Sponges are classified as animals because they are multicellular, heterotrophic, have no cell walls, and contain a few specialized cells.
- movement -
Sponges are sessile, meaning that they live their entire adult life attached to a single spot.
- body symmetry -
Sponges are asymmetrical; they have no front or back ends, and no left or right sides.
- body structure -
A sponge can be thought of as a large, cylindrical water pump (outside poors, inside hollow cavity). The body of a sponge forms a wall around a large central cavity through which water is circulated continually. Choanocytes are specialized cells that use flagella to move a steady current of water through the sponge. Water then leaves through the osculum, a large hole at the top of the sponge. The movement of water through the sponge provides a simple mechanism for feeding, respiration, circulation, and excretion
- feeding -
Sponges are filter feeders that sift microscopic food particles from the water. Digestion is intracellular, meaning that it takes place inside cells. As water moves through the sponge, food particles are trapped and engulfed by choanocytes that line the body cavity. These particles are then digested or passed on to archaeocytes. The archaeocytes complete the digestive process and transport digested food throughout the sponge.
- respiration, circulation, and excretion-
Sponges rely on the movement of water through their bodies to carry out body functions. As water moves throughout the body cavity, oxygen dissolved in the water diffuses into the surrounding cells. At the same time, carbon dioxide and other wastes, such as ammonia, diffuse into the water and are carried away.
Cnidarians are soft-bodied, carnivorous animals that have stinging tentacles arranged in circles around their mouths. They are the simplest animals to have body symmetry and specialized tissues.
- examples -
Jellyfishes, hydras, sea anemones and corals
Cnidarians get their name from the cnidocytes, or stinging cells, that are located along their tentacles. Cnidarians use these cells for defense and to capture prey.
- body symmetry -
Cnidarians are radically symmetrical (multiple lines of symmetry). They have a central mouth surrounded by numerous tentacles that extended outward from the body.
- mode of feeding -
Cnidocytes, or stinging cells, that are located along their tentacles paralyze the pray. After paralyizing its prey, a cnidarian pulls the prey through its mouth and into its gastrovascular cavity, a digestive chamber with one opening
- nerve net (response) -
Cnidarians gather information from their environment using specialized sensory cells. Both polyps and medusas have a nerve net. A nerve net is a loosely organized network of nerve cells that together allow cnidarians to detect stimuli such as the touch of a foreign object.
- hydrostatic skeleton -
Different cnidarians move in different ways. Some cnidarians, such as sea anemones, have a hydrostatic skeleton. The hydrostatic skeleton consists of a layer of circular muscles and a layer of longitudinal muscles that, together with the water in the gastrovascular cavity, enable the cnidarian to move.
Mollusks are soft-bodied animals that usually have an internal or external shell.
- body structure, including the terms foot, mantle, and visceral mass -
The body plan of most mollusks has four parts: foot, mantle, shell, and visceral mass. The muscular foot takes many forms, including flat structures for crawling, spade-shaped structures for burrowing, and tentacles for capturing prey. The mantle is a thin layer of tissue that covers most of the mollusk's body, much like a cloak. The shell is made by glands in the mantle that secrete calcium carbonate. The shell has been reduced or lost in slugs are some other mollusk groups. Just beneath the mantle is the visceral mass, which consists of the internal organs.
- open circulatory system--
In an open circulatory system, blood is pumped through vessels by a simple heart.
- nervous systems/brains of shelled mollusks and non-shelled mollusks-
Clams and other two-shelled mollusks typically lead inactive lives, burrowing in the mud or sand. They have a simple nervous system consisting of small ganglia near the mouth, a few nerve cords, and simple sense organs, such as chemical receptors and eyespots.
In contract, octopi and their relatives, such as the octopus are active and intelligent predators that have the most highly developed nervous system of all invertebrates. Because of their well-developed brains, these animals can remember things for long periods and may be more intelligent than some vertebrates. Octopi are capable of complex behavior, such as opening a jar to get food inside, and they have been trained to perform different tasks for a reward or to avoid punishment.
The three major classes of mollusks are gastropods, bivalves, and cephalopods.
Gastropods include pond snails, land slugs, sea butterflies, sea hares, limpets, and nudibranchs. Gastropods are shell-less or single-shelled mollusks that move by using a muscular foot located on the ventral side.
Common bivalves include clams, oysters, mussels, and scallops. Bivalves have two shells that are held together by one or two powerful muscles.
Cephalopods include octopi, squids, cuttlefishes, and nautiluses. Cephalopods are typically soft-bodied mollusks in which the head is attached to a single foot. The foot is divided into tentacles or arms.
Arthropods have a segmented body, a tough exoskeleton, and jointed appendages.
- exoskeleton -
Arthropods are surrounded by a tough external covering, or exoskeleton. The exoskeleton is like a suit of armor that protects and supports the body. It is made from a protein and carbohydrate called chitin (same as in fungi cell walls).
- jointed appendages -
Appendages are structures such as legs and antennae that extend from the body wall.
