2/17/2017. Lec. 11: Ch. 32 Deuterostomes

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1 Lec. 11: Ch. 32 Deuterostomes Deuterostomes Radial cleavage Indeterminant blastomeres Blastopore becomes anus Coelom forms by outpouching of the gut (enterocoelous) Phylum Echinodermata - Characteristics Deuterostomate development Anus develops first Radial indeterminant cleavage Enterocoelous Secondary pentamerous radial symmetry Sexual reproduction Fertilization external Water vascular system (coelomic) Open circulatory system (coelomic) Calcareous endoskeleton (made of ossicles) Echinodermata Characteristics, cont d Complete digestive system (usually) No excretory system Excretion and gas exchange through skin and tube feet No cephalization Oral/Aboral axis No complex CNS brainless Nerve rings and net Mutable connective tissue ( catch tissue ) Echinoderm body plan oral/aboral Reproduction in echinoderms Separate sexes (most species) External fertilization Bilaterally symmetrical larval forms in early stages of some classes Water Vascular System Linked to outside via madreporite & stone canal Controls water-powered locomotion With tube feet (podia) extending outside body Each foot serviced by an ampulla (small pump) Feet often used for gas exchange & excretion 1

2 Feeding Strategies in Echinoderms Echinoderms suspension feed, deposit feed, harvest algae, or harvest other animals. See deposit feeding sea urchin: In most cases, the podia play a key role in obtaining food Phylum Chordata - Characteristics Bilateral, deuterostomate, coelomate, cephalization, etc. Notochord axial support structure Dorsal, tubular nerve cord Ciliated pharyngeal slits for gills and/or filter-feeding Post-anal, muscular tail Notochord Skeletal structure that provides support Longitudinal, flexible rod between digestive tube and nerve cord Dorsal, hollow nerve cord Name kind of says it all Develops from a plate of ectoderm that rolls into a tube, gives rise to CNS in some chordates Pharyngeal slits Grooves or slits along the side of the pharynx that open to the outside of the body Allow water to enter mouth but exit body without passing through digestive system Function as filter-feeding device in some, respiratory device in others Muscular, post-anal tail Again, name kind of says it all Musculature in tail, and elsewhere, is segmented Subphylum Cephalochordata lancelets Subphylum Urochordata - The Tunicates 2

3 Larva exhibits typical chordate morphology Now for Vertebrate Diversity What s a vertebrate? Phylum Chordata Craniate Vertebrates have extensive skull Backbone Composed of linearly arranged vertebrae May be simple prongs of cartilage or complex boney structures Encloses spinal cord in most Class Myxinoidea The Hagfishes (jawless) Characteristics Formerly, hagfish and lamprey together in agnatha (jawless fishes) Have cartilaginous skull, but no jaw or vertebrae Have tooth-like formations of keratin in mouth Hagfish produce LOTS of slime in response to predators (as in liters/minute) Slime defense video! Class Petromyzontoidea (the lampreys also jawless) Jawless fish with small pieces of cartilage along dorsal hollow nerve cord Many are ectoparasites Attach to fish with sucker-like mouth Rasp hole in fish and consume blood Others filter-feed And then came JAWS! Advent of the Jaw Gnathostomes Vertebrates that have jaws Jaws are hinged structures, often bearing teeth, used to grip food Arose from portion of skeleton that previously supported anterior gill slits Lateral line system In aquatic gnathostomes Row of microscopic cells sensitive to vibrations Later modifications for sensing electrical fields Class Chondrichthyes the cartilaginous fish Little change in 300my Large and successful predators including sharks, rays and skates Skeleton composed of cartilage, some impregnated with calcium Heavy calcification found only in teeth 3

4 Osteichthyes the bony fish No longer independent class Classes Actinopterygii (ray-finned), Actinistia (coelocanths), and Dipnoi (lungfish) Almost all have ossified (bony) endoskeleton Over half of known vertebrate species are represented by these classes Hey, let s take a walk Origin of tetrapods Tetrapods: gnathostomes with limbs and feet Limbs with feet replace pectoral and pelvic fins Originated ~ mya Numerous adaptations for life on land Bones of pelvic girdle fused to vertebrae No gill slits (as adults) Pharyngeal slits give rise to ears, glands, etc. Ears adapted for airborne sound Class Amphibia The salamanders, frogs, and legless caecilians Amphibian means two lives Aquatic larvae undergo metamorphosis to adults that may or may not be aquatic Most respire through skin so are limited to moist environments Random Animal of the Day! Smallest Vertebrate Animal in the World Paedophryne amanuensis Just 7.7mm long! Discovered 2012 Papua New Guinea Bonus Activity Describe the cleavage pattern of deuterostomes (radial or spiral, determinate or indeterminate) Echinoderms are radially symmetrical; why are they still classified as bilaterians? The evolution of bilateral symmetry occurred fairly early in animal evolution, and most animals are bilaterally symmetrical and exhibit varying degrees of cephalization. Can you think of any reason why starfish would evolve to become radially symmetrical? Think about how they live and interact with their environments. Name the four characteristics found in all chordates, and describe the function of each minute break The Amniotes 4

