Animal Form And Function Part 1 - Invertebrates Biology PFHS Lecture Outline: What is an animal? Origin of animal body form diversity Correlation between form and function Organization of body plans into grades Views of animal diversity
What is an animal? How do we define an animal? While there are exceptions to nearly every criterion for distinguishing an animal from other life forms, the following criteria, when taken together, create a reasonable definition. 1. Animals are multicellular eukaryotes. 2. Animals are Heterotrophs: Cannot make their own food - cannot convert simple inorganic molecules into complex organic molecules. They must take in preformed organic molecules through ingestion, eating other organisms or organic material that
is decomposing. Plants are Autotrophs they can synthesize their nutrition from simple inorganic molecules into complex organic molecules. 3. Animal cells lack cell walls that provide structural supports for plants and fungi. Cell Membrane: Every cell is enclosed in a membrane. The membrane is a double layer of lipids (lipid bilayer) but is made quite complex by the presence of numerous proteins that are important to cell activity.
Animal Cell Cell Wall: Prokaryotic cells, fungi cells, and plant cells have a rigid cell wall in addition to the cell membrane that is made up of polysaccharides. The cell wall provides and maintains the shape of these cells and serves an extra protective barrier. Plant Cell 4. Locomotion: Animals are capable of moving from one place to another. This complex function is achieved by
coordinated functioning of two unique tissue types. i. Nervous tissue for impulse conduction ii. Muscle tissue for movement. Exception: Some animals do not have locomotor ability sedentary. 5. Reproduction: Most animals reproduce sexually, with the diploid stage usually dominating the life cycle. In most species, a flagellated haploid sperm fertilizes a haploid egg. The fertilized diploid egg - zygote - undergoes cleavage, a succession mitotic cell divisions, leading to the formation of a multicellular, hollow ball of cells called the
blastula. 6. Characteristics that are true for most animals, but not all The multicellular bodies of animals are held together with the extracellular proteins, especially collagen. In addition, other structural proteins create several types of intercellular junctions, including tight junctions, desmosomes, and gap junctions, that hold tissues together. Animals have skeleton endoskeleton (bones) or exoskeleton (shells) that provides rigidity of
form. Correlation between Form and function Animals show a correlation between body form (structure) and function. Form fits function at all the levels of life, from molecules to organisms. Knowledge of a structure provides insight into what it does and how its works. Conversely, knowing the function of a structure provides insight about its construction. Therefore, sometimes distinction between anatomy and physiology is blurred.
Animal Classification: Living animals are classified in to 35 different phyla based body plans. Most are marine phyla, only a few terrestrial phyla most species diversity is in the ocean. We will cover about 13 of these phyla
Four basic features of animal body plan are the basis for classification of animals into various phyla.: Body symmetry Germ Layer Coelom Development pattern 1. Body Symmetry: Mainly based on anatomical features in adults and certain
details of embryonic development. The symmetry of an animal generally fits its lifestyle. i. Radial Symmetry ii. Bilateral Symmetry iii. Asymmetry (not common) i. Radial Symmetry: Many radial animals are sessile or planktonic and need to meet the environment equally well from all
sides. Multiple planes of symmetry ii. Bilateral symmetry: Animals that move actively are bilateral. Head, anterior end, encounters the environment -food, danger, and other stimuli. Bilateral symmetry is associated with cephalization, concentration of sensory equipment on the anterior end head. Cephalization leads to the development of central nervous system.
Dorsal Posterior Single plane of symmetry Anterior Ventral 2. Germ Layers: Three germ layers: Ectoderm: forms the outer covering and, the central nervous system (if present). Endoderm: lines the digestive tract and the organs derived from it, such
as the liver and lungs of vertebrates. Mesoderm: lies between the endoderm and ectoderm and develops into muscles and other organs e.g., kidneys and gonads. i. Diploblastic: have two germ layers ectoderm and endoderm. e. g., the radiata. ii. Triploblastic: have three germ layers ectoderm, endoderm and mesoderm. e. g., the bilateria 3. Coelom: The germ layers form a cavity around the internal organs Coelom. Coelom has many functions.
