1. Animals, Part 1 Invertebrates

2. ANIMAL KINGDOM Welcome to your Kingdom!
Animal diversity extends far beyond humans, dogs, cats, birds, and fish. There are up to 200 million living species of animals in the world today. This vast diversity encompasses a spectacular range of variation, from corals to crocodiles. First, we will consider the characteristics that all animals share as well as those that make them different and divide them into taxonomic groups.

3. Animals
Animals are multicellular, heterotrophic eukaryotes with tissues that develop from embryonic layers. Animals differ from both plants and fungi in their mode of nutrition. Plants are autotrophic (make their own food) eukaryotes capable of generating energy through photosynthesis. Fungi are heterotrophs (cannot make their own food) that grow on or near their food, releasing enzymes that digest food outside their bodies. Unlike plants, animals cannot make their own energy so they ingest food, either by eating other living organisms or by eating nonliving organic material. But unlike fungi, animals use enzymes to digest their food after they have ingested it.

4. Protists
Protists are prokaryotes. Plants, fungi, and animals are eukaryotes. Plants, fungi, and animals are multicellular, but animals do not have cell walls like plants and fungi. Cell walls function for structural support. Since animals do not have cell walls, their bodies are held together by proteins, the most abundant being collagen. Collagen is a protein that is secreted by animal cells and deposited outside of the cell boundary, between other cells. The area between cells is called the matrix. Thus, collagen deposits are called an extracellular matrix. Animals have two specialized types of cells that are not seen in any other multicellular organism: muscle cells and nerve cells. Therefore, animals are capable of movement and impulse conduction.

5. Reproduction
Protists usually reproduce by binary fission; they simply duplicate themselves asexually and split in two. Plants and fungi can often reproduce both sexually and asexually. Animals usually reproduce sexually. In most species, a small, flagellated sperm cell fertilizes a larger, non-motile egg, forming a zygote that contains genetic information from both parents. The zygote then undergoes a succession of mitotic cell divisions and develops with layers of embryonic tissues that will develop into a fully mature adult body.

6. Reproduction
Some animals (like humans) develop directly into adults through stages of maturation, but many animals also include at least one larval stage. A larva is a sexually immature form of an animal that looks different from the adult stage, usually eats different food, and may even have a completely different habitat than the adult, as in the case of the tadpole. Animal larvae eventually undergo metamorphosis to transform into the adult animal.

7. Clades and Grades
A clade is defined as a group of organisms consisting of a single common ancestor and all the descendants of that ancestor. Clades are further subdivided by their general appearance. A group of animal species that share the same level of organizational complexity is known as a grade. For instance, slugs and snails are in the same grade, even though snails have shells and slugs do not. Within a grade, organisms are further differentiated according to their body plan.

8. BODY PLANS
Animals can be categorized according to their symmetry (or lack thereof). Most sponges, for example, lack symmetry altogether. Among the animals that do have symmetrical bodies, symmetry can take different forms. Some animals exhibit radial symmetry, such as sea anemones: any imaginary slice through the central axis divides the animal into mirror images. Bilateral symmetry is found in animals such as a lobster or human, which have a mirror image only on the right half and left half of the body, but the top and bottom are different and the anterior (head) and the posterior (tail) ends are different.

9. BODY PLANS
Many animals with a bilaterally asymmetrical body plan (such as arthropods and mammals) have sensory equipment concentrated at the anterior end, along with a central nervous system (brain) in the head. The symmetry of an animal generally fits its lifestyle. Many animals with radial symmetry are sessile (live attached to an object) or planktonic (drifting or weekly swimming, such as jellyfish). Their symmetry allows them to meet the environment equally well from all sides. In contrast, bilateral animals generally move actively from place to place. Their central nervous system enables them to coordinate complex movements involved in crawling, burrowing, flying, or swimming.
Those organisms that have bilateral symmetry are grouped into a category called the Bilateria. They can be further divided into invertebrates and vertebrates.

