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Phylum Arthropoda—means “jointed feet/legs” Class Crustacea—named for their hard exoskeleton •Segmented protostome coelomates, with a hard exoskeleton made of chitin •Usually divided into three body regions, head, thorax and abdomen •Jointed appendages primitively biramous, and may be present on all body regions •All species have two pr antennae, mandible, two pairs of maxillae at some stage •dioecious 1st ant 2nd ant Generalized biramous appendage mandible •Most crustacea hatch from an egg into a nauplius larva with biramous appendages a nauplius larva with 1st antennae, 2nd antennae, and mandible –all swimming appendages at this stage Order Copepoda—”kope” means oar and “poda” means foot in greek •More or less cylindrical segmented body (0.5-2mm in length) •Segmented appendages on head and thorax, and two setose caudal rami •Have a simple single anterior eye & a pr of conspicuous 1st antennae used for swimming •Very diverse group (>6000 species) •planktonic or benthic organisms in all marine and fw environments 3 suborders of free living copepods in dorsal view >2300 spp 25% FW >450 spp 25% FW >2800 spp 10% FW The two most common suborders in freshwater are the Cyclopoida and Calanoida Cyclopoida In calanoids the prosome contains six segments, in cyclopoids only five urosome prosome Articulation point The prosome incluses the, head and most of the thorax The urosome includes the posterior thoracic segment (s) and the abdomen Calanoida Diacyclops thomasi—a predatory cyclopoid Note caudal ramus with 2 large tail spines and two setae Epischura—an omnivorous calanoid Note: female abodomen “bent” to the right, caudal ramus with three stout setae Diaptomus sicilis—a herbivorous calanoid 5th thoracic leg of the male Each caudal ramus with 5 long setae The copepod body—head appendages, antennae & mouthparts ♂ ♀ ♂antennule modified for clasping the female http://images.google.ca/imgres?imgurl=http://www.uni-oldenburg.de/zoomorphology/Graphiken/tickles.gif&imgrefurl=http://www.unioldenburg.de/zoomorphology/morphology.html&h=81&w=143&sz=2&hl=en&start=18&tbnid=rjHXNvDkKHGikM:&tbnh=53&tbnw=94&prev=/images%3Fq%3Dco pepod%2Bbody%26svnum%3D10%26hl%3Den%26lr%3D%26sa%3DG The copepod body—thoracic legs ♀ ♂ ♀ Peraeopods 1-4 are swimming legs Peraeopod 5 is adapted for handling the spermatophore http://images.google.ca/imgres?imgurl=http://www.uni-oldenburg.de/zoomorphology/Graphiken/tickles.gif&imgrefurl=http://www.unioldenburg.de/zoomorphology/morphology.html&h=81&w=143&sz=2&hl=en&start=18&tbnid=rjHXNvDkKHGikM:&tbnh=53&tbnw=94&prev=/images%3Fq%3Dco pepod%2Bbody%26svnum%3D10%26hl%3Den%26lr%3D%26sa%3DG Filter-feeding by a calanoid copepod •Copepods filter-feed by generating currents with their 1st antennae and their thoracic appendages.. •Water from small eddy currents around the mouthparts is drawn over the fine setae of the maxillae, where small algae are collected and moved to the mouth. http://www.ucmp.berkeley.edu/arthropoda/crustacea/images/copepoda03.jpg Copepod reproduction --males produce spermatophores and deposit them in the genital area of the female Eggs from the egg sac are released when the female moults, and the sperm from the spermatophore enter the female genital pore and fertilize the next batch of eggs A female copepod,with two egg sacs, carrying the spermatophore, deposited by a male, with her genital appendages spermatophore http://www.uni-oldenburg.de/zoomorphology/Spermatophore.html Precopula—a male copepod grasps the female with his large 1st antennae http://www.uni-oldenburg.de/zoomorphology/Praecopula1.html Copepod nauplius Copepodite stage •There are six naupliar stages, and 5 copepodite stages which resemble adult copepods except that they are not sexually mature •The life cycle usually requires at least a month, but In some species a prolonged diapause can occur in some of the copepodite stages •Calanoids and harpacticoids can produce both resting eggs and eggs that hatch right away—the rest can range of a developmental delay to a fully encysted diapause stage of several months. http://fmel.ifas.ufl.edu/kits/cycle.htm