Phylum
belongs in the clade with true tissues called
.
Phylum Cnidaria.
Cnidarians are diploblastic and may exist in polyp and medusa stages
in their life cycle.
Tentacles are armed with cnidocytes to capture prey.
class Hydrozoa
class Scyphozoa
class Cubozoa
class Anthozoa
Cnidaria exhibit a radial symmetry that can take the form of a sessile
polyp or a swimming 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.
The life cycle of the Cnidarian 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.
A cnidocyte is a specialized cell containing a stinging capsule called
nematocyst.
When the "trigger" in the nematocyst is stimulated by touch or by
chemicals, a coiled thread shoots out, puncturing and injecting poison
into prey.
Phylum Cnidaria, Class Hydrozoa.
Both medusa and polyp stages present; the polyps are often colonial.
Hydra eating (polyp):
Portuguese man-of-war (medusa):
Phylum Cnidaria, Class Scyphozoa.
Jellies,\ and sea nettles have free-swimming medusae.
The polyp stage is often absent or reduced.
Moon jelly: 
Thimble jellies:
Phylum Cnidaria, Class Cubozoa.
Box jellies and sea wasps have box-shaped medusae and complex eyes.
Their tentacles are highly toxic; some are more potent than cobra
venom.
Sea wasp: 
Phylum Cnidaria, Class Anthozoa.
Sea anemones, sea fans and most corals have only the polyp stage and
are often colonial and sessile.
Sea anemone:
Phylum
are flatworms with a gastrovascular cavity.
Phylum Platyhelminthes (flatworms).
class Turbellaria
class Trematoda
class Cestoidea
Phylum Platyhelminthes, Class
Turbellaria.
Planarians have a mouth at the tip of a pharynx to take food into the
gastrovascular cavity (intestines).
Waste is excreted through the mouth.
The nervous system is organized into two nerve cords and clustered in
anterior ganglia.
Eyespots (ocelli) can detect light.
Planaria:
Phylum Platyhelminthes, Class
Trematoda.
Trematodes (flukes) are parasites that use two suckers to attach to
primary host (human).
Sexual reproduction takes place in the primary host: a female fits
into a groove on the male's body.
Juveniles mature in intermediate hosts such as snails.
The motile larvae that escape from the intermediate host are called
"cercaria".
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.
Phylum
are soft-bodied animals.
Phylum Mollusca.
Molluscs include snails, clams, and octopuses.
class Gastropoda:
embryonic torsion.
class Bivalvia
class Cephalopoda
Molluscs have a body plan with three
main parts:
- Muscular foot for movement.
- Visceral mass that contains the organs.
- Mantle that secretes a shell, if present.
Phylum Mollusca, Class Gastropoda.
Snails and slugs secrete slime on which they crawl.
Slugs have lost their outer shell.
Nudibranchs are sea slugs that use gills for gas exchange.
Nudibranch predator:
Embryonic torsion in a gastropod. Because of torsion (twisting of the
visceral mass) during embryonic development, the digestive tract of a
mature gastropod is coiled and the anus is near the anterior end of
the animal.
Phylum Mollusca, Class Bivalvia.
Clams, mussels, scallops, oysters have a shell with two valves and
paired gills.
They feed by passing water through siphons, and often anchor
themselves in the substrate with their muscular foot.
Clam locomotion:
Phylum Mollusca, Class Cephalopoda.
Squids, octopuses, cuttlefish, chambered nautiluses are the only
molluscs that exhibit cephalization: development of a head.
They have a closed circulatory system that enables them to move
quickly by jet propulsion using siphons.
Tentacles are used to capture prey.
Phylum
are segmented worms with a true
.
Phylum Annelida.
Annelids are coelomates that exhibit segmentation in their body plan.
class Oligochaeta
class Polychaeta
class Hirudinea
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 with separate mouth and anus.
Circular and longitudinal muscles enable it to move by peristaltic
locomotion.
Earthworm locomotion:
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".
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.