Its fluid cushions the internal organs, helping to prevent internal injury. The noncompressible fluid of the body cavity can function as a hydrostatic skeleton against which muscles can work. The present of the cavity enables the internal organs to grow and move independently of the outer body wall. A coelom the body cavity - could be a true coelom or a false coelom. Based on the type of coelom and presence or absence of a coelom and animal could be classified as:
Coelomate Pseudocoelomate (false coelom) Acoelomate (no coelom) Coelomates are organisms with a true coelom, a fluid-filled body cavity completely lined by mesoderm. The inner and outer layers of tissue that surround the cavity connect dorsally and ventrally to form mesenteries, which suspend the internal organs. Pseudocoelomates, have a body cavity, but it is not completely lined by mesoderm, e.g., rotifers (phylum Rotifera) and the roundworms (phylum Nematoda).
Acoelomates have a solid body and lack a body cavity, e.g., (the phylum Platyhelminthes) . 4. Development pattern: DEUTEROSTOMES PROTOSTOMES (a) Cleavage (zygote divides into ball of cells) Spiral
cleavage (b) Gastrulation (cells invaginate to form gut) Radial cleavage Mouth Pore becomes mouth
Pore becomes anus Anus (c) Coelom formation Gut Mesoderm Block of solid mesoderm splits to form coelom
Coelum Gut Mesoderm Mesoderm pockets pinch off of gut to form coelom Major Steps in Animal Form and Function Choanoflagellates Poriferans
Protist ancestor Ectoderm Multi-cellularity Endoderm Cnidarians Ectoderm
Mesoderm Endoderm Two tissue layers Mouth Protostomes Anus Body cavity Three tissue layers, a body cavity, and
bilateral symmetry Developing mouth Ectoderm Mesoderm Endoderm Deuterostomes Anus New forms of embryological, development, including the formation of the mouth secondarily
Porifera Porifera Poriferans are commonly referred to as sponges. fossil sponges are among the oldest known animal fossils, dating from thelate precambrian. The approximately 5,000 living sponge species are classified in the phylum Porifera
Porifera Sponges are characterized by the possession of a feeding system unique among animals. Poriferans don't have mouths; instead, they have tiny pores in their outer walls through which water is drawn. Cells in the sponge walls filter goodies from the water as the water is pumped through the body and out other larger openings. The flow of water through the sponge is unidirectional, driven by the beating of
flagella which line the surface of chambers connected by a series of canals. Sponge cells perform a variety of bodily functions and appear to be (b) Central cavity Gelatinous middle layer with skeletal materials and motile cells that can become gametes
Microvilli Collar cell Motile cell Pore Central cavity Collar cells are similar in form to choanoflagellate protists, suggesting that animals derived from
colonial choanoflagellates Skeletal material (spicule) Fig. 13.04 Porifera Form symbiotic relationships with bacteria and fungi Produce a wide array of
chemical defense compounds Useful for Medicinal lead compounds Discodermalide a potent anticancer compound in clinical trials Introduction to Cnidaria Jellyfish, corals, and other stingers. . . Cnidarians are incredibly diverse in form, as evidenced by colonial siphonorphores, massive medusae and corals, feathery hydroids, andbox jellies with complex eyes.
Yet, these diverse animals are all armed with stinging cells called nematocysts. Cnidarians are united based on the presumption that their nematocysts have been inherited from a single common ancestor. There are four major groups of cnidarians: Anthazoa - which includes true corals, anemones, and sea pens Cubozoa - the amazing box jellies with complex eyes and potent toxins Hydrozoa - the most diverse group with siphonophores, hydroids, fire corals, and many medusae Scyphozoa - the true jellyfish. Cnidaria There are four major groups of cnidarians:
Anthazoa - which includes true corals, anemones, and sea pens Coral Reef Ecosystems Coral reefs and other marine ecosystems, however, contain more varied life forms than do land habitats. All but one of the world's 35 phyla are found in marine environments -- 15 exclusively so. Coral reefs are found in shallow waters, extending to depths of 30 meters and cover 15 percent of the world's coastline (0.2% of the total area of oceans)
Fish production on these reefs and on the adjacent continental shelf could amount to nearly 10 percent of global fisheries production if fully exploited. Coral reefs also protect coastal areas from erosion. In the case of coral atolls, coral provides the foundation of the island itself. In the Indian Ocean, 77 percent of isolated islands and island archipelagoes are built exclusively of reef depositions. Affiliated Ecosystems Coral reefs stand out from other marine environments because of their species diversity, but many coral reef species also depend on other affiliated ecosystems.
