Animal Evolution I. Animal Characteristics A. Most animals share the following characteristics: 1. Multi-cellular 2. Eukaryotic 3. Heterotrophy a. Ingestion b. Carbohydrates stored as glycogen 4. No cell walls a. Cell junctions i. Desmosomes ii. Gap junctions iii. Tight junctions 5. Differentiated body cells a. Hierarchal organization i. Tissues ii. Organs iii. Organ systems b. Permit specialized function 6. Nervous tissue a. Electrical and chemical communication among cells of the body b. Unique animal trait 7. Muscle tissue a. Movement b. Unique animal trait 8. Sexual reproduction a. Flagellated motile sperm b. Non-motile egg c. Diploid dominant life cycle d. Elaborate embryological development i. Cleavage to form blastula ii. Gastrulation of blastula to form tissue iii. Larvae that undergoes metamorphosis may be present II. Overview of Animal Phylogeny A. Parazoan 1. Lack tissue 2. Animals with tissue are classified eumetazoa 3. Simple anatomy B. Eumetazoa 1. Divisions
a. Radiata i. Exhibit radial symmetry b. Bilateria i. Bilateral symmetry C. Radiata 1. Body symmetry a. Oral and aboral surfaces b. No sides (eg., front) 2. Diploblastic a. Two germ layers i. Endoderm ii. Ectoderm
D. Bilateria 1. Surfaces a. Dorsal b. Ventral c. Anterior d. Posterior e. Left/right 2. Cephalization a. Concentration of sensory structures at the anterior end 3. Gastrulation yields three germ layers a. Triploblastic i. Endoderm ii. Ectoderm iii. Mesoderm 4. Fate of germ layers a. Ectoderm i. Animal s outer covering ii. CNS b. Endoderm i. Innermost germ layer ii. Lines archenteron iii. Lining of internal organs that are continuous with the outside world c. Mesoderm i. Located between ectoderm and endoderm ii. Forms muscles and most internal organs E. Body cavities 1. Animals can be group based on the presence, type and development of a body cavity
a. Acoelomate b. Pseudocoelomate i. Fluid-filled cavity between gut tube and outer body wall ii. Lacks complete mesodermal lining c. Coelomate i. Fluid-filled cavity between gut tube and outer body wall ii. Complete mesodermal lining 2. Function of coelom a. Hydrostatic skeleton b. Cushion organs c. Allows for growth of internal organs and for their movement independent of the body wall
F. Coelomate evolutionary lines
1. Protostomes a. Spiral cleavage b. Determinant cleavage c. Schizocoelous coelom formation d. Blastopore forms mouth 2. Deuterostomes a. Radial cleavage b. Indeterminant cleavage c. Enterocoelous coelom formation d. Blastopore forms anus
Invertebrate Diversity Phylogeny I. Parazoa P. Porifera (sponges) II. Radiata P. Cnidaria C. Hydrozoa (polyp and medusa) C. Scyphozoa (medusa dominant) C. Anthozoa (polyp only) P. Ctenophora III. Acoelomates P. Platyhelminthes (flatworms) C. Turbellaria C. Trematoda
C. Cestoidea IV. Pseudocoelomates A. Rotifera B. Nematoda (roundworms) V. Coelomates: Protostomes P. Mollusca C. Bivalvia (clams, oysters, mussels and scallops) C. Polyplacaphora (chiton) C. Gastropoda (snails and slugs) C. Cephalopoda (squids and octopuses) P. Annelida (segmented worms) C. Oligochaeta C. Polychaeta C. Hirudinea P. Arthropoda Subphylum Trilobitomorpha Subphylum Chelicerata C. Merostomata (horseshoe crab) C. Arachnida Subphylum Crustacea C. Crustacea Subphylum Hexapoda C. Insecta C. Chilopoda C. Diplopoda VI. Coelomates: Deuterostomes P. Echinodermata C. Asteroidea C. Echinodea C. Holothuroidea Parazoa I. P. Porifera
A. Characteristics 1. Sessile 2. Lack tissue a. Two layers of loosely associated unspecialized cells b. Mesohyl separates cell layers 3. Body parts a. Spongocoel b. Osculum i. Excurrent opening c. Epidermis i. Single layer ii. Outer surface
d. Porocyte i. Forms pores that connect spongocel to outside environment ii. Incurrent channel e. Choanocyte i. Collar cell ii. Major cell of inner cell layer iii. Flagellum surrounded by fingerlike projections iv. Flagellum creates current and food particles are trapped by collar v. Food is phagocytized f. Mesohyl i. Non-cellular gelatin separating cell layers g. Amoebocyte i. Wandering cells in mesohyl ii. Take food from chaonocytes and deliver to other cells iii. Secrete skeletal elements iv. Gamete formation h. Spicule i. Skeletal fibers ii. Calcium carbonate or silica iii. Located in mesohyl i. Spongin i. Proteinaceous skeletal fiber ii. Flexible
