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WKU Bio 225 Zoology Unit 2 Notes
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Covers reproduction annelids, arthropods, some molluska, and rotifers
Transcript
Zoology Notes
9-12-18
Phylum Platyhelminthes
Lophotrocozoan Protostomes
Adaptions for parasitism: reduced digestive system
From 1mm to more than a meter (extremely skinny, even in long individuals)
Triploblastic (all 3 skin layers)
Acoelomate: body cavity
Most are parasitic but some are free living aquatic
Bodies dorso-ventrally flattened
Incomplete digestive tract
Monoecious
Adaptations for parasitism:
Reduced digestive system
Tough outer covering: tegument found when going from one organism to another
Monoecious: large gonads (hermaphrodite)
Regenerative Powers: Planarians can survive fragmentation
Excretory System: removes nitrogenous waste and maintains water balance (osmoregulation) in body
Class Turbellaria
Usually free-living
Dorso-ventrally flattened body
Cephalization/ Sensory Receptors: organs that collect information about the environment nodules on side of head “smell” water, eye spots
Movement: bilateral symmetry, cilia and muscular undulation
Class Cestoda: tapeworm
Endoparasites
Scolex and proglottids
No digestive tracts microtriches on tegument (fingers for more surface area)
Taenia solium: pork tapeworm juveniles (cysticerci) can encysts in human muscle and nervous tissue
Class Tematoda
Parasitic flukes
Anterior suckers
Digestive tract present
Often have vertebrate host/ mollusk intermediate host
Schistosoma: blood fluke
Phylum Nemertea: ribbon worms
About 1000 marine species
Most small < 20cm long
Similar to Planaria, but dioecious (separate male and female)
Proboscis
Complete digestive system
Simple circulatory system
Tissues
Cardiac muscle: involuntary, uninucleated, striated muscle found only in the heart of vertebrates
Branched
Intercalated disks
Pacemaker
Smooth muscle: also called non-striated or involuntary muscle
No striations, uniculeate
Encircle blood vessels, the intestine or other ducts
Unit 2
09-19-2018
Bivalvia
Class Cephalopoda (squid, octopuses, cuttlefishes)
All marine predators with highly developed nervous systems
Foot is modified for directing water as it is forced out of the mantle cavity and is fringed with tentacles
Ancestral cephalopods had straight shell which have been lost (octopi) or coiling (Nautilus). Squid only have a thin remnant of the shell
Locomotion: cephalopods move by using the mantle cavity to form a water jet. Octopuses usually walk
Squid swim backwards so that they can see predator as they are trying to get away from it
Organ systems of cephalopods are well-developed thinking and active predators; more energy and organ needs
One set of gills – use mantle to force water flow
Closed circulatory system: blood leaving heart goes to body tissues, then to gills, accessory hearts increase blood pressure as blood enters gill
Nervous System is very well developed: largest brain of any invertebrate
Cephalopod eye is not homologous with vertebrate eye but is remarkably similar neural connection
Don’t have blind spot in eyes like humans
Octopuses are very smart, can learn quickly through positive and negative reinforcement, observational learning (very important)
Camouflage: Octopuses can change their color and shape
Communication: octopuses used movements of the arms and color change to communicate
Reproduction: dioecious, sperm packaged in a structure called a spermatophore
Hectocotylus, a specialized tentacle transfers a spermatophore to the mantle cavity of the female
No free-living larvae stage
Adaptive radiation
Habitat: everywhere
Body plan: shell or no shell
Nervous system sensory organs
Feeding: food sources everywhere for snails
Phylogeny: Lophotrochozian Protostomes
Phylum Annelida: Lophotrochozoan Protostome
Characteristics
15,000 species
Trochophore Larvae
Body composed repeated segments (metamerism) separated by septa little specialization of segments (ancestral) same in earthworm or lobster
Advantage: parts of the body can be manipulated individually
Anterior end of animal has a prostomium
Posterior end of animal has a pygidium
New segments are added in front of the pygidium during growth
Setae (“hair”): hair-like spikes that can be used to grip sediment (not hair!)
