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Click on the picture of the animal, its name, or the evolutionary innovation for information.

bulletPorifera
bulletUC Berkeley: Porifera
bullet U of M Animal Diversity Web: Porifera
bulletWonderful World of Sponges
bulletBody plan: no symmetry, no true tissues; only four cell types: choanocytes, amoebocytes, porocytes and pinacoderm. Skeleton of spicules composed of silica or calcium carbonate, and/or protein.  Digestion is intracellular, witrhin the choanocytes.  Sexual reproduction via expulsion of sperm into the water column; asexual reproduction by fragmentation.
bulletCnidaria
bulletUC Berkeley: Cnidaria
bullet U of M Animal Diversity Web: Cnidaria
bulletCorals and sea anemones
bulletBody plan: radial symmetry, two germ layers supporting several tissue types, including muscle and nervous.  Specialized cells (cnidocytes) used for capturing/stunning prey.  Digestion is extracellular within a gastrovascular cavity with a single mouth/anus.  Many species alternate between a sexual, motile medusa and an asexual, sessile hydra that reproduces by fragmentation or budding.
bulletPlatyhelminthes
bullet UC Berkeley: Platyhelminthes
bullet U of M Animal Diversity Web: Platyhelminthes
bulletAttack of the killer worms: an earthworm-eating flatworm
bulletBody plan: bilateral symmetry with obvious cephalization, three embryonic germ layers with determinate development. Gastrovascular cavity with a pharynx (still only one opening).  Cestodes have no digestive system because they live within the intestines of larger animals.  Ciliated flame cells collect nitrogenous wastes and dump them  out to the external environment.  Most are hermaphroditic; many exchange sperm.  Asexual reproduction by fragmentation.  Many parasitic forms have complex life cycles involving multiple hosts.
bulletNematoda
bullet U of M Animal Diversity Web: Nematoda
bullet Images of nematode parasites
bulletBody plan: bilateral symmetry with 3 germ layers.  Body cavity is a pseudocoelom.  Complete digestive system with separate mouth and anus, although relatively unspecialized.  Flame cells used for ammonia excretion, similar to flatworms.  Have only longitudinal muscles for locomotion.  Most are dioecious, with male and female individuals.  About evenly split between free-living (aquatic and terrestrial) and parasitic forms.
bulletRotifera
bulletUC Berkeley: Rotifera
bulletBody plan: similar to nematodes, but with these differences: they are enclosed by a chitin exoskeleton, sometimes jointed at the foot.  They have a ring of cilia at the anterior end that is used for both filter feeding and locomotion, they have both longitudinal and transverse muscle layers.
bulletMollusca
bulletUC Berkeley: Mollusca
bullet U of M Animal Diversity Web: Mollusca
bullet In search of the giant squid...
bulletBody plan: bilateral and triploblastic.  Body cavity is a true coelom, completely lined with mesoderm.  Three body parts: stomach/foot, visceral mass, and mantle. An open circulatory system with a 2-chambered heart, except in cephalopods, which have a closed circulatory system.  The digestive system is complex, having a well-defined stomach and intestine, as well as accessory glands.  Metanephridia filter wastes from the coelomic fluid, dumping them into the mantle cavity.  The mantle cavity also contains gills; in terrestrial snails, the mantle cavity serves as a lung.  Bivalves and gastropods are hermaphroditic, but most are obligate out-crossers; cephalopods are dioecious and fertilize eggs internally.  Some cephalopods are the largest known invertebrates; many have color vision, recognizing both shape and movement, and they are intelligent enough to solve simple puzzles.
bulletAnnelida
bulletUC Berkeley: Annelida
bullet U of M Animal Diversity Web: Annelida
bullet Earthworm dissection site
bullet A dissected earthworm (Cornell University)
bulletComposting using earthworms: Wormwoman.com
bulletBody plan: bilateral and triploblastic, with a coelom and a complete digestive system.  Like mollusks, they have metanephridia (1 pair per segment).  unlike all the preceding phyla, they are segmented, with a septum between each segment that divides the coelom up into a series of compartments.  they use longitudinal and circular muscles working against the constant volume of coelomic fluid in each segment for locomotion; this is called a hydrostatic skeleton.  They are hermaphroditic, but most are obligate out-crossers.  Fertilization and embryonic development take place outside the body, in a tough mucus cocoon filled with nutritive substances.  They have a closed circulatory system with multiple peristaltic "hearts" that work in parallel.  Giant axons from their ventral nerve cord are often used in medical research.
bulletArthropoda
bulletUC Berkeley: Arthropoda
bullet U of M Animal Diversity Web: Arthropoda
bulletUSC Cockroach webcam
bulletBody plan: bilateral and triploblastic, with a coelom and a complete digestive system.  Arthropods are also segmented, but development assigns specific roles to each segment based on how far it is from the head.  They are covered with a tough exoskeleton of chitin, with jointed, paired appendages (Arthropoda means "jointed legs" in Greek).  They have an open circulatory system that moves the hemolymph ("blood") around within a hemocoel, a body cavity separate from the coelom.  Nitrogen excretion in insects is via Malpighian tubules connected to the upper end of the hindgut.  Many species (particularly insects) have air-filled tracheae that lead from spiracles in the abdomen to all parts of the body.  Insects are by far the most numerous of all living things (in terms of species count), with well over half of all named species.
bulletEchinodermata
bullet UC Berkeley: Echinodermata
bullet U of M Animal Diversity Web: Echinodermata
bulletCrown of Thorns starfish
bulletBody plan: bilateral and triploblastic, with a coelom and a complete digestive system.  Echinoderms are pentamerous and appear to have radial symmetry, but upon dissection they are found to be bilateral.  Unlike all other invertebrate phyla, echinoderms are deuterostomes - as the primitive gut develops within the embryo, the blastopore becomes the anus instead of the mouth.  They share this feature with the Chordata.  They move and hold onto prey by means of a unique water vascular system and rows of tube feet on their rays.  Their platy skeleton is covered with living tissue, so it is technically an endoskeleton, and grows with the animal.
bulletChordata
bulletUC Berkeley: Chordata
bullet U of M Animal Diversity Web: Chordata
bulletFrogland - including the Random Frog Generator
bulletBody plan: bilateral and triploblastic, with a coelom and a complete digestive system.  Deuterostome development.  Closed circulatory system.  Chordates possess four distinguishing characteristics sometime during their development: a notochord (a stiff cartilaginous rod dorsal to the gut cavity) a hollow nerve cord dorsal to the notochord, cartilaginous gill arches in the neck region separated by pouches of soft tissue, and a post-anal tail.  In more advanced chordates, the notochord serves as the model for a spinal column and skull that enclose and protect the central nervous system, and the gill arches and pouches are used for various other structures if gills are not needed.  Upper and lower jaws, ear bones, and the larynx are made from the arches, and the middle ear, tonsils, adenoids, and other glands are made from the gill pouches.  Higher chordates also have two pairs of variously adapted appendages.  The skeleton that supports them is internal and - unlike the exoskeletons of invertebrates - is living tissue and grows with the animal.
bulletCrossword Puzzles
bulletProtista to Cnidaria
bulletPlatyhelminthes to Mollusca
bulletAnnelida and Arthropoda
bulletEchinodermata and Chordata