Often, coral reefs, mangroves, and sea grass beds are linked physically and biologically: 1. reefs serve as breakwaters that allow coastal mangroves to develop; 2. the calcium of the reef provides the sand and sediment in which mangroves and sea grasses grow; and 3. the mangroves and sea grass communities provide energy input into the coastal ecosystem and serve as spawning, rearing, and foraging habitat for the many of the species associated with the reefs. Coral Reefs
Mangroves Sea Grass Beds Coral Reef Ecosystems Some Facts and Figures on Coral Reefs as a Fishery Resource Healthy coral reefs can produce more than 20 metric tons of fish and other edible marine products per square kilometer per year. Unfortunately, 95% of the country's coral reefs are various stages of deterioration due to destructive and illegal practices, siltation and sedimentation, and pollutants from industrial and domestic wastes and construction activities, among others. The Destruction of Coral Reefs Fishing practices destructive to coral reefs include muro-ami,
cyanide fishing, trawl fishing, indiscriminate harvesting, and dynamite fishing. Blast or dynamite fishing alone destroys an average of one to three square meters of corals per blast. consider this -- coral grows very slowly at an average of one to two inches a year. Thus, it takes hundreds of years to grow a coral reef! Cnidaria There are four major groups of cnidarians: Hydrozoa - the most diverse group with siphonophores, hydroids, fire corals, and many medusae
Cnidaria There are four major groups of cnidarians: Scyphozoa the true jellyfish Cnidaria There are four major groups of cnidarians: Cubozoa - the amazing box jellies with complex eyes and potent toxins (e) Radial body plan
Jellyfish, from top Nerve cell Nematocyst discharged (f) Tentacle Nematocystbearing cell Mouth
Epidermis Epidermis Gastrodermis Mesoglea Polyp form Gastrovascular cavity Medusa form
Mesoglea Mouth Muscle cells Digestive enzymesecreting cell Fig. 13.05 Slide 4
Treatment for Stings Primary first aid for any jellyfish sting should be to minimize the number of nematocysts discharging into the skin and to reduce the harmful effects of the venom. If stung by a jellyfish, the victim should carefully remove the tentacles that adhere to the skin by using sand, clothing, towels, seaweed or other available materials. As long as tentacles remain on the skin, they will continue to discharge venom. A variety of substances have been used to reduce the effects of jellyfish stings. Meat tenderizer, sugar, vinegar, plant juices and sodium bicarbonate have all been used with varying degrees of success. Methylated spirits and other forms of alcohol formerly recommended for inhibiting stinging cells actually stimulate them and
may increase pain and cause severe skin reactions. Picric acid and human urine also cause a discharge of nematocysts and should not be used. Victims of serious stings should make every effort to get out of the water as soon as possible to avoid drowning. If swelling and pain from more serious stings persists, prompt medical attention should be sought. Recovery periods can vary from several minutes to several weeks. Adult female medusa Tentacle
Gonad Adult male medusa Egg Sexual reproduction Sperm New medusa Zygote Development Planula
larva Cilia Asexual reproduction Stack of developing medusae Differentiation Hydra-like polyp
Fig.13.06 Protostomes Fruit fly larva, cross section First opening becomes the mouth Anus Fig. 13.08a Platyhelminthes (Flatworms)
Platyhelminthes Reproduction is by both sexual and asexual means. For sexual reproduction, planarians are hermaphroditic organisms. Asexual reproduction is accomplished by fragmentation followed by regeneration, and many of these free-living flatworms have remarkable regenerative abilities. As a result of this, the turbellarian flatworms have contributed a great deal of information to our knowledge of regeneration.
