Phronima sedentaria (Forskal, 1775) Common name(s):
Synonyms: Cancer sedentarius, Phronima borneensis, Phronima novaezealandiae, Phronima spinosa, Phronima tenella
Phylum Crustacea  Subphylum Crustacea  Class Malacostraca  Subclass Eumalacostraca  Superorder Peracarida  Order Amphipoda  Suborder Hyperiidea Superfamily Phronimoidea  Family Phronimidae
	Phronima sedentaria, about 2 cm long, swimming in its characteristic manner with its head and anterior body inserted into a salp barrel (tunic). except this one has a ring of babies strung around the inside of the tunic. Found in lights at night near Sharpe Cove dock by Jamie Fields.
	(Photo by:  Dave Cowles, July 2024)

Description:  Hyperiidean amphipods are strictly marine and pelagic. This unique planktonic epipelagic and mesopelagic genus specializes in inserting its head and anterior body into a salp barrel (tunic), as seen above.

How to Distinguish from Similar Species:  The combination of physical structure and the behavior of  swimming along with a salp barrel on its head is unique for this genus. Several species live in different oceans.

Geographical Range:  North and South Pacific, North Atlantic, Gulf of Mexico, Mediterranean

Depth Range:  In my experience, epipelagic and mesopelagic.

Habitat:  Oceanic waters (pelagic); although sometimes nearshore around docks.

Biology/Natural History:  This species cuts up salps to produce their distinctive barrels. Gelatinous species they are associated with include the Ctenophore Beroe, Ihlea punctata, Salpa fusiformis, S. aspera, Thalia democratica, and Pyrosoma sp. In some CalCOFI trawls there has been a positive correlation between Phronima sedentaria and Salpa aspera abundances (Lavaniegos and Ohman 1998). The amphipods deposit their young inside the salp barrels as well. Predators of Hyperiidean amphipods include tuna, salmon, and baleen whales.

References:

Dichotomous Keys:
  Kozloff, 1987, 1996 (simply mentions the species).
  Carlton, 2007: (simply mentions the species).

General References:

Scientific Articles:

Diebel, Carol A., 1988. Observations on the anatomy and behavior of Phronima sedentaria (Forskal) (Amphipoda: Hyperiidea). Journal of Crustacean Biology 8:11 pp. 79-90.  https://doi.org/10.1163/193724088X00107

Laval, Philippe, 1978. The barrell of the pelagic amphipod Phornima sedentaria (Forsk.) (Crustacea: hyperiidea). Journal of Experimental Marine Biology and Ecology 33:3 pp. 187-211.

Lavaniegos, Bertha E. and Mark D. Ohman, 1998. Hyperiid amphipods as indicators of climate change in the California Current. Proceedings of the Fourth International Crustacean Congress, 1998 pp. 489-509

Web sites:

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

Here is a  movie of it swimming in the lab.

This close-up view shows the babies deposited inside the salp barrel and the large eyes of the amphipod. Photo by Dave Cowles, July 2024

Authors and Editors of Page:
Dave Cowles (2024):  Created original page
CSS coding for page developed by Jonathan Cowles

Salish Sea Invertebrates web site provided courtesy of Walla Walla University