Marine Crustaceans That Are Sessile

Subphylum Crustacea - the crustaceans

(crabs, shrimp, etc)

Defining features of the crustaceans:

Two pairs of antennae

In contrast, Arachnids have no antennae, and insects have one pair.

First pair of mouthparts are mandibles for biting and chewing

In contrast, Arachnids have chelicerae

Most species have 2 additional pairs of mouthparts called maxillae

Underside of a crab, showing mandibles:

Crustacean lifestyles and habitats:

Most are aquatic, including freshwater and marine habitats

Along with the annelids (which are especially important in the sediments), crustaceans are often among the most abundant and influential invertebrates in marine environments.

Some are terrestrial

Some terrestrial species live entire lives on land (e.g. terrestrial isopods - the pillbugs and sowbugs)

Many terrestrial species must return to water to breed, and have aquatic larvae (e.g. most terrestrial crabs)

The crustaceans include species that are:

predators (some are FIERCE predators!)

herbivores

scavengers

filter feeders

parasites

In other words, this phylum does it all!

Unlike many of the other animal groups, marine crustaceans DO NOT release eggs and sperm into water.

crustaceans have internal fertilization

mating occurs just after female molts, while exoskeleton still soft

crustaceans normally carry egg until they hatch, and release larvae into water.

most marine crustaceans have planktonic larval stages

some exceptions:

amphipods and isopods carry young until they are well-developed miniature versions of adults.

A bit of crustacean anatomy

Diagram of major organ systems:

Circulatory (red)

Digestive (orange)

Ventral nerve cord (bright green)

Excretory (blue-green)

Reproductive (dark pink)

Circulatory and respiratory systems:

Heart (including small holes called ostia through which "blood" enters heart):

Cross-section of body (e.g. of a crayfish) showing circulatory system (red), digestive system (orange), and gills (lavendar-purple):

Note: water is moved through gill chamber by modified appendages on each side of head called gill bailers . Water is drawn through openings near lower rear of animal (just in front of tail) on each side of the body, and it exits gill chamber through openings on each side of the lower portion of the head, on either side of the mouth.

Dissected crab (that had been preserved in formaldehyde, with pink latex injected into circulatory system), showing heart (pink thing in center), gills (sort of pink things on left and right), gastric mill (the object below the heart in this photo). Note: the head region of crab is facing bottom of picture.

A sampling of some of the major crustacean groups:

Class Branchiopoda - water fleas, brine shrimp, fairy shrimp, etc.

Cladocerans -"Water fleas" (e.g. Daphnia)

very common filter feeders

most species freshwater

"hop" through water propelled by antennae

most species parthenogenic (and all female) when conditions are good, males only present when conditions deteriorating.

sexual reproduction results in "resting eggs" resistant to drying and freezing.

Nice photos of Cladocerans can be found at:

Cladocera web site: http:default.html

Brine Shrimp (popularly known as "sea monkeys") - very cool animals!

don't live in the sea

don't look like most of the photos found here -> http://www.sea-monkeys.com/

live in hypersaline environments (e.g. Great Salt Lake, Utah)

major form of animal life (just about ONLY animal) in Great Salt Lake.

"resting eggs" harvested in vast quantities

hatch in about 24 hours in saltwater, providing live larvae invaluable in aquaculture for feeding baby fish

brine shrimp egg harvesting and sales is a big business (e.g. see http://www.brineshrimpdirect.com/ )

adult shrimp harvested and sold frozen as fish food

Here is a live adult female (these are lovely creatures when alive!):

in temporary freshwater bodies of water (that dry up in summer), very similar animals known as fairy shrimp can be found in the Spring.

Class Ostracoda - the ostracods, or seed shrimp

major group in freshwater and marine habitats

look like bivalve with shrimp body inside

antennae stick out at front, legs reach out as animal scurries about

If you are really inspired about ostracods, here is an Australian site with more info: Ostracods: http:ostbiol.html

Class Copepoda - the copepods

This is one of the most diverse classes of crustaceans- over 7500 species!

Aquatic, both freshwater and marine

Extremely abundant

Many are planktonic and play major roles in marine ecosystems

Many are sort of teardrop shaped with large antennae that propell them in a jerky start and stop sort of motion (this sort of movement is very typical of many copepods)

predators, filter-feeders (often feeding on planktonic algae), etc.

