Transcript Bio Unit 10 Comparing Invert. s.g.

Comparing Invertebrates
-
There are some four million different kinds of animals
and plants in the world. Four million different
solutions to the problems of staying alive.
- David Attenborough
Ediacaran Period – 600 million years ago.
First multicellular animals with bilateral symmetry and segmentation
Spriggina an Ediacaran fossil displaying bilateral symmetry,
cephalization and segmentation.
Ediacaran ocean scene. This was the last period of the Precambrian
and led to the Cambrian Period.
Cambrian Explosion – 542 million years ago. Most major phyla appeared
here. A fantastic and sudden appearance of hundreds of different species.
In just a few million years animals had evolved complex body plans. They
had acquired specialized cells, tissues and organs.
Invertebrate cladogram – this shows the appearance of
evolutionary advances.
Specialized cells lead to tissues and tissues working together lead to
organs.
Radial symmetry – body parts from the center
Bilateral symmetry – right and left halves
Echinoderms have Radial Symmetry
Star fish
Sea Urchin – Sea Hedgehog
Sand Dollars
Brittle Stars
The two main forms of cnidarians, polyp and medusa have radial
symmetry.
Nomura’s jellyfish – 2 m, 450 lbs.
Coral Polyps – like anemones
Cephalization – nervous tissue becomes concentrated on one end of an
organism.
This allows for organisms to respond to the environment in more
sophiscated ways.
The three germ layers – ectoderm, endoderm and mesoderm
Segmentation – allows for specialization of different parts and
minimal new genetic material as each segment is similar to the
next.
Coelom – a fluid filled cavity between the digestive tube and the outer
body wall. It serves as a buffer between the outer wall and the inner
organs.
Intracellular digestion – takes place in the cytoplasm of the cells of the
organism. This is found in molluscs, cnidarians and Poriferans.
This is a view of the Giant Barrel Sponge – the largest member of the phyla
porifera (pore bearing). It is a filter feeder.
Extracellular digestion – Enzymes catalyse the digestion of the food
outside the cells and the molecules are absorbed into the blood or
body fluids
Cnidarian digestion
Flatworm digestion
In both animals there is one opening. So wastes will go out the same tube
that the food went in.
Digestive tract – one way flow from mouth to anus. Specialized cells
help to digest the food, move the food, absorb nutrients, get rid of
wastes, making the whole system more efficient.
Porifera respiration. Sponge cells absorb oxygen directly from the
water. They eliminate carbon dioxide the same way.
Cnidarian Respiration. There are no respiratory organs. Both cell
layers absorb oxygen from the water.
Cnidarian cnidoctye. An explosive cell containing harpoon like cnida
which also has a toxin. Some species (portugeese man of war, sea
wasp) are dangerous to people.
Box jellyfish (class Cubozoa) are cnidarians distinguished by their cubeshaped medusa. Some species produce extremely potent venom. Three are
among the most venomous creatures in the world. Stings from these are
extremely painful and sometimes fatal to humans.
Box Jellyfish
A stinging victim
Portuguese Man of War. This cnidarian’s nematocysts (cnidocytes)
can also penetrate human skin and leave a painful rash.
Respiratory system. The purpose of this system is to bring oxygen to
the cells of the body and to eliminate carbon dioxide from the body.
All have a large surface area and all are moist. In the anatomy of a
typical mollusc (a gastropod – snail) the paired gills can be seen.
Squid Gills. Squid are in the class cephalopoda (head footed) and the
phylum mollusca.
Respiration in land invertebrates. Respiratory surfaces are covered with
water or mucus. These organs are usually covered to minimize water loss.
Sow bugs or wood lice are crustaceans that breathe through paddle shaped
hind legs. (pleopodal lungs).
Arachnids. Spiders breathe through specialized structures
called book lungs.
Insects breathe through a series of openings (spiracles) that lead to
tiny vessels (tracheal tubes) that bring oxygen to the cells of the body.
Open circulatory systems. Blood is only partially contained within a system
of vessels. One or more hearts pump blood through vessels into a system of
spongy cavities (sinuses). Arthropods and most molluscs.