10. ANIMAL KINGDOM A. PORIFERA (no symmetry; sponges)
B. CNIDARIA (radial symmetry; jellyfish)
C. BILATERIA (bilateral symmetry; all other animals)
  1. INVERTEBRATES
a) PLATYHELMINTHES (flatworms)
b) NEMATODA (roundworms)
c) ANNALIDA (segmented worms)
d) MOLLUSCA (snails, clams, squid, octopus)
e) ARTHROPODA (spiders, insects, crabs)
f) ECHINODERMATA (starfish)
2. VERTEBRATES

11. INVERTEBRATES
Most of the animals alive today are invertebrates. Invertebrates account for 95% of known animal species and all but one of the animal phyla listed above. Invertebrates occupy almost every habitat on earth, from scalding water released by deep-sea hydrothermal events to the rocky, frozen ground of Antarctica.

12. PORIFERA A. PORIFERA (no symmetry; sponges)
Sponges are sessile and have a porous body and choanocytes. The term “sessile” refers to it being anchored in one spot. Animals that are “sedentary” are those that do not move much. Sponges are so sedentary that they were mistaken for plants by the ancient Greeks.
Sponges have complex tissues. They lack a digestive tract, lack body symmetry, and have no nerves or muscles.

13. PORIFERA
Living in both fresh and marine (salt) water, sponges are suspension feeders: they capture food particles suspended in the water that pass through their body. Their body resembles a sac perforated with pores. Water is drawn through the pores into a central cavity, and then flows out of the sponge through a larger opening. Sponges lack true tissues, but the sponge body does contain several different cell types. Lining the interior of the central cavity are flagellated choanocytes, or collar cells. A choanocyte is a flagellated cell which sweeps water through a sponge’s body. The flagella move back and forth, generating a water current, and the collars trap food particles that the choanocytes then ingest by phagocytosis.

14. PORIFERA
Most sponges are hermaphrodites (named for the Greek god Hermes and goddess Aphrodite), meaning that each individual has both male and female sexual reproductive organs. Almost all sponges exhibit their hermaphroditism in sequence, functioning first as one sex and then as the other. Gametes (either an egg or a sperm) arise from the choanocytes. The eggs stay within the sponge, but the sperm are carried out of the sponge by the water current. Cross-fertilization results from some of the sperm being drawn into neighboring individuals. Fertilization occurs within the sponge, where the zygotes develop into flagellated, swimming larva and disburse from the parent sponge. Upon settling on a suitable substrate, a larva develops into the sessile adult.

15. PORIFERA
Sponges produce a variety of antibiotics and other compounds that researchers can use to fight human diseases. For example, one compound in marine sponges can kill penicillin-resistant strains of the bacterium Streptococcus. Other research is being done to find anti-cancer agents from sponges. Also, sponges are made of glass-like fibers that are one of the strongest glasses known to man. By studying the glass sponge, scientists could learn how to create unbreakable glass. It may also hold the secret to making glass at room temperature, instead of the extremely high temperatures required to do so today.

16. CNIDARIA B. CNIDARIA (radial symmetry; jellyfish)
Cnidarians have radial symmetry, a gastrovascular cavity, and cnidocytes. This is one of the oldest animal groups, and they have diversified into a wide range of both sessile and floating forms, including jellyfish, corals, and hydras. The basic body plan of a cnidarian is a sac with a central digestive compartment called the gastrovascular cavity. A single opening to this cavity functions as both mouth and anus.

17. CNIDARIA
There are two variations on this body plan: the sessile polyp and the floating medusa. Polyps are cylinder- shaped organisms that adhere to a substrate (like a rock) and extend their tentacles, waiting for prey. Examples of the polyp form include hydras and sea anemones. A medusa is a flattened, mouth-down version of the polyp. It moves freely in the water by a combination of passive drifting and contractions of its bell-shaped body. An example is a free-swimming jellyfish (called a “jellie). The tentacles of a jellie dangle from the mouth area, which points downward. Some cnidarians exist only as polyps or only as medusae; others have both a medusa stage and a polyp stage in their life cycle.