bulletMulticellularity - complex organisms can only develop after cells figure out how to stick together, specialize, and cooperate.
bulletSymmetry and Tissues - symmetry implies directionality and allows for further specialization; grouping of cells into specialized tissues and organs is the next logical step.
bulletBilateral symmetry - bilateral symmetry improves the ability to move, and is the first step toward cephalization and development of a central nervous system.
bulletBody cavity - a fluid-filled cavity allows for gas and nutrient exchange in a thicker, larger body.  Tissue thickness is no longer limited to the distance that oxygen can diffuse easily through tissues.
bulletCoelom - a fluid-filled body cavity entirely lined with mesoderm isolates the internal organs (particularly the digestive system) from the body wall.  This allows greater freedom of movement without the problems associated with distortion of the internal organs when the animal moves, and allows them to work independently of body movement.
bulletSegmentation -segmentation of the body from head to tail allows for additional specialization of each segment during embryonic stages.
bulletJointed appendages and exoskeleton - found in arthropods and related phyla, this provides rigid support and muscle attachment, and great range of movement.  The downside to an exoskeleton is that to grow, the animal must shed it and grow a new one.  During this time it is softer and not as mobile, so it is more prone to predation.
bulletDeuterostome development and endoskeleton - deuterostome vs. protostome development means that the animal is turned upside down and backwards in the early embryonic stages (the tail  becomes the head, and the nerve cord runs along the dorsal, not the ventral surface).  Oddly, this is an advantage in terms of mobility.  An internal skeleton is a huge advantage over an external skeleton, too - the skeleton can now grow with the animal, and provide support for a larger body.
bulletNotochord - This cartilaginous rod forms just under the nerve cord in chordates, providing support and - in higher chordates - develops into the spinal column and skull, thus protecting the central nervous system from damage.  It is the basis of the vertebrate skeleton.


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