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

Figure 28-6b Page 542 Osculum Epidermal cell Spongocoel Incurrent pores Porocyte Water movement Spicule Collar cell Amoeboid cell in mesohyl Microvillus Flagellum Nucleus Figure 28-6b Page 542 Collar

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

Figure 30-2 Page 577 Digestive gland Stomach Gonad Digestive gland Tube feet Tube feet Anus Ampulla Gonad Spine Dermal gill Pedicellariae 5 mm Tube feet Figure 30-2 Page 577

Phylum Chordata Very successful Includes 3 subphyla, some invertebrate Urochordata – tunicates Cephalochordata – lancelets Vertebrata

2 out of 3 chordate subphyla are invertebrates Chordata 2 out of 3 chordate subphyla are invertebrates Echinodermata sea urchins) (sea stars, Cephalochordata (lancelets) Hemichordata (acorn worms) Urochordata (tunicates) Vertebrata Cranium, vertebral column Notochord, dorsal tubular nerve cord, pharyngeal slits, postanal tail Deuterostome ancestor

Tadpole Larva

Figure 30-6 Page 581 Chordata Cephalochordata Echinodermata sea urchins) (sea stars, Cephalochordata (lancelets) Hemichordata (acorn worms) Urochordata (tunicates) Vertebrata Figure 30-6 Page 581 Deuterostome ancestor

Subphylum Cephalochordata: The Lancelet or Amphioxus Branchiostoma sp. Tentacles Nerve cord Notochord Gill slits Intestine Caudal fin Tentacles Endostyle Atrium Gonads Atriopore Anus

Craniates V e r t e b r a t e s Jawless fishes Amniotes Cephalaspidomorphi (lampreys) (cartilaginous fishes) Chondrichthyes (ray-finned fishes) Actinopterygii Cephalochordata (lancelets) Urochordata (tunicates) (hagfishes) Myxini (coelacanths) Actinistia (lungfishes) Dipnoi Mammalia Amphibia Reptilia (birds) Aves Amniotic egg Limbs Lungs (for swim bladder) Jaws Vertebrae Chordate ancestor