18. CNIDARIA
Cnidarians are carnivores that use tentacles arranged in a ring around their mouth to capture prey and to push food into their gastrovascular cavity, where digestion begins. The undigested remains are egested through the mouth/anus. The tentacles are armed with batteries of cnidocytes, unique cells that function in defense and the capture of prey. Cnidocytes contain cnidae (from the Greek word meaning nettle, or stinging thorn). A cnidae is a capsule-like organelle that delivers a chemical sting. Some cnidae have very long threads that stick to or entangle small prey that bump into its tentacles.

19. BILATERIA C. BILATERIA (bilateral symmetry; all other animals)
The development of a head where sensory structures are concentrated accompanied the evolution of bilateral symmetry.

20. INVERTEBRATES 1. INVERTEBRATES a) PLATYHELMINTHES (flatworms)
1) Trematoda (blood flukes)
2) Cestoda (tapeworms)
b) NEMATODA (roundworms)
c) ANNALIDA (segmented worms)
1) Oligochaetes (earthworms)
2) Hirudinea (leeches)
d) MOLLUSCA
1) Gastropods (snails and slugs)
2) Bivalves (clams, oysters, muscles, and scallops)
3) Cephalopods (octopuses and squid)
e) ARTHROPODA
1) Cheliceriforms (spiders)
2) Myriapods (millipedes and centipedes)
3) Insects
4) Crustaceans (crabs)
f) ECHINODERMS (starfish)

21. PLATYHELMINTHES PLATYHELMINTHES (flatworms)
Flatworms have no radial symmetry; they live in marine, fresh water, and damp earth habitats. In addition to many free living forms, flatworms include many parasitic species, such as flukes and tapeworms. Flatworms are named because their bodies are thin; the smallest are nearly microscopic, while some tapeworms can be over 20 m long. Flatworms have no anus, but have a highly branched gastrovascular cavity with only one opening. Although there are four classes of flatworms, we will only discuss the two that are parasites: Trematoda and Cestoda.

22. Trematodes
1) Trematodes (blood flukes) live as parasites in or on other animals. Many have suckers for attaching to internal organs or to the outer surfaces of the host. Reproductive organs occupy nearly the entire interior of these worms. Trematodes parasitize a wide range of hosts. Many require an intermediate host in which larvae develop before infecting the final host where the adult worms live. For example, Trematodes that parasitize humans spend part of their lives in snail hosts million people around the world are infected with blood flukes. Individual flukes can survive in humans for more than 40 years.

23. Cestoda
2) Cestoda (tapeworms) are parasites that live inside vertebrates, including humans. The anterior end, or scolex, has suckers or hooks that lock the worm to the intestinal lining of the host. Tapeworms have no digestive tract of any sort, and no gastrovascular cavity; they absorb nutrients directly from the host intestine. The length of the tapeworm is a long ribbon of units called proglottids, which are sacs of sex organs. Mature proglottids, loaded with thousands of eggs, are released from the tail end of a mature tapeworm and leave the host body in feces.

24. Cestoda
If the feces contaminates food or water ingested by other animals such as pigs or cattle, the tapeworm eggs develop into larva that form cysts in the muscles of these animals. Humans acquire these larvae by eating undercooked meat, and the worms develop into mature adults within the human. Large tapeworms can block the intestines and rob enough nutrients from the human host to cause nutritional deficiencies.

25. NEMATODA NEMATODA (roundworms)
Roundworms are among the most widespread of all animals; they are found in most aquatic habitats, in the soil, in moist tissues of plants, and in body fluids and tissues of animals. They do not have a segmented body. Their size ranges from 1 mm to more than 1 m in length, tapering to a fine tip at the posterior end. The body is covered by a tough coat called a cuticle; as the worm grows it periodically sheds the old cuticle and secretes a new, larger one.

