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Transcript
The sea jellies, flatworms and rotifers Tom Hartman www.tuatara9.co.uk Animal form and function 1 Module 11112 MCQs from handout 8 Another MCQ test Evaluate the following statements: 1. 2. 3. 4. 5. humans are triploblastic there is one type of sponge that fishes for its prey ctenophores have blind ended guts nematocysts (cnidocysts) are captured from sea slugs cnidocysts evert to puncture prey and deliver their stings Animals All other animals (bilateralia) Radiata Sponges Choanoflagellates Fungi The radiata • • • • • Radial symmetry Two cell layers Jelly sandwich (with some cells) Nematocysts Gut has one opening…. Phylum Ctenophora • Radial symmetry • Two cell layers with gelatinous mesoglea in which muscle fibres run. • Eight rows of fused cilia. • Muscular tentacles with sticky spirocyst-like organelles. • Tissues but no organs. • Complete gut! • No polyp stage. Phylum ctenophora • One species found in the North Atlantic was introduced accidentally to the Black sea (via ballast tank flushing) where they became the dominant predator of plankton. • Caused the collapse of the anchovy fisheries. • Biomass was estimated to be 1,000,000 tons! • Accidental introduction of a predator has reduced this (also a ctenophore). • Pest species recently found in the Baltic, Caspian and North seas. Leaving the radiata • Leading hypotheses agree on major features of the animal phylogenetic tree. • Zoologists currently recognize about 39 animal phyla. • New levels of complexity. Animal pole Vegetal pole New levels of complexity 1. Cleavage • Cleavage is spiral and determinate = protostome development • Cleavage is radial and indeterminate = deuterostome development Protostome development (examples: molluscs, annelids, arthropods) Eight-cell stage Spiral and determinate Deuterostome development (examples: echinoderms, chordates) Animal pole Eight-cell stage Radial and indeterminate Vegetal pole All other animals (bilateralia) Deuterostomes Protostomes Animals Radiata Sponges New levels of complexity 2. Fate of the Blastopore • In protostome (spiral cleavage) development – The blastopore becomes the mouth • In deuterostome (radial cleavage) development – The blastopore becomes the anus Mouth Anus Digestive tube Mouth Mouth develops from blastopore Anus Anus develops from blastopore New levels of complexity 3. A new cell layer • Triploblastic animals • Blastocoel is ‘invaded by cells as the gastula matures. • These mesenchyme cells organise the internal architecture and some become the mesoderm. • Mesoderm spawns organs and tissues between the ‘skin’ and the ‘gut’. Gastrulation in a sea urchin embryo Key Future ectoderm Future mesoderm Future endoderm Blastocoel Mesenchyme cells Vegetal plate Vegetal pole Animal pole Gastrulation in a sea urchin embryo Key Future ectoderm Future mesoderm Future endoderm Animal pole Blastocoel Mesenchyme cells Vegetal plate Vegetal pole Blastocoel Filopodia pulling archenteron tip Archenteron Blastopore Mesenchyme cells 50 µm Gastrulation in a sea urchin embryo Key Future ectoderm Future mesoderm Future endoderm Animal pole Blastocoel Mesenchyme cells Vegetal plate Vegetal pole Blastocoel Filopodia pulling archenteron tip Archenteron Blastopore Mesenchyme cells Blastocoel 50 µm Archenteron Ectoderm Mesenchyme: (mesoderm forms future skeleton) Mouth Blastopore Digestive tube (endoderm) Anus (from blastopore) Protostomes All other animals (bilateralia) Ecdysozoa Lophotrochozoa Deuterostomes Animals Radiata Sponges Ecdysozoa Insects, cruscatea, myriapods, arachnids Protostomes Velvet worms Round worms Lophotrochozoa Strange bivalves Snails, octopi, bivalves, etc. Triploblastic Bilateralia Eumetazoa Deuterostomes Segmented worms Flat worms Wheel mouths Lanclets, vertebrates, etc. Starfish, urchins, etc. Comb jellies Radiata Diploblastic Parazoa Anemones, hydras, etc. Sponges Layers • Animal embryos – Form germ layers, embryonic tissues, including ectoderm and endoderm. • Diploblastic animals Ectoderm – Have two germ layers. • Triploblastic animals – Have three germ layers: mesoderm. Endoderm Adult derivatives of the three embryonic germ layers in vertebrates ECTODERM • Epidermis of skin and its derivatives (including sweat glands, hair follicles) • Epithelial lining of mouth and rectum • Sense receptors in epidermis • Cornea and lens of eye • Nervous system • Adrenal medulla • Tooth enamel • Epithelium or pineal and pituitary glands MESODERM • Notochord • Skeletal system • Muscular system • Muscular layer of stomach, intestine, etc. • Excretory system • Circulatory and lymphatic systems • Reproductive system (except germ cells) • Dermis of skin • Lining of body cavity • Adrenal cortex ENDODERM • Epithelial lining of digestive tract • Epithelial lining of respiratory system • Lining of urethra, urinary bladder, and reproductive system • Liver • Pancreas • Thymus • Thyroid and parathyroid glands Where on the tree? Ecdysozoa Insects, cruscatea, myriapods, arachnids Protostomes Velvet worms Round worms Lophotrochozoa Strange bivalves Snails, octopi, bivalves, etc. Triploblastic Bilateralia Eumetazoa Deuterostomes Segmented worms Flat worms Wheel mouths Lanclets, vertebrates, etc. Starfish, urchins, etc. Comb jellies Radiata Diploblastic Parazoa Anemones, hydras, etc. Sponges Or possibly Ecdysozoa Protostomes Insects, cruscatea, myriapods, arachnids Velvet worms Round worms Lophotrochozoa Strange bivalves Snails, octopi, bivalves, etc. Triploblastic Bilateralia Platyzoa Eumetazoa Segmented worms Wheel mouths Flat worms Lanclets, vertebrates, etc. Deuterostomes Starfish, urchins, etc. Comb jellies Radiata Diploblastic Parazoa Anemones, hydras, etc. Sponges Flat worms Phylum Platyhelmithes • 1. 2. 3. 4. 5. 6. 7. 8. Big changes from all animals branching earlier. Bilaterally symmetrical. SuperTriploblastic in development. phylum Tissues and organs. Bilateralia Definite anterior end with cephalisation. Simple nervous system and brain. Many have eyes. Muscular system/cilia for movement. Free living and parasitic. • Turbellarians • Flukes (trematodes) – parasitic • Tapeworms (cestodes) – parasitic • No circulatory system therefore: • Flat to cope with O2/CO2 diffusion. • Sac like or branched gut. – Gut delivers nutrients in absence of circulatory system. – Gut absent in some parasitic forms (a derived feature). • A solid body: no cavities. • Excretory/osmoregularity organs (protonephridia). A planarian in cross section A solid body with no spaces or cavities: ACOELOMATE. Parasites can have an extraordinarily complex life cycle. Generalised fluke life cycle Reproduction • Mostly hermaphrodite with complex reproductive systems with some species reliant on asexual reproduction: they tear in half! • This has lead to some vital observations on the nature of development and chemical gradients. Regeneration in Planaria End of lecture