By Lee Geraci
Geographic Range
Palaemonetes pugio can be found on the eastern shore of the United States. Its range extends from Maine to Texas. (Collins, 1981)
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)
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: [link]:
Not Evaluated.
US Federal List: [link]:
No special status.
CITES: [link]:
No special status.
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For More Information
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Contributors
Lee Geraci (author), Western Maryland College.
Louise a. Paquin (editor), Western Maryland College.