26. NEMATODA
Nematodes have a digestive canal, although they lack a circulatory system. Nutrients are transported throughout the body by way of a fluid. Nematodes have muscles that produce a thrashing motion when they contract.
Nematode reproduction is sexual; the sexes are separate and females are larger than males. A female may deposit 100,000 fertilized eggs per day. There are 25,000 known species, most of which are not parasites and live in moist soil and decomposing organic matter on the bottoms of the lakes and oceans. They play an important role in decomposition and nutrient cycling.

27. NEMATODA
Many nematodes are important agricultural pests that attack the roots of plants. Some nematodes parasitize animals. Humans host at least 50 nematodes species, including pinworms and hookworms. One notorious nematode is Trichenella, the worm that causes trichinosis. Humans acquired this nematode by eating undercooked infected pork with juvenile worms and encyst in the muscle tissue. Within the human intestine, the juveniles develop into adults, burrow through the body and travel to other organs, including muscles, where they encyst.

28. ANNALIDA ANNALIDA (segmented worms)
Annalida means “little rings”. They live in the sea, fresh water, and damps soil. They range in length from 1 mm to 3 m, the lakes of a giant Australian earthworm. They are divided into three classes, but we will discuss two: Oligochaetes (earthworms) and Hirudinea (leeches).

29. Oligochaetes 1) Oligochaetes (earthworms)
Oligochaetes (“Oligo” means “few” and “chaetes” means “hairs”) are named for their sparse bristles. Earthworms eat their way through the soil, extracting nutrients as the soil passes through the digestive canal. Undigested material, mixed with mucus secreted into the canal, is excreted through the anus. Earthworms till the earth, adding to their feces to improve the texture of the soil.

30. Oligochaetes
Earthworms are hermaphrodites, but they cross- fertilize. Two earthworms mate by aligning themselves in such a way that they exchanged sperm, and then they separate. The received sperm are stored temporarily while an organ secretes a mucus cocoon. The cocoon slides along the worm, picking up the eggs and then the stored sperm. The cocoon then slips off the worm’s head and remains in the soil while the embryos develop. Some earthworms can also reproduce a sexually by fragmentation followed by regeneration.

31. Hirudinea 2) Hirudinea (leeches)
The majority of leeches inhabit freshwater, but there are also marine and terrestrial leeches found in moist vegetation. Some are parasites that suck blood by attaching temporarily to other animals, including humans. The host is usually oblivious to this attack because the leach secretes an anesthetic. It then secretes another chemical, hirudin, which prevents the blood from coagulating. The parasite then sucks as much blood as it can hold, often more than 10 times its own weight. After the gorging, a leech can last for months without another meal.

32. Hirudinea
Until this century, leeches were frequently used for blood-letting. It was thought that diseases were carried in the blood, and if the blood was drained, the patient would recover. Today they are used to drain blood that accumulates in tissues following certain injuries or surgeries. Researchers are also investigating the potential use of hirudin to dissolve unwanted blood clots that form during surgery or as a result of heart disease.

33. MOLLUSCA MOLLUSCA (snails, clams, squid, octopus)
Mollusks have a muscular foot, a visceral mass, and a mantle. This category includes snails and slugs, oysters and clams, and octopuses and squids. Most mollusks are marine, though some inhabit freshwater, and there are snails and slugs that live on land. The term “mollusks” means “soft”, but most mollusks are protected by a hard shell of calcium carbonate. Slugs, squids, and octopuses have a reduced internal shell or have lost their shell completely during evolution.

34. MOLLUSCA
The body of a mollusk has three main parts: a muscular foot, used for movement; a visceral mass containing most of the internal organs; and a mantle, a fold of tissue that drapes over the visceral mass and secretes a shell if one is present. Many mollusks feed by using a strap-like rasping organ called a radula to scrape up food. Most mollusks have separate sexes, but many snails are hermaphrodites. Their lifecycle usually includes a larval stage.