Short hard setae: terrestrial worms
Longer flexible setae: aquatic worms
Complete Digestive tract
Musculature with longitudinal and circular muscles
Flexible cuticle: secreted by epidermis (not cellular)
Respiration: mainly by diffusion across skin
Gills and parapodia (increases surface area) as accessory structures
Excretion by paired nephridia in each segment
Sexual reproduction: monoecious or dioecious
Trochophore larvae
Asexual reproduction: budding and fragmentation
Class Oligochaeta (oligo = few ; chaeta = long hair)
3,000 species, mostly terrestrial and freshwater
Australian earthworm can be meters long
Respiration: no specialized structures for gas exchange, cutaneous (cuticle) respiration
Must keep cuticle moist for oxygen to diffuse into body
Drought: if surface dries out, no respiration occurs go deep into soil
Flood: can’t get oxygen from water, go to surface to get air
Circulatory System: closed in most, respiratory pigments (hemoglobin) dissolved in blood fluid, also contains amoeboid cells
Complete Digestive system: mouth pharyx esophagus crop (stores food) gizzard (helps “chew” food; sand helps break down detritus) intestine rectum (absorbs water) anus
Typhlosole: invagination of dorsal surface of digestive tract, increases surface area
09-21-18
Excretory System: pair of nephridia per segment
Nephridia: generalized term for excretory systems that empty outside the organism
Protonephridia: excretory system with tubes ending at flame cells
Metanephridia: excretory system with a tube that takes in coelomic fluid and releases waste outside the body through a nephridiophore
Nephrostome: where fluid goes in
Bladder: where liquid is stored
Nephridiopore: where excretion is released
Terrestrial: urea
Aquatic: ammonia
Nervous System: bi-lobed brain, ventral nerve cord, a pair of ganglia branch off in each segment
No eyes but simple photoreceptors in epidermis evolved from eyes
Reproduction: Monoecious (Hermaphroditic) but cross-fertilize with another worm
Sperm are transferred to the mates seminal receptacle. Mucus band secreted by clitellum accepts eggs and sperm, fertilization is external
Class Polychaeta: clam worms many arms
10,000 species, marine worms
Parapodia: pair extensions on each segment, used in respiration and locomotion
Well developed head: eyes, jaws, tentacles
Eyes vary from simple photo sensors to image-resolving eyes with a lens for focusing
Other sensory organs: Statocyst: orientation; Nuchal organ: chem sensory
Some polychaetes are predatory (such as errant polycheate) while others are filter feeders (Christmas tree worm) or deposit (planktonic rain)
Many polychaetes burrow in sediments: may use tube to set up water currents
Reproduction: no permanent sex organs, gonads develop in the wall of coelom and deposit eggs/sperm into coelom
Some produce specialized reproductive segments posteriorly
Atoke: anterior section
Epitoke: posterior reproductive section
In synchrony with other members of the population, the epitokes separate from the atoke and swim to surface where they rupture releasing gametes
Advantage: atoke is still safe in burrow while epitoke make perilous journey to surface to mate
Class Hirudinida; leeches
Mostly fresswater but a few terrestrial and marine
Usually < 6 cm but upt to 30cm
Body plan: usually 34 segments (may look like more due to superficial annuli)
Septa between segments lost
Suckker at both ends
Dorsoventrallly flattened
No setae
Digestive tract modified for storage of large volumes of blood from host
Leeches release Hirudin into food when feeding anti-coagulant
Phylogeny: Annelids are Lophatrochozian Protosomes
Ogligochaetes and Hirudinae are sister taxa, rest are basal
Reproduction
Asexual Reproduction: production of individuals without gametes
Advantages
Only need one individual
No genetic change- good if environment is stable
All individuals are producing offspring
More efficient at passing on genes
Disadvantages
No recombination of genes
Types:
Unicellular: Fission (mitosis)
Multicellular: mitosis
Budding
Gemmulation
Fragmentation/regeneration
Parthenogenesis eggs from diploids
Sexual Reproduction: the production of new individuals by the union of gametes, usually from two different parents
