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Lecture Topics • What is an animal? • Evolutionary trends in animals • Introduction to some representative animal phyla What is an Animal? • Animals are very diverse but do share some general common characteristics – Multicellular heterotrophic eukaryotes – Ingest food – Diploid – Capable of locomotion – Reproduce sexually, but asexual reproduction is common – Lack cell walls • Appear to be a monophyletic group Evolutionary trends • Germ Layers – embryonic cell layers – Begin with single undifferentiated layer • E.g., Porifera – Diploblastic – two germ layers: • E.g., Cnidaria • Ectoderm (outer) Skin & nerves • Endoderm (inner) Gut – Triploblastic – adds a third germ layer – E.g., Arthropoda • Mesoderm (middle) Muscle, many organs Evolutionary trends • Digestive tract – Begins with no digestive tract • E.g., Porifera – Blind sac with food in and waste back out • E.g., Cnidaria – One way gut – tube within a tube • E.g., Annelida Triploblastic Body Plans • Acoelomates – Solid body construction • Pseudocoelomates – Lined on only outer side with mesoderm – No mesentery • Coelomates – Completely surrounded by mesoderm – Mesentery suspends gut from body wall Evolutionary trends • Body symmetry – Asymmetry = None • Porifera – Radial symmetry = Symmetric (mirror image) about oral-aboral axis • Cnidaria (mostly?) – Bilateral symmetry = Symmetric only about one plane • Pretty much everything else Sections, Directions, and Symmetry Evolutionary trends • Cephalization -- formation of a distinct head – Associated with Bilateral symmetry – Puts sensory organs and mouth in the lead – Generally considered an adaptation for an active lifestyle – Contrast Porifera, Cnidaria, Echinodermata with Annelida and Arthropoda Segmentation, Metamerism, and Tagmatization or Tagmosis • Segmentation – division of body into distinct segments able to operate independently of one another • Metamerism – serial repetition of body parts – Contrast Nematoda vs Annelida or Arthropoda • Tagmatization – organization of segments into functional units (e.g., head, thorax, abdomen) – Contrast Annelida vs. Arthropoda Sponges: Phylum Porifera • Germ Layers – None – Very loosely organized – can sift cells and will regenerate • Digestive tract – None – Choanocytes filter food from water, amebocytes transfer nutrients • Coelom – None • Symmetry – None • Segmentation – None Unique Structures • Spicules – Silica or calcium carbonate • Spongin – Flexible protein • Choanocytes – Collar cells – similar to choanoflagellates – Drive water flow in ostia and out osculum Osculum Epidermal cell Spongocoel Incurrent pores Water movement Porocyte Spicule Collar cell Flagellum Microvillus Collar Amoeboid cell in mesohyl Nucleus Figure 28-6b Page 542 Jellyfish, Anemones, Corals, Hydra : Phylum Cnidaria or Coelenterata • Germ Layers – Two, with gelatinous mesoglea between endoderm and ectoderm • Digestive tract – Blind sac – food enters and exits through mouth • Coelom – None • Symmetry – Radial • Segmentation – None Unique Structures • Cnidocytes with Nematocycts – Stinging cells with venomous harpoons • Polyp – Sessile form e.g., Anemone, Hydra • Medusa – Swimming form, e.g., Jellyfish Two major clades of animals: Protostomes vs. Deuterostomes • Embryonic origin of gut – Protostome = First Mouth – Mouth arises from blastopore – first invagination of blastula (hollow ball of embryonic cells) – Deuterostome = Second mouth – Anus arises from blastopore • Early development – Protostomes – Determinate, spiral cleavage, coelom originates from solid mass of cells – Deuterostomes– Indeterminate, radial cleavage, coelom originates as pouches off gut Fig. 32.3 Phylogeny undergoing revision • Protostomes now divided into two clades – Spiralia – Ecdysozoa (animals that molt) • Flatworms previously considered separate clade -Acoelomates • Nematodes and rotifers previously considered pseudocoelomates (not protostome coelomates) but molecular evidence suggests protostome ancestry (details change with new data) • Now flatworms, nematodes, and rotifers considered simplified coelomates – Flatworms in Platyzoa within Spiralia – Nematodes in Ecdysozoa Segmented Worms: Phylum Annelida • • • • • Germ Layers – Three Digestive tract – One way gut Coelom – True coelom Symmetry – Bilateral Segmentation – Yes, with metamerism Snails, Bivalves, Cephalopods: Phylum Mollusca • Germ Layers – Three • Digestive tract – One way gut • Coelom – True coelom with mesentery – lined with mesoderm on both inner (gut) and outer (body wall) surfaces • Symmetry – Bilateral • Segmentation -- ? Chitons have serial plates Unique Structures • Radula – Rasping structure on “tongue” • Calcium carbonate shell (absent in slugs, internal in most cephalopods) secreted by mantle Giant squid Architeuthis dux • World’s largest invertebrate (18m, 900kg) Ecdysozoa Protostomes that molt • Arthropods – Rulers of the planet! (insects, spiders, crustaceans, etc.) Insects, Arachnids, Crustaceans, Myriapods, etc.: Phylum Arthropoda • • • • • Germ Layers – Three Digestive tract – One way Coelom – True coelom Symmetry – Bilateral Segmentation – Yes, with tagmatization (head, thorax and abdomen or cephalothorax and abdomen or head and trunk) Unique Structures • Jointed Appendages • Chitinous exoskeleton (remember chitin?…) • Wings (insects) • Chelae (crabs) Photographer: Alan Gornick Jr. ©Aris Multimedia Entertainment, Inc. 1994 Deuterostomes • Echinoderms • Chordates Phylum Echinodermata • • • • • Germ Layers: Three Digestive tract: One way Coelom Symmetry: Bilateral (“pentaradial”) Segmentation: In arms? Unique Structures • Water vascular system with tube feet • Pedicellaria -- tiny pincers on flexible stalks • Dermal skeleton of calcium carbonate Digestive gland Stomach Gonad Digestive gland Tube feet Tube feet Anus Ampulla Gonad Spine Dermal gill Pedicellariae Tube feet 5 mm Figure 30-2 Page 577 Phylum Chordata • Very successful • Includes 3 subphyla, some invertebrate – Urochordata – tunicates – Cephalochordata – lancelets – Vertebrata Vertebrata Cephalochordata (lancelets) Urochordata (tunicates) Hemichordata (acorn worms) Echinodermata (sea stars, sea urchins) Chordata 2 out of 3 chordate subphyla are invertebrates Cranium, vertebral column Notochord, dorsal tubular nerve cord, pharyngeal slits, postanal tail Deuterostome ancestor Tadpole Larva Cephalochordata (lancelets) Chordata Deuterostome ancestor Figure 30-6 Page 581 Subphylum Cephalochordata: The Lancelet or Amphioxus Branchiostoma sp. Tentacles Nerve cord Notochord Gill slits Intestine Caudal fin Tentacles Endostyle Atrium Gonads Atriopore Anus Chordate ancestor Jaws Vertebrae Jawless fishes Limbs Lungs (for swim bladder) Mammalia Aves (birds) Reptilia Amphibia Dipnoi (lungfishes) Actinistia (coelacanths) Actinopterygii (ray-finned fishes) Chondrichthyes (cartilaginous fishes) Cephalaspidomorphi (lampreys) Myxini (hagfishes) Cephalochordata (lancelets) Urochordata (tunicates) Craniates V e r t e b r a t e s Amniotes Amniotic egg