35. Gastropods
About three quarters of all mollusks are gastropods. Most are marine, but garden snails and slugs are among the gastropods that have adapted to land. Most gastropods have a single, spiral shaped shell into which the animal can retreat when threatened. They often have a distinct head with eyes at the tips of its tentacles. They move by a rippling motion of their foot. They use their radula to graze on algae or plants. Several species, however, are predators, and their radula is modified for boring holes into the shells of other mollusks. In these species, the teeth of the radula form poison darts that are used to subdue prey.

36. Bivalves
Another class of mollusks is the Bivalves, which include many species of clams, oysters, muscles, and scallops. Bivalves have a shell divided into two halves, hinged at the middle, and powerful muscles to draw them tightly together. Bivalves have no distinct head, and the radula has been lost. Some bivalves have eyes and sensory tentacles along the outer edge of their mantle. Most bivalves are suspension feeders. They trap fine food particles in mucus that coats their gills, and cilia (small hairs) sweep the particles into their mouth. Most bivalves lead rather sedentary lives. Sessile muscles secrete strong threads that tether them to rocks, docks, boats, and the shells of other animals. However, clams can pull themselves into the sand or mud, using their muscular foot for an anchor, and scallops can skitter along the sea floor by flapping their shelves, rather like the mechanical false teeth sold in novelty shops.

37. Cephalopods 3) Cephalopods
Cephalopods are active predators. They use their tentacles to grasp prey and their beak-like jaws to attack and inject an immobilizing poison. The foot of a cephalopod has become modified to include a muscular siphon and parts of the tentacles and head (cephalopod means “head-foot”). Most octopuses creep along the sea floor in search of crabs and other food. Squids dart about by drawing water into their cavity and then firing a jet of water through their siphon like a water balloon releasing. They change directions by pointing the siphon in different directions.

38. Cephalopods
The chambered Nautilus is the only cephalopod that still has a shell. Cephalopods are the only mollusks with a closed circulatory system, well developed sense organs, and a complex brain. The ability to learn and behave in a complex manner is probably more critical to fast-moving predators then to sedentary animals such as clams. Most species of squid are less than 75 cm long, but the giant squids that live in the deep ocean may be larger than 20 m in length. These species feed on large fish; their remains have been found in the stomachs of sperm whales, which are probably their only natural predator.

39. ARTHROPODA ARTHROPODA (spiders, insects, crabs)
Arthropods are segmented coclomates that have an exoskeleton and jointed appendages. This includes crustaceans, spiders, and insects. There are about a billion billion arthropods in the world, most of which are insects. The success of arthropods it's largely related to their segmentation, hard exoskeleton, and jointed appendages (arthropod means “jointed feet”). Arthropod appendages are variously adapted for walking, swimming, feeding, sensory reception, copulation, and defense. This permits the division of labor among different regions.

40. ARTHROPODA
The body of an arthropod is completely covered by the cuticle, an exoskeleton (external skeleton). The exoskeleton and it is paper thin and flexible over the joints. The rigid exoskeleton protects the animal and provides points of attachment for the muscles that move the appendages. But it also means that an arthropod cannot grow without occasionally shedding its exoskeleton and producing a larger one. This process is called molting, and it requires energy. The recently molted arthropod is also vulnerable to dangers until its new, soft exoskeleton hardens.
 Arthropods have well-developed sensory organs, including eyes, smell receptors, and antennae that function in both touch and smell. These are concentrated at the head of the animal.

41. ARTHROPODA
Like many mollusks, arthropods have an open circulatory system in which the fluid called hemolymph is propelled by a heart to the tissues and organs. The term blood is reserved for fluid in a closed circulatory system. A variety of organs specialized for gas exchange exists in arthropods. Most aquatic species have gills that allow for increased surface area in contact with the surrounding water from which they absorb oxygen. Most insects have tracheal systems, which are branched air ducts leading into the body. There are four major groups of arthropods.

42. Cheliceriforms 1) Cheliceriforms
Cheliceriforms have claw-like feeding appendages called chelicerae which serve as pinchers or fangs. Most of the marine Cheliceriforms are extinct except for sea spiders and horseshoe crabs. Most modern Cheliceriforms are arachnids, a group that includes scorpions, spiders, ticks, and mites.
Ticks and mites are mainly parasitic arthropods. Nearly all ticks are bloodsucking parasites on the body surfaces of animals. Parasitic mites live on a variety of animals and plants.