Advantages
Genetic recombination: offspring genetically unique
Genetic variation comes from:
exchange of genes between homologous chromosomes during crossing over
Shuffling of homologous chromosomes in meiosis (independent assortment)
Random fusion of gametes
Disadvantages
Need 2 parents: must expend energy to find, identify (court), and copulate with mate
Genetic recombination is counter productive if conditions are stable
Only half the individuals are producing offspring Males use resources and contribute little energy to producting new members to the population
Less efficient at pass on genes- offspring are only half your genes (clone is 100%
09-24-2018
Types of sexual reproduction
Bisexual: union of gamete from male (spermatozoon) and Female (Ovum)
Dioecious species: individuals either male or female
Hermaphroditism: species are Monoecious each individual produces sperm and egg, individuals called hermaphrodites
Sequential hermaphroditism: individual changes sex during life
Cells
Somatic Cells: cells that make up the body of an individual except gametes
Gametes: haploid sex cells (usually called sperm and egg)
Primordial germ cells: cells that give rise to gametes through the process of meiosis and cytokinesis
Organs
Primary sex organs: where gametes are produced- also called gonads (testis and ovary)
Accessory sex organs: penis, vagina
Syngamy: the union of two gametes to form a zygote
Gametogenesis: the process of gamete production
Spermatogenesis: the formation of sperm occurs in the testis
The testis are composed of coiled tubes called seminiferous tubules
Spermatogonia (2n) : mitosis, one produces Primary spermatocye, othe does not go into meiosis, one
Primary spermatocyte (2n): starts meiosis
Secondary spermatocyte (2n): cells at the end of meiosis I
Sperm (n): found in the lumen of the seminiferous tubules
Sertoli cells: in seminiferous tubules, nourish sperm cells
Characteristics of mature sperm
Head: Acrosome (cover nucleus, contains digestive enzymes), Nucleus
No cytoplasm
Midpiece: mitochondria
Tail: Flagellum
Nematode: sperm that attaches to substrate and crawls
Ova
Oogenesis: formation of the ovum occurs in the ovary
Oogonia (2n): divides by mitosis and produces primary oocyte
Primary Oocyte (2n): undergo meiosis I. Unequal cytokinesis results in 1 secondary oocyte
Secondary oocyte (n): undergo meiosis II. Unequal cytokinesis resulting in 1 (n) ovum
Polar bodies: other cells produced by meiosis that do not contain organelles, discarded
Meiosis I begins in developing embryo, meiosis II is not complete until after sperm enters the egg
Fertilization can be internal or external
External: sperm and egg are expelled from bodies
Internal: sperm transferred from male and female; sperm may be stored in spermatheca (seminal receptacle) for future use common in invertebrates
Path of sperm: urogenital system
Testes
Epididymis
Vas deferens
Urethra
Cloaca (birds, reptiles): vent to transfer sperm
Path of ovum:
Produced in follicles (tissues surrounding the developing egg) in ovary, the release is called ovulation
Egg enters oviduct: a shell may be formed around the egg (zygote) (birds, reptiles)
Zygote enters uterus (mammals)
Spermatheca: used to store sperm
Sperm competition: different deposits of sperm in spermatheca from several different mating; some males will remove sperm from spermatheca or attach until eggs are laid (safe guarding)
Oviparous animals release their eggs into the environment before fertilization or zygotes after fertilization
Ovoviviparous animals retain the fertilized egg (zygote) internally but do not supply any additional nutrients to the zygote (guppies)
Viviparous animals are those that retain the zygote in the mother who provides nourishments to the developing young (mammals and sharks)
09-26-2018
Reproductive hormones
Hormones: molecules that are produced in one part of the body and stimulate a response in another part of the body (target or receptor cells)
Male: Testosterone: produced the Leydig cells found between the seminiferous tubules of the testes
Female: hormones from the brain and ovaries function to control the release of gametes and the state of the uterus
