Neognathophausia gigas (Willemoes-Suhm, 1875)

Common name(s): 
Synonyms:  Gnathophausia drepanephora, Gnathophausia gigas
Phylum Arthropoda
 Subphylum Crustacea
  Class Malacostraca
   Subclass Eumalacostraca
    Superorder Peracarida
     Order Lophogastrida
       Family Lophogastridae (or Gnathophausiidae)
Gnathophausia gigas from 700-800 m, San Clemente Basin, CA
(Photo by: Dave Cowles, May 1996)
Description:  This bright red lophogastrid mysid has a long rostrum lined with spines.  It does not have dorsal spines on the abdomen.  The antennal scale is whole, lanceolate, without a distinctly isolated distal part separated from the proximal part by an articulation.  The external margin of the antennal scale is serrated, with 3-9 (or 2-7) large spines.  Supraorbital spine is well developed.  Dactyls of thoracopods 3-8 elongated, lanceolate, with 8-10 spines along nearly the entire length of the inner margin.  The pleural plates of abdominal segments 2-5 have a rounded anterior lobe and spiniform posterior lobe.  The epimeral plates of the sixth abdominal segment are knitted together ventrally to form an indivisible plate with a deep cleft at the distal end.  Maximum length to 16.4 cm.  Probably attain maturity at about 12 cm.

How to Distinguish from Similar Species:N. ingens has a relatively shorter rostrum with smaller serrations.  Its antennal scale is ovate with small spines.  Its supraorbital spine is small or may be absent.  Both the anterior and the posterior lobes of the pleuralplates of abdominal segments 2-5 are pointed.  Unlike Gnathophausia gracilis, this species does not have prominent dorsal spines on the abdominal segments.

Geographical Range:  Cosmopolitan in tropical and temperate waters (to 60 degrees N and 69 deg S); from S Alaska south in our waters.

Depth Range:  600-4400 m

Habitat:  Bathypelagic.  Seems to live in waters of approximately 4 degrees C

Biology/Natural History:  Reach sexual maturity at about 12 cm total length (including rostrum).  Spination and relative length of rostrum is greater in smaller individuals, which originally led to small individuals being called the separate species G. drepanephora.  This species is less common than is N. ingens off our coast (at least off California)

Lophogastrids were formerly thought to be a type of mysid.  This species lives permanently below the euphotic zone.  Neognathophausia gigas swims constantly, primarily with the pleopods, with some participation by the thoracic exopods (Cowles, personal observations).

Gnathophausia means "light-jaw".  This species has a gland on its second maxillae (mouthparts) from which it spews a brilliantly luminescent cloud into the water when disturbed.  Luminescence seems to be a function of diet, since animals of a related species, Neognathophausia ingens, maintained on non-luminescent food in the laboratory gradually lose their ability to luminesce, while if luminescent food is restored they can regain their luminescence (Frank et al., 1984).

Neognathophausia gigas is sometimes parasitized by an ellobiopsid flagellate protozoan, Amallocystis fascitus, which forms a cluster of white filaments on the ventral side of the anterior abdominal segment.  The parasite seems to be associated with the main nerve ganglion in this segment, and is associated with hypertrophy of the ganglion.  In N. ingens it also retards sexual maturation such as retarded development of oostegites in females and feminizing changes in males.


 
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References:

Dichotomous Keys:
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.  Canadian Special Publication of Fisheries and Aquatic Sciences 93.  ISBN 0-660-12096-8

Pequegnat, L.H., 1965.  The bathypelagic mysid Gnathophausia (Crustacea) and its distribution in the eastern Pacific Ocean.  Pacific Science 19: 399-422
 
 
 
 
 

General References:
 

Scientific Articles:
Ortmann A.E., 1906.   Schizopod Crustaceans in the United States National Museum- the Families Lophogastridae and Eucopiidae. Government Printing Office, Washington DC

Pequegnat, Linda H., 1965.  The bathypelagic mysid Gnathophausia (Crustacea) and its distribution in the eastern Pacific Ocean.  Pacific Science 19:4 399-421
 

Web sites:
 


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


The relatively long spines (compared with Neognathophausia ingens) and the serrations on the rostrum can be seen in this dorsal view.  Photo by Dave Cowles, May 1996
Notice the two spines forming a crescent shape at the tip of the telson, which is characteristic of Gnathophausia and Neognathophausia.
 


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