Eumetazoa: Radiata I. P. Cnidaria A. Body plans 1. Two forms 2. May occur at some point in life cycle 3. Polyp a. Sessile b. Adheres to substratum c. Oral end surrounded by tentacles 4. Medusa a. Bell-shaped b. Passive drifting or weak contraction of bell c. Downward facing oral opening surrounded by tentacles 5. Cnidocytes
a. Stinging cells b. Eversible capsule i. Contains cnidae B. Characteristics 1. Gastrovascular cavity a. Filled with water b. Acts as a hydrostatic skeleton c. Simple nerve net i. no brain C. Classification 1. Hydrozoa a. Life cycle include polyp and medusa body forms 2. Scyphozoa a. Life cycle is medusa dominate 3. Anthozoa a. Life cycle is exclusively polyp II. P. Ctenophora
A. Comb jellies 1. Body plan a. Spherical or ovoid b. Surface contains 8 rows of comblike plates i. Fused cilia ii. Used for locomotion c. Retractable tentacles Eumetazoa: Bilateria Acoelomates I. Phylum Platyhelminthes
A. Flatworms are characterized by the following features: 1. Bilateral symmetry - well-suited for movement in a specific direction 2. Cephalization - definite "head" end with concentration of sense organs 3. Three cell layers 4. Organ level of organization 5. Reproduction is mostly sexual a. Most organisms are hermaphroditic but cross-fertilization is generally the rule b. Fertilization is internal (asexual reproduction occurs only in free-living species) 6. No circulatory system a. Diffusion only B. Classification 1. Class Turbellaria a. Non-parasitic 2. Class Cestoda (tapeworms)
a. Body parts i. Scolex ii. Neck iii. Stroblia iv. Proglottids b. No digestive system i. Absorb nutrients through cuticle 3. Class Trematoda (flukes) II. Parasitism A. Charateristics
1) Parasites often have complex life cycles involving one to several hosts 2) They often show modifications in their means of obtaining nutrients, such as: a) Reduction of digestive tract (endoparasites). b) Direct absorption of food through body wall (endoparasites). c) Development of storage areas for ingested food (ectoparasites). 3) They show a tremendous increase in reproductive capabilities by means of: a) Greater egg production. b) Presence of asexual reproductive in their life history 4) They often have larval stages which permit passage from one host to the next 5) Endoparasites usually have reduced sense organs 6) Parasites often have adhesive organs (hooks, suckers) for attachment to host Pseudocoelomates I. Characteristics A. Pseudocoelom 1. Body cavity not lined by peritoneum. 2. Pseudocoel allows for movement a. Fluid acts a hydrostatic skeleton 3. Fluid in cavity acts as a circulatory system a. Diffusion is easier in a fluid-filled cavity 4. Complete digestive tract with mouth and anus (2 openings) a. One-way movement of food and allows for specialization of different regions of the digestive tract 5. Cuticle a. Protective structure surrounding the epidermis b. Cuticle may also help prevent desiccation 6. Bilateral symmetry
II. Phylum Rotifera A. Characteristics 1. Following are present a. "Foot" - tail-like appendage that secretes cement and is used for anchorage b. "Wheel of cilia" (corona) - functions in locomotion, draws food into mouth c. Mastax - specialization of the pharynx d. Syncytial body (cell membranes disappear) e. Small size and cell constancy (every individual of a species has the same number of cells) f. Simple excretory system g. No circulatory system h. May reproduce by parthenogenesis, reproduce sexually prior to period of adverse environmental conditions
III. Phylum Nematoda (roundworms) A. Characteristics 1. Following are present a. Largest group of pseudocoelomates, ubiquitous b. Many free-living forms c. No true segmentation, no appendages, no proboscis d. Sexes separate, male usually smaller than female
Coelomates: Protostomes I. Characteristics A. Pseudocoelom 1. Presence of a true coelom a. Body cavity lined by peritoneum 2. Digestive tract surrounded by muscle 3. Circulatory system II. P. Annelida: Segmented worms A. Characteristics 1. Metamerism a. Division of the body into similar parts or segment arranged in a linear series 2. Closed circulatory system 3. Excretion by means of a pair of nephridia per body segment 4. Chitinous setae (except in leeches) 5. Well-developed coelom which is divided by septa (except in leeches)
