IB-202-4

1. IB-202-4 3-15-06

2. Most animals have bilateral symmetry • The vast majority of animal species belong to the clade Bilateria • Which consists of animals with bilateral symmetry and triploblastic development

3. Developmental Patterns (Deuterostome andProtostome) • Based on certain features seen in early development • Many animals can be categorized as having one of two developmental modes: protostome development or deuterostome development

4. Deuterostome development (examples: echinoderms, chordates) Protostome development (examples: molluscs, annelids, arthropods) (a) Cleavage. In general, protostomedevelopment begins with spiral, determinate cleavage.Deuterostome development is characterized by radial, indeterminate cleavage. Means at the 8 cell stage you can separate out a cell and will develop into a complete individual Eight-cell stage Eight-cell stage Spiral and determinate Radial and indeterminate Cleavage • In protostome development • Cleavage is spiral and determinate • In deuterostome development • Cleavage is radial and indeterminate Figure 32.9a

5. (b) Coelom formation. Coelom formation begins in the gastrula stage. In protostome development, the coelom forms from splits in the mesoderm (schizocoelous development). In deuterostome development, the coelom forms from mesodermal outpocketings of the archenteron (enterocoelous development). Coelom Archenteron Coelom Mesoderm Blastopore Mesoderm Blastopore Enterocoelous: folds of archenteron form coelom Schizocoelous: solid masses of mesoderm split and form coelom Figure 32.9b Coelom Formation • In protostome development • The splitting of the initially solid masses of mesoderm to form the coelomic cavity is called schizocoelous development • In deuterostome development • Formation of the body cavity is described as enterocoelous development. Red represents mesodermal cells.

6. Mouth Anus Digestive tube Anus Mouth Mouth develops from blastopore Anus develops from blastopore Figure 32.9c Fate of the Blastopore • In protostome development • The blastopore becomes the mouth • In deuterostome development • The blastopore becomes the anus. Note two layers of mesoderm lining body cavity.

7. Figure 33.9 Flat Worms

8. Flatworms • Members of phylum Platyhelminthes • Live in marine, freshwater, and damp terrestrial habitats • Have a gastrovascular cavity and are flattened dorsoventrally (significance=don’t need a circulatory system as diffusion is adequate to meet nutrient distribution from the gut, gas exchange and waste disposal needs because of short distance from cell to environment • Although flatworms undergo triploblastic development • They are acoelomates (body cavity solid)

9. Flatworms are divided into four classes

10. Figure 33.9 Class Turbellaria • Turbellarians • Are nearly all free-living and mostly marine

11. Digestion is completed within the cells lining the gastro- vascular cavity, which has three branches, each with fine subbranches that pro- vide an extensive surface area. Pharynx. The mouth is at the tip of a muscular pharynx that extends from the animal’s ventral side. Digestive juices are spilled onto prey, and the pharynx sucks small pieces of food into the gastrovascular cavity, where digestion continues. Undigested wastes are egested through the mouth. Gastrovascular cavity Eyespots Ganglia. Located at the anterior end of the worm, near the main sources of sensory input, is a pair of ganglia, dense clusters of nerve cells. Ventral nerve cords. From the ganglia, a pair of ventral nerve cords runs the length of the body. Figure 33.10 Planaria • The best-known turbellarians, commonly called planarians • Have light-sensitive eyespots and centralized nerve nets. Cephalization-concentration of sensory organs and nerve bodies (ganglia) at the anterior end. Allows them to avoid light, seek food etc.

12. Other Flatworms are parasitesMonogenea and Trematoda • Monogeneans and trematodes • Live as parasites in or on other animals • Parasitize a wide range of hosts

13. Mature flukes live in the blood vessels of the human intestine. A female fluke fits into a groove running the length of the larger male’s body, as shown in the light micrograph at right. 1 Male Female 1 mm These larvae penetrate the skin and blood vessels of humans working in irrigated fields contaminated with infected human feces. 5 Blood flukes reproduce sexually in the human host. The fertilized eggs break through blood vessel wall into the digestive tract and exit the host in feces. 2 The eggs develop in water into ciliated larvae. These larvae infect snails, the intermediate hosts. 3 Asexual reproduction within a snail results in another type of motile larva, which escapes from the snail host. 4 Snail host Figure 33.11 Life cycle of blood fluke (Schistosoma) • Trematodes that parasitize humans • Spend part of their lives in snail hosts

14. Most monogeneans • Are parasites of fish

15. Proglottids with reproductive structures 200 µm Hooks Scolex Sucker (Cestode) Tapeworm • Tapeworms (highly specialized for parasitic life) • Lack a digestive system—absorb nutrients from intestinal lumen. Specialized head for attachment to gut wall.

16. Rotifers • Rotifers, phylum Rotifera • Are tiny animals that inhabit fresh water, the ocean, and damp soil and are of interest because of their prolonged asexual reproduction.