Copepods can sometimes be very colourful—mostly as a result of carotenoids that they obtain from their food (algae) and accumulate Copepods from fishless ponds Copepods from ponds with fish The effect of zooplanktivorous fish onvertical migration of herbivorous zooplankton Order Cladocera—common name “water fleas”-•a thin bivalve carapace usually enclosing the body except the head, used as a brood chamber •4-6 flattened leaf-like thoracic appendages with setae used for filter-feeding •2nd antennae large and used for swimming—a jerky up and down motion •1st antennae (antennules) small contains sense organs •no larval stage, newborns resemble adults •Life cycle alternating between parthenogenesis and sexual stage 1-2nd antenna 2-compound eye 3-digestive gland 4-esophagus 5-heart 6-ocellus eye 7-antennule 8-thoracic (filtering) legs 9-ovary 10-anal claws (furca) 11-postabdomen 12-brood chamber 13-carapace 14-rudder bristle 15-tail spine http://www.cladocera.de/cladocera/cladocera.html Fecal pellets Zooplankton such as Daphnia filter-feed using currents generated by their thoracic appendages. Fecal pellets sediment rapidly to the bottom Male cladocera are usually produced from parthenogenetic eggs under adverse environmental conditions Males are usually much smaller than females have a reduced beak (rostrum), no brood chamber •elongated antennule •A grasping appendage with a hook •after being fertilized by a male the female produces an ephippial egg in her brood chamber Ephippial eggs are special resistant eggs that have a resistent coat made from the brood pouch. They can lie dormant in the mud for months or sometimes even years. http://images.google.ca/imgres?imgurl=http://www.microscopyuk.org.uk/mag/imgmar02/daphnia_male.jpg&imgrefurl=http://www.microscopy uk.org.uk/mag/artmar02/waterfleamale.html&h=450&w=321&sz=33&hl=en&start=2&tbnid=56Ssww0b39aoM:&tbnh=127&tbnw=91&prev=/images%3Fq%3Dmale%2Bdaphnia%26svnum%3D10%26hl%3Den%26lr%3D%26sa%3DG Bosminidae--Bosmina First antennae large, extending forward from the rostrum in the form of a tusk Chydoridae, Chydrorus—carapace projecting forward into a blunt rostrum and covering the head with a shield. Daphniidae, Ceriodaphnia—head small and depressed, rostrum absent, cervical sinus present Polyphemidae, Polyphemus Note that the carapace covers only the brood chamber and not the thoracic appendages, tail spine fairly long A predator on small zooplankton Note the carapace covers only the brood sac and not the swimming legs This is a predator on other zooplankton Around 10 mm long The tail spine is very long, with a series of barbs—protection from predation by small fish Another Polyphemid, Bythotrephes—an exotic invader from Asia. Note the forward projecting head shield of the carapace Very large postabdomen and anal claw Eurycercus—a large (>5mm) littoral chydorid Crawls around on vegetation and feeds on epiphytes mainly Chydorid cladocera feeding on epiphytes from submerged macrophytes http://www.hi.is/~arnie/ecercus.gif Leptodora Polyphemus Holopedium Sida Diaphanosoma Leptodora Polyphemus Holopedium Sida Diaphanosoma Chydoridae Daphnidae Bosminidae Macrothricidae Moinidae Daphnia Ceriodaphnia Scapholeberis Simocephalus Daphnia Ceriodaphnia Scapholeberis Simocephalus Daphnia Ceriodaphnia Scapholeberis Simocephalus Order Notostraca—”shield shell” (3-4cm) •Common name tadpole shrimp, 12 species •Cephalothorax covered by a large shield-like carapace •1st antenna small uniramous, 2nd antenna reduced or absent, maxillipeds absent •, the 1st pr thoracic appendages enlarged and protruding from under the carapace •next 10pr thoracic appendages phyllopodous (leaf-like) swimming/feeding legs, plus many smaller appendages on the abdomen •Telson with 2 long whip like caudal rami •Can be either dioecious, hermaphrodites or parthenogenetic, most often the latter. •Freshwater, brackish or saline temporary ponds, shallow, fishless lakes, omnivores •Worldwide distribution, some species are pests in rice paddies, others are endangered species •Well adapted to temporary ponds because their eggs can diapause and dry up completely •“living fossils” a fossil record extends back 350 million years (Devonian) •Two genera Triops and Lepidurus Triops cancriformis—the oldest extant species on the planet The modern species is identical to fossils identified from the Triassic http://www.aquarienclub.de/pics/triops_cancriformis.jpg Triops, resting egg Day 1, metanauplius Day 3 shield present Day 6 subadult Day 2 metanauplius Adult Triops 2-3 weeks The eggs can survive drying and freezing and can last in dried up ponds for decades Temporary pond habitat http://www.cst.cmich.edu/users/mcnau1as/zooplankton%20web/Triops/images/triops.jpg A. Dorsal anatomy Note the three eyes, 2 compound, and median ocellus, and the depressions for the maxillary gland B. Ventral anatomy C. The maxilla D. Thoracic appendage used for swimming and channeling food to the mouth http://www.cst.cmich.edu/users/mcnau1as/zooplankton%20web/Triops/images/triops.jpg Order Anostraca—without hard shell (1-15cm) •Common name “fairy shrimp”, “brine shrimp” •Body soft and flexible, not covered by a shell •1st & 2nd antennae uniramous, sometimes prehensile •>11pr of phyllopodous (leaf-like) swimming/feeding legs on the thorax •Usually dioecious, except some brine shrimp which are parthenogenetic •Freshwater, brackish or saline temporary ponds, shallow, fishless lakes, omnivores or carnivores •Worldwide distribution •Well adapted to temporary ponds because their eggs can diapause and dry up completely •“living fossils” a fossil record extends back 500 million years •8 families eg •Artemidae •Branchinectidae •A few dozen spp. Artemia—the brine shrimp found in hypersaline inland waters eg the Dead Sea or the Great Salt Lake, Utah. Artemia showing the extended distal “blade” of the second antenna Most Artemia are parthenogenetic females, but some populations are dioecious Order Conchostraca—”clam shell” (1-15cm) •Common name “clam shrimp”, •With a dorsally hinged bivalved carapace completely enclosing the head and body, including the legs •1st antennae uniramous, 2nd antennae biramous •>11pr of phyllopodous (leaf-like) swimming/feeding legs on the thorax •Dioecious or parthenogenetic •Freshwater, brackish or saline temporary ponds, shallow, fishless lakes •Filter feeders/ omnivores •Worldwide distribution •Well adapted to temporary ponds because their drought resistant eggs •fossil record extends back to the Devonian •7 families, >30 spp •Eg Lynceidae Lynceus is a common Conchostracan in Alberta http://animaldiversity.ummz.umich.edu/site/resources/Grzimek_inverts/Conchostraca/Lynceus_gracilicornis.jpg/me dium.jpg http://crustacea.nhm.org/peet/conchostraca/media/morph.jpg Hypothesized evolutionary relationships of the various Branchiopod orders These Crustacea were abundant in the sea long before terrestrial and inland water habitats were colonized by plants and animals. Why do you think they have survived much longer than most other Paleozoic animal groups Cladocera Anostraca Notostraca Conchostraca Ostracoda Branchiura Cladocera Copepoda Malacostraca http://www.snv.jussieu.fr/bmedia/PetitBuffon/crustaces/ostracodes/284BB.jpg The famous white cliffs of Dover are composed mainly of Ostracod fossils http://www.uky.edu/OtherOrgs/KPS/images/ostracodnelson.jpg Order Ostracoda—”ostracon” means shell in Greek •Abundant in freshwater and marine environments. > 8000 living species. Freshwater ostracods are usually smaller than 1 mm. > 10,000 or so fossil species from the Late Cambrian period (about 500 million years ago) to recent times. •Their great abundance and widespread distribution have made them useful index fossils for dating marine sediments, notably in oil exploration. •the most complete fossil record of any crustacean group. •littoral zone among the submerged plants, but also in the profundal benthos. •swim smoothly with appendages extended from between the two halves of their carapace. • When disturbed, they withdraw their limbs and clamp the halves of their tiny shells tightly together. •Sexes are separate and females brood eggs in the chamber of the carapace. •males must tranfer sperm to the female before the eggs are laid and a special