Hermaphrodite An organism which has both male and female organs, and produces both male gametes (sperm) and female gametes (eggs). The organism can have both types of organs at the same time (simultaneous hermaphrodite) or have one type early in life and the other type later in life (sequential hermaphrodite). Platyhelminthes Class Trematoda (Flukes) The flukes are all parasitic organisms; the adult stage living in or on a wide variety of vertebrate animals. Of
the groups the blood flukes are the most important as they are the causative agents for the human disease known as Schistosomiasis. This debilitating disease affects some 400,000,000 persons in Asia, Africa, parts of South America and the Caribbean Class Cestoda (Tapeworm) Tapeworms are elongate, intestinal parasites consisting of an anterior scolex for attachment and numerous body segments called proglottids. They are highly modified to a parasitic existence and have no digestive system. Tapeworms also have complicated life histories. Tape Worms
The adult lives in the small intestine. It is hooked onto the intestinal wall by a structure called a rostellum which is sort of like a hat with hooks on it. The tapeworm also has six rows of teeth to grab on with. Once docked like a boat to the host intestinal wall, the tapeworm begins to grow a long tail. The tapeworm absorbs nutrients through its skin as the food being digested by the host flows past it. Older segments are pushed toward the tip of the tail as new segments are produced by the
neckpiece. By the time a segment has reached the end of the tail, only the reproductive tract is left. When the segment drops off, it is basically just a sac of tapeworm eggs. 28 foot tape worm (b) The flatworm body plan Dorsal Posterior Left
Right Head Anterior Ventral Direction of movement (c) Organ sytems Nervous system
Seminal vesicle Mouth Muscular tube (phaynx) Digestive system Ovary Eyespot Brain Fig. 13.09 Platyhelminthes
(Why are flatworms flat??) The simplest animals that are bilaterally symmetrical and triploblastic (three tissue layers) Flatworms have no body cavity (NO COELEM) other than the gut They lack an anus; the same pharyngeal opening both takes in food and expels waste. Because of the lack of any other body cavity, in larger flatworms the gut is often very highly branched in order to transport food to all parts of the body. The lack of a cavity also constrains flatworms to be flat; they must respire by diffusion, and no cell can be too far from the outside, making a flattened shape
necessary. Protostomes Fruit fly larva, cross section First opening becomes the mouth Anus Fig. 13.08a Annelids The phylum includes earthworms and their relatives, leeches, and
a large number of mostly marine worms known as polychaetes. Various species of polychaete are known as lugworms, clam worms, bristleworms, fire worms, sea mice, and "EWWW! I stepped on that THING!" Annelids can be told by their segmented bodies. Polychaetes (meaning "many bristles") have, predictably, many bristles on the body, while earthworms and leeches have fewer bristles. There are about 9000 species of annelid known today. Annelids are triploblastic and contain a coelom They also have well developed organs. Annelids
The internal organs of annelids are well developed. They include a closed, segmentally-arranged circulatory system and a digestive system with mouth and anus. Gases are exchanged through the skin. The nervous system includes a pair of cephalic ganglia attached to double nerve cords that run the length of the animal along the ventral body wall. Annelids have some combination of tactile organs, chemoreceptors, balance receptors, and photoreceptors; some forms have fairly well developed eyes, including lenses. Anus 5 Hearts Crop Gizzard
Brain Mouth Blood Nerve Coelom Intestine vessel cord (d) A segment Partitions (septa)
Excretory units (nephridia) Blood vessel Intestine Funnel Nerve cord Excretory pores Bristles
(setae) Fig. 13.11d Protostomes Fruit fly larva, cross section First opening becomes the mouth Anus Fig. 13.08a
Phylum: Mollusca Mollusks are triploblastic coelomates, some have very well-developed brains and are thought to be very intelligent (ie octopus) There is one thing that all mollusks have in common: a foot. The foot is used for different purposes in each class, as you will see. Here are four classes of mollusks:
Gastropoda Polyplacophora Bivalvia Cephalopoda (c) The mantle forms a cavity surrounding body organs, and secretes the shell Digestive gland
