drawing of Heptacarpus sitchensis cleaning its gills with its doubled 2nd pair of chelated pereopods (see drawing lower Right). Bauer 1981 J Crust Biol 1: 153.

NOTE  a control group of shrimps is created by removing pairs of non-grooming walking legs

Close view of setal morphology on the 3rd
maxillipeds of the shrimp Heptacarpus sitchensis

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Research study 3

photograph of midwater shrimp Eusergestes similis courtesy Dave Cowles, Walla Walla University, WashingtonThe Pacific sergestid shrimp Eusergestes similis is a midwater-inhabiting, vertically migrating species found commonly along the coasts from California to British Columbia.  Although it is not normally encounted in shallow-water shore areas, some studies on its swimming behaviour done using a remotely operated camera platform in Monterey Bay, California may be interesting to researchers.  Propulsion is provided exclusively by the pleopods and routine swimming speed is around 7-8cm . sec-1 (equivalent in a mature animal to about 1.7 body lengths . sec-1).  Sergestes swims continuously save for bouts of grooming and responses to touches on the antennae.  Swimming, at least that observed here, is mostly in the vertical plane, and both upward and drawing showing swimming actions of the pleopods in the midwater shrimp Eusergestes similisdownward movements are done by active swimming.  Thrust on the propulsive stroke is maximised by extending and separating the pleopods, and extending the setae, while drag is minimised on the recovery stroke by retracting the pleopods, holding them in apposition, and folding the setae.  The pleopods beat metachronously at about 4 cycles . sec-1 in a direction from back to front ("adlocomotory" wave; see drawing on Right).  Although not discussed by the author, one can calculate that a 5-cm body-length individual living at about 425m depth during the day would take about 1h to swim 300m up to its average nighttime feeding depth of 125m.  Cowles 1994 J Crust Biol 14: 247. Photograph courtesy Dave Cowles, Walla Walla University, Washington

NOTE like many mid- to deep-water inhabiting crustaceans, Eusergestes is reddish in colour. Although the actual function of the colour is not known, the absence of red wavelengths of light at depth would cause the shrimp to appear black

NOTE  a ROV operated by the Monterey Bay Aquarium Research Institute (MBARI). The author discusses possible effects of the ROV’s lights on observed swimming directions

Dorsal view of a swimming E. similis of total body length 5cm.  In these views, the
3rd-5th pairs of pleopods are in varying degrees of recovery stroke, while the 2nd has
just commenced its power stroke and the 1st is about to commence its power stroke

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