Invertebrates Chapter 6 Animals Without Backbones Animals that lack a backbone are called invertebrates. It is estimated that 97% of all species of animals are invertebrates. With the exception of insects, most invertebrates are marine, which means they live in the ocean. Sponges SPONGES They are animals that are complex aggregations of specialized cells. They are among the simplest multicellular animals. Nearly all sponges are marine and all are sessile, which means they live on the bottom or attached to something. Pore-Bearers They come in many shapes and sizes but they all have tiny pores that allow water to enter and circulate. Organic planktonic material is filtered out of the water and eaten. Sponges are called porifera or pore bearers and lack true tissues. Movement of Water The outer surface is covered with flat pore cells which allow water to enter. Water is pumped into a larger canal lined with collar cells. The cells have flagellum that creates a currents and a thin collar that traps food that is later ingested. Water then leaves the through osculum, a large opening at the top of the sponge. Since the sponge actively filters food actively, they are known as filter feeders.
Pore Cells and the Osculum In through the pore cells and out through the osculum. Growth and Support As sponges grow larger they need support. Spicules are siliceous or calcareous supporting structures. Most also have a skeleton made of sponging, an elastic but resistant fiber made of protein. Asexual Reproduction Sponges can reproduce asexually when braches or buds break off and grow into larger sponges. Sexual Reproduction Sponges can also reproduce sexually by producing gametes that are either large nutrient rich eggs or smaller sperm with flagellum. Most sponges can produce both eggs and sperm but some are male or female. The sperm enters the sponge and fertilizes the egg. The gametes are released directly into the water and this is called spawning.
Specialized Tissues CNIDARIANS These organisms are more complex than sponges. They have tissues specialized to perform specific functions. These are sometimes called coelenterates and include sea anemones, jelly fish and corals. Radial Symmetry Radial symmetry means body parts are repeated around the central part of the body. Repeats around a central mouth Polyp and Medusa Stage Medusa Stage The two types of cnidarians are polyps-a sac-like attached stage or a bell like medusa. Both have a centrally located mouth surrounded by tentacles. The mouth opens into a blind gut where food is digested. Cnidarians discharge nematocysts, unique stinging structures. Large bell shape with reproductive, feeding and stinging structures below.
Polyp Stage Structure on the bottom with all of the tissue located on the top. Hydrozoans Hydrozoans consist of feathery or bushy tiny colonies of polyps that attach to pilings, shells or seaweed. The reproductive polyps form tiny medusae that release gametes. The fertilized eggs develop into free swimming larvae and will settle to the bottom and form a polyp that will form a colony and continue life. Free Swimming Stage Scyphozoans or jellyfish has the medusae as the dominant life stage and are common in all oceans. They swim with rhythmic contractions of the bell but is limited and they primarily move with the current.
Jellyfish Life Cycle Solitary Stage Anthozoans are solitary or colonial polyps and include sea anemones, stony corals and sea fans. Sea Anemone Life Cycle Feeding in Cnidarians Almost all cnidarians are carnivores and usually use nematocysts that are discharged with a fluid filled capsule. After ingestion the food passes to a gut where it is digested. Nematocysts Tentacles Nematocysts are individual cells usually on the outer surface of the organism which have a variety of functions, most usually in defense or capture of prey species. These cells are known as stinging cells sometimes used to inject toxins which in some cases are toxic to man. Nematocysts can be dangerous because the stick to surfaces and wrap around objects penetrating surfaces or secreting toxins.
WORMS Bilateral Symmetry Radial vs. Bilateral These organisms are only symmetrical in one direction and have a front (anterior) and a back (posterior). They also have a back surface (dorsal) and a belly surface (ventral). Flatworms Flatworms are the simplest bilateral invertebrates that have organs and organ systems. They have a simple brain and nervous system that coordinates the movement of the muscular system.
Parasitic Flatworms There are about 20,000 species of flatworms some are carnivores and others (flukes) are parasites that live on other organisms tissues. Adult flukes can only live in vertebrates. The larvae can live in invertebrates but cannot become adults unless they are ingested by a vertebrate. Flukes are commonly found in fishes, whales and birds. Tapeworms attach themselves inside the intestines and absorb the nutrients the host takes in. Some can grow up to 50 feet in length. One Way to Get it Out Ribbon Worms Ribbon worms have a complete digestive system, a circulatory system and a proboscis which is a long fleshy tube used to entangle prey. They are found throughout all of the oceans but are primarily found in shallow temperate waters. One species can grow up to 100 feet in length. Polycheate Worms Polycheate worms have segmented bodies and each segment is equipped with parapodia, containing stiff, sharp bristles called setae. Polycheates have a closed circulatory system and gills to help provide enough oxygen to the organism. These organisms are usually around 2-4 inches in length and crawl on the bottom or live under rocks.