long leg is used to do this. •Some freshwater species are parthenogenetic, and males of these species are unknown. Ostracods are little more than a head. •the typical 5 pr of crustacean head appendages, •but only 1-3 pr of thoracic appendages •and a caudal fork at the posterior end. Ostracods have no growth rings on the carapace because it is shed at each moult Cypris is shown in typical feeding mode, with its shell opened to allow the mouth parts to graze epiphytes from a filament of Oedogonium, propelled by two pairs of legs bearing long claws and a caudal furca. The prominent black spot of the single eye can be seen near the hinge of the shell. http://www.micrographia.com/specbiol/crustac/ostraco/ostr0100/cypris00.htm Candona species are generally white all over and live in the profundal sediments of lakes Candona candida—a species found in profundal lake sediments http://biology.missouristate.edu/ostracods/Ostracod%20Website/Candona%20distincta%202a.jpg Candona decora Candona ohioensis Candona caudata Candona indigena Cyclocypris ovum Cyclocypris ampla Order Amphipoda—”amphi means both” Mostly marine benthic organisms,>7000 spp •>100 fw species, adults 5-30 mm long •elongate and more or less compressed laterally. no carapace, •head with chewing mouthparts, omnivores (algae detritus, large specimens carnivorous) •2 pr antennae, 1pr mandibles, 2 pr maxillae • 8 thoracic appendages •1pr maxillipeds, 2pr gnathopods, 5 pr walking/swimming legs . •5 pr pleopods, abdominal appendages •Eggs held within a brood pouch on the ventral side of the females thorax—young leave the pouch when the female moults •Males have enlarged gnathopods for holding the female during precopula Amphipod appendages Mouthparts of an amphipod http://www.faunaitalia.it/keys/images/gammar1.gif In some species the enlarged 2nd gnathopod of the male is very conspicuous Gammarus in precopula, the male will carry the female for about a week or so until she moults, at which point he will insert the spermatophore http://www.shef.ac.uk/aps/mbiolsci/amy/gammarus.jpg Gammarus fasciatus, the most common gammarid in eastern Canada Gammarus lacustris—found throughout the northern hemisphere in glaciated regions, the only gammarid in Alberta, http://www.usask.ca/biology/skabugs/Candlelakebugs/CLcrustacea/gammarus.JPG Hyalella azteca—found throughout North and South America One of the two amphipod species found in Alberta Diporeia, a profundal benthic amphipod in large lakes This is what we call a glacial relict, because it only occurs in large lakes that were once part of a proglacial lake. Proglacial lakes •Following the retreat of the last glaciation most of the Canadian landscape was covered by proglacial lakes •Species tolerant of coldwater (salmonid and coregonids) became very widespread. •Opportunities for dispersal of cool and warmwater species were much more limited because these water bodies disappeared with the ice. Waterton Lakes were at one time part of a proglacial lake system, and the upper lake has both Diporeia and Mysis. Amphipods can feed and grow during winter on under ice diatoms http://www.oceanexplorer.noaa.gov/explorations/02arctic/logs/mis_sum_ice/media/amphipod_600.jpg Lake Baikal—the largest and oldest lake in the world, > 1700 m deep Has more than 270 species of amphipods over 95% of which occur nowhere else Lake Baikal has a rich endemic fauna of molluscs and fish as well, and even has its own endemic seal population http://www.raphaelk.co.uk/web%20pics/Russia/first/Lake%20Baikal.jpg Endemic amphipods of Lake Baikal Pallasea cancellus Acanthogammarus maximus Paragarjajewia petersi Odontogammarus calcaratus Boeckaxelia potanini http://www.naturalsciences.be/amphi/eulimnogam.htm Order Mysidacea—oppossum shrimp Free swimming, shrimp like crustaceans (1.5-3 cm) >800 species mostly marine in shallow coastal waters, and some in the deep sea—mostly omnivorous A few have invaded freshwaters ( around 25) •Eyes stalked. Carapace covering the thorax •9 pr thoracic appendages (1pr maxillipeds, 8pr biramous swimming legs enclosing the marsupium—brood chamber) •The marsupium is formed from