Sergia tenuiremis (Kroyer, 1855)

Common name(s): Ocean sergestid

Synonyms:
Phylum Arthropoda
 Subphylum Crustacea
  Class Malacostraca
   Subclass Eumalacostraca
    Superorder Eucarida
     Order Decapoda
       "Natantia" (shrimp--not a formal taxonomic category)
        Suborder Dendrobranchiata
         Family Sergestidae
Sergia tenuiremis captured below 500 m depth off Point Conception, CA, Sept 1992.  This photo is of a preserved specimen which has lost its darker original color.  The animal has also lost its long, fragile second antennae which are longer than the body.
(Photo by: Dave Cowles Oct 2006)
Description:  This mesopelagic, mostly oceanic, vertically-migrating shrimplike prawn is not a true (Caridean) shrimp because the epimera of abdominal segment 2 do not overlap those of abdominal segments 1 and 3.  Also, the gills are dendrobranchiate (featherlike--photo) instead of platelike (phyllobranchiate) gills as seen in true (Caridean) shrimp.  As with most sergestids the rostrum is short, less than 1/10 the length of the carapace (photo) and the first three pereopods have tiny chelae (photo).  The tiny rostrum points obliquely upward and forward and has an blunt tip (photo).  Both the carapace and the abdomen are slender and laterally compressed, especially the last abdominal segment.  There are no spines just behind and above the eye (supraorbital) or behind and below the eye (hepatic) (photo).  The eyestalks have a tubercle on their inner (medial) margin (photo).  Undamaged specimens have very long antennae, with the proximal portion of the flagellum rigid and extending forward and laterally, then a sharp kink, and a very long flexible section that trails back beside the animal's body through the water.  The fragile antennae are often damaged or lost during capture, as happened with the animal shown here.  The carapace of live individuals is red and purple, the abdomen is red.  The eyestalks are clear.  The animal may have bioluminescent photophores (in my experience, it has very few) but not a bioluminescent organ of pesta.  Total length:  Males to 6.3 cm, females to 7.5 cm.

How to Distinguish from Similar Species: Eusergestes similis lives at shallower depths and has a bioluminescent organ of pesta.  It has no tubercle on the eyestalks but it does have a supraorbital and a hepatic spine on the carapace.  Its rostrum is pointed and the body is partly transparent.

Geographical Range:  Worldwide: Pacific, Atlantic, Indian oceans

Depth Range:  570-1000 m or deeper

Habitat:  Bathypelagic

Biology/Natural History:  This bathypelagic species is widespread but not as common as are many other bathypelagic crustaceans along our coast.  Near the Canary Islands it appears to vertically migrate to near the surface at night.  Sergestids swim through the midwater, using their long antennae to detect vibrations of potential prey which they grasp with their pereopods.



 
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References:

Dichotomous Keys:
  Kozloff 1987, 1996
  Wicksten, 2009

General References:
  Butler, 1980

Scientific Articles:
Cowles, David L.; Childress, James J.; Wells, Mark E., 1991.  Metabolic rates of midwater crustaceans as a function of depth of occurrence off the Hawaiian Islands: Food availability as a selective factor?  Marine Biology 110: pp. 75-83

Flock,M.E.; Hopkins,T.L., 1992.  Species composition, vertical distribution, and food habits of the sergestid shrimp assemblage in the eastern Gulf of Mexico.  J. Crustacean Biology 12:2 pp. 210-223

Foxton, P., 1969.  The morphology of the antennal flagellum of certain of the penaeidea (Decapoda,Natantia).  Crustaceana 16:2 pp. 33-42

Kikuchi,T.; Nemoto,T., 1986.  List of pelagic shrimps(Crustacea:Decapoda) from the Western North Pacific.  Bulletin of Biogeographical Society of Japan 41:7 pp. 51-59

Pearcy,W.G.; Forss,C.A., 1966.  Depth distribution of oceanic shrimps (Decapoda;Natantia) off Oregon.  J. Fisheries Research Board Canada 23:8 pp. 1135-1143
 

Web sites:
 



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



This closeup of the side of the carapace shows the dendrobranchiate (branching like a feather) gills underneath.  This gill pattern is characteristic of dendrobranchiate decapods such as Penaeids but is not seen in true shrimp or in crabs.



As in most seregestids, the rostrum is very short.  Unlike Eusergestes similis, the rostrum of Sergia tenuiremis is blunt.    There are no supreaorbital or hepatic spines on the carapace.



Unlike Eusergestes similis, there is a tubercle on the medial eyestalks in Sergia tenuiremis.  In this view the animal is facing left.
 

Pereopods 1-3 have tiny chelae.  This is a photo of the propodus and dactyl of pereopod 2.  The scale behind is millimeters.  Note also how the pereopods have many setae The posterior 2 pereopods (#4 and 5) are not chelate.  This photo shows the carpus, propodus, and dactyl of pereopod 5.  Note that the setae are all in the same plane, a configuration often seen on appendages used for swimming.



The pleopods are feathery and used for swimming.  This view is of pleopods 2-4 (from left to right)
 
 
 



Authors and Editors of Page:
Dave Cowles (2006):  Created original page