Hymenodora frontalis Rathbun, 1902

Common name(s): Pacific ambereye
Synonyms:
Phylum Arthropoda
 Subphylum Crustacea
  Class Malacostraca
   Subclass Eumalacostraca
    Superorder Eucarida
     Order Decapoda
      Suborder Pleocyemata
       Infraorder Caridea (true shrimp)
        Family Oplophoridae
A female Hymenodora frontalis carrying eggs.  Caught 1000-1500 m depth off Pt. Conception, CA.  Note the yellowish eye, almost devoid of black pigment, and the large egg size.
(Photo by: Dave Cowles, May 1995)
Description:    This is a true shrimp from the family Oplophoridae, which lives in deep midwater offshore.  True (Caridean) shrimp have the second abdominal epimera overlapping that of segment 1 and 2.  Family Oplophoridae is almost entirely midwater and has exopodites on its pereopods (photo).  Hymenodora are deepliving, non-vertically migrating species that have almost no pigment in their small eyes, giving them a golden color (photo, photo), and usually have very soft exoskeletons (they are frequently damaged when captured by net).  None of their abdominal segments has a median dorsal ridge. H. frontalis has a longer rostrum than the other local Hymenodora species. The rostrum extends past the cornea of the eye and even past the peduncle of the first antennae (photo, photo).  The eyestalk has a strong tubercle on the median side near the cornea (photo).  The telson is truncate instead of rounded at the end, and has terminal spines (photo).  Unlike the other Oplophorids, which tend to be dark red in deepliving species and half red in vertical migrators, the color of Hymenodora is orange-red, darker on carapace and on eggs.  Maximum length:  To about 58 mm.

How to Distinguish from Similar Species: The rostrum of H. frontalis is longer than that of other Hymenodora, extending beyond the peduncle of the first antennae (see photo, photo).

Geographical Range: Pribilof Islands, Bering Sea to San Clemente Island, CA

Depth Range: 200 to 3000 m

Habitat: Bathypelagic

Biology/Natural History: This bathypelagic species lives very deep in midwater.  Its exoskeleton is so soft that it is often damaged on capture.  Note that it has unusually large eggs for an Oplophorid shrimp.  It is one of the most common deepliving Oplophorid shrimp off British Columbia.  It is not a vertical migrator.


 
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References:

Dichotomous Keys:
  Chace 1986
  Kozloff 1987, 1996
  Wicksten, 2009

General References:
Butler TH (1980) Shrimps of the Pacific Coast of Canada. The Canadian Bulletin of Fisheries and Aquatic Sciences 202: 1–280
 Chase, Fenner A., 1986.  The Caridian Shrimps (Crustacea: Decapoda) of the Albatross Philippine Expedition, 1907-1910, Part 4:  Families Oplophoridae and Nematocarcinidae.  Smithsonian Contributions to Zoology Number 432.  Paperback, 82 pp.

Scientific Articles:
Wasmer, Robert A., 1967.  Bathypelagic shrimps (Penaeidea and Caridea) from the eastern North Pacific.  Master's thesis, Walla Walla College, College Place, WA.  86 pp.


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



Another photo of a gravid female.  Photo by Dave Cowles in San Clemente Basin, CA, 1996.  Caught at 1000-1500 m depth.
 


This gravid female was captured in San Clemente Basin, CA in May 1966.  Frame from a video by Dave Cowles.  Click Here to see the video



This side view of a preserved specimen shows the rostrum which extends well beyond the corneas of the eyes and even exceeds the peduncle of the first antenna.
Note also the pereopods.  Oplophorids, unlike most other families of true shrimp, has exopods (exopodites) on its pereopods.  The exopodites of the pereopods are short,
curved backward and used for swimming.  The endopodites of the pereopods are longer, extended forward, and used for manipulating objects.
The eye pigment in Hymenodora is always pale, even in living specimens.



In this closeup dorsal view of the head, the median tubercles on the eyestalks near the corneas can be seen.  From a presereved specimen.



This is a closeup dorsal view of the telson and uropods.  The uropods are shorter than the telson and fringed with long setae.  The telson is truncate (not rounded) on the end, with two long spines at the corners (one of which is broken off on this individual).  Photo of a preserved individual.
 
 


Authors and Editors of Page:
Dave Cowles (2005):  Created original page