a set of interlocking setose plates projecting medially from the basal segments of the thoracic appendages. •The eggs which are fertilized by a spermatophore as they are laid in to the pouch, hatch inside and the young, which resemble immature adults are carried in the pouch before being released. •5 pr of biramous abdominal appendages (pleopods), some of which are modified for insertion of the spermatophore •1pr of uropods at the posterior end containing a “statocyst” between the endopods—a balance organ, a fluid-filled sac with tiny granules and innervated tiny hairs. •Dioecious, mating usually occurs in large aggregations Mysids are important prey for pelagic fish, but they are well defended Mysids are quite transparent, and when there is little light they are hard for fish to see They vertically migrate, coming up at night to feed on zooplantkon such as Daphnia, and go back down at first light. During the daytime they hang out deep in the water column, near the bottom or even buried in the sediment, depending on how much light there is. Freshwater mysids are also important glacial relicts and have a restricted range because of this. They have however been introduced to many lakes because fisheries managers thought that this would improve fisheries yields This has largely backfired because Mysis tends to compete with epilimnetic zooplanktivorous fish, and because of their vertical migrations are difficult for these fish to consume. Map of the Southern Extent of glaciation in North America http://www.nationalatlas.gov/articles/geology/features/glaciallimit.html Glacial Lakes in Montana at the southern margin of the glaciers Note the separation of the Cordilleran and the Continental Glacier near the continental divide Also note the series of glacial lakes that form along the southern margin of the continental glacier from the damming of tributaries of the Missouri River. http://formontana.net/shores.html Map of Montana showing the southern boundaries of the Cordilleran and Continental glaciers http://images.statemaster.com/images/maps/MT.jpg Proglacial lakes in southwestern Alberta and Montana (around 12,000 Bp) western extent of the continental glacier Present Waterton lakes Probable Waterton glacial lake at the height of the Wisconsin glaciation >12,000 yr bp. This lake would have been fed by the St.Mary’s, Belly, and the Waterton Rivers This lake likely contained Mysis, Diporeia, deepwater sculpin, burbot, lake trout, lake whitefish, pygmy whitefish, probably artic grayling, sticklebacks, and several species of suckers. Eastern extent of the cordilleran glaciers Genetic studies indicate that many lake trout populations across western Canada came from this glacial refugium For a genetic study of lake trout that disucusses the contribution of genes from the Waterton Refugium, see History and evolution of lake trout in Shield lakes: past and future challenges Chris C. Wilson Ontario Ministry of Natural Resources Nicholas E. Mandrak Department of Fisheries and Oceans http://www.nrdpfc.ca/pubs/Wilson%20and%20Mandrak%202003%20(lake%20trout%20book%20chapter).pdf This is a book chapter not a journal article. A PDF of it can be obtained from the above website address. Glacial Lake Missoula around 13,000 bp Lake Missoula formed from the blockage of the northern fork of the Missouri River by glaciers. This lake filled up and crossed over the continental divide and discharged periodically through Washington state to the Pacific Ocean in a massive cascade. This happened every 50 yr or so for at least a thousand years. Some of the shorelines of this lake were as high as 4200 ft elevation. Order Decapoda—shrimps, crabs, lobsters,crayfish •Name means 10 legs—i.e 5pr. Of walking legs •shrimp like crustaceans (2-15 cm) •>8000 species mostly marine and benthic, some pelagic—mostly omnivorous •Some shrimps, crayfish and crabs have invaded freshwaters (>300 spp mostly crayfish, 1 present in Alberta Orconectes virilis) •The Cambaridae is believed to have branched off from marine lobsters and invaded freshwater during the late Cretaceous and diversified in rivers and lakes of NA, Europe and Asia. •Eyes stalked. Carapace covering the cephalothorax and enclosing the gills—branchial chamber •Rostrum present plus 19 pr of appendages Orconectes virilis •5 head appendages, 8 thoracic appendages (3pr maxillipeds, 5pr of walking legs, 1st pr chelate, all 8 with gills at the base) •5 pr of biramous abdominal appendages (pleopods), 1st pr of which are modified in the male for copulation (hemipenes). 