Rocinela propodialis Richardson, 1905

Common name(s): 

Synonyms:  Rocinela propodialis
Phylum Arthropoda 
Subphylum Crustacea 
Class Malacostraca 
Subclass Eumalacostraca 
Superorder Peracarida 
Family Aegidae 
Rocinela propodialis, 2 cm long, found actively swimming at 15 m depth by Kirt Onthank while he was Scuba diving near the sandy bottom of Burrows Bay, WA
(Photo by:  Dave Cowles, July 2016)

Description:  As a member of suborder Flabellifera, this species has flattened uropods lateral to the pleotelson but not arching over it, and together with the pleotelson forming a caudal fan (photo).  The body is not more than 5x as long as wide. This species is about twice as long as wide. Both rami of the uropods are well-developed and flattened and do not roll up into a ball (photo).  They also do not extend past the posterior end of the pleotelson.  The outer uropod ramus is slightly shorter and narrower than the inner ramus.  The outer margins of both rami are lined with long spines, and the inner margin with long setae.   The species has 4 or 5 pleonites visible dorsally in front of the pleotelson (pleonite 1 is hidden beneath the last pereonite) (photo).  The outer margins of most or all of the pereonites have points projecting posterolaterally.  The dactyls of pereopods 1-3 are curved into hooks for holding on to the fish which they parasitize (photo).  The propodus of these 3 pereopods has a large expansion on the medial side, with 6 teeth of about equal size (photo).  The propodus and dactyl of these legs are approximately the same length.  The last four pereopods have numerous spines (photo).  The eyes are large and separated by a distance of approximately the diameter of the eye (photo).  The flagellum of antenna 1 has only 4-6 articles and reaches approximately to the end of the peduncle of antenna 2 (photo). The flagellum of antenna 2 has 16 articles and reaches the posterior margin of the second pereonite.  The rostrum is shaped like a truncated triangle; not drawn out into a spatulate shape with side projections (photo). The type specimen was reported to be brown with small black dots, although it was not described until several years after it was caught.  Perhaps this golden color with white dots will change to brown with black dots upon preservation (see photo).

How to Distinguish from Similar Species:  The very similar R. angustata has a propodus only about half as long as the dactyl on the anterior 3 grasping pereopods, and with only 4 instead of 6 teeth along the inner propodus margins. Rocinela tridens has a rostrum drawn out into a spatulate shape with side projections. R. belliceps has a pointed rostrum.

Geographical Range:  East Pacific; as far north as Departure Bay, British Columbia but apparently not found as far south as California (not found in the Light and Smith manual). Thesingle type specimen (a male) was found in 1903 by the Albatross Expedition at station 4205 in Admiralty Inlet near Port Townsend, WA and described in by Harriett Richardson in 1905. 

Depth Range:  The type specimen was taken at 15-26 fathoms (27-48 meters)

Habitat:  Presumably near sandy or rocky bottoms or on bottom-dwelling fish

Biology/Natural History:  This species parasitizes the gill regions of cartilaginous fish such as rays, and on bony fish such as halibut, rockfish, and other fishes.  It may at times (such as this occasion) be found swimming freely in the water.

A related species, R. signata, has been known to repeatedly attack and bite human divers in the Caribbean. (Garzon-Ferreira, 1995.  Bulletin of Marine Science 46:3 pp 813-815).



Dichotomous Keys:
  Kozloff, 1987, 1996

General References:

Scientific Articles:
Fee, A.R., 1920.  The isopoda of Departure Bay and vicinity, with descriptions of new species, variations, and colour notes.  Contributions to Canadian Biology and Fisheries 2.

Richardson, Harriet, 1905.  Isopods from the Alaska Salmon Investigation.  Bulletin of the Bureau of Fisheries Vol. XXIV, 1904 pp 209-221. (Original description is here)

Richaradson, Harriet, 1905.  Monograph on the Isopods of North America.  Bulletin of the United States National Museum No. 54, Washington Government Printing Office.

Web sites:
Schotte, M., B. F. Kensley, and S. Shilling. (1995 onwards). World list of Marine, Freshwater and Terrestrial Crustacea Isopoda. National Museum of Natural History Smithsonian Institution: Washington D.C., USA.

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

Dorsal view of the pleotelson

This dorsal view of the pleotelson shows the flattened uropods lined with spines on the outer margin and setae on the inner margin.  It also shows the 4-5 pleonites which are visible in front of the pleotelson.
Posterior pereopods

This view of the ventral side shows the spines on the posterior pereopods.

Anterior pleonites
This ventral view of the anterior 3 pereonites show the curved dactyls, which are about as long as the propodus.  It also shows the medial expansions of the propodus of these pereonites, armed with 6 teeth.  The merus of these pereonites has 3 blunt spines.  Note also that the flagellum of the first antenna has only 4-6 articles.

Dorsal view of the head
This dorsal view of the head shows the large eyes separated by about the diameter of an eye; the truncated triangular rostrum, and the fact that the first antenna has only 4-6 articles in its flagellum.

Here is the same individual several days after being preserved in formalin.  The dark colors and black do indeed seem to be more prominent after preservation.

Authors and Editors of Page:
Dave Cowles (2016):  Created original page
CSS coding for page developed by Jonathan Cowles (2007)

Salish Sea Invertebrates web site provided courtesy of Walla Walla University