BSC 2011C Chapter 29 notes

Chapter 29 : Animal Kingdom

General characteristics of animals

1) chemoheterotrophs ( eat food to digest internally )
2) store glycogen
3) no cell walls
4) mainly sexual reproduction, but some have asexual
5) have nerves and muscles ( except sponges ).

Invertebrates
They have no backbone, and make up 95% of animal species.

First fossils appear about 900 million years ago ( marine ).
First land invertebrates 450 million years ago.
First winged insects 300 million years ago.

Trends in the evolution of animals
1) Cells become more specialized, and form tissues.
2) Radial symmetry ( circular body with no left or right side ) changes to bilateral symmetry.
3) Sense organs become concentrated in the front, or head, of the animal : cephalization.

Phylum Porifera (Sponges)

10,000 species. Are similar to 900 million year old fossils. Simple body, often separated as Parazoa ( beside animals) because they have no nerves, no muscles etc.
The body is sac-like with a single large opening or osculum. Filter feeders, usually marine. Water enters small holes in the side, pushed by flagellated choanocytes or collar cells. Amoebocytes distribute food around the body, and also form sex cells and spicules. Spicules can be made of calcium carbonate, silica or flexible spongin.

Most sponges are hermaphrodite; sperm is released into the water. Larvae swim to a new area, then become sessile ( attached ). Sponges are commercially harvested in Florida.

Three types of body organization in sponges:
1) Asconoid : water enters straight cells in the sponges side eg Leucosolenia
2) Syconoid : water goes through two canals in an "S" shape. eg Sycon
3) Leuconoid : water enters canals leading to chambers where food is removed. eg Euspongia

Drugs from sponges : bastadins : anti-cancer drugs; papuamine : anti-fungal drug.

Phylum Cnidaria

10,000 species. Ancient : fossils go back 700 million years. They have radial symmetry (circular bodies). They are predators, use cnidocytes (stinging cells) to catch their prey. These are animals with true tissues : eumetazoa (different from the Parazoa, which are sponges).
They have two tissue layers : epidermis (skin) and gastrodermis (gut) with a jelly-like mesoglea sandwiched in between. Sac-like body with one opening. They have two body types :

floating medusa ( eg jellyfish ).
sessile polyp ( eg coral ).

Cnidaria have nerves and muscles for movement and feeding. They have both sexual and asexual reproduction. Sexual reproduction (sperm + egg) produces a planula larva.

Class Hydrozoa
Have polyp and medusa stage, polyp usually dominant. Polyp reproduces asexually to form medusa. Medusa produce sperm and egg, that grow into a planula larva, which eventually settles as a polyp. eg Hydra, Obelia

Class Scyphozoa ( jellyfish )
Medusa stage dominant, some have no polyp stage. Usually have 4 gonads and 4 orals arms for feeding. Statocysts respond to gravity. A glowing protein from jellyfish is very useful in research. eg Aurelia

Class Anthozoa
Polyp stage is dominant, no medusa stage. Tentacles in groups of 6, never in groups of 8. There are two main orders :
Order Scleractinia ( corals ).
Corals secrete a protective tube of calcium carbonate. Corals are often mutualistic with algae, particularly dinoflagellates. Dust blown from the Sahara carries fungi like Aspergillus which seems to be infecting coral reefs in the Caribbean. eg Montastrea

Order Actiniaria ( sea anemones ).
Sea anemones protect themselves with stinging tentacles. They often have cilia on the tentacles to help collect food.
eg Metridium

Phylum Ctenophora (Comb jellies)

Only 100 species. Radial symmetry. Their body is mainly mesoglea for buoyancy. They move using 8 rows of cilia. They have a Y shaped digestive system: a mouth and 2 anuses. Ctenophora are predators ; they catch food on sticky colloblasts ( glue cells ) on their tentacles. They are hermaphrodite, and can fertilize themselves. Comb jellies were probably one of the first animals to evolve. eg : Leucothea

Body plans of animals

Acoelomate	Pseudocoelomate	Coelomate
Have no cavity between the outer wall and the gut	Have a cavity (coelom) between the gut and muscle layers	Have a coelom surrounded by muscles, with more muscles around the gut
Platyhelminthes	Nematoda Rotifera	Annelida Arthropoda Chordata

Phylum Platyhelminthes (Flatworms)