Gonad Blood-filled cavity Heart Coelom Excretory organ Anus Shell Tentacle
Mantle cavity Gill Water flow Head Mouth The rasp-like radula helps obtain food
Nerve cords Gut The muscular foot aids In locomotion Fig. 13.12c Gastropoda There have been nearly 35,000 living species and 15,000 fossil species identified, including spirally-coiled snails, flat-shelled limpets, shell-less nudibranchs, whelks, abalones, pteropods and
terrestrial snails and slugs. Most have a single, usually spirally coiled shell into which the body can be withdrawn, but the shell is lost or reduced some important groups. Gastropods have a muscular foot which is used for "creeping" locomotion in most species. Most gastropods have a well-developed head that includes eyes, 1-2 pairs of tentacles, and a concentration of nervous tissue (ganglion). Gastropods are dioecious, and some forms are hermaphroditic. Hermaphroditic forms exchange bundles of sperm to avoid selffertilization; Gastropoda
Torsion in Gastropods Gastropods initially have a basic bilateral symmetry like most mobile animals. The mouth sits at one end anteriorly and the anus sits at the other end posteriorly. During development however, the digestive system and the rest of the internal organs turn-sometimes 90 degrees, sometimes up to 180 degrees so that the anus is then situated over the mouth. This process occurs early in development in most cases and usually occurs in two steps. A foot retractor muscle develops and at a certain stage in development, this retractor muscle is pulled and the internal body organs and digestive tract turn 90
degrees in a counterclockwise fashion. This turn usually occurs within a few minutes or hours. Why Torsion? Of course the obvious question is why would a gastropod rearrange its digestive system and other organs-including gills and nerves, so that its anus is above its head. This doesnt seem to be a good adaptation to anything. Besides the hygiene considerations, it also limits growth since the body is doubled over on itself, and nerves are bent into a figure eight. The result is the visceral hump prevalent in most gastropods.
Polyplacophora (Chitons) They are flattened, elongated animals with eight overlapping dorsal shell plates or "valves," bordered by a thick "girdle" formed from the mantle. The mantle cavity encloses the foot, with which chitons cling to rocky surfaces. Chitons have a single heart, a pair of kidneys, a simple nervous system comprising two pairs of nerve cords that connect near the mouth, and sense organs including eyes and chemosensory organs. Chitons are dioecious.
All are marine. Most species live in the rocky intertidal zone, but some can be found at great depths. They graze on algae, scraping algal cells from the substrate with a radula. Polyplacophora Bivalvia Clams, scallops, mussels Like other molluscs, bivalves have a fleshy mantle encasing the visceral mass and a muscular foot. Unlike gastropods and cephalopods, bivalves secrete two shells rather than one. Additionally, bivalves have lost the radula, which
is presumed to be a primitive feature among all mollusks. Bivalves Scallops Clams Muscles Bivalves Cephalopods
What group of animals can change color faster than a chameleon plus change texture and body shape? has three hearts pumping blue blood? is jet powered, has members in all oceans of the world ? has inspired legends and stories since recorded history? is thought to be the most intelligent of invertebrates and yet is related to animals such as clams and oysters? has members that can squeeze through the tiniest of cracks? is related to garden slugs yet has eyes and other senses that rival our own? and can make their own 'smoke screen' or 'decoys' out of ink? Cephalopods, the group in which scientists classify octopuses, squid, cuttlefish and nautiluses can do all these things and more.
Protostomes Fruit fly larva, cross section First opening becomes the mouth Anus Fig. 13.08a Nematoda Roundworms (nematodes) are bilaterally symmetrical, worm-like organisms that are surrounded by a strong,
flexible noncellular layer called a cuticle. A true coelom is lacking, instead, nematodes have a "pseudocoel" formed directly from the cavity of the blastula (rather than as a result of the division or folding of mesoderm). No cilia or flagellae are present. Some nematodes have specialized cells that excrete nitrogenous wastes; in others, canals or canals plus these specialized cells are present. Nematodes do not have flame cells. Most nematodes are dioecious, but some are hermaphrodites.
