EEB204H1 - Study Notes 3.docx

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Ecology & Evolutionary Biology
Corey Goldman

EEB204H1 STUDY NOTESCHAPTER TWENTYTHREE ANIMAL DIVERSITY IINVERTEBRATESModern medicine gets assistance from invertebrates animals without a backbone via the medicinal leech for treatment of a wide range of illnesses Would suck out the tainted blood that was believed to be the primary cause of disease thBy the beginning of the 20 century leeches no longer had a place in the toolkit of modern medicine and had become a symbol of the ignorance of an earlier ageToday they have made a comeback They are used to treat a surgical complication known as venous insufficiencyApplied to the affected area the leeches make small painless incisions and sucking blood into their stomachs prevent blood from clottingWHAT ARE THE KEY FEATURES OF ANIMALSThe group is defined by a list of characteristicsNone of these characteristics are unique to animals but together they distinguish animals from members of other taxonomic groupsAnimals are eukaryotesAnimals are multicellular Animal cells lack a cell wallAnimals obtain energy by consuming other organismsTypically reproduce sexuallyAre motile during some stage of their livesMost animals are able to respond rapidly to external stimuli WHICH ANATOMICAL FEATURES MARK BRANCH POINTS ON THE ANIMAL EVOLUTIONARY TREEBy the Cambrian period most of the animal phyla that currently populate Earth were already presentCertain features mark major branching points on the animal evolutionary treeTISSUESoOne of the earliest major innovations in animal evolution was the appearance of tissuesoThe only animals that have retained the ancestral lack of tissues are the spongesoIn sponges cells may have specialized functions but they act more or less independently and are not organized into tissuesSYMMETRYoAll animals with true tissues also have symmetrical bodiesoIt can be bisected along at least one plane such that the resulting halves are mirror images of one anotheroTwo groups radial symmetry and bilateral symmetryoIn radial symmetry any plane through a central axis divides the object into roughly equal halves oIn bilateral symmetry the animal is divided into mirror image halves only along one particular plane through the central axisoDistinction between the symmetry tied to a corresponding difference in the number of tissue layers called germ layers that ariseduring embryonic development oAnimals with radial symmetry have two germ layers an inner layer of endoderm line the gut cavity and an outer layer of ectoderm covers the outside of the bodyoBilaterally symmetrical animals have a third layer called the mesoderm which lies between the endoderm and the ectoderm forms muscle and when present the circulatory and skeletal systemsoAdult echinoderms like sea stars are radially symmetrical yet our evolutionary tree places them squarely within the bilaterally symmetrical groupoSo the immediate ancestors of echinoderms must have been bilaterally symmetrical and the group subsequently evolved radial symmetry a case of convergent evolution oRadially symmetrical animals tend either to be sessile or to drift around on currentsoAll parts of their bodies are more or less equally likely to encounter foodoMost bilaterally symmetrical animals are motile and resources such as food are most likely to be encountered by the part of the animal that is closest to the direction of movement oBilateral symmetry is also accompanied by cephalization the concentration of sensory organs and a brain in a defined head region produces an anterior head end where sensory cells organs and nerve cells and organs for ingesting food are concentrated the other end is the posterior and may feature a tailBODY CAVITIESoBilateral animal phyla have fluidfilled cavity between the digestive tube and the outer body walloIn an animal with a body cavity the gut and body wall are separated by a fluidfilled spaceoBody cavities are absent in radially symmetrical animals oBody cavity can serve a variety of functions acts as a kind of skeleton providing support for the body and a framework against which muscles can act organs are suspended within serves as a protective buffer between the organs and the outside world oBody cavity structure varies among phylaoMost widespread type of body cavity is a coelom lined with a thin layer of tissue that develops from mesoderm oPhyla whose members have a coelom are called coelomates which include annelids arthropods mollusks echinoderms and chordates oA pseudocoelom is not completely surrounded by mesodermderived tissue oPseudocoelomates include roundwormsoSome have no body cavity at all and are known as acoelomates example is flatworms EMBRYOLOGICAL DEVELOPMENT differs for bilateral symmetryoCan be grouped into two categories protostome and deuterostomeoIn protostome development the coelom forms within the space between the body wall and the digestive cavity solid mass of mesoderm splits to form coelomoIn deuterostome development the coelom forms as an outgrowth of the digestive cavity mesoderm pockets pinch off of digestive cavity to form coelomoAlso differ in the pattern of cell division immediately after fertilization and by which the mouth and anus are formedoAnnelids arthropods flatworms roundworms and mollusks exhibit protostome development echinoderms and chordates are deuterstomes EVOLUTIONARY LINES for protostomesoEcdysozoans whose members have bodies covered by an outer layer that is periodically shedoLophotrochozoans whose members have a special feeding structure called a lophophore and pass through a particular type of developmental stage called a trochophore larva WHAT ARE THE MAJOR ANIMAL PHYLAMajority of animals are invertebrates
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