17. 0.1 mm Figure 33.13 • Rotifers are smaller than many protists (largest 2 mm) • But are truly multicellular and have specialized organ systems (digestive tract with mouth and anus, body cavity but is pseudocoelom-not lined by mesoderm).

18. Rotifer Reproduction • Rotifers reproduce by parthenogenesis (unfertilized eggs develop into adult females) which produce more females from unfertilized eggs. • Without sexual reproduction, deleterious mutations should accumulate that would make the organism less fit. However this has been going on for 35 million years and how they flout the general rule against long-lived asexuality is a puzzle.

19. Figure 33.15 Nemerteans • Members of phylum Nemertea • Are commonly called proboscis worms or ribbon worms, pseudocoelom)

20. The nemerteans unique proboscis • Is used for defense and prey capture (some inject toxin into prey) • Is extended by a fluid-filled sac • Nemerteans also have a closed circulatory system (none of the other phyla we talked about have this). • The blood is contained in vessels distinct from fluid in the body cavity but there is no heart. Fluid moved through the system by contraction of body wall. (Antarctic nemerteans can capture a 6 inch long fish and ingest it. Cut them in half and regenerate). Mucous contains tetrodotoxin -a nerve toxin).

21. The Annelids Segmented worms.

22. Table 33.4 • The phylum Annelida is divided into three classes

23. Oligochaetes • Oligochaetes (class Oligochaeta) • The earth worms (fish bait) • Are named for their relatively sparse chaetae, or bristles made of chitin • Include the earthworms and a variety of aquatic species

24. Earthworms eat their way through the soil, extracting nutrients as the soil moves through the alimentary canal • Which helps till the earth, making earthworms valuable to farmers

25. Coelom. The coelom of the earthworm is partitioned by septa. Allow Independent movement of body wall. Metanephridium. Each segment of the worm contains a pair of excretory tubes, called metanephridia, with ciliated funnels, called nephrostomes. The metanephridia remove wastes from the blood and coelomic fluid through exterior pores. Each segment is surrounded by longitudinal muscle, which in turn is surrounded by circular muscle. Earthworms coordinate the contraction of these two sets of muscles to move (see Figure 49.25). These muscles work against the noncompressible coelomic fluid, which acts as a hydrostatic skeleton. Cuticle Epidermis Septum (partition between segments) Circular muscle Many of the internal structures are repeated within each segment of the earthworm. Longitudinal muscle Anus Chaetae. Each segment has four pairs of chaetae, bristles that provide traction for burrowing. Dorsal vessel Intestine Tiny blood vessels are abundant in the earthworm’s skin, which functions as its respiratory organ. The blood contains oxygen-carrying hemoglobin. Nerve cords Ventral vessel Cerebral ganglia. The earthworm nervous system features a brain-like pair of cerebral ganglia above and in front of the pharynx. A ring of nerves around the pharynx connects to a subpharyngeal ganglion, from which a fused pair of nerve cords runs posteriorly. Nephrostome Clitellum Pharynx Esophagus Metanephridium Crop Giant Australian earthworm Intestine Gizzard Mouth Subpharyngeal ganglion Ventral nerve cords with segmental ganglia. The nerve cords penetrate the septa and run the length of the animal, as do the digestive tract and longitudinal blood vessels. The circulatory system, a network of vessels, is closed. The dorsal and ventral vessels are linked by segmental pairs of vessels. The dorsal vessel and five pairs of vessels that circle the esophagus of an earthworm are muscular and pump blood through the circulatory system. • Anatomy of an earthworm Table 33.23

26. Parapodia Figure 33.24 Polychaetes • Members of class Polychaeta • Possess paddlelike parapodia that function as gills and aid in locomotion, bristles and gas exchange.

27. Figure 33.1 • Polychaete Christmas tree worm • “Feathers” used to trap food particles which are moved along their base to the mouth--also gas exchange.

28. Figure 33.25 Leeches • Members of class Hirudinea (1 to 30 cm, tropics) • Are blood-sucking parasites, such as leeches. Secrete hirudin (anticoagulant) and drink 10 x their body weight in blood. Medicinal leech used to drain blood from injured finger.

29. Nematoda (non-segmented round worms) • Grouped with arthropods in Ecdysozoa clade because covered with cuticle that it sheds as it grows

30. 25 µm Figure 33.26 • The cylindrical bodies of nematodes (phylum Nematoda) • Are covered by a tough coat called a cuticle

31. Fluid filled pseudocoelom acts as a hydroskeleton that the circular and longitudinal muscles work against • Great numbers of nematodes live in moist soil and lake bottoms. Are agriculture pests (corn root worm) and parasites of animals and humans. These include pinworms and round worms in the intestinal tract.