43. Arachnids
Arachnids have a head that has six pairs of appendages: chelicerae, a pair of appendages that function in sensing or feeding, and four pairs of walking legs. Spiders use their fang-like chelicerae, which are equipped with poison glands, to attack prey. As the chelicerae chew the prey, the spider spills digestive juices onto the torn tissues. The food softens, and the spider sucks up the liquid meal. A unique adaptation of many spiders is the ability to catch insects by constructing webs out of silk, a liquid protein produced by abdominal glands. The silk is spun by organs called spinnerets into fibers that solidify. Each spider engineers a style of web characteristic of its species and builds it perfectly on the first try.

44. Arachnids
Various spiders also use silk in other ways: as a drop line for rapid escape, as a cover for eggs, and even as a gift wrap for food that males offer females during courtship. Spider webs are more lightweight, flexible, and waterproof than anything known to man, and it is also many times stronger than steel. Scientists want to synthesize it to make rip-proof clothing, from children’s garments to military uniforms. Scientists have spliced spider venom genes into corn and other food crops as a "natural pesticide" to deter insects and birds from feeding on the plants.

45. Scorpions
Scorpions have two appendages that are pinchers specialized for defense and the capture of food. The tip of the tail has a poisonous stinger. Scientists are using scorpion venum for brain-cancer therapy.

46. Myriapods
2) Myriapods
Myriapods (many feet) include millipedes and centipedes. They are all terrestrial (live on land). Millipedes have a large number of legs, but fewer than the “thousand” their name implies. Millipedes have similar segments over most of the body. Each segment has two pairs of legs. Millipedes eat decaying leaves and other plant matter. Centipedes are carnivores. Each segment has one pair of legs like the millipedes, but centipedes have poison claws on their foremost trunk segment that paralyze prey and aid in defense.

47. Insects
Most insects have three body parts. They are the head, thorax, and abdomen. Insects live in almost every terrestrial habitat and in fresh water, and flying insects fill the air. However, insects are rare in the oceans, where crustaceans are the dominant arthropods. Flight is one key to the great success of insects. An animal that can fly can escape many predators, find food and mates, and disperse to new habitats much faster than an animal that must crawl on the ground. Many insects have one or two pairs of wings that emerge from the thorax. Because the wings are extension of the cuticle and not true appendages, insects can fly without sacrificing any walking legs. By contrast, the flying vertebrates (birds and bats) have one of their two pairs of walking legs modified into wings and are generally quite clumsy on the ground.

48. Insects
Dragonflies were among the first insects to fly. The wings of bees and wasps are hooked together and move as a single pair. Butterfly wings operate in a similar fashion because the anterior pair overlaps the posterior wings. In beetles, the posterior wings function in flight, while the anterior ones are modified as covers that protect the flight wings when the beetle is on the ground or burrowing.

49. Insects
Many insects undergo metamorphosis during their development. In the incomplete metamorphosis of grasshoppers, the young (called nymphs) resemble adults but are smaller and lack wings. The nymph goes through a series of molts, each time looking more like an adult. Insects with complete metamorphosis have larval stages specialized for eating and growing that are known by such names as maggot, grub, or caterpillar. The larval stage looks entirely different from the adult stage, which is specialized for dispersal and reproduction. Metamorphosis from the larval stage to the adult occurs during a pupal stage. Although caterpillars chew on leaves, moths and butterflies take in nectar by sucking it through a tube consisting of modified mouthparts.

50. Insects
Reproduction in insects is usually sexual, with separate male and female individuals. Adults come together and recognize each other as members of the same species by advertising with bright colors (butterflies), sound (crickets), or odors (moths). Fertilization is generally internal. Sperm are deposited directly into the female’s vagina in most cases. Many insects mate only once in a lifetime. After mating, a female often lays her eggs on an appropriate food source where the next generation can begin eating as soon as it hatches.