Estrus cycle: reproductive cycle of most mammals
Female only receptive to copulation during estrus
Endometrium (nutrient rich layer) is absorbed if no pregnancy
Menstrual Cycle: reproductive cycle found in monkeys, apes, and humans. Females are receptive throughout cycle (Menstration)
Pituitary gland of brain produces:
Follicle-stimulating hormone (FSH)
Luteinizing Hormone (LH): released and egg goes to uterus
Estrogen; produced by follicle (around growing egg)
Progesterone : produced by the corpus luteum. Increases during ovulation
Human Chorionic Gonadotropin (hCG): hormone produced by developing embryo
Development
Fertilization (syngamy): the union of sperm and egg
Restores diploid state in zygote
Stimulate mitotic division
Layers of the outer covering of mature egg (sea urchin)
Jelly layer
Vitelline envelope
Plasma membrane
When the sperm contact the vitelline envelope, species specific proteins bind to receptors
The sperm penetrates the vitelline membrane and the sperm membrane fuses with the plasma membrane
Prevention of Polyspermy: the fertilization of an egg by more than one sperm
Fast block: the time frame of seconds; a change in the electrical potential of the plasma membrane prevents any other sperm from fusing with it
Cortical reaction (slow block): time frame of 1 minute; vesicles (cortical granules) fuse with the egg membrane. Water diffuses in fertilization membrane, Pronuclei of egg and sperm fuse to form zygotic nucleus.
Stages of development
Fertilized egg (zygote)
Cleavage stage: zygote divides repeatedly by mitosis no increase in size
Blastula: hollow chamber develops in the center of the morula (blastocoel)
Gastrulation: invagination of cells forms the primitive gut (archenteron)
Neurogenesis: (only in Chordata) nerve cord develops
Organogenesis: formation of the organs of the body; takes months to develop
How zygote develops will be greatly affected by the amount of yolk in the ovum
Isolecithal egg: little yolk, yolk evenly distributed (echinodermis, mammals)
Mesolecithal egg: moderate amount of yolk, unevenly distributed (amphibians)
Vegetal pole: hemisphere of the egg with the most yolk
Animal pole: hemisphere with the least yolk
Telolecithal egg: large amount of yolk, unevenly distributed (fist, reptiles, birds); cytoplasm found in blastodisc
Patterns of cleavage: The differences in the amount and distribution of yolk will affect how cleavage proceeds
Holoblastic cleavage: cytokinesis divides the cell in two
Found in isolecithal and mesolecithal eggs
In mesolecithal eggs, the vegetal pole divides slower resulting in fewer cells than in the animal pole. The blastocoel is in the animal pole
Merolastic Cleavage: cytokinesis
Symmetry of Cleavage
Radial cleavage: as cells divide , the cells appear stacked parallel to a central axis
Found in amphibians and echinoderms: characteristic of deuterostomes
Spiral Cleavage: as cells divide, the stacked layers lie in the furrows from the layer below
Found in annelids, Mollusca, and Arthropoda- characteristics of protostomes
During gastrulation the three germ layers are generated Ectoderm, Mesoderm, endoderm
There are two basic patterns by which the mesoderm layer originates
Enterocoelous: mesoderm forms as pouches off the archenteron seen in Deuterostomes
Schizocoelous: Mesoderm cells develop around the base of the archenteron seen in Protostomes
Development in telolecithal eggs
Meroblastic cleavage: cleavage only occurs in the active cytoplasm results in layers of cells
Primitive streak: groove down central axis of blastodisc
During gastrulation, cells start to differentiate (the process by which a cell becomes specialized)
Neurogenesis (Chordata): development of the nerve cord from ectoderm tissue
Neural plate forms neural fold that form a tube hallow nerve cord
Neural crest cells split off tube, develop into: cranial nerves, pigment cells, bones of the skull, parts of endocrine glands
Organogenesis: development of the organs of the body. Embryo (2 weeks to 2 months), organ systems are developing
Cell Fates: as cells divide and the number of cells in the body increase, the cells are induced to use different genes. During this process, called differentiation, the cells turn into one of the mature cell types
