Download Phylum Arthropoda—means “jointed feet/legs”

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