Stylomysis grandis (Goes, 1868)

Common name(s):  [none?]

Synonyms: Stylomysis grandis
Phylum Arthropoda 
Subphylum Crustacea 
Class Malacostraca 
Subclass Eumalacostraca 
Superorder Peracarida 
Suborder Mysina 
Family Mysidae 
Stylomysis grandis female found in low intertidal tide pool at Swirl Rocks.  Carapace length 4.5 mm, total length 10.5 mm.  Dorsal view
(Photo by:  Dave Cowles, July 2012)

Description: This mysid does not have numerous long spines on its carapace and abdomen.  The cornea of the eye is not divided into two portions (photo).  The scale of antenna 2 has a rounded tip and both the inner and outer margins have setae (photo).  The carapace is not expanded laterally and anterolateral margin of the carapace is rounded (photo). The last abdominal segment is smooth, with no transverse folds.  It has a nearly straight posterior dorsal margin, without an acute mid-dorsal projection (photo).  The telson is not cleft (photo).  It has two large spines on the end and a row of many spines of equal size along each margin (photo).

How to Distinguish from Similar Species:  Several other mysid species have acute anterolateral margins on the carapacePacificanthomysis nephrophthalma has a telson with alternating sets of shorter spines among the longer spines along the lateral margins.

Geographical Range:  At least in the Bering Sea, Sea of Okhotsk, and Arctic Ocean.  K. Derjugen (1912) lists this species in an article about Arctic Ocean species in the collection from the Murmansk Marine Laboratory near St Petersburg, Russia.  A UN project document for NW India (Gujarat?) lists this species as occurring in that portion of the northern Indian Ocean.

Depth Range:

Habitat:  I found clusters of this mysid hovering around kelp in a low intertidal tidepool (photo).

Biology/Natural History:  This species is probably pelagic or benthopelagic.  It swims vigorously with its pereopods (thoracic appendages).  Inner branches of these same pereopods make up the oostegites (flaplike covers which fit together into a marsupium (pouch) to shelter the eggs and larvae on the female's abdomen).  Wing (1975) reports in Fishery Bulletin 73: 169-185 that the ellobiopsid parasite Thalassomyces albatrossi (a protist) parasitizes a close relative of this species.  Ellobiopsids typically appear as a stringy white mass attached to the ventral side of the anterior abdominal segments.  The Great Soviet Encyclopedia states that mysids such as this can be found from the surface to a depth of 7 km and also in brackish waters, lakes, and rivers and that they serve as food for herring, sprat, perch, cod, and other fish.  The accompanying photo with the article in the Great Soviet Encyclopedia, however, is of an amphipod rather than a mysid.  This species is one of the food items for young ribbon seals.  They can be found near the sea ice over the continental shelves in spring feeding on algae under the ice.



Dichotomous Keys:
  Kozloff, 1987, 1996

General References:

Scientific Articles:
Boveng, P.L., J.L. Bengston, T.W. Budkley, M.F. Cameron, S.P. Dahle, B.A. Megrey, J.E. Overland, and N.J. Williamson, 2008.  Status review of the ribbon seal (Histriophoca fasciata).  NOAA Technical Memorandum NMFS-AFSC-191.

Derjugen, K., 1912.  Die Murmansche biologische station der K. naturforscher Gesellschaft zu St. Petersburg und ihre arbeiten im Nordischen Eismeer.  Proceedings of the Seventh International Zoological Congress, Boston, 19-24 August, 1907

Kathman, R. D., W. C. Austin, J. C. Saltman, and J. D. Fulton. 1986. Identification manual to the Mysidacea and Euphausiacea of the northeast Pacific. Department of Fisheries and Oceans,Ottawa, Canada. 411 p.

Web sites:

General Notes and Observations:  Locations, abundances, unusual behaviors:

Swarm in tidepool

Here is the swarm of mysids in the tidepool the above individual was sampled from.  Photo by Dave Cowles, July 2012

Side view
This side view shows the large pouch (marsupium) the females use to carry their eggs and larvae.  The marsupium is made up of flattened, leaflike inner projections of the legs called oostegites.  Only the females have oostegites.  The anterolateral corner of the carapace is rounded instead of having a sharp projection.

Characterisitics used for identifying this species:
The telson is not cleft.  It has a row of equal-length setae along the lateral margins and two longer setae at the tip. Dorsal view.

Eye and antennal scale
The eye is not divided into two portions.  The antennal scale of antenna 2 is rounded on the end and has setae along both lateral margins.

Last abdominal segment
The posterior end of the last abdominal segment is nearly straight, without a dorsal projection toward the telson.  None of the abdominal segments have dorsal transverse folds.

Other interesting views:
Abdomen underside
This view of the underside of the abdomen shows that the pleopods (abdominal appendages) are very small and feathery.  The underside of the marsupium can also be seen, as well as several powerful pereopods with which the animal swims.

Authors and Editors of Page:
Dave Cowles (2012):  Created original page
CSS coding for page developed by Jonathan Cowles (2007)

Salish Sea Invertebrates web site provided courtesy of Walla Walla University