B. Classification 1. Class Polychaeta a Characteristics i. Parapodia ii. Many setae 2. Class Oligochaeta (earthworms) a. No parapodia b. Few setae c. Hermaphroditic d. Segmented 3. Class Hirudinea a. Leeches b. Fluid-feeding c. Reduced coelom
III. P. Mollusca: A. Characteristics 1. Mollusks are characterized by possession of the following features: a. Radula (rasping organ) present (except in bivalves) b. Mantle present (formed from folds of dorsal body wall) c. Shell secreted by mantle (shell absent in some cephalopods) d. Open circulatory system e. Ventral body wall specialized as foot mainly used for locomotion (foot not present in cephalopods) f. Reduced coelom g. Separate sexes (except in some snails which are hermaphrodites)
B. Classification 1. Class Bivalvia (mussels and clams) a. Laterally compressed b. Possess a shell with two valves hinged dorsally c. Foot is also laterally compressed d. Head is greatly reduced in size e. Large gills i. Filter-feeder f. No radula 2. Class Polyplacophora (chitons) a. Flattened bodies b. Shell composed of 8 simple plates 3. C. Class Gastropoda (snails) a. Torsion 4. D. Class Cephalopoda (cuttlefish) a. Swim by expelling water b. Carnivorous c. Reduced shell
IV. P. Arthropoda A. Characteristics 1. Bilateral symmetry with three (3) germ layers 2. Body is usually segmented and jointed externally a. Head, thorax and abdomen are variously distinct or fused 3. Hard exoskeleton containing chitin 4. Complete digestive tract including mouth parts with lateral jaws adapted for chewing or sucking 5. Open circulatory system a. Heart is dorsal b. Blood is distributed by arteries to organs and tissues c. Returning through the body sinuses to the heart 6. Reduced coelom 7. Respiration via gills, trachea, book lungs or body surface 8. Separate sexes a. Internal fertilization B. Differences between the Arthropods and Annelids 1. Arthropods a. Lack of cilia b. Lack of internal septa c. Reduced coelom d. Open circulatory system e. Separate sexes f. Exoskeleton g. Jointed appendages h. Compound eyes C. Subphylum Trilobitomorpha 1. Extinct
D. Subphylum Chelicerata 1. Characteristics a. Lack jaws b. Claw-like chelicerae i. Venomous fangs in spiders c. Four pairs of walking legs 2. Class Merostomata a. 5 or 6 pairs of abdominal appendages i. Modified as gills b. Spike-like telson at the end of the body c. Separate sexes 3. Class Arachnida (spiders, scorpions, mites and ticks) a. Division of body into a prosoma and an abdomen b. Predaceous i. Use chelicerae with terminal fangs to inject poison into prey c. Four pairs of legs d. Excretion by means of Malphigian tubules e. Respiration by means of book lungs, trachae or both f. No antennae
E. Subphylum Crustacea 1. Characteristics a. Have jaws b. Antenna c. Various number of paired appendages i. Including three or more pairs of walking legs 2. Class Crustacea (ex. barnacles and shrimp) a. Maxillae and mandible b. Two pairs of antennae (as head appendages) c. Compound eyes d. Pimarily aquatic (most marine)
F. Subphylum Uniramia 1. Characteristics a. Unbranched appendages b. One pair of antennae on the head B. Class Insecta 1. Distinct head, thorax and abdomen 2. Digestive tract of fore, mid and hind gut 3. Respiration by means of trachea 4. Separate sexes 5. Excretion by means of Malpighian tubules
6. Single pair of antennae 7. Two patterns of development a. Incomplete metamorphosis i. Larvae resemble small adults ii. Molts result in forms closer to adult form b. Complete metamorphosis i. Multiple larval stages 1. Larvae eat and grow ii. Pupation 1. Larval tissue is broken down 2. Adult is formed by the division and differentiation of this tissue iii. Adult form mates and reproduces C. Class Chilopoda (centipedes) 1. Pair of antenna 2. 12 or more segments 3. Two pairs of mandibles and maxillae 4. Complete digestive tract D. Class Diplopoda (millipedes) 1. Two pairs of walking legs per segment