Feeding in Worms Most are carnivores and feed on particles that settle to the bottom and are called suspension feeders. Beard Worms Beard worms live in a tube and lack a digestive system. They absorb nutrients through the tentacles found near the head end. Molluscs Molluscs Snails, clams and octopuses are familiar forms of molluscs. There are over 110,000 species. Soft body protected by a calcium carbonate shells. The body is covered by a thin layer of tissue that produces the shell called the mantle.
Muscular Foot Squid and Octopus The body is bilateral in symmetry with a ventral, muscular foot used for locomotion. Molluscs could have a head that includes eyes and other sensory organs. Some molluscs have the shell internal (squids) or even absent (sea slugs and octopuses). Types of Molluscs Three types of molluscs we will talk about are gastropods (snails), bivalves (clams, oysters, mussels and scallops) and cephalopods (squid and octopus). Gastropods Gastropods commonly known as snails are the most common and varied group of molluscs with over 75,000 species and most are marine. They are typically a coiled body mass tucked into a shell. Most molluscs use the radula to scrape algae off of rocks. Other molluscs are soft bottom feeders or even carnivores.
Feeding A radula made of chitin, which is a ribbon of small teeth used in rasping food from surfaces. Gas exchange is through small paired gills. Bivalves Bivalves are clams, mussels, oysters and other similar molluscs. They retain the body plan and are compressed in a two-valved shell. There is no head or radula and the gills are used for breathing as well as filtering small food particles. The inner part of the shell is lined with the mantle so the body sits in the mantle cavity. Strong muscles are used to keep the shell closed. Clams Bury Themselves Clams will use their shovel shaped foot to bury themselves in the bottom sediment. If the clam is below the surface, it uses a siphon to bring the water in and out of the mantle cavity.
Mussels and Oysters Byssal Threads Not all bivalves will bury themselves. Mussels attach to rocks using byssal threads to stay attached. Oysters will cement their left shell to hard surfaces often other oysters. Some oysters have the ability to coat irritating parasites with a shiny layer of calcium carbonate called a pearl. Oysters Attached and The Pearl Scallops Some bivalves are not buried or attached but have the ability to move by ejecting water out of the mantle cavity. Scallops are an example of this. The largest bivalve is the giant clam and can grow to about 3 feet wide. http://www.youtube.com/watch?v=8ncbmxkvnfi http://www.youtube.com/watch?v=hss7bicidvs&feature=related Cephalopods Cephalopods include octopuses, squid, cuttlefish. They are agile swimming carnivores. All 650 species are marine with arms equipped with suckers to capture prey.
Movement They have eyes and a thick muscular mantle that forms a mantle cavity that houses the head and 2 of the 4 gills. The water enters through the open end of the mantle cavity and is forced out through a muscular tube called the funnel. The funnel can be pointed in any direction to allow a full range of motion. Feeding and Safety Octopuses have 8 long arms and lack a shell. They are common bottom dwellers and range in size from about 5 inches up to 30 feet. They are efficient hunters and bite with a pair of beak-like jaws. If necessary, they can emit a dark ink produced by the ink sac, to distract potential predators.
Digestive System The digestive system has a separate mouth and anus with salivary and digestive glands. Snails will use the radula, cephalopods have a beak-like mouth and bivalves will filter feed small particles. Nervous System The nervous system ranges from a simple mass of nerve cell called a ganglia to a single brain that coordinates and stores information. Octopuses and cuttlefish have considerable intelligence and a capacity for learning. Fertilization Most species of molluscs have separate sexes but some are hermaphrodites. In bivalves and some snails fertilization is external. In cephalopods and most snails, fertilization is internal where a packet of sperm is inserted into the female and fertilization can occur. Some molluscs produce a planktonic larvae while others will produce eggs and will protect them until the mother dies. Eggs Attached to Bottom Arthropods
Arthropods Arthropods make up the largest phylum of animals with over 1,000,000 species, many are insects. Some of the animals we will talk about will include barnacles, shrimps, lobsters and crabs. Arthropod Body Plan The arthropod body is bilateral in symmetry, segmented and contains jointed appendages like legs and mouth parts. They have a tough non-living chitinous exoskeleton that the muscles attach to. In order to grow, the arthropod must molt or shed their exoskeleton. Positives of an exoskeleton are protection but size is limited because of the ridged exoskeleton. Crustaceans Crustaceans which include shrimp, crabs and lobsters are specialized for life in the water with gills and the appendages are made for swimming, crawling, mating, feeding and attaching to other animals. They possess two pairs of antennae which are usually used to sense their external environment. Small Crustaceans-Copepods Small crustaceans include Copepods, Isopods, Krill, Beach Hoppers and Barnacles. Copepods are small and are found in the plankton. They filter feed using their mouthparts and stay afloat by using the pair of first antenna. Some are even parasitic.