20,000 species. Acoelomate. Bilateral symmetry ( have a left and right side ). Typically found in water ( predators ), or as parasites. They are flat because gas exchange and food distribution is by diffusion through the skin, and a flat surface has a large surface area for diffusion.
Freshwater species have flame cells to remove excess water (like a simple kidney). Flatworms have one opening to the digestive system. They move using muscles and cilia pushing against slime. Flatworms are predators and have have slight cephalization:
they can detect light ( using eyespots) and chemicals ( using auricles).
Their prey is covered in mucus and adhesive. Some species stab their prey with their penis. Flatworms are hermaphrodite but have no self fertilization. They decide which one will be male by "penis fencing"

Classes of Platyhelminthes

Class Turbellaria
Free living predators, usually marine. Example : Dugesia. Photo

Class Trematoda ( flukes )
10,000 species. Parasites, usually of fish, often have molluscs eg snails as an intermediate host.
eg Schistosoma lives in the human blood near the intestine. Causes schistosomiasis in humans. Adult females live in a groove in the males body. The larval stage is cercaria, which can burrow through the skin. The disease is contracted by swimming or bathing in freshwater that is infected with the cercaria.

eg Clonorchis ( Chinese liver fluke ). Eggs from humans infect snails, then cercaria from snails infect fish which are eaten by humans. The disease is contracted by eating undercooked, or raw, fish.

Class Cestoda ( tapeworms )
Intestinal parasites, have no mouth or digestive system. The front of the body is the scolex with 4 suckers and hooks to attach to the hosts intestines. The main part of the body consists of proglottids ( produce sperm and eggs ). Human tapeworms can have fish, cows or pigs as intermediate hosts, and are contracted by eating undercooked meat. eg : Taenia: Tapeworm

Phylum Rotifera

Pseudocoelomate. Live in freshwater. Rotifers have very small bodies ( roughly 1mm long ). Tube-like digestive system ( separate mouth and anus ). The body is divided into 3 parts : corona, trunk, foot. The corona has cilia to push food towards the mouth. The mastax grinds up food. Cement glands in the foot attach to solid surfaces. Rotifer video

In some species the males are very small, live only a few hours and have no digestive system. One class of Rotifer has no males only females: the females reproduce by parthenogenesis ( asexual ). eg : Filinia

Phylum Nematoda

100,000 species. Pseudocoelomate, bilateral symmetry. They live in soil, water and as parasites. Some nematodes damages crops, by eating the roots. However others are beneficial, because they kill insect pests.

Nematodes have a separate mouth and anus ( tube-like digestive system ). Their body is covered by a thick cuticle of collagen. They move using longitudinal muscles, which push against the fluid-filled body ( hydrostatic skeleton ). They usually reproduce sexually and they are dioecious ( female usually larger than male ). Sperm is amoeboid, not flagellated.
Sense organs : ocelli ( detect light ), amphids ( detect chemicals ).

The genus Caenorhabditis is used in studying embryo development.. Recent experiments with Caenorhabditis have also investigated how long animals live. Life

Nematoda: examples of human parasites

Wuchereria causes elephantiasis ( or lymphatic filariasis). It lives in the lymph vessels, spread by mosquito bite. It causes painful swelling. It often infects the legs or arms. Medication controls the infection, but does not kill the worms in the lymph.

Ascaris ( lungworm ) lives in lungs and intestines. Roughly one billion people worldwide are infected. The eggs are eaten (on unwashed fruit and vegetables), the larvae migrate through blood to lungs, molt, climb up to the throat, then back down to intestines where they mature.

Trichinella (pork roundworm ) lives in muscle. It forms cysts in pig muscle which are eaten, then move from the intestines to human muscles. Infection is now rare in the US. Factsheet.. Did this kill Mozart?

Necator ( hookworms ) live in the intestines. The larvae burrow through the skin of the feet, move to the intestines. They feed on blood ( rasping mouthparts ). Hookworms produce anti-coagulant and a protein that inhibits white cells. Hookworm factsheet
Some physicians have suggested that the rise in allergies over the last 50 years is due to the eradication of hookworm and other parasitic worms: Eat worms, feel better.

Enterobius ( pinworm ) live in the colon. The females lay eggs outside the rectum at night. The eggs itch, and are transmitted by the hands or in the air. Eggs are detected under the microscope with the "Scotch tape test". Life cycle
Pinworm infect 10% adults, 30% children in the US.

Medically, most roundworm infections are confirmed by finding eggs, or larvae, in the feces.

Last edited October 2009, David Byres, dbyres@fscj.edu