32. Encysted juveniles Muscle tissue 50 µm Figure 33.27 Can acquire this parasite from eating uncooked pork of infected swine. The encysted juveniles mature and migrate from your intestine into the intestinal muscle. Produce more juveniles which migrate to the heart where they encyst forming calcium deposits. Avoid the immune system. Make muscle cell bigger to house them and vascularization. Painful inflammation. • Trichinosis (Trichinella) a human disease

33. Phylum Mollusca • Includes snails and slugs, oysters and clams, and octopuses and squids • Most molluscs are marine • Though some inhabit fresh water and some are terrestrial • Molluscs are soft-bodied animals • But most are protected by a hard calcium carbonate shell • Molluscs have a muscular foot, a visceral mass, and a mantle

34. Anatomy of Molluscs • All molluscs have a similar body plan with three main parts • A muscular foot • A visceral mass • A mantle

35. Heart. Most molluscs have an open circulatory system. The dorsally located heart pumps circulatory fluid called hemolymph through arteries into sinuses (body spaces). The organs of the mollusc are thus continually bathed in hemolymph. Nephridium. Excretory organs called nephridia remove metabolic wastes from the hemolymph. The long digestive tract is coiled in the visceral mass. Visceral mass Coelom Intestine Gonads Mantle Stomach Radula. The mouth region in many mollusc species contains a rasp-like feeding organ called a radula. This belt of backward- curved teeth slides back and forth, scraping and scooping like a backhoe. Mantle cavity Shell Mouth Radula Anus The nervous system consists of a nerve ring around the esophagus, from which nerve cords extend. Gill Nerve cords Foot Mouth Esophagus Figure 33.16 Generalized Anatomy of a mollusc

36. Most molluscs have separate sexes • With gonads located in the visceral mass • The life cycle of many molluscs • Includes a ciliated larval stage called a trochophore

37. Apical tuft of cilia (a) An ectoproct, a lophophorate Mouth (b) Structure of trochophore larva Figure 32.13a, b Anus Trochophore Larva • Other phyla • Go through a distinct larval stage called a trochophore larva

38. Table 33.3 They look very different, live in diverse environments and have different life histories • There are four major classes of molluscs

39. Figure 33.17 Chitons • Class Polyplacophora is composed of the chitons • Oval-shaped marine animals encased in an armor of eight dorsal plates (Firmly attached to rocks in the intertidal region of the ocean). Try and pry off of a rock-home range.

40. A land snail wiith protective shell (a) A sea slug. Nudibranchs, or sea slugs, lost their shell during their evolution. Gills on dorsal surface. (b) Figure 33.18a, b Gastropods • About three-quarters of all living species of molluscs • Belong to class Gastropoda

41. Most gastropods • Are marine, but there are also many freshwater and terrestrial species • Possess a single, spiraled shell • Slugs lack a shell • Or have a reduced shell

42. Stomach Mantle cavity Intestine Anus Mouth Figure 33.19 Torsion in Gastropods • The most distinctive characteristic of this class • Is a developmental process known as torsion, which causes the animal’s anus and mantle to end up above its head. To accomodate shell?? Some have flattened shells (abalone). Head with eye stalks. Modified radula as poisonous dart (marine cone snail toxin can kill humans).

43. Figure 33.20 Bivalves • Molluscs of class Bivalvia • Include many species of clams, oysters, mussels, and scallops. Were used as food sources by early man as well as today. • Have a shell divided into two halves

44. Hinge area Coelom Gut Mantle Heart Shell Adductor muscle Mouth Anus Excurrent siphon Palp Water flow Foot Incurrent siphon Mantle cavity Gill Figure 33.21 Anatomy of a Bivalve • The mantle cavity of a bivalve • Contains gills that are used for feeding as well as gas exchange

45. Cephalopods • Class Cephalopoda includes squids and octopuses • Carnivores with beak-like jaws surrounded by tentacles of their modified foot • Closed circulator system • Well developed eye similar to vertebrate eye (lens, retina etc) • Very active life style. Squid can feed on herring by zipping through a school. Herring capable of rapid swimming. • Elaborate sex where male inserts packets of sperm into mantle cavity of female. (Will look at squid in lab). • Ink gland for escape.

46. (a) Octopuses are considered among the most intelligent invertebrates. Figure 33.22a • Most octopuses • Creep along the sea floor in search of prey

47. (b) Squids are speedy carnivores with beaklike jaws and well-developed eyes. Figure 33.22b • Squids use their siphon • To fire a jet of water, which allows them to swim very quickly

48. (c) Chambered nautiluses are the only living cephalopods with an external shell. Have rudimentary eye without lens like a pin hole camera. Shell is chambered and put less dense ammonium chloride in chamber for flotation. Less dense than seawater. Figure 33.22c ` • One small group of shelled cephalopods • The chambered nautiluses, survives today • Huge nautilus fossils in northern Africa