Download I. Structure - Biology Diva

29.1 – Sponges (phylum Porifera)
I. Structure
A. Not organized into tissues, has masses of specialized cells embedded in
a gel-like substance called mesoglea, has cell recognition
B. Asymmetrical
C. Ostia – tiny openings (pores) in the body wall through which water enters
D. Oscula – larger body opening through which water exits removing waste
with it
E. Sessile – early in life they attach to the sea bottom or a submerged
surface and remain there for life (although they do move from time to time,
up to three millimeters a day)
F. Bag shaped with a large internal cavity with one or more oscula (large
openings) located in the top wall
G. Choanocytes – (a.k.a. collar cells)cells with flagella that line the internal
cavity that draw water into the sponge as they beat and function as a sieve
that traps plankton and other tiny organisms to be digested intracellularly,
nutrients from this digestion are released into the mesoglea
H. Amoebocytes – specialized cells that pick up nutrients from the
mesoglea and move about the sponge supplying other cells with nutrients
and carrying away their waste
I. Skeleton –
1. Made of a flexible protein fiber called sponging or tiny needles of silica
or calcium carbonate called spicules. A few sponges have both
2. Found throughout the mesoglea
3. Sponges are grouped into 3 classes based on the composition of the
skeleton
a) Calcareous – made of calcium carbonate spicules
b) Glass – made of silica spicules
c) Demosponges – made of spongin
II.
Reproduction
A. Reproduce asexually and sexually
B. Asexual forms of reproduction
1. Sponge will break off a fragment which develops into a new sponge
2. Budding – Swelling on adult that develops into a new organism
3. When conditions are harsh (cold or dry) sponges form gemmules,
clusters of Amoebocytes encased in protective coats and sealed with
ample food to last through harsh weather. If the sponge dies these
clusters will form a new sponge when conditions improve.
C. Sexual Reproduction
1. Sponges are hermaphrodites (have both egg and sperm, produced at
different times to prevent self-fertilization)
2. Sperm cells from one sponge enter through the pores of another, collar
cells pass them into the mesoglea where the eggs reside and fertilization
occurs. Fertilized eggs develop into larvae and leave the sponge, after a
brief swimming stage the larvae attach to an object and develop into a new
sponge.
29.2 – Cnidarians (phylum Cnidaria)
I. Structure
A. Radial symmetry
B. Arranged into tissues that arise from the endoderm and ectoderm
C. Two basic body forms (may be one type, or alternate between them)
1. Medusa – free-floating, jellylike, and often umbrella shaped
2. Polyp – usually attached to an object and tubelike, Have a fringe of
tentacles surrounding the mouth (located on the free end of the organism)
D. Cnidarians have two layers of cells (arise from the ectoderm and
endoderm) and are filled with middle layer of mesoglea.
E. Cnidocytes – stinging cells located on the tentacles that contain small
barbed harpoons called nematocysts which are used for defense and to
spear prey. Nematocysts may contain deadly toxins or chemicals designed
to stun, explodes forcefully into prey which is then pushed into the
gastrovascular cavity.
F. Have a gastrovascular cavity for extracellular digestion, enzymes break
down food into small fragments which are engulfed by the cells lining the
cavity. Digestion is completed intracellularly.
II.
Classes of Cnidarians
A. Hydrozoans
1. Colonial marine organism
2. Have medusa and polyp stages
3. Two types:
a) Freshwater – less common but more familiar (ex. hydra), lives in
ponds, lakes and streams. Attach to rocks or water plants by means of a
sticky secretion produced in the basil disk. Some hydra move by
tumbling like a slinky.
b) Marine – more complex, cells exhibit specialization. (ex. man-of-war)
A gas filled chamber allows it to float while tentacles hang into the
water below entangling their prey.
4. Reproduction of Hydrozoans
a) Most are colonial organisms whose polyps reproduce asexually by
budding, the buds develop into polyps which separate from the colony
and live independently.
b) Other species reproduce a sexually and sexually, some are
hermaphrodite but in most species the sexes are separate. First, polyps
bud to form a colony asexually. The polyps then give rise to male and
female medusas which release egg or sperm into the water, the gametes
fuse and produce zygotes that develop into free-swimming larvae called
planulae. Planulae settle on the ocean bottom, and become polyps,
which bud into a new colony and the cycle repeats.
B. Scyphozoa (Jellyfish)
1. Range in size from as small as a thimble to as large as a mattress
2. Active predators which entangle and sting prey with their tentacles.
Toxins from their nematocysts can be extremely potent.
