Pentidotea resecata (Stimpson, 1857)Common name: Concave isopod, eelgrass isopod, cut-tailed isopod, seaweed isopod, kelp isopod, transparent isopod
|Synonyms: Idotea resecata, Idothea resecata|
|Pentidotea resecata found by Heidee Leno at Shannon Point.|
|Photo taken by Heidee Leno, July 2002|
How to Distinguish from Similar Species: No other local isopod has a concave posterior margin to its pleotelson.
Habitat and Geographical Range: Pentidotea resecata generally appear from Alaska to the tip of Baja California and Mazatlan (Mexico). They prefer to be among eelgrass (Zostera) or kelps (Macrocystis and Pelagophycus).
Depth Range: Intertidal to 18 m
Biology/Natural History: When placed
on a substratum, the isopod will reorient itself along the long axis of
its substratum and if placed otherwise, it immediately reorients itself.
P. resecata prefers to feed on algae such as Macrocystis,
porra, Eisenia arborea, Pterygophora californica, and
Egregia laevigata, or on eelgrass (Zostera). These
animals appear to be temperature and salinity sensitive. A temperature
of 15 degress Celsius is an optimum temperature for P. resecata.
If temperatures reach between 29 and 31 degrees Celsius, the animal will
die. If the isopod is placed in fresh water it survives a little
over an hour in comparison with 33 hours in 125% seawater. Development
of these isopods is a bit unclear, but studies show that the general body
form changes little during growth. Features such as segment number
and setae number vary directly with size, each molt providing further change.
The species blends in with the kelp or eelgrass that it is on, and can
also swim well using its pleopods.
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Flora and Fairbanks, 1966 (as Idothea (Pentidotea) resecata)
Kozloff, 1987, 1996
Smith and Carlton, 1975
Johnson and Snook, 1955 (as Pentidotea resecata)
Lamb and Hanby, 2005
Morris et al., 1985
O'Clair and O'Clair, 1998
Ricketts et al., 1985
Lee, W. L. and B. M. Gilchrist, 1972. Pigmentation, color change, and the ecology of the marine isopod Idotea resecata (Stimpson, 1857). Journal of Experimental Mararine Biology and Ecology 10: 1-27
McCluskey, Richard Laverne, 1966. Dietary regulation of growth and mortality in the isopod, Idotea resecata (Stimpson). Master's thesis, Walla Walla College. 23 pp.
Menzies, R.J. and R.J. Waidzunas, 1948. Post-embryonic growth changes in the isopod Pentidotea resecata (Stimpson) with remarks on their taxonomic significance. Biological Bulletin 95: 107-113
This male, 5 cm long not counting antennae, was found clinging to eelgrass in Padilla Bay. Note that this individual, from eelgrass, is greener than is usually seen in individuals which are feeding on brown algae. Males often have a prominent greenish stripe (or greenish-white in this indvidual) down the dorsal side. Photo by Dave Cowles, July 2008
This underside view of the same male as the above photo shows the flaplike uropods which enclose the pleopods on the ventral side of the pleon (to the left). Photo by Dave Cowles, July 2008
In this photograph of the mouthparts, the scalpel is holding out the maxilliped. The main, subchelate branch of the maxilliped can be seen just below and partly overlapping the scalpel blade. The maxillipedpalp, which has 5 articles (difficult to count in this photo), crosses the scalpel blade in front of the brown blotch. The darkened, sclerotized mandibles can be seen just above and to the left of the scalpel blade. Photo by Dave Cowles, July 2008
This large male, captured by Joanna Cowles and Shelley McLarty in Padilla Bay, is 6.4 cm long, much larger than the largest reported size for this species. Photo by Dave Cowles, August 2014