Holmesimysis costata

Taxon-Order: 
Mysidacea

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Distribution: 
San Francisco, California to Baja California.
Habitat: 
Benthic on sand bottoms but can also be found in kelp.
Size: 
8 - 12 mm
Diet: 
Omnivorous.
Predators: 
White seaperch.
Useful Facts or Characters: 

Abdominal segments 1-5 have folds and ridges on the dorsal surface.  Tip of telson has two pairs of spines; the inner pair is longer than the outer pair.  Fourth pleopod of the adult male is highly modified and much longer than other pleopods.

Natural History: 

This species is closely related to Holmesimysis sculpta.  It has been used as a indicator of water quality.

References: 

Tattersall, W.M. (1951) A review of the Mysidacea of the United States National Museum. Bulletin of the United States National Museum No. 201: 1-292.