3. Reproduction of Scyphozoa
a) Spend most of their life as medusa reproducing sexually
b) Go through a short polyp stage, at which time they reproduce first
asexually through budding and releasing medusas, which then sexually
reproduce by releasing egg and sperm into the water.
4. Other similar species to jellyfish
a) Comb jellies – have only a medusa stage and have no Cnidocytes
b) Box jellies – shaped like a cube and have short to non-existent polyp
stage, may inflict severe pain or death on humans
C. Anthozoans
1. Largest class of Cnidarians, exist only as polyps
2. Typically have a thick stalklike body topped with tentacles
3. Occur in groups of six
4. Reproduce sexually by releasing egg and sperm into the ocean,
fertilized eggs develop into planulae that settle and become polyps, or
asexually by forming buds
5. Provide a place for symbiotic algae like dinoflagellates to live and
reproduce in return for food they produce. Bright colors from algae.
6. Most familiar types are sea anemones and corals
a) Sea anemones are soft bodied polyps found in costal areas all over
the world, may be quite colorful, most do not grow very large, feed on
fish that happen to swim within reach of their tentacles. Highly
muscular and complex, react to touch. May reproduce by tearing itself
into two halves.
b) Corals are polyps that live in colonies called reefs. Most (with the
exception of soft corals) excrete a tough outer skeleton which is
cemented to the skeletons around it. As corals die new ones form on top
building the reefs.
29.3 Flatworms (phylum Platyhelminthes)
I. Structure
A. Bilaterally symmetrical
B. Acoelomate
C. Arranged into tissues and organs that arise from endoderm, mesoderm
and ectoderm
D. Flat shape places most cells in close contact with the environment
permitting respiration by diffusion through the body. (No need for a
respiratory or circulatory system)
E. Gastrovascular cavity runs close al all tissues giving ready access to
food molecules. (No need for a circulatory system)
II.
Three major classes of flatworms
A. Turbellaria
1. Most are live in marine environments; however a few (ex. planarians)
live in freshwater.
2. Freshwater varieties such as planarians are easier to raise in captivity
and are therefore the most widely studied (ex. Dugesia)
a) Nervous system has a brain and two main nerve cords connected by
cross branches, light sensitive “eye spots” are connected by nerve cells
to the brain.
b) Feed by extending the pharynx out of the mouth cavity
c) Highly branched intestine enables nutrients to pass close to all
tissues.
d) Reproduces asexually in the summer by attaching its posterior to a
surface and stretching into two parts. Also reproduce sexually, two
hermaphroditic individuals simultaneously transfer sperm to each other
then release the fertilized eggs in clusters in an enclosed area. Eggs
hatch in 2-3 weeks.
e) Maintain water balance by bringing in water through osmosis and
flame cells (cilia covered cells resembling a candle) drawing water out
B. Cestoda
1. Parasitic flatworms commonly known as tapeworms
2. Use suckers and hooklike structures to permanently attach to the inner
wall of the host intestines
3. Food digested in the host intestine is absorbed directly through the skin
4. Grow by producing proglottids (rectangular body sections) immediately
behind their head; each proglottis is completely reproductive making
tapeworms hard to eliminate
5. Proglottids are continually added allowing the tapeworm to grow up to
12 m (40 ft) long.
6. Most tapeworms are found in vertebrates and there are about a dozen
kinds found in humans. One such worm is ingested in the larvae form from
infected beef that has not been cooked well enough!
C. Trematoda
1. Largest class of flatworms contains parasites called flukes which have
two types.
a) Endoparasites – live inside hosts, have a thick skin called tegument.
b) Ectoparasites – live on the outsides of hosts
2. Simple bodied with few organs, since they get nutrients from the hosts
the fluke digestive system is not developed.
3. Use suckers to attach to host, and the pharynx to suck nutrients from
the host body.
4. Complex life cycles with more then one host, one of which may be
human and may cause disease
29.3 Roundworms (phylum Nematoda)
I. Structure
A. Pseudocoelomate – movement of fluid through the pseudocoelom
serves as the circulatory and respiratory systems, food and gasses move
in and out of the body by diffusion
B. Long cylindrical body with a one-way digestive system
C. Flexible, thick epidermis and cuticle give the worn its shape and
protection
D. Under the epidermis lies a layer of muscle which pulls on the cuticle
above it and pseudocoelom below whipping the body from side to side.
E. Most are microscopic but some may grow as long as 1 ft or more
II.
Roundworm infections
A. Common in dogs, about 50 other species are damaging to crops and/or
humans (ex. hookworms)
B. Complex life cycles with more then one host, one of which may be
human and may cause disease
C. Live for long periods of time in the soil and can be contracted through
the skin on the bottom of the feet