This amphipod species is found in freshwater drainages throughout North America. It is a native of the Mississippi River and its drainages, as well as most river systems in the Atlantic River Plain, including the Delaware, Hudson and Chesapeake. It also occurs throughout the Great Lakes of the United States and their drainages, although it is unclear if it is native to these areas. These amphipods are also found throughout drainages in northeastern Canada (St. Lawrence River and its drainages and gulf), as far north as Prince Edward Island. Recently there have been reports of this species from the United Kingdom and Finland, where they were likely introduced via shipping.
Biogeographic Regions: nearctic (Native ); palearctic (Introduced )
Individuals are white or clear in color (variations likely dependent on diet, water temperature and/or age), with brown or green stripes on their bodies and proximal appendage segments. Their bodies are laterally compressed, and they have two pairs of antennae on their cephalophorax. This species is distinguished from others in its family by its accessory flagellum, which has 2-7 segments, on the first set of antennae. The first set of antennae are longer than the second set. The body has seven free thoracic segments, an abdomen with six segments, and a minute telson at the end of the organism. Each of the seven thoracic segments have segmented legs; one segment, the coxa, plays an important role in reproductive activity. The coxa also marks the beginning of the gills, which run from the second to the sixth pair of legs. The first two sets of legs are specialized for grasping, and are called gnathopods. The rest of the legs are relatively unspecialized, and are called pereiopods. The first three abdominal segments have paired pleopods (legs used for swimming), and the last three abdominal segments bear paired uropods, which form a fin with dorsal spines. The eyes are unstalked, well-developed, medium-sized, and kidney shaped.
Females have large pouches called oostegites on the the inside of the legs (coxal area) used to carry eggs. Males usually have larger gnathopods (appendages used in feeding and mating) than females. Paired testes or ovaries are found ventrally on either side of the heart, appearing as long strands.
Range length: 5 to 14 mm.
Other Physical Features: ectothermic ; bilateral symmetry
Sexual Dimorphism: sexes shaped differently
This species prefers unpolluted, clear, cold waters, including springs, streams, pools, ponds, and lakes. They prefer highly oxygenated, shallow, still areas, with lots of vegetation or debris for coverage, as they tend to avoid light. When found in rivers, they cluster near the bottom at the edges of backwaters. This species can tolerate some salinity (only up to 1%) and is sometimes found in estuaries. Many scientists categorize them as cold water stenotherms, meaning that they require a narrow range of cold temperatures in order to survive (10-15°C, with temperatures of 20-24°C being tolerable, and temperatures above 34°C causing death).
Range depth: 0 to 3 m.
Habitat Regions: temperate ; freshwater
Aquatic Biomes: benthic ; lakes and ponds; rivers and streams; brackish water
Other Habitat Features: estuarine ; intertidal or littoral
Depth range (m): 1 - 10
Depth range (m): 1 - 10
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These amphipods prefer benthic regions of water bodies because they feed on the detritus, zooplankton and microplantae found there as well as the feces of Dreissena species (freshwater mussels). They are categorized as scavengers, and though they eat meat, they very rarely attack living animals to feed (though they will eat newly dead aquatic animals). They are even known to chew on and eat cotton or linen threads (parts of fishing nets). There are some records of cannibalism in this species, particularly amongst males. Recent research has indicated that types of food consumed may shift throughout the life cycle, with smaller individuals feeding mainly on detritus and larger individuals having a more varied diet.
Animal Foods: carrion ; aquatic crustaceans; zooplankton
Plant Foods: leaves; algae; phytoplankton
Other Foods: detritus
Primary Diet: carnivore (Eats non-insect arthropods); herbivore (Algivore); omnivore ; planktivore ; detritivore ; coprophage
This species of amphipod is an important detritivore in its ecosystem and a key food source for many other species. It has commensalistic relationships with a number of algae and sessile protozoan which live on its body. They also form an important relationship with Dreissena sp. (freshwater zebra mussels), feeding on their fecal matter. The mussels also excrete mucous on which algae, an important food source for these shrimp, feed. This species is also an intermediate host for a number of parasites, including tapeworms, acanthocephalan, and nematodes, and is host to a parasitic water mold (currently undescribed).