1pr of biramous flat uropods and a telson at the posterior end. •All species dioecious, •Crayfish—Cambaridae, Astacidae, Parastacidae—in fw and estuaries. •Crayfish copulate in fall, eggs are carried >50 on the abdomen of the female, and hatch in the spring as juveniles—no larval stage and carry their newly hatched young under their abdomen. •After the second molt the young leave the mother as 3-4 wk old juveniles. Usually about 10 molts/yr may live for up to 8yr. http://asm.wku.edu/faculty/Lienesch/225/225images/crayext2.jpg O. virilus range in Alberta •In 1980, it was confined to the lakes and streams of the Beaver River drainage—a tributary of the Churchill R which flows across N. Sask and Manitoba into Hudson Bay. •Since then it has spread up the North and South Saskatchewan rivers and has become quite abundant as far west as Edmonton and Lethbridge. •Why has its distribution expanded so much in recent years? Although the lobster (Homaridae) is a close marine relative of the Cambaridae, the life cycle is very different and probably represents the ancestral pattern from which the crayfish life cycle evolved. Immature adult Post larva Mysis larva •Lobsters produce thousands of small eggs, which leave the mother immediately upon hatching. •It hatches into a planktonic larva which resembles a mysis and feeds on plankton and is dispersed passively by ocean currents. Thus its ecological niche as a larva is completely different from the adult. •They invest less energy into each egg than a crayfish does, but the tiny planktonic larvae can make up the difference by feeding themselves and growing as they drift. •After about 10 days or so it becomes a postlarva and settles to the substrate to become a benthic adult lobster. •Young lobsters could end up settling hundreds of km from their mother because of the scale of movement made possible by having larvae that drift within ocean currents. A young crayfish, on the other hand, will not end up dispersing very far from its mother. http://mainegov-images.informe.org/dmr/rm/aquarium/teachers_guide/lobster_internal_anatomy.jpg Freshwater shrimp—Palaemonetes •Adult size about 5 cm, live about 1yr and die after reproducing— semelparous •The freshwater shrimps exhibit direct development (no planktonic larva in its life cycle) just like the crayfish •Large eggs hatch into juvenile shrimp that remain attached to the mothers abdomen for several weeks. Most of these species are found in the US, Mexico and Central America http://www.anemoon.org/spuisluis/Palvar_01.jpg Contrast the freshwater shrimp life cycle with that of coastal marine shrimp •Marine shrimp hatch into a nauplius, metamorphose to a protozoea which remains planktonic drifting in ocean currents. •It then becomes a mysis larva which seeks out nearshore areas, settling on the outgoing tide and dispersing on the ingoing tide. •Juvenile post larve develop into young adults in esturaries and inside barrier islands. Full grown adults return to sea to mate and spawn. •Just like the lobster, the larval niche is planktonic, and again, the marine shrimps can disperse over considerable distances because of their passively drifting marine larvae. Their freshwater relatives have again simplified their life cycles (no planktonic stage, and reduced the spatial scale of dispersal). •Crabs are also part of the Decapoda and they have the same basic appendage array that crayfish and shrimp have, with the exception that their abdomen is much reduced and folded in under the carapace. •While most crabs are marine, freshwater crabs of the family (Potamidae) are common in Asia, Africa, Central and South America— all places where crayfish are not present. •Like other freshwater decapods