- are among the most primitive extant crustaceans

- primitive features include:

- many segmented body

- little specialization of appendages

- very primitive nervous system

- divided into 4 orders:

- Anostraca; fairy shrimp

- Notostraca; tadpole shrimp

- Conchostraca; clam shrimp; sometimes divided into:

- Spinicaudata

- Laevidcaudata

- Cladocera; water fleas; now divided into

- Anomopoda

- Ctenopoda

- Onychopoda

- Haplopoda

- Order Anostraca- fairy shrimp

- elongated, somewhat cylindrical, separated from other branchiopods by not having a carapace

- have a pair of compound stalked eyes and single eyespot

- first antennae slender and inconspircuous

- second antennae large and swollen; in males enlarged for clasping of females during copulation

- some have frontal appendages in males located between second antennae- aid in clasping

- thorax has 11 or 17 segments in North American species

- each segment with a pair of appendages which function for

- locomotion

- food gathering

- respiration

- posterior to the thorax is genital region or trunk

- has the reproductive organs

- in males have two penes

- in females there is an ovisac for egg development

- posterior to the trunk is the abdomen, has 7 segments

- fairy shrimp range from 5-100 mm in length

- are dioecious with internal fertilization

- males usually less abundant than females

- are distributed locally and sporadically

- in habit temporary ponds or pools

- presence of adults is very seasonal

- generation time is very short; usually about 3 weeks or as long as 24 weeks

- all are freshwater except Artemia salina - the brine shrimp, which lives in brine lakes, e.g., Great Salt Lake.

- normally fairy shrimp not in ponds with fish because of temporary nature of habitat so most predation pressure due to amphibians and carnivorous insects

- eggs laid in pond just before drying when they attach to vegetation

- may also be dispersed this time by wind or attachment to large animals

- hatching of eggs usually requires drying period

- eggs hatch into a nauplius larva that molts often before adulthood

- fairy shrimp swim up-side-down

- feed on microorganisms and detritus via filter feeding

 

- Order Notostraca- tadpole shrimp

- have a large rounded carapace that covers the head and thorax; separates it from other orders in class

- segments or "body rings" have more than one pair of appendages, unique to this group

- body rings are actually two fused segments

- first 11 rings are the thorax

- remaining rings are the abdomen

- may have from 35 to 70 pairs of appendages depending on species

- inhabit temporary pools in western U.S.

- not good swimmers so creep and burrow into substrate

- eggs maintained by females in ovisacs attached to 11^th segment

- feed on microorganisms and detritus

 

- Order Conchostraca (recently divided into: Spinocaudata and Laevicaudata)

- are the clam shrimp; will treat them together

- characterized by possession of what appears to be a bivalve shell- actually the carapace that is folded

- has growth lines, each indicating a single ecdysis or molt

- body divided into 2 regions: head and trunk

- head is conspicuous, and is produced into a rostrum anteriorly

- has sessile compound eyes

- first antenna small and uniramous

- second antenna are biramous; used for swimming

- trunk with 10-32 pairs of legs with uniform appearance, but decrease posteriorly

- in male first 2 pair with hooks for copulation

- are free swimming, living near bottom of lakes, ponds and temporary ponds or pools

- have very spotty distribution and are extremely seasonal, but are widespread

- are filter feeders feeding on microorganisms and detritus

- females cement eggs to her abdominal appendages

- when she molts eggs remain on exuvium and fall to bottom where they hatch

 

- Order Cladocera (some recent publications divide it into 4 orders: Anomopoda, Ctenopoda, Onychopoda, Haplopoda - we’ll treat them as a single order)

- more than half of the 800 living species of branchiopods are cladocerans

- most closely related to conchostracans; share a bivalve carapace

- size ranges from 0.2 to 3.0 mm

- all have a distinct head and a bivalve carapace

- have a single sessile compound eye and a smaller ocellus

- antennules (first pair of antennae) with sensory hairs, function in olfaction

- second antennae are the main organs for locomotion

- jerky swimming is the rule

- body divided into head, thorax and abdomen

- thorax usually has 5 pairs of appendages

- abdomen has no appendages

- respiration is done across the surfaces of the legs and the wall of the carapace

- most are filter feeders, but some (Chydoridae) live on the bottom, and are modified for collecting fine particulate organic matter off the bottom.

- the genera Polyphemus and Leptodorus are predators

 

- Reproduction

- males usually rare

- most of the year females produce eggs parthenogenetically- therefore producing only female eggs (usually about 2-20)

- eggs deposited in dorsal brood chamber (ephippium) where they hatch

- Environmental stimuli can cause production of mictic eggs that can produce a haploid male (n) which produces sperm that can fertilize mictic eggs to form 2n females.

- mictic fertilized eggs overwinter and can withstand freezing and drying

- water fleas have short life span- usually about 3-4 weeks

- varies due to temperature, latitude, and altitude, and food supply

 

- life cycle: egg- juvenile- adolescent- adult

- some show cyclomorphosis

- seasonal changes in morphology; go from round headed to "helmet headed" (conehead)

- usually happens in summer with warm water temperatures

- exact cause is unknown, but theories include:

- bouancy theory

- nutritional change

- temperature changes

- most cladocerans also exhibit daily vertical migration

- live in deep waters during the day

- migrate to shallow waters at night

- it is usually related to food gathering