Annelid.html: 33_01XmasTreeWorm.jpg
A Christmas tree worm, a marine invertebrate, Phylum Annelida.
animal.html: 33_07AnimalPhyla.jpg
anthozoa.html: 33_07CnidariaDiversityD.jpg
Phylum Cnidaria, Class Anthozoa.
Sea anemones, sea fans, most corals
have only the polyp stage and are often colonial and sessile.
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arachnid.html: 33_31Arachnids.jpg
Phylum Arthropoda, Class Cheliceriformes.
Horseshoe
crabs, scorpions, spiders,
ticks, mites have chelicerae and pedipalps in their mouth parts that may be modified as pincers.
They possess four pairs of legs.
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arthropoda.html: 33_29ArthropodAnatomy.jpg
External anatomy of an arthropod.
ascaris.html: 33_Ascaris.jpg
Phylum Nematoda, Class Ascaris.
Giant intestinal roundworms are a serious pig and human parasite in tropical areas with poor sanitation.
asteroidea.html: 33_40EchinodermDiversityA.jpg
Phylum Echinodermata, Class Asteroidea.
Sea stars have star-shaped body with multiple arms; mouth directed to substrate.
bivalve.html: 33_21ClamAnatomy.jpg
Phylum Mollusca, Class Bivalvia.
Clams, mussels, scallops,
oysters have a shell with two valves with paired gills.
They feed by passing water through siphons, and often anchor themselves in the substrate with their
muscular foot.
cephalopod.html: 33_22Cephalopoda.jpg
Phylum Mollusca, Class Cephalopoda.
Squids, octopuses, cuttlefish, chambered nautiluses
have tentacles to capture prey .
They are the only molluscs with a closed circulatory system that enables them to move quickly
by jet propulsion using siphons.
chiton.html: 33_17Chiton_U.jpg
Polyplacophora (chitons) are marine, have a shell with 8 plates, a muscular foot and
radula, but no head.
cnidaria.html: 33_05PolypMedusa.jpg
Cnidaria
possess tentacles armed with cnidocytes
to capture prey, and exhibit a radial symmetry that can take the form
of a sessile polyp or a floating medusa.
The gastrodermis lines a gastrovascular cavity for digestion;
a single opening to this cavity functions as both mouth and anus.
A gelatinous mesoglea is sandwiched between the epidermis and gastrodermis.
A simple nerve net comprises its nervous system.
cnidocyte.html: 33_06HydraCnidocyte.jpg
This type of cnidocyte contains a stinging capsule, the nematocyst,
which itself contains an inverted thread. When a “trigger” is stimulated by touch or by certain chemicals,
the thread shoots out, puncturing and injecting poison into prey.
concentricycloidea.html: 33_40EchinodermDiversityF.jpg
Phylum Echinodermata, Class Concentricycloidea.
Sea daisies have a disk-shaped body ringed with small spines.
crinoidea.html: 33_40EchinodermDiversityD.jpg
Phylum Echinodermata, Class Crinoidea.
Sea lilies, feather stars have feathered arms surrounding upward-pointing
mouth.
crustacea.html: 33_38CrustaceanDiversity.jpg
Phylum Arthropoda, Class Crustacea.
Crabs, shrimp,
barnacles
have two pairs of antennae and three or more pairs of legs.
Many are decapods and have 10 legs.
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cubozoa.html: 33_07CnidariaDiversityC.jpg
Phylum Cnidaria, Class Cubozoa.
Box jellies, sea wasps have box-shaped medusae and complex
eyes.
Their tentacles are highly toxic; some are more potent than cobra venom.
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earthworms.html: 33_23Earthworm_U.jpg
Phylum Annelida, Class Oligochaeta.
Earthworms
have "few chaetae" (setae), which are bristles made of chitin that aid in anchoring the body to burrow.
The body is segmented.
Circular and longitudinal muscles enable it it move by peristaltic locomotion.
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echinoderm.html: 33_39SeaStarAnatomy.jpg
Echinodermata. possess a bumpy or spiny skin that covers an endoskeleton.
The madreporite is used to filter water into a sea star's
water vascular system, which consists of a ring canal and five radial canals
and terminates in branches called tube feet.
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echinoidea.html: 33_40EchinodermDiversityC.jpg
Phylum Echinodermata, Class Echinoidea.
Sea urchins, sand dollars are roughly spherical or disk-shaped;
five rows of tube feet enable slow
movement.
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elephantiasis.html: 33_Elephantiasis.jpg
Elephantiasis is caused when a filarial nematode,
transmitted by mosquitoes, lodges in the lymphatic system.
fluke.html: 33_11BloodFlukeLifCycl.jpg
Phylum Platyhelminthes, Class Trematoda.
Trematodes (flukes) are parasites that use two suckers to attach to primary host;
symptoms include enlarged liver and spleen.
Sexual reproduction takes place in the primary host:
a female fits into a groove on the male’s body.
Most life cycles include intermediate hosts such as freshwater snails.
The motile larvae that escape from the intermediate host are called "cercaria".
gastropod-torsion.html: 33_19GastropodTorsion.jpg
Embryonic torsion in a gastropod.
Because of torsion (twisting of the visceral mass) during embryonic development,
the digestive tract is coiled and the anus is near the anterior end of the animal.
gastropod.html: 33_18GastropodDiversity_LP.jpg
Phylum Mollusca, Class Gastropoda.
Snails and slugs
secrete slime on which they crawl.
Nudibranchs are sea slugs that have lost their shell, and use gills for gas exchange.
A unique feature of gastropods is the process of torsion
during development.