the freshwater forms have abandoned their ancestral marine life cycle in favour of direct development •They also lay fewer larger eggs and retain the young on their abdomen for several weeks after they hatch. •No native freshwater crabs are found in NA, however, the blue crab has expanded its freshwater range in NE US, and the Asian mitten crab has become common in S. California rivers. http://www.nmu.edu/biology/Neil/MainFWC-website/assets/Life%20Cycle.GIF The fw crab life cycle •Few large eggs •hatch as immature adults—no zoea or megalops The zoogeography of the freshwater crabs •Freshwater crabs (mostly Potamidae) are found in SE Asia, the Indo-Pacifc, Australia, Africa, and C and S America. •They are distinctly absent from N America, most of Europe, and Siberia, areas occupied by Crayfish suggesting a possible competitive interaction between the two groups at some point in their evolutionary history. http://www.nmu.edu/biology/Neil/MainFWC-website/FWCphylogeny.html •There is very minimal overlap between fw crabs and the Cambaridae and Astacidae (slight amount in N.Asia, Eurasia, and C. America), however the Parastacidae overlap with crabs in Australia, Madagascar. •Recently some very old crayfish fossils, have been found on Antarctica (Permian)> 100 my old, extending the known fossil history of crayfish by over 65 my. http://tolweb.org/tree/ToLimages/world_dist.gif The blue crab is the most common crab on the east coast of NA, and its life cycle is similar to other marine crabs, which more or less resembles that of marine shrimp and lobster. •They lay thousands of tiny eggs, which leave the parent upon hatching. •Hatch into a planktonic zoea larva •Metamorphose into a megalopa, which settles and then a postlarval juvenile stage •Immature adults migrate a considerable distance up rivers, but adults always return to spawn at sea. Close-up of a crab zoea larva Adult blue crab http://www.serc.si.edu/education/resources/bluecrab/images/L_lifecycle_jpg.jpg A west coast invader has also appeared. Mitten crabs form extensive burrow networks in stream banks causing bank destabilization and increased erosion Eriocheir sinensis The Chinese mitten crab has been introduced to Britain, continental Europe, and recently California--in boat ballast or as imported seafood, possibly intentional release. •It was first detected in the San Francisco Bay in 1992. •Distribution expanded rapidly throughout the estuary and river systems over the next few years. •The crab is unique because adult crabs reproduce in brackish or salt water in winter and juvenile crabs migrate upstream to freshwater in spring. Mitten crabs reside in freshwater for as long as five years. •In late summer and fall, mature adults begin to migrate downstream to brackish water, where they reproduce. They die soon after reproduction. http://cswgcin.nbii.org/(xeoewduktclnluzafw0qy245)/utility/image.aspx?ImageName=mitten2 The planktonic zoea larvae The Chinese mitten crab has a fairly typical crab life cycle except that juveniles and adults makes extensive upstream migrations following the settlement of the postlarvae. Although it can life for up to 5 years in freshwater and, as a result, travel a long way up the rivers, it ultimately has to return to the sea to reproduce, and this will limit the extent to which it can colonize inland water habitats, since the young will have to recolonize the habitat that their parents did. How would this life cycle have to change in order to allow the mitten crab to truly colonize fresh water habitats? •Order Isopoda •Mostly terrestrial species but marine and freshwater taxa are also common, omnivorous scavengers. •Body dorsoventrally flattened Asellus spp. •Head with 2 pr antennae (1st Ant longer, 2nd short), mandibles, and 2pr maxillae. •7 thoracic segments with walking legs—move by slow crawling •A distinct telson with 2 biramous uropods. Dioecious, eggs develop in a ventral pouch on female, hatch as immature adults, and stay on the mother for a few moults. •No aquatic isopods have as yet been reported from Alberta. http://www.ens-newswire.com/ens/apr2005/20050404_musselmap.jpg