51. Insects
Animals as numerous, diverse, and widespread as insects are bound to affect the lives of all other organisms, including humans. On the one hand, we depend on bees, flies, and many other insects to pollinate our crops. On the other hand, insects are carriers for many diseases, including African sleeping sickness (tsetse fly), and malaria (mosquitoes). Furthermore, insects compete with humans for food: in parts of Africa for instance, insects claim about 75% of the crops. Trying to minimize their losses, farmers in the United States spend billions of dollars each year on pesticides, spraying crops with massive doses of some of the deadliest poisons ever invented.

52. Crustaceans
While arachnids and insects thrive on land, crustaceans have remained in aquatic environments. Crustaceans typically have branched appendages that are extensively specialized. Lobsters and crayfish, for instance, have a toolkit of 19 pairs of appendages. The anterior most appendages are antennae; crustaceans are the only arthropods with two pairs. Three or more pairs of appendages are modified as mouthparts, including the hard mandibles. Walking legs are present in the thorax, and unlike insects, crustaceans have appendages on the abdomen. A lost appendage can be regenerated.

53. Crustaceans
Sexes are separate in most crustaceans. In the case of lobsters and crayfish, the male uses a specialized pair of abdominal appendages to transfers sperm to the female. Most aquatic crustaceans go through one or more swimming larval stages.
Some crustaceans are called isopods, which can be found in water or on land. Among the terrestrial isopods are the pill bugs, common on the undersides of moist logs and leaves.

54. Crustaceans
Lobster, crayfish, crabs, and shrimp are all called the decapods. The cuticle of decapods is hardened by calcium carbonate, forming a protective shield. Most decapods are marine. Crayfish, however, live in fresh water, and some tropical crabs live on land.
Copepods are small crustaceans such as krill (“whale food”), which live on algae. Krill are a major food source for whales and humans, and are also used as an agricultural fertilizer.

55. Crustaceans
Barnacles are a group of mostly sessile crustaceans whose cuticle is hardened into a shell. Most barnacles anchor themselves to rocks, boat hulls, and other submerged surfaces. The adhesive they use is as strong as any synthetic glue. To feed, they extend appendages from their shell to strain food from the water. Other barnacles live as parasites inside hosts such as crabs.

56. Crustaceans
If barnacles are allowed to accumulate on a ship's hull, the ship will travel slower in the water, or it will have to burn more fuel to keep up its speed, than it would otherwise. A six-month growth of barnacles can result in having to burn 40 to 45 percent more fuel to maintain cruising speed. Removing barnacles from ships' hulls costs ship owners more than $125 million a year. Although many new ideas have been tested, the best way to keep barnacles from growing on a ship's hull is still to paint the hull with copper bottom paint.

57. Crustaceans
Barnacle cement, the substance the animals use to glue themselves to ships' bottoms and to rocks, has attracted the interest of doctors. A layer of this cement 3/10,000 of an inch thick over one square inch will support a weight of 7000 pounds. It is even stronger than epoxy cement. At temperatures above 6000°F the glue will soften but not melt, and at 380°F the cement will not crack. It does not dissolve in most strong acids, bases, organic solvents, or water. If man could learn to manufacture this cement, which barnacles have been using for millions of years, it could be used to mend broken bones and hold fillings in teeth.

58. ECHINODERMATA ECHINODERMATA (starfish)
Starfish and most other echinoderms (meaning “spiny skin”) are slow moving or sessile marine animals. A thin skin covers and endoskeleton of hard plates. They are prickly from skeletal bumps and spines. Unique to echinoderms is the water vascular system, a network of canals that branch into the extensions called tube feet that function in locomotion and eating. Sexual reproduction of echinoderms usually involves separate male and female individuals that release their gametes into the water. The six classes of echinoderms are sea stars, brittle stars, sea urchins and sand dollars, sea lilies and feather stars, sea cucumbers, and sea daisies.