Copepod showing water flow patterns that aid in food capture:

Copepod with paired egg sacs:

Photos of some freshwater copepods can be found here: Freshwater copepod photos: http:zoop-copep.htm

Some copepods are parasitic on fish. These look like crustaceans when larvae, but are worm-like as adults!

See: Lernea sp. (anchor worms)

Class Cirripedia - the barnacles

bizarre, sessile, filterfeeding crustaceans

"A shrimp that stands on its head and kicks food into its mouth with its feet"

all species are marine

very common animals, attached to all sorts of things, including rocks, wood, clams, crabs, sea turtles, whales.....

have motile larvae that look like typical crustacean larvae

Diagrams of adult goose barnacles (most other barnacles don;t have this sort of muscular stalk):

Additional barnacle photos: Australian Barnacle gallery

Some barnacles are parasitic....and really bizzare parasites at that!

e.g., Sacculina, a parasite of crabs:

see Diagram of Sacculina

also see: Malin Werner-Sacculina researcher (includes photos of Sacculina larvae)

See Barnacles: Aquarium Frontiers Library if you would like more information on barnacles, including the really strange parasitic ones (optional reading).

Class Malacostraca - crabs, lobsters, shrimp, and others

almost 3/4 of all known crustaceans

includes the largest crustaceans

Here are a few of the major orders:

Order Decapoda - the decapods

Decapod means "ten legged" (though often first pair are claws, not walking legs)

at least 8500 described species (1/3 of the known crustaceans)

marine, freshwater, land

very diverse lifestyles and diets (just about everything you can imagine)

this is the most familiar group of crustaceans, including most of the larger crustaceans, including:
Shrimp - adapted for swimming: Nice shrimp photos

Crabs - adapted for walking: Nice crab photos
tail is reduced and curled under body

Lobsters and crayfish - intermediate: a few photos

others

Order Amphipoda - the Amphiods

more than 5500 species

mostly small in size

marine, freshwater, a few on land (on beaches)

herbivores and scavengers mostly, some predators and parasites

COMMON animals

typically laterally compressed

A typical amphipod:

Freshwater amphipods like the one pictured above are quite small (average length usually about 1/2 inch or smaller, depending on species) but can be exceedingly abundant (dozens per square meter....or even hundreds per square meter sometimes!), and are important food for many animals (fish, birds, etc).
In Minnesota, amphipods living in marshes and other wetlands are particularly important for migrating Lesser and Greater Scaups - ducks with blue bills that are commonly refered to as "bluebills"

Bluebill populations are declining, and shrinking amphipod populations seem to be the cause.
An article on bluebills and their dependence on amphipods can be found here ---> http://www.dnr.state.mn.us/volunteer/sepoct07/bluebills.html

A slide show showing these birds can be found here: http://www.dnr.state.mn.us/volunteer/sepoct07/bluebills_slideshow.html

Order Isopoda - the Isopods

more than 4000 species

mostly marine, but some very commons ones in freshwater and on land
the terrestrial isopods (pillbugs and sowbugs) are the only fully terrestrial crustaceans in most areas.
For more info see: Terrestrial isopods: http:isoinfo.htm

mostly scavengers, omnivores, but some predators and parasites

dorsoventrally flattened (a major thing that distinguishes them from the amphipods)

Diagrams of typical isopods (top and bottom):

Photos and info re: nasty fish predators/parasites that are isopods:
Parasitic isopod on fish: http:page.cgi?list=Damsels&filename=A7056.jpg

Article on isopods by Ron Shimek....parasitic/carnivorous isopods are discussed at end of article: http://reefkeeping.com/issues/2002-05/rs/index.htm

Also see photos of giant deep sea isopods:

http://www.abc.net.au/science/news/stories/s812802.htm

http://www.whozoo.org/Anlife2001/chelsy/clh_Bathynomus.htm

Are there other orders in this class?

YES...lots of others

too many to go into here!

A few final crustacean tidbits

(sorry, no shrimp sauce to go with these tasty morsels of knowledge!)

A few amazing crustaceans:

Japansese spider crab:

See also: http://www.glf.dfo-mpo.gc.ca/sci-sci/crab-crab/images/ph_bigcrab-e.jpg

Mantis shrimp (stomotopods) - truly one of the pinnacles of arthropod evolution!
What are stomatopods?

What's Special about Stomatopods?

Stomatopods in Multimedia - some really cool film clips