Nematoda Although they are small, nematodes are incredibly abundant. If all the nematodes in the Willamette River were combined into one huge animal, it would be over 20 meters long (see image left). Laid end-to-end they would encircle the earths equator. Nematoda Nematodes are almost unbelievably abundant. One study reported
around 90,000 individual nematodes in a single rotting apple. Another reported 236 species living in a few cubic centimeters of mud. The number of described species is around 12,000, but too little attention has been paid to these animals and the true number may be closer to 500,000. Many nematodes are free living and play critical ecological roles as decomposers and predators on microorganisms. But nematodes also include parasitic species, a number of which affect humans directly or indirectly through their domestic animals. These include the common roundworms, which probably infest more than half the world's humans; hookworms; trichina, the worms that cause trichinosis; and filarial worms, primarily tropical parasites that cause diseases such as filariasis (elephantiasis) and onchocerciasis
(river blindness). Nematoda Protostomes Fruit fly larva, cross section First opening becomes the mouth Anus Fig. 13.08a
Arthropoda . . . the REAL rulers of the Earth. . . Diplopoda Chilopoda Arachnida Insecta Crustacea
Chordates Arthropods Echinoderms Cnidarians Annelids Other (Ctenophores, Platyhelminths, Brachiopods,
Nematodes, Hemichordata) Mollusks Sponges Nematodes Platyhelminthes By nearly any measure, the most successful animals on the planet are the arthropods. They have conquered land,
sea and air, and make up over three-fourths of all currently known living and fossil organisms, or over one million species in all. Arthropoda Despite this unbelievable diversity, the basic body plan of arthropods is fairly constant. Arthropods have a stiff cuticle made largely of chitin and proteins, forming an exoskeleton that
may or may not be further stiffened with calcium carbonate. They have segmented bodies and show various patterns of segment fusion (tagmosis) to form integrated units (heads, abdomens, and so on). The phylum takes its name from its distinctive jointed appendages, which may be modified in a number of ways to form antennae, mouthparts, and reproductive organs. (d) Hormonal control Periodic releases of ecdysone (molting hormone) Molt
Molt Molt Larva Larva Adult Pupa High
Low Very low Level of juvenile hormone Fig 13.16d Insect Adaptations The most distinguishing characteristic of an insect's head is the mouthparts. They may be designed for chewing food, for sucking it or lapping it up. The
housefly uses its it's mouthparts are used for mopping; up liquid food. The end of the labium functions like a sponge. A butterfly sucks up its food through a part of the maxillae that forms a tube. The mosquito also sucks ups its food. All of its mouthparts, except the labium, form a needle-like tube called a fascicle. The ground beetle is a carnivore; it has large
mandibles adapted for piercing and cutting prey. Insect Adaptations The legs of all insects are made up of the same basic parts - femur, trochanter, coxa, tibia and tarus, but they can differ considerably. At left, is the rear leg of a cockroach. It is long and lean, made for running. They have spines which point backward. They are used for holding onto surfaces. Compare it to the rear leg of the grasshopper. It has a large, strongly-muscled femur to help it
leap into the air. The Honeybee's back legs are covered with hair. Pollen sticks to the them and is collected into a special area on the leg called a pollen basket. The Water Beetle's legs are fringed with hair which helps push it through the water. The Mole Cricket's legs are short and spadelike, making them especially useful for digging. Insect Adaptations Cockroach
Moth Mosquito Honeybee Antennae are sensory structures to help the insect find out more about its surroundings. The structure of some, such as the cockroach, moth and mosquito are adapted in different ways to increase the surface area for sensory cells. The bee's antennae have a simpler, more robust shape.
Insect Adaptations Lacewing Moth Beetle Most insects have membranous wings; such wings are very thin and like cellophane. Many have venation, a system of thickened lines in the wings, such as the lacewing. The wings of butterflies and moths are not membranous. Rather they are covered with small dust-like scales.