- tracheal tubes/spiracles -
Most terrestrial arthropods breathe through a network of branching tracheal tubes that extend throughout the body. Air enters and leaves the tracheal tubes through spiracles, which are small openings located along the side of the body.
(first respiratory system!)
- book lungs -
Book lungs are organs that have layers of respiratory tissue stacked like the pages of a book.
- Malpighian tubules -
Most terrestrial arthropods, such as insects and spiders, dispose of nitrogenous wastes using Malipighian tubules. Malpighian tubules are saclike organs that extract wastes from the blood and then add them to the feces, or digestive wastes, that move through the gut.
When they outgrow their exoskeleton, arthropods undergo periods of molting. During molting, an arthropod sheds its entire exoskeleton and manufactures a larger one to take its place (outgrows its previous exoskeleton).
Arthropods are classified based on the number and structure of their body segments and appendages-particularly in their mouthparts.
The three major groups of arthropods are crustaceans, spiders and their relatives, and insects and their relatives.
Crustaceans typically have two pairs of antennae, two or three body sections, and chewing mouthparts called mandibles. This subphylum includes organisms such as crabs, shrimps, lobsters, crayfishes, and barnacles (primarily aquatic).
Chelicerates have mouthparts called chelicerae and two body sections, and nearly all have four pairs of walking legs. Members of this subphylum include horseshoe crabs, spiders, ticks, and scorpions.
Centipedes, millipedes, and insects all belong to the subphylum uniramians. Uniramians have jaws, one pair of antennae, and unbranched appendages.
Insects have a body divided into three parts-head, thorax, and abdomen. Three pairs of legs are attached to the thorax.
73% insects: 4% vertebrates
The growth and development of insects usually involve metamorphosis, which is a process of changing shape and form. Insects undergo either incomplete metamorphosis or complete metamorphosis.
The immature forms of insects that undergo gradual or incomplete metamorphosis, such as the chinch bug, look very much like adults. These immature forms are called nymphs.
Many insects, such as bees, moths, and beetles, undergo a more dramatic change in body form during a process called complete metamorphosis. These animals hatch into larvae that look and act nothing like their parents. They also feed in completely different ways from adult insects.
Ants, bees, termites, and some of their relatives form complex associations called societies. A society is a group of closely related animals of the same species that work together for the benefit of the whole group.
(Queen bee, drowns, worker bees; communication [dance])
Echinoderms are characterized by spiny skin, an internal skeleton (endoskeleton), a water vascular system, and suction-cuplike structures called tube feet. Most adult echinoderms exhibit five-part radial symmetry. Don't have cephalization.
- water vascular system -
The water vascular system (system of internal tubes unique to echinoderms), which is filled with fluid, carries out many essential body functions in echinoderms, including respiration, circulation, and movement.
- tube foot -
Attached to each radial canal are hundreds of tube feet. A tube foot is a structure that operates much like a suction cup. Each tube foot has a sucker on the end. Muscles pull the center of the sucker upwards, forming a cup shape. This action creates suction on the surface to which the foot is attached, so the tube foot pulls on the surface.
Classes of echinoderms include sea urchins and sand dollars; brittle stars; sea cucumbers; sea stars (carnivorous; can lose an arm and grow it back); sea lilies and feather stars.
Flatworms are soft, flattened worms that have tissues and internal organ systems. They are the simplest animals to have three embryonic germ layers, bilateral symmetry, and cephalization.
- acoelomate -
Flatworms are known as acoelomates means "without coelom." A coelom is a fluid-filled body cavity that is lined with mesoderm.
- feeding -
Free-living flatworms can be carnivores that feed on tiny aquatic animals, or they can be scavengers that feed on recently dead animals. Like cnidarians, flatworms have a gastrovascular cavity with a single opening, or mouth, through which food and wastes pass. Near the mouth is a muscular tube called a pharynx. Flatworms extend the pharynx out of the mouth. The pharynx then pumps food into the cavity. Once inside, food is digested by cells of the gut, or digestive cavity, where digestion and nutrient absorption take place. Digested food diffuses from the gastrovascular cavity into all other body tissues.
Parasitic worms feed on blood, tissue fluids, or pieces of cells within the host's body. Many parasitic worms obtain nutrients from foods that have already been digested by their host. Therefore, most parasitic worms do not need a complex digestive system. Many parasitic species have a digestive tract that is simpler than that of free-living forms. Some species have a pharynx that pumps food into a pair of dead-end intestinal sacs for digestion. Tapeworms, of the other hand, have no digestive tract at all. They live within the intestine of their host, such as a cow or a human, and simply absorb digested nutrients that are in their host's intestine.
- flame cells -
Some flatworms have flame cells that function in excretion. Flame cells are specialized cells that filter and remove excess water from the body. They also remove metabolic wastes such as ammonia and urea. Many flame cells are joined together to form a network of tubes that empties into the outside environment through tiny pores in the animal's skin.
- eyespot -
Many free-living flatworms have what look like eyes near the anterior end of their body. Each "eye" is actually an eyespot, or group of cells that can detect changes in the amount of light in their environment.
The three main groups of flatworms are turbellarians (free-living), flukes (parasite), and tapeworms (parasite).