Lepidurus packardivernal pool tadpole shrimp

Geographic Range

Vernal pool tadpole shrimp (Lepidurus packardi) are endemic to the California Central Valley, with the majority of individuals found in the Sacramento Valley. They have also been found in areas east of the San Francisco Bay to the Sacramento River Delta and in a few scattered locations in the San Joaquin Valley. (Rogers, 2001)


Vernal pool tadpole shrimp occur in a wide variety of seasonal habitats. These include vernal pools, clay flats, alkaline pools, ephemeral stock tanks, and roadside ditches and ruts. Habitats include small, clear, well vegetated vernal pools to exceedingly turbid, alkali scald pools or large winter lakes. Typically, they are found in habitats that are deeper than 12 centimeters, retain water for 15 to 30 days and do not experience wide daily temperature fluctuations. Average pond depth of wetlands is 15.2 centimeters. Vernal pool tadpole shrimp are not currently known to use highly saline habitats. (Helm, 1998; Rogers, 2001)

  • Aquatic Biomes
  • temporary pools
  • Range depth
    0.12 (low) m
    0.39 (low) ft
  • Average depth
    0.152 m
    0.50 ft

Physical Description

Vernal pool tadpole shrimp are typical members of the genus Lepidurus. They are distinguished from most other nearctic Lepidurus species by having a nuchal organ intersected by a line drawn between the posterior apices of the eyes. The nuchal organ is a large, light-sensitive tubercle behind the eyes thought to be used for perception. There is no set number of body rings (segments of the thorax and abdomen) or pairs of legs for the species, but most individuals fall in the ranges of 24 to 29 body rings and 30 to 35 pairs of legs. The first 11 body rings are defined as the thorax, with the remainder constituting the abdomen. The rings may be incomplete or coil the trunk more than once and they can bear multiple pairs of appendages.

The caudal lamina is truncate, meaning that a thin plate completely surrounds the abdominal region that could be considered the tail of the organism, and is 0.1 to 0.3 times the length of carapace. Mature individuals have triangular sulcus spines, with numerous small spines of varying shapes sometimes found in double rows separating the larger spines. Smaller individuals have large acute spines, 1.2 to 1.5 times as long as they are broad. Older individuals may have the largest sulcus spines rounded. The endites three, four, and five of the second thoracic appendages project beyond the carapace margin. In males, they may be used for grasping females during copulation.

Length of adult vernal pool tadpole shrimp ranges from 15 to 86 mm from the anterior margin of the carapace to the tip of the caudal lamina. They can reach very large sizes; one specimen from Stanislaus County, California measured 86 mm from the anterior carapace margin to the apex of the caudal lamina.

They may vary in coloration, depending on habitat, but are most commonly green. In highly turbid water, this species may be nearly translucent to buff colored with brown mottles. In slightly turbid to clear water, color may be more variable. Coloration may be light green, dark green, dark green mottled with brown, chocolate brown, brown with green mottles, or black. (Rogers, 2001)

  • Sexual Dimorphism
  • sexes alike
  • Range length
    15 to 86 mm
    0.59 to 3.39 in


Vernal pool tadpole shrimp hatch when proper conditions are met at the beginning of the spring season. If these conditions are not met, the eggs remain in a diapausal state for up to 10 years until proper conditions are met. After hatching, they reach sexual maturity within three weeks. This allows vernal pool tadpole shrimp to hatch, mature, and produce eggs quickly after pools refill. Vernal pool tadpole shrimp can produce multiple generations in a single wet season, and adults will remain present and reproductive in the pool until these temporary pools dry up completely. (Ahl, 1991; Simovich, 1998)


Vernal pool tadpole shrimp are either hermaphroditic or parthenogenic. (Rogers, 2001)

Reproduction occurs throughout the spring wet season when females average between 10 and 12 mm in carapace length. A female can produce thousands of cysts or fertilized eggs during her short lifespan and fecundity increases with size.

Females deposit eggs on vegetation and other objects located along pool substrates. These cysts and fertilized eggs are drought-resistant, sticky, and readily adhere to plant matter and sediment particles. When vernal pools dry, the eggs remain on the surface of the dried pool or become embedded in the substrate up to a few centimeters deep, where they enter a diapausal state. They remain there during the hot, dry summers and cold winters until the pools refill from rainwater and appropriate conditions for hatching occur. Some eggs hatch the following season when the pool refills, whereas others may remain dormant for up to 10 years before they hatch. (Ahl, 1991; Alexander and Schlising, 1998; Simovich, 1998)

  • Breeding interval
    It is unknown how frequently females may breed during their short lifespan.
  • Breeding season
    Breeding occurs in the spring wet season.

Parental investment after fertilization and egg-laying is not present in vernal pool tadpole shrimp.