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hexapoda.html: 33_35GrasshopperAnatomy.jpg
Phylum Arthropoda, Class Hexapoda.
Insects,
springtails
have three pairs of legs and usually two pairs of wings. The body is divided into head, thorax, abdomen.
holothuroidea.html: 33_40EchinodermDiversityE.jpg
Phylum Echinodermata, Class Holothuroidea.
Sea
cucumbers
have five rows of tube feet and additional tube feet modified as feeding tentacles.
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horseshoe.html: 33_30HorseshoeCrabs.jpg
Horseshoe crabs (Limulus polyphemus).
Common on the Atlantic and Gulf coasts of the United States, these “living fossils” have changed little in hundreds of
millions of years. They have survived from a rich diversity of cheliceriforms that once filled the seas.
hydrozoa.html: 33_07CnidariaDiversityA.jpg
Phylum Cnidaria, Class Hydrozoa.
Obelia,
man-of-war
) have both polyp and medusa stages in most species.
Polyp stage is often colonial, some cells may be specialized.
hydrozoan_cycle.html: 33_08ObeliaLifeCycle.jpg
The life cycle of the hydrozoan Obelia. alternates between a
sessile polyp stage and a swimming medusa stage.
Do not confuse this with the alternation of generations in plants in which
the haploid and diploid generations are both
multicellular.
In animals, only the unicellular gametes are haploid.
insect.html: 33_37InsectDiversityA.jpg
leech.html: 33_25Leech_UP.jpg
Phylum Annelida, Class Hirudinea.
Leeches have flattened segments with no chaetae.
Suckers at the anterior and posterior ends attach to food.
Some species such as Hirudo medicinalis secrete hirudin to prevent blood from coagulating,
and are used as medicinal leeches to drain blood from an injury.
mollusca.html: 33_21ClamAnatomy.jpg
Molluscs have a body plan with three main parts:
myriapoda.html: 33_33MilliCenti.jpg
Phylum Arthropoda, Class Myriapoda.
Millipedes (class Diplopoda) have two pairs of legs on each trunk segment.
Centipedes (class Chilopoda) have one pair of legs per trunk segment.
nautilus.html: 33_22Nautilus.jpg
nematoda.html: 33_26FreeLivingNematode_LP.jpg
Nematoda belong in the clade
Ecdysozoa.
They are covered with a tough exoskeleton (cuticle) which must be
shed or molted through a process called ecdysis as the animal grows.
nudibranch.html: 33_18Nudibranch.jpg
ophiuroidea.html: 33_40EchinodermDiversityB.jpg
Phylum Echinodermata, Class Ophiuroidea.
Brittle stars have a distinct central disk; long, flexible arms; tube feet lack suckers.
phylogeny.html: 33_02AnimalPhylogeny.jpg
Except for sponges (phyla Calcarea and Silicea), all animals have tissues and belong in Eumetazoa.
Most animals exhibit bilateral symmetry and are classified in
Bilateria.
polychaete.html: 33_24Polychaete.jpg
Phylum Annelida, Class Polychaeta.
These marine segmented worms have a well-developed head.
Each segment has a pair of parapodia (“almost feet”) with "many chaetae".
rotifera.html: 33_13Rotifer-L.jpg
Rotifers are smaller than many protists,
but are multicellular and have specialized organ systems.
The crown of cilia is a lophophore, placing them in the Lophotrochozoa.
Rotifers reproduce by parthenogenesis,
in which females produce offspring from unfertilized eggs; some species lack males entirely.
scallop.html: 33_20Scallop.jpg
This scallop has many eyes peering out from each half of its hinged shell.
scyphozoa.html: 33_07CnidariaDiversityB.jpg
Phylum Cnidaria, Class Scyphozoa.
Jellies, sea nettles have free-swimming medusae.
The polyp stage is often reduced.
Moon jelly
Thimble jellies
sponge.html: 33_04SpongeAnatomy.jpg
Sponges contain
calcareous (calcium carbonate) or siliceous (silica)
spicules
embedded in
spongin
that provide support.
Sponges are suspension feeders that lack true tissues, though they have a few specialized
cells.
sponge_spawn.html: 33_Purple_Vase_Sponge_Callyspongia_plicifera.jpg
Sponges lack true tissues and are suspension feeders.
Most exhibit sequential hermaphroditism, functioning first as one sex and then as the other;
males and females must release gametes
at the same time.
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tapeworm.html: 33_12TapewormAnatomy.jpg
Phylum Platyhelminthes, Class Cestoidea.
Tapeworms are parasites that use a scolex to attach to host intestines with hooks and suckers.
Many segments of proglottids produce eggs
and break off after fertilization.
trichinella.html: 33_27Trichinella.jpg
Phylum Nematoda, Class Trichinella.
Juveniles of Trichinella encysted in muscle can cause trichinosis
when they are ingested by eating undercooked pork or other meat.
In the intestine, juveniles mature into adults and mate, producing more juveniles, which encyst in muscles.
trilobite.html: 33_28Trilobite.jpg
A trilobite fossil.
Trilobites were common denizens of the shallow seas throughout the Paleozoic
era but disappeared with the great Permian extinctions about 250 million years ago.
turbellaria.html: 33_10PlanarianAnatomy.jpg
Phylum Platyhelminthes, Class Turbellaria.
Planarians have a mouth at the
tip of a pharynx to take food into the gastrovascular cavity (intestines).
Waste is egested through the mouth.
The nervous system is organized into two
nerve cords
and clustered in anterior
ganglia.
Eyespots (ocelli) can detect light.
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