The cephalopods are exceptions to the other molluscs in that they have a
closed circulatory system. Their blood is blue because of the pigment
hemocyanin which is different from our pigment (hemoglobin)
Annelids have a closed circulatory system.
Insects have an open circulatory system. The blood moves from the
hearts into the body sinuses and is collected again near the head
Excretory system controls the loss of water and gets rid of nitrogenous
waste. (ammonia) Flatworms use a system of flame cells to eliminate
excess water. Ammonia diffuses directly through the animals skin.
Annelids like the earthworm change ammonia to urea in the
nephridia and excrete it. This process helps to save water.
Some insects and spiders use Malpighian tubules to change the
ammonia into uric acid. This is excreted along with the solid waste as
a thick paste. This saves the animal a lot of water.
Cnidarians are the first phyla with a specialized nervous system. It is
composed of a simple nerve net that helps to coordinate motion of the
animal.
The more complex the animal the more developed the nervous system.
From simple nerve nets there appear ganglia, lumps of nervous tissue, and
finally a brain in the head that controls the nervous system.
Cnidarians, flatworms, this roundworm, annelids and certain molluscs have
hydrostatic skeletons. These skeletal systems consist of a fluid filled cavity
that provides support and a place for muscles to push.
Exoskeletons. In arthropods a outer, hard covering composed of the
protein chitin. Sun spiders, like this one from the Las Vegas area have
an exoskeleton made of chitin
Endoskeletons are structural supports located inside the body. Sea stars and
other echinoderms have an endoskeleton made of calcified plates.
The sunflower seastar is the largest starfish with a maximum arm
span of 3.3 ft.
Sexual Reproduction – most invertebrates reproduce sexually during
at least a part of the life cycle. In sponges sperm and egg combine to
form a free swimming larva that settles and develops into a sponge.
Life cycle of a jellyfish
1–3 Larva searches for site, 4–8 Polyp grows
9–11 Polyp strobilates12–14 Medusa grows
Life cycle of a cnidarian polyp. (Coral, Sea Anemone)
Elkhorn coral at Molasses Reef Florida keys. These hard
corals contain thousands of polyps.
Sexual planaria are hermaphrodites each animal possessing both
testicles and ovaries. Each planarian gives and receives sperm. Eggs
develop inside the body.
Nematode Sexual reproduction. Most species have a male and a female
worm. The eggs may hatch inside the female or they are deposited outside.
Annelid sexual reproduction. Earthworms are hermaphroditic. Sperm will
be exchanged and a cocoon will form around the clitellum were the eggs
and sperm will unite. The young worms are like the adults.
Cephalopods like this cuttlefish are male and female. Fertilization is
internal here but can be external with other speices.
Arthropod sexual reproduction. Most have males and females. Some
external fertilization, but most internal fertilization. Most lay eggs though
scorpions give live birth.
Echinoderm sexual reproduction. Male and females with the release
of eggs and sperm externally and tied to the rhythm of the moon.
Asexual reproduction in sponges. Three ways: by fragmentation,
budding and producing gemmules. Gemmules are like spores and are
produced by dying sponges
Cnidarian asexual reproduction – polyps can reproduce by
budding. Hydra commonly reproduces this way.
Flatworm asexual reproduction – Planaria will spontaneously pinch
off a part of the tail, which will become another planarian
Round worms do not have asexual behavior, but many parasitic ones
have very complicated life cycles that involve one or more
intermediate hosts.
Annelid Asexual reproduction. Limited to polychetes. Earthworms
(oligochetes) can regenerate a lost tail, but do not reproduce
asexually. Sabellid worm in parchment tube budding.
Arthropod asexual reproduction. Barnacles are hermaphroditic. Some
insects (aphids) can reproduce by parthenogenesis. Parthenogenesis
involved the growth and development of embryos without fertilization.
Aphid parthenogensis
Echinoderms have a great capacity for regeneration. Some species
can reproduce by parthenogenesis and a few can reproduce asexually.
Echinoderm regeneration. In this case one arm can regenerate the
rest of the body.