Ecosystem Impact: biodegradation
- Capillospirura pseudoargumentosa (Order Spirurida, Phylum Nematoda)
- Cosmocephalus obvelatus (Family Acuariidae, Phlyum Nematoda)
- Cystidicola farionis (Order Spirurida, Phylum Nematoda)
- Tetrameres crami (Order Spirurida, Phylum Nematoda)
- Spiny headed worms (Phylum Acanthocephala)
- Tapeworms (Class Cestoda, Phylum Platyhelminthes)
Fishes (such as yellow perch) are the main predators of this species. They are also prey to birds, insects, and amphibians. These amphipods are very sensitive to any water movement and will quickly dart away and/or burrow into substrate as an escape mechanism.
- Yellow perch (Perca flavescens)
Life History and Behavior
This species is highly sensitive to water disturbances, which it senses with its antennae and other appendages. They sense predators through movement and chemical cues. Their eyes are highly developed as well, and potential mates communicate through a mating dance.
Communication Channels: visual ; tactile ; chemical
Perception Channels: visual ; tactile ; vibrations ; chemical
Newly fertilized eggs develop and are carried in their mother's oostegites until they have hatched and their appendages have formed; this can take from 2-4 weeks, depending on water temperature and other environmental conditions. Young are released into the water after the mother molts into her tenth instar. This species grows and achieves new phases of its life cycle through a series of molting and instars (periods between molting). The first five instar phases are considered to be juvenile phases, in which the sexes are indistinguishable. Once the sixth instar is reached, males and females are visually distinguishable (though their sexes are determined at fertilization). Once reaching their eighth instar, usually within 2 months of hatching, males and females enter the nuptial phase and pair for the first time, only mating once before dying. They typically complete their life cycle within a year.
These amphipods typically complete their life cycle within a year and reproduce once. They undergo 15-20 molts during their lives; length of instars (and therefore longevity) depends largely on water temperature.
Status: wild: 2.5 years.
Status: wild: 1 years.
Mating occurs following a female's molt and ovulation. Males attracts females by performing a mating dance. Once they have paired, the male grasps his partner and swims with her, using his appendages to maneuver her body so that he can use his pleopods to insert sperm into her brood pouch, where eggs are fertilized. This species is monogamous, though a male and female may mate multiple times during one pairing.
Mating System: monogamous
A ninth phase male will typically pair with a female in her eighth instar who is about to molt. The female, who remains passive throughout, is seized by the male. He carries her on his back, holding her with his gnathopods. If the female has not molted yet, the pair will remain together until she does, separating briefly in order for her to molt. The pair may copulate several times over the next 24 hours, each time taking less than a minute. Once his uropods have come into contact with her oostegites, a male ejaculates sperm and his partner uses her pleopods to sweep them into her pouch. Her oviducts then open, allowing the eggs to be fertilized; females do not store sperm. Males disperse following mating; females carry eggs in their pouches until they have hatched and juveniles have grown appendages. Egg clutches are known to have as many as 23 and as few as 8 eggs.
Breeding interval: This species mates once during its life.
Breeding season: These animals breed between April and November, depending on water temperatures.
Range number of offspring: 8 to 23.
Range gestation period: 1 to 3 weeks.
Range time to independence: 2 to 4 weeks.
Average age at sexual or reproductive maturity (female): 2 months.
Average age at sexual or reproductive maturity (male): 2 months.
Key Reproductive Features: semelparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); ovoviviparous
Females carry their eggs until they have hatched and juveniles have grown appendages. Once this has happened, she molts, releasing them into the open water and ending her parental care. Males exhibit no parental investment following mating.
Parental Investment: female parental care ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Female)
This species has no special conservation status.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
Relevance to Humans and Ecosystems
There are no known adverse effects of this species on humans.
This amphipod species is considered a good biomonitor, as its health can indicate the presence and toxicity of pesticides and chemicals. It absorbs nickel, cadmium, and lead and so, by looking at the levels of these compounds in their systems, scientists can evaluate water toxicity, and potentially locate sources of polluting run off.
Positive Impacts: research and education
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