Flies and mosquitoes have one pair of wings. Some insects - such as the ant and termite - are wingless. Most insects have two pair of wings. They can be prominent as in the lacewing and butterfly, or modified to be less obvious. The beetle's front pair of wings provide a hard or leather-like covering that protects the back pair when they are not being used. Insects are Important the majority of insects are found in the warm and moist tropics. Insects have adapted to a broad range of habitats, successfully finding their own niche, because they will consume almost any substance that has nutritional value. Insects perform a vast number of important functions in our ecosystem. They aerate the soil, pollinate blossoms, and control
insect and plant pests; they also decompose dead materials, thereby reintroducing nutrients into the soil. Burrowing bugs such as ants and beetles dig tunnels that provide channels for water, benefiting plants. Bees play a major role in pollinating fruit trees and flower blossoms. Gardeners love the big-eyed bug and praying mantis because they control the size of certain insect populations, such as aphids and caterpillars, which feed on new plant growth. Finally, all insects fertilize the soil with the nutrients from their droppings. Insects Blend into their Environment Insects can be brightly colored
Sea urchin larva, cross section Second opening becomes the mouth Blastopore becomes the anus Echinodermata
Spiny skin = phylum name No cephalization w/ oral & aboral surfaces Internal skeleton Water vascular system/tube feet Radial symmetry Water Vascular System Network of canals creating hydrostatic pressure to help the
starfish move WATER VASCULAR SYSTEM Water enters through sieve plate or madreporite on aboral surface into a short, straight stone canal Stone canal connects to a circular canal around the mouth called the ring canal Five radial canals extend down each arm & are connected to the ring canal Radial canals carry water to hundreds of paired tube feet Echinoderm Classes
Non-vertebrate chordates Related to chordates Similar in structure to invertebrates Subject of controversy Unifying Themes 1. Chordate evolution is a history of innovations that is built upon major invertebrate traits They display many of the basic traits that first evolved in the invertebrates: bilateral symmetry, cephalization, segmentation, coelom, "gut" tube, etc. 2. Chordate evolution is marked by physical and behavioral specializations
For example the forelimb of mammals has a wide range of structural variation, specialized by natural selection 3. Evolutionary innovations and specializations led to adaptive radiations - the development of a variety of forms from a single ancestral group Characteristics of the Chordates Notochord, dorsal hollow nerve cord, pharyngeal gill slits, blocks of muscle, postanal tail Characteristics of the Chordates The notochord All chordate embryos have a notochord, a stiff but flexible rod that
provides internal support Remains throughout the life history of most invertebrate chordates; among, present only in the embryos of vertebrate chordates Characteristics of the Chordates cont. Dorsal Hollow Nerve Cord (=Spinal Cord) A fluid-filled tube of nerve tissue that runs the length of the animal, dorsal to the notochord Present in chordates throughout embryonic and adult life Characteristics of the Chordates cont.
Pharyngeal gill slits Pairs of opening through the pharynx Invertebrate chordates use them to filter food Juvenile fishes use them to them for breathing In adult fishes the gill sits develop into true gills In reptiles, birds, and mammals the gill slits are vestiges, occurring only in the embryo Characteristics of the Chordates cont. Blocks of Muscle - Myotomes Surrounding the notochord and nerve cord are blocks of muscle myotomes Postanal Tail
The notochord, nerve cord, and the myotomes extend to the tail Found at some time during a chordate's development SubPhylum Urochordata Marine animals; some species are solitary, others are colonial. Sessile as adults, but motile during the larval stages Possess all 5 chordate characteristics as larvae Settle head first on hard substrates and undergo a dramatic metamorphosis (e.g., tail, notochord, muscle
segments, and nerve cord disappear) SubPhylum Urochordata cont. Adult body is covered by an outer envelope or tunic; composed of fibers of tunicin embedded in a mucopolysaccharide matrix Tunic encloses a basketlike pharynx, that is perforated by gill slits Tunicates are filter feeders; plankton is trapped in a sheet of mucus
and cilia later direct the food-laden mucus to the stomach Water leaves the animal via an excurrent siphon Chordate Metamerism Body segmentation (i.e. metamerism) appears to have evolved in two lineages of the chordates: the Cephalochordates and the Vertebrates; probably occurred after divergence from the Urochordates However, segmentation in the chordates does not involve the coelom The cephalochordates and the chordates movement is accomplished by contraction of muscle fibers that are arranged in segmented blocks - myotomes
Presumably, segmentation of muscles developed as an adaptation for undulatory swimming and rapid burrowing SubPhylum Cephalochordata Exclusively marine animals Although they are capable of swimming, they usually are buried in the sand with only their anterior end being exposed SubPhylum Cephalochordata cont. All chordate characteristics are present throughout their life history They are filter feeders: inside of the oral hood is lined with cilia wheel organ These cilia, plus cilia in the pharynx help generate a water current
Water and suspended food particles pass through the oral hood, equipped with projections called cirri that strain larger particles Feed by secreting a mucous net across the gill slits to filter out food particles that are present in the water. The End