Determined: the point at which a cell has differentiated so it cannot be induced to become a different type of cell
Totipotent Cell: can develop into an embryo and eventually individual
Deuterostomes: regulative (can form more embryos)
Protostomes: mosaic (will die)
Skin
Integument: protective outer covering of the body
Invertebrates: epidermis, sometimes covered by a non-cellular cuticle
Vertebrate integument
2 basic layers
Epidermis: layer of cells of ectodermal origin
Dermis: layer of cells of mesodermal origin
Epidermis gives rise to hair, feathers, scales, and claws
Stratified squamous epithelium
The proximal layers undergo mitosis
Keratin and lipids produce tough waterproof barrier 4
Stratum Corneum: layer of cells that have undergone keratinization, resistant to water
Skeletal Systems
Hydrostatic Support
Exoskeleton
Endoskeleton (chordates and echinoderms) from mesoderm origins
Notochord: large cells within a fibrous sheath covered by an elastic sheath
Cartilage: (Chondrocytes imbedded in a protein gel with strands of collagen (another protein)
Bone: Osteocytes imbedded in a matrix of collagen and calcium phosphate salts
Endochondral bone: develops from cartilage
Intramembranous bone: sheets of cells that lay down CaP (skull cap, pelvis, shoulder blade)
Spongy bone: inside of bone, cavities to store other materials (bone marrow)
Compact bone: outer part of bone, solid bone material
9-28-2018
Phylum Rotifera: Roto-wheel, fera – bearing
Characteristcs
Mostly freshwater
Few marine species
Lophotrochozoan protostomes
Trochophore larvae
Have Pseudocoelom
Corona: ciliated structure on anterior end used for generating water currents (feeding and locomotion)
Lorica: protective plates or rings, from fibrous layer in epidermis
Nervous system: bi-lobed brain (cephalization)
Reproduction: both asexual and sexual
Parthenogenesis: most of the year reproduction is asexual population is composed of females that produce diploid amictic eggs.
When conditions worsen, females produce haploid mictic eggs
If not fertilized, eggs develop into haploid males
If males fertilize the eggs then develop into diploid zygote called a dormant egg
Phylum Nematoda: nematos = thread
Characteristics
25,000 species described
Have pseudocoelom
Density of billions per acre
Ecdysozoan protostomes (molting)
Many are parasitic: infect most plants and animals
Ascaris lumbricodies: large roundworm of humans (infect up to 25% of human population in some US SE areas)
Often pass through stomach during life cycle
Cuticle: non-cellular, secreted by hypodermis (epidermis)
Longitudinal muscles are used to make the body wiggle for locomotion
Different from earthworm (no circular muscle)
High coelomic pressure: higher pressure inside of body than outside
Sexual dimorphism:
Copulatory spicules
Sperm have no flagellum ameboid movement
Females can release 200,000 eggs/day
Some nematode examples
Hookworm: enter through skin and migrate to intestine where they feed on hosts blood
Can crawl 5ft from feces
Outhouses- 10ft holes to stop infections
Trichinella spiralis: cause trichinellosis (very rare in US); enters through undercooked pork, young enter bloodstream and encyst in various tissues (especially muscle)
Pinworm: most common nematode parasite (16% adults/30% children). Females migrate at night to lay eggs around anus
Filarial worms: infect lymphatic system associated with growth of connective tissue and swelling of extremities. Elephantiasis, river blindness, dog heartworm (45%; spread from mosquitoes)
Additional Phyla that have a pseudocoelom
10-1-2018
Phylum Arthropoda: “jointed foot”
Characteristics
About 1.1 million species described
Body composed repeated segments (metamerism) but septa have been lost
In contrast to annelids, much specialization of segments is seen
Tagmosis: the fusion of segments to form a larger specialized body sections
Head: appendages used a sensory and feeding structure
Thorax: Contains many organs and legs used for locomotion
Abdomen: man contain organs (esp. reproduction) or be used in locomotion
Body Structures
Arthropods exhibit much more specialization of appendages
Functions: sensory, feeding, locomotion, reproduction
