Body Form and Internal StructureThe body of the crayfish is divided into two regions: the cephalothorax, which has sensory, feeding, and locomotor functions; and the abdomen, which has locomotor and visceral functions (Miller and Harley, 1992). Figure 1a shows a lateral view of the internal structure of a male crayfish. Figure 1b shows a cross section of the thorax in the region of the heart.
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Source: Miller and Harley, 1992 |
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in the region of the heart Source: Miller and Harley, 1992 |
Return to Table of ContentsAppendagesBoth segments of the crayfish have appendages specialized for various functions, such as food handling and consumption, respiration, sensory, defense, locomotion, and reproduction (Barr, 1994; Miller and Harley, 1992; Pennak, 1989). Table 1 summarizes the functions of each type of appendage.
| Appendage | Function |
| 2 pairs of antennae | sensory functions |
| 3 pairs of mouth parts |
|
| 3 pairs of maxillipeds | manipulate food towards mouth and each also bears a gill |
| 1st pereiopod | chiliped or claw used in defense and capturing food |
| 4 pairs of periopods | walking legs |
| 5 pairs of pleopods or swimmerets |
|
| 5 uropods | compose the flat, flipper-like tail used in swimming and escape responses |
Sources: Barr, 1994; Lockwood, 1968; Miller and Harley, 1992; Pennak, 1989
Return to Table of ContentsDigestive SystemThe digestive tract (figure 1a) consists of the foregut, which includes an enlarged stomach, part of which is specialized for grinding; the midgut, which extends from the foregut; and the hindgut, which leads to the anus and functions in water and salt regulation (Miller and Harley, 1992; Snodgrass,1965). The digestive gland secretes digestive enzymes and aids in the absorption of the products of digestion (Pennak, 1989).
The excretory organs (figure 1a) are also called the antennal glands because they are located at the base of the second antenna. They exrete the waste products of blood filtration; ammonia is the primary waste product (Miller and Harley, 1992). Ammonia is also excreted across the gill surfaces and by diffusion across thin parts of the exoskeleton (Snodgrass, 1965).
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Respiratory SystemCrayfish use gills to perform respiration. The gills (figure 1b) are located in between the carapace (the exoskeleton of the cephalothorax) and the lateral body wall, in the branchial chamber (Miller and Harley, 1992). Oxygen and carbon dioxide are exchanged between the blood and water across the gill surface as water is circulated through the branchial chamber by the beating of the gill bailer on the second maxilla (Pennak, 1989).
Return to Table of ContentsCirculatory SystemThe circlatory system of the crayfish is centred around a muscular heart with dorsal, anterior, and posterior arteries leading away from it (figure 1b). Branches of these vessels empty into the sinuses of the hemocoel (the large tissue spaces containing blood). The ventral sinus collects the blood, the blood travels through the gills, and then returns to the pericardial sinus surrounding ther heart (Miller and Hurley, 1992; Snodgrass, 1965).
Return to Table of ContentsNervous SystemThe crayfish nervous system is composed of a ventral nerve cord fused with segmental ganglia, and the supresophageal and subesophageal ganglia (figure 1a and 1b) (Miller and Harley, 1992). Giant neurons in the ventral nerve cord function in escape responses (Bliss, 1990). The supraesophageal and subesophageal ganglia control the head appendages in response to sesory input recieved from receptors (Miller and Harley, 1992).
Return to Table of ContentsEndocrine SystemThe endocrine glands release hormones into the blood which circulate and create responses from certain target tissues (Miller and Harley, 1992). The hormones control functions, such as ecdysis, sex determination, colour change and regulation of heart rate (Bliss, 1990; Lockwood, 1968; Miller and Harley, 1992)
Return to Table of ContentsSensory Structures
Sources: Miller and Harley, 1992; Pennak, 1989; Snodgrass, 1965.
Return to Table of ContentsSexual Characteristics and ReproductionCrayfish have separate male and female sexes (dioecious) and the gonads are located in the dorsal portion of the thorax (figure 1a) (Miller and Harley, 1992). Mating occurs just after the female has molted, usually in the spring. The male deposits sperm near the openings of the female gonoducts (at the base of the 3rd periopods) and uses the two modified pleopods to guide the sperm into the female sperm receptacle.
Fertilization occurs after copulation, as the eggs, sperm, and a sticky fluid are released into a protected chamber created by the female curling her abdomen under. The clutch of several 100 eggs remain attached to the female pleopods for several weeks. The young hatch as juvenile instars and remain attached to their mother for several days. Once they leave their mother, they begin an adult life and reach maturity in anywhere from a few months to a year. The average life span for a crayfish is two to three years (Miller and Harley, 1992; Barr, 1994).
Return to Table of ContentsPredator / Prey RelationshipsCrayfish are an important link in the food chain of the aquatic community (Crocker, 1968; Lodge and Kershner, 1994). They feed on living animals and plants, and also consume a fair amount of dead plants, dead or dying animals, and detritus (Creed, 1994; Crocker and Barr, 1968). There is also a large number of species of other animals known to eat crayfish (Lodge, 1994).
Crayfish have been reported to be preyed upon by at least 46 species of fish, 10 amphibians, 20 reptiles, 38 birds, and 6 mammals (including humans) (Crocker and Barr, 1968). Crayfish are preyed upon heavily by fish, such as trout, pickerel, and bass, and they may be eaten by other invertebrates. For example, very young crayfish are often eaten by dragonfly nymphs (Barr, 1994).
