Animal Diversity Web

Ge­o­graphic Range

Palae­mon­etes pugio can be found on the east­ern shore of the United States. Its range ex­tends from Maine to Texas. (Collins, 1981)

• Biogeographic Regions
• nearctic
  • native

Habi­tat

Palae­mon­etes pugio nor­mally in­hab­its the areas where fresh and salt­wa­ter com­bine. Their basic habi­tat is the salt marshes and con­nect­ing streams. These areas can in­clude small tidal creeks, tidal guts, and ditches with low salin­ity. (Daiber, 1982) With the ap­proach of cold weather, P. pugio has been known to move to deeper wa­ters. (An­der­son, 1996)

• Aquatic Biomes
• rivers and streams
• coastal

Phys­i­cal De­scrip­tion

Palae­mon­etes pugio has a smooth cara­pace and ab­domen. Grass shrimp also have three pairs of legs. The sec­ond pair is the strongest, while the third pair lacks chelae (claws). A well-de­vel­oped ros­trum (horn-shaped struc­ture be­tween the eyes) pos­sess­ing dor­sal and ven­tral teeth is pre­sent in this species, lo­cated be­tween its com­pound eyes on its head. P. pugio has a tail with two pairs of spines, on pair lo­cated dor­sally, the other lo­cated pos­te­ri­orly (An­der­son, 1996). The pleura (side plates) of the sec­ond ab­dom­i­nal somite (sec­tion) over­lap the pleura of the first and third ab­dom­i­nal somite (Zim­mer­man, 2000). The ab­dom­i­nal pleura are rounded in this species (An­der­son, 1996).

Male adults reach an av­er­age length of 23.5 mm. Fe­male adults bear­ing eggs are usu­ally about 30.0 mm while those with­out eggs are usu­ally about 26.2 mm. The fe­males un­dergo a pe­riod of growth just be­fore their breed­ing sea­son in the sum­mer. (Daiber, 1982) The adults rarely grow be­yond 50 mm. P. pugio are trans­par­ent with yel­low col­or­ing and brown spots. (An­der­son, 1996)

• Other Physical Features
• ectothermic
• bilateral symmetry

Re­pro­duc­tion

Palae­mon­etes pugio re­pro­duces an­nu­ally when the water warms up. Fe­males bear­ing eggs have been demon­strated to be in much greater sup­ply at 30 de­grees Cel­sius and above. The fe­males con­tin­u­ously pro­duce eggs dur­ing the breed­ing sea­son. Fer­til­ized eggs take be­tween 15-20 days to ma­ture and new eggs are pro­duced 1-2 days after the hatch­ing of a pre­vi­ous group. Larger fe­males tend to pro­duce big­ger eggs and larger quan­ti­ties of eggs. (Daiber, 1982) Fe­males can pro­duce any­where be­tween 250-450 eggs in a sea­son. (An­der­son, 1996)

Be­fore spawn­ing, the ovaries in the fe­male be­come more dense and vis­i­ble. Ad­di­tional setae are de­vel­oped that will later hold the fer­til­ized eggs. The fe­male molts be­fore mat­ing can occur and the males do not stay with or guard fe­males. In­stead, the male must make con­tact with the fe­male's ex­oskele­ton to re­al­ize that mat­ing is pos­si­ble. Mat­ing must occur within seven hours of the molt. (An­der­son, 1996)

Dur­ing cop­u­la­tion, the male and fe­male move their gen­i­tal re­gions to close prox­im­ity. The male in­serts a sper­matophore into the fe­male's gen­i­tals where it re­mains until the eggs are ready for fer­til­iza­tion, usu­ally within seven hours after the sper­matophore has been in­serted. Then through en­zyme ac­tion, part of the sper­matophore dis­solves, al­low­ing the sperm to fer­til­ize the eggs. The fer­til­ized eggs are then se­cured to the body by the setae. The fe­male holds the eggs until the lar­vae are ready to hatch. The lar­vae break free from the egg mem­brane through their strug­gling, os­motic swelling of the inner mem­brane, and ven­ti­la­tory move­ments by the mother. (An­der­son, 1996)

Be­hav­ior

P. pugio ju­ve­niles ma­ture at one and a half to two months. At this time, they are usu­ally 15-18 mm long. Their life span is 6-13 months. Some early spring-hatched shrimp will mate as adults by the end of the sum­mer, other late sum­mer-hatched shrimp will wait until after win­ter to mate. (An­der­son, 1996)

Preda­tors: Mum­mi­chog (Fun­du­lus het­e­ro­cli­tus), Banded Kil­li­fish (Fun­du­lus di­aphanus), Blue-Spot­ted Sun­fish (En­nea­can­thus glo­rio­sus). (Batzer, 1999)

Par­a­sites: Coc­cidia, Mi­crosporid­i­ans, Trema­todes, Isopods, and Leeches. (An­der­son, 1996) The par­a­sitic iso­pod Probopy­rus pan­dal­i­cola com­monly in­fests P. pugio, caus­ing a no­tice­able bulge around the gills. (Lipp­son, 1984)

Food Habits

P. pugio adults prey on oligochaetes, poly­chaetes, and harpacti­coid cope­pods. (Bax­ter, 1999)

P. pugio lar­vae feed upon zoo­plank­ton, algae, and de­tri­tus. (An­der­son, 1996)

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

P. pugio serves as a vital food source to many valu­able com­mer­cial and sport fishes (An­der­son, 1996). It has also been rec­og­nized as a use­ful bioas­say test or­gan­ism. This has led to much re­search in­volv­ing grass shrimp and toxic chem­i­cals (An­der­son, 1996).

Con­ser­va­tion Sta­tus

• IUCN Red List

  No special status

• US Federal List

  No special status

• CITES

  No special status

Con­trib­u­tors

Lee Geraci (au­thor), West­ern Mary­land Col­lege, Louise a. Paquin (ed­i­tor), West­ern Mary­land Col­lege.

Ref­er­ences

An­der­son, G. Au­gust 26, 1996. "Tax­on­omy: Species Shrimp, Grass" (On-line). Ac­cessed April 30, 2001 at http://​fwie.​fw.​vt.​edu/​WWW/​macsis/​lists/​M070010.​htm.

Bax­ter, D., R. Rader, S. Wissinger. 1999. In­ver­te­brates in Fresh­wa­ter Wet­lands of North Amer­ica: Ecol­ogy and Man­age­ment. New York: John Wiley & Sons, Inc.

Collins, Jr., H. 1981. Harper & Row's Com­plete Field Guide to North Amer­i­can Wildlife: East­ern Edi­tion. New York: Harper & Row, Pub­lish­ers, Inc..

Daiber, F. 1982. An­i­mals of the Tidal Marsh. New York: Van Nos­trand Rein­hold Com­pany.

Lipp­son, A., R. Lipp­son. 1984. Life in the Chesa­peake Bay. Bal­ti­more: The Johns Hop­kins Uni­ver­sity Press.