  • Parental Investment
  • no parental involvement
  • pre-fertilization
    • provisioning
    • protecting
      • female


The lifespan of vernal pool tadpole shrimp ranges from a few hours up to a few months, while pools still retain water. (Alexander and Schlising, 1998; Rogers, 2001)


Vernal pool tadpole shrimp are primarily bottom-dwelling invertebrates that both crawl through the substrate and swim. They use a pair of ventral appendages called phyllopods to propel themselves forward through the water. They climb over objects along the substrate and dig through the sediments of the pool substrate. There is currently no information available about any kind of social structure within populations. (Simovich, 1998)

Home Range

The home range size of Lepidurus packardi is unknown.

Communication and Perception

Vernal pool tadpole shrimp have a fused pair of eyes on the dorsal surface that are likely used to aid in locating both food and potential mates when reproduction is sexual. The nuchal organ is hypothesized to serve a chemosensory function. (Rogers, 2001)

Food Habits

Adults are omnivorous. They feed primarily on detritus found on the substrate of temporary pools, but they capture living organisms, such as fairy shrimp Anostraca and other invertebrates. Vernal pool tadpole shrimp consume plant detritus, various zooplankton, and insect larvae that they come across while digging through pool substrate. They use their ventral appendages to collect and filter food particles in the substrate and show a preference for animal detritus. (Simovich, 1998)


Vernal pool tadpole shrimp are subject to predation by water birds. Both mature individuals and diapausing eggs are consumed by birds. Some of the eggs that are consumed will pass through the birds digestive tract unharmed, which is how vernal pool tadpole shrimp disperse. (Rogers, 2001)

  • Anti-predator Adaptations
  • cryptic
  • Known Predators
    • waterfowl

Ecosystem Roles

Vernal pool tadpole shrimp provide a food source for organisms such as water birds and are hosts for parasitic organisms such as the metacercariae of flukes in the genus Echinostoma. This parasitism results in the castration of the vernal pool tadpole shrimp. Birds digging through the substrate aids in stirring up detritus into the water column for filter feeders to consume. (Ahl, 1991)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

Vernal pool tadpole shrimp provide no benefits to humans, although they are important members of native ecosystems.

Economic Importance for Humans: Negative

There are no adverse effects of the vernal pool tadpole shrimp on humans.

Conservation Status

Vernal pool tadpole shrimp are currently considered endangered as a result of habitat loss and their restricted range. ("Species Profile for Vernal Pool tadpole shrimp (Lepidurus packardi)", 2010)


Carey Wu (author), The College of New Jersey, Keith Pecor (editor), The College of New Jersey, Tanya Dewey (editor), University of Michigan-Ann Arbor.



living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


flesh of dead animals.


uses smells or other chemicals to communicate


having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.


an animal that mainly eats decomposed plants and/or animals


particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).


a period of time when growth or development is suspended in insects and other invertebrates, it can usually only be ended the appropriate environmental stimulus.

  1. active during the day, 2. lasting for one day.

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

external fertilization

fertilization takes place outside the female's body


union of egg and spermatozoan


a method of feeding where small food particles are filtered from the surrounding water by various mechanisms. Used mainly by aquatic invertebrates, especially plankton, but also by baleen whales.


mainly lives in water that is not salty.


having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.


having the capacity to move from one place to another.


specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.


active during the night


reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.


development takes place in an unfertilized egg


photosynthetic or plant constituent of plankton; mainly unicellular algae. (Compare to zooplankton.)


an animal that mainly eats plankton

seasonal breeding

breeding is confined to a particular season


remains in the same area


reproduction that includes combining the genetic contribution of two individuals, a male and a female


lives alone


uses touch to communicate


that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).


uses sight to communicate


animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)


U.S. Fish & Wildlife Service. 2010. "Species Profile for Vernal Pool tadpole shrimp (Lepidurus packardi)" (On-line). Accessed February 22, 2010 at http://ecos.fws.gov/speciesProfile/profile/speciesProfile.action?spcode=K048.

Ahl, J. 1991. Factors affecting contributions of the tadpole shrimp, Lepidurus packardi, to its oversummering egg reserves. Hydrobiologia, 212: 137-143.

Alexander, D., R. Schlising. 1998. Patterns in time and space for rare macroinvertebrates and vascular plants in vernal pool ecosystems at the Vina Plains Preserve, and implications for pool landscape management. Ecology, Conservation, and Management of Vernal Pool Ecosystems - Proceedings from a 1996 Conference: 161-168.

Helm, B. 1998. Biogeography of eight large Branchiopods endemic to California. Ecology, Conservation, and Management of Vernal Pool Ecosystems - Proceedings from a 1996 Conference: 124-139.

Rogers, D. 2001. Revision of the nearctic Lepidurus (Notostraca). Journal of Crustacean Biology, 21: 991-1006.

Simovich, M. 1998. Crustacean biodiversity and endemism in California’s ephemeral wetlands. Ecology, Conservation, and Management of Vernal Pool Ecosystems - Proceedings from a 1996 Conference: 107-118.