Small Crustaceans-Amphipods Amphipods (Beach Hoppers) are small and have a compressed body. Most are under 2 cm and the head curves downward. These are common along the shore feeding on the debris that washes ashore. Others can burrow into the skin of whales or live in the plankton. Small Crustaceans-Krill Krill are planktonic and are about 6 cm and look a lot like shrimp. They can be found in the billions in colder water and are the primary food source for whales, penguins and many other fish. Small Crustaceans-Barnacles Barnacles are filter feeders that live their adult life attached to boats, rocks, docks and as well as moving things like crabs and whales. They live under heavy calcareous plates which can open and let the feathery filtering appendages out called cirri, which are actually legs that sweep the water.
Hermaphroditic Animals Barnacles are hermaphroditic and can either donate sperm to a neighbor or accept sperm from a neighbor. Decapods Shrimp, lobsters and craps are called decapods because they have 10 appendages. They have 5 pairs of walking legs of which the first two are usually claws used to obtain food or for defense. Body Plan-Shrimp and Lobsters Shrimps and lobsters tend to have laterally compressed bodies with elongated abdomens (tails) we love to eat. Shrimps are typically scavengers and feed on bits of dead plants and animals on the bottom. Hermit crabs with are not crabs at all live in an abandoned gastropod shell and will sometimes have sea anemones as added protection.
Body Plan-Crabs In crabs the abdomen is tucked under the cephalothorax. The abdomen is visible as a flat, V shaped plate in males; in females it is expanded and U-shaped for carrying eggs. Feeding and Digestion As for digestion, many small crustaceans will filter-feed using stiff hair-like bristles on some of the appendages. Other bristles will move the food along to the mouth.some bottom crustaceans, like shrimp, will have some appendages for walking and others called maxillipeds that are turned forward and sort food on the way to the mouth. Where the Food Goes The food passes to a stomach that typically have chitinous teeth or ridges for grinding the food. The stomachs, some have two chambers, will have digestive glands and absorb nutrients. The intestines end in an anus. Nervous System The nervous system is centralized with a small brain. The sensory organs are well developed and have compound eyes usually at the end of a movable stalk and can be used like periscopes. They have a keen sense of smell using chemicals in the water. They use a variety of signals to communicate with each other using claws, legs or antennas. Male, Female or Both The sexes are separate in most crustaceans. The males usually use specialized appendages to deliver the sperm to the female. In decapods, the mating usually takes place after the female molts. The females of many species can hold the sperm for a while and use it to fertilize separate sets of eggs at different times. Larvae Many crustaceans have planktonic larvae that look nothing like the adult.
ECHINODERMS ECHINODERMS Echinoderms include starfish, sand dollars, sea cucumbers and sea urchins and show radial symmetry. Only the adults are radial, the larvae are bilateral. Their radial symmetry is based on five repeating pieces and lack a head. Oral Side-MOUTH The two sides of an echinoderm are referred to as the oral side (the side containing the mouth) and the aboral side is the side without the mouth. Spiny Skin Echinoderms typically have a complete digestive track and an internal skeleton called an endoskeleton. Although sometimes the spikes look like they are external, they are really covered with a thin layer of ciliated tissue. Echinodermata means spiny-skinned. Water Vascular System Echinoderms have tube feet which are muscular extensions of water vascular system. These tube feet are used for adhesion as well as locomotion.
Water Vascular System Arms on a Starfish Starfish usually have five arms that radiate from a central disk, although some sea stars can have up to 50. The arms are somewhat flexible due to interconnected calcium carbonate plates. Starfish Feeding Most sea stars are predators of bivalves, snails, barnacles and many other bottom living creatures. Sea Urchins Sea Urchins have an endoskeleton made of movable spines. Locomotion occurs by the movable spines. The mouth is on the Bottom and the anus is on the Top
Feeding-Aristotle's Lantern They feed on either attached or floating seaweeds and seagrasses. The mouth is directed downward and has a system of jaws and muscles called Aristotle s Lantern. Sand Dollars Not all echinoderms have spines and five arms. Sand dollars are an example of this. Digestive System Many feed by extending the stomach outward and secreting digestive enzymes and begin digestion. The nutrients are then absorbed and the stomach is pulled back into the body. Nervous System The nervous system is a simple nerve net that coordinates the movement of the tube feet and spines with the absence of a brain.
Reproduction The sexes are separate in most echinoderms. The gonads shed the eggs and sperm into the water at the same time. The fertilized egg goes into the plankton and has bilateral symmetry. Some will not have planktonic larvae and will brood the young in pouches under the body. Regeneration Asexual reproduction takes place in some sea stars and sea cucumbers if the central disk is intact or present. This type of reproduction is called regeneration. Regeneration of a Lost Limb