Crayfish are omnivores, consuming both plant and animal matter. Most Ontario species primarily eat living or recently killed invertebrates, such as insects and snails, and fresh vegetation (Barr, 1994). Aquatic vascular plants and algae compose a major part of their diet. Dead and decaying plant and animal matter is also consumed, however, this is probably not their main source of nourishment. Crayfish do not prey on larger animals, such as fish, but they have been known to prey on other crayfish which have recently moulted and are still soft (Crocker and Barr, 1968).
Return to Table of ContentsSymbiotic RelationshipsSymbiosis is the biological association of two individuals or populations of different species. Crayfish are involved in both commensalism, in which neither species is harmed , and parasitism, in which the crayfish is harmed and the other species benefits (Pennak, 1989).
Commensalism
The surface of the crayfish shell is used as a place of attachment for a wide variety
of organisms, such as ostracods and branchiobdellids (Crocker and Barr, 1968).
Parasitism
Crayfish are involved as hosts in a variety of protozoan, fluke, tapeworm,
and nematode cycles (Crocker and Barr, 1968).
Return to Table of ContentsHabitat of Ontario CrayfishOntario Crayfish inhabit a variety of freshwater ecosystems, the most common being lakes and streams. Some of the other habitats in which crayfish are found include, water logged fields, stagnant ditches, and subterranean cave waters (Barr, 1994; Crocker and Barr, 1968).
Crayfish typically conceal themselves in muddy water, among, aquatic vegetation, under rocks, or in underground burrows (Crocker and Barr, 1968). The burrowing crayfish are found only in fragile wetland areas, marshes, swamps, and ditches where soil is saturated with water for most of the year. The crayfish use their claws and tail to excavate the burrow and carry the mud to the surface. Some leave the mud at the entrance to the burrow, some move it elsewhere, and some build a clay chimney over the burrow entrance. The chimney can be upto 12 cm high and forms a good defense against terrestrial predators, such as snakes. The hole at the top may also be plugged with a ball of clay to provide more protection (Barr, 1994).
There is some evidence that most Ontario crayfish can burrow if necessary to escape from habitat that is drying out. They will dig very deep, straight burrows so they can follow the retreat of the water table (Barr, 1994).
There are at least nine species of closely related crayfish inhabiting Ontario (Barr, 1994). Table 2 indicates the most common habitats of these crayfish species. In the Hamilton Harbour ecosystem, crayfish are mostly found in rocky tributary streams and rivers, and rocky areas along the shoreline.
| Common Name and Species Name | Habitat |
| The Northern Clearwater Crayfish Orconectes propinquus |
rocky streams and rivers; shores of clear, stony ponds and lakes; has been observed to burrow |
| The Virile Crayfish Orconectes virilis |
rocky streams and rivers; some in slow moving streams with muddy substrates; some in deep stony bottomed lakes |
| The Calico Crayfish Orconectes immunis |
shallow, slow moving streams with muddy substrates and rooted aquatic vegetation; stagnant ponds and ditches; often burrow to escape drying habitats |
| The Appalachian Brook Crayfish Cambarus bartonii |
fast flowing, cool, rocky streams; lakes; brooks |
| The Robust Crayfish Cambarus robustus |
large rivers; fast streams; lakes |
| The Digger Crayfish Fallicambarus fodiens |
marshy fields; drainage ditches; marshes; ponds; burrowing species |
| The Rusty Crayfish Cambarus rusticus |
streams; rivers; lakes |
| The Obscure Crayfish Cambarus obscurus |
streams; rivers; lakes |
| The Meadow Crayfish Cambarus diogenes |
wet meadows; burrowing species |
Sources: Barr, 1994; Crocker and Barr, 1968
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| Source: University of Texas, 1997 |
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ReferencesBarr, D. Summer 1994. "Not Your Common Crayfish." Seasons.
Vol. 33, No. 2. Federation of Ontario Naturalists.
Bliss, D.E. 1990. Shrimps, Lobsters and Crabs: Their Fascinating Life Story. New York:
Columbia University Press.
Creed, R.P. Oct 1994. "Direct and indirect effects of crayfish grazing in a stream community."
Ecology. Vol. 75., Iss. 7.
Crocker, D.W., and D.W. Barr. 1968. Handbook of the
Crayfishes of Ontario. Life Sciences Miscellaneous Publications, Royal Ontario Museum.
Toronto: University of Toronto Press.
Lockwood, A.P.M. 1968. Aspects of the Physiology of Crustacea.
London: Oliver and Boyd.
Lodge, D.M., and M.W. Kershner. 1994. "Effects of omnivorous crayfish (orconectes rusticus)
on a freshwater littoral food web." Ecology. Vol. 75, Iss.5.
Miller, S.A., and J.P. Harley. 1992. Zoology: The Animal Kingdom (Volume III).
Dubuque, Iowa: Wm. C. Brown Publishers.
Pennak, R.W. 1989. Freshwater Invertebrates of the United States.
3rd ed. New York: John Wiley and Sons.
Snodgrass, R.E. 1965. A Textbook of Arthropod Anatomy. New York: Hafner
Publishing Co.
University of Texas. 1997. WWW site
URL: www.texas.edu/depts/tnhc/.www/crayfish.crayhome.html
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