Presence of antenna and mandible are important taxonomic characters
The cuticle of Arthropods is greatly modified from that annelids: more durable, specialized for molting
Molting: process of shedding old cuticle and secreting a new one
Cuticle contains two laters
Epicuticle: outermost layer; first thing that is made for molting
Procuticle: innermost; contains chitin (nitrogenous polysaccharide); proteins and calcium salt: increase rigidity, made of two layers
Exocuticle: secreted prior to molting temporary protection
Endocuticle: secreted after molting, forms tough durable shell
The cuticle of Arthropods is greatly modified from that of annelids more durable specialized for molting
Organ Systems
Arthropods have various adaptations for gas exchange- tracheal system – branching system of tube that deliver atmospheric gases directly to cells
Malpighian Tubules: An arthropod adaptation of terrestrial life excretory vessels that releases into the digestive tract
Use uric acid for waste
Metaporphosis is an adaptation seen in insect Arthropods that decreases competition between larvae and adults- the body form changes between larvae and adult
Holometabolous metamorphosis
Metamorphosis is rapid
Egg
Larva (specialized for feeding)
Pupa (larva undergoes drastic metamorphosis into adult)
Adult (specialized for dispersal and reproduction)
Menimetabolous Metamorphosis
Metamorphosis is more gradual
Egg
Nymph
Adult
Wings: outgrowth of cuticle, not a modified leg
No wings Rigid wings Hidden wings Non- hidden (one set of wings disappears and used for balance)
Subphylum Trilobita; all extinct
Very successful from pre-Cambrian to carboniferous (about 200my)
Body with head thorax and abdomen
Two grooves running longitudinally
Subphylum Chelicerata: horseshoe crab, spiders
First pair of appendages modified into Chelicerae which are used to grasp food or inject poison
Four or five pairs of walking legs
No mandibles or antennae
Class Merostomata- horseshoe crabs
Living fossils: have changed little through time
Synchronize mating by moon/tides
Cephalothorax: head and thorax fused 2 simple, 2 compound eyes
Telson: most posterior segment tail spine, anus
10/3
Class Arachnida: spiders, ticks, scorpions
80,000 species
4 Pair walking legs, 1 pair pedipalps, 1 pair Chelicara (fangs)
Four pairs of eyes
Spinning gland produces webbing: used in capture of prey, creating shelter, protecting eggs
Subphylum Myriapoda: “many footed”, centipedes, millipedes
One pair of antennae
Appendages uniramous: one leg (not pincers) contrast with crustaceans
Mandibles
Terrestrial adaptations: trachea and malpighian tubules
Class Chilopoda: centipedes
Dorsoventrally flattened with many segments
Tubular, usually with segments
Two pair of legs per segments
Subphylum Crustacea: “shell”
70,000 species described
Most are marine but are important and abundant in freshwater; there are a few terrestrial species
Most mobile, some sessile (barnacles)
2 pair of antenne
Pair of mandibles: bi-ramous legs modified for masticating food
Exoskeleton of crustaceans is very strong, fortified with calcium. Areas around joints are not calcified so flexibility is not lost
Characteristics:
Excretory system: antennal glands function mostly in osmoregulation (maintaining water balance): ammonia diffuses across thin parts of cuticle
Reproduction:
Sexual: usually cross fertilize
Asexual: may be parthenogenic
Development is usually indirect with a larval form called a nauplius
Class Malacostraca: largest and most diverse taxa of Crustacea (20K species)
Includes crabs, crayfish, shrimps- mostly marine but some freshwater and terrestrial
Subphylum Hexapoda- “6 foot”
Over 1 million species described (250-380 k beetles)
One pair of antennae
Appendages uniramous (contrast with crustacean biramous legs)
Terrestrial adaptations: trachea and malpigian tubules
Mouth with mandibles
Three tagmata: head, thorax, abdomen
Typically 2 pairs of wings
Phylogeny
Arthropods were once thought to have evolved from Annelids, current phylogenies place them with ecdysozans
Arthropodization (Tagmosis) may have happened a few times in evolutionary history Arthropoda may be polyphyletic
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