5 Amniotes are tetrapods that have a terrestrially adapted egg Amniotic egg = an egg that has a watertight shell or case enclosing a membrane-bound water supply (the amnion), food supply (the yolk), and waste sac (allantois) Living representatives are reptiles (including birds) and mammals Include many extinct groups that we will not cover Four extraembryonic membranes (membranes that are not part of the embryo itself) Amnion: protects embryo within fluid-filled sac that cushions embryo against shock Four extraembryonic membranes Allantois: Sac for disposal of embryonic wastes Also serves a respiratory function Four extraembryonic membranes Chorion: Completely surrounds embryo (as well as allantois and yolk sac), functions in gas exchange Four extraembryonic membranes Yolk sac: contains the yolk, which is a stock of nutrients for the developing embryo From Amniotic Egg to Placental Development Two groups left Reptiles & Birds (Class Reptilomorpha) Have scales that contain keratin Waterproof barrier that prevents desiccation and releases dependence on water Also prevents respiration through skin Have lungs for gas exchange Lay shelled eggs Body temperature regulation Reptiles are ectothermic, absorbing external heat as the source of body heat Birds are endothermic, using metabolism to keep the body warm Birds an interesting case Numerous adaptations for flight, mostly about weight reduction Wings and feathers obvious, also no urinary bladder, one ovary, hollow skeleton, toothless, four chamber heart, flow-through lungs, acute vision Class Mammalia Unique adaptations Mammary glands that produce milk Hair Layer of body fat under skin Generally larger brain capable of learning Relatively long duration of parental care 5

6 Differentiation of teeth Three major lineages Monotremes Found only in Australia/New Guinea Represented by platypus and echidnas Lay eggs and secrete milk from glands onto fur (no nipples) Marsupials More widely distributed Include kangaroos, opossums, koalas Embryo develops in uterus nourished by placenta (derived from extraembryonic membranes), born live (not in eggs), further development in maternal pouch Eutherians (placental mammals) Placenta more complex than marsupials Longer period of pregnancy Young complete embryonic development within uterus Group includes humans and other primates Primates The lineage consists of two main groups: the prosimians ( before-monkeys ) and the anthropoids ("human-like") Primates The lemurs, tarsiers, monkeys, and apes Most have hands and feet adapted for grasping Anthropoids have fully opposable thumb Group includes monkeys, apes, and humans Opposable thumb means ventral surface of thumb can touch the ventral surface of all four fingers of the same hand Have you seen the dramatic lemur? It is actually a tarsier Funny video: Hominoids Hominoids - The primates called apes (Gibbons lesser apes), Orangutans, Gorillas, Chimpanzees, and Humans 6

7 Humans are bipedal and have larger brains than other hominoids Earliest Homo sapiens date to about195,000 years ago Human Evolution Evidence now suggests approximately 20 extinct species of hominins Hominins are a monophyletic group which includes Homo sapiens and extinct, bipedal relatives Common misperceptions: We did not evolve from chimpanzees, though both groups likely share a recent common ancestor (~6-7mya) Evolution of humans is not the ladder most imagine Several species likely co-existed over evolutionary time Many dead ends throughout history Human Evolution The fossil record contains evidence for five main groups of hominins. Ardipithecus is oldest hominin known; over 4mya Australopithecines have larger jaws and smaller braincases than Homo; bipedal Paranthropus were robust australopithecines with broader skulls; large sagittal crest and cheek bones Early Homo were early humans with narrower faces, smaller jaws, and larger braincases; made tools Recent Homo date from 1.2 mya to present; included Cro Magnon, a population of extinct Homo sapiens, and H. neanderthalensis; both had larger braincases than modern humans Recent Discovery: Hobbit People? 2003 discovery of fossil remains on island of Flores in Indonesia Named Homo floresiensis Inhabited Flores from 100,000 to 12,000 years ago, but resembles a smaller version of a much more ancient hominin Was it just a modern human with a disorder? Evidence suggests it was a separate branch on our evolutionary tree Hominid ( great ape ) Traits Bipedalism the ability to walk upright on two legs Required significant modification of skeletal structure, stresses are much different than for tree-dwelling ancestors Only truly found in humans; a synapomorphy that defines hominins Tool Use modifying objects for a specific function Determining the origin of tools is difficult, but occurred early in human evolution Cut marks have been found on bones dating to 2.5mya Many modern hominoids (and other animals) use tools, so not really unique to hominins That s all for today 7

Animals II: The Chordates

Animals II: The Chordates Phylum : Chordata Subphylum: Urochordata: Tunicates Cephalochordata: Lancelets Vertebrata: Vertebrates Chordate Characteristics Bilaterally symmetrical, coelomate animals Complete