The Deuterostomes

1. The Deuterostomes Echinoderms and Chordates

2. Developmental Variations • During embryonic development, the process of gastrulation forms the digestive cavity. • Gastrulation varies in the animal kingdom • No gastrulation (placozoans) • Incomplete gastrulation • Forms a gastrovascular cavity with one opening • Complete gastrulation • Forms a digestive tract with 2 openings

3. Animals with Complete Gastrulation • Complete gastrulation forms a true digestive tract with 2 openings, the mouth and the anus • In protostome animals, the first opening of the gastrula forms the mouth • In deuterostome animals, the second opening of the gastrula forms the mouth

4. Deuterostome Phyla • There are 3 phyla characterized by deuterostome development • Echinoderms • Sea Cucumbers, Crinoids, Sea Stars, Brittle Stars and Sea Urchins • Hemichordates • Acorn Worms and Pterobranchs • Chordates • Tunicates, Lancelets, Jawless fish and Vertebrates

5. Phylum Echinodermata • The echinoderms are unusual in the animal kingdom in that they have a great deal in common with the chordates and hemichordates, but also differ in ways that do not appear anywhere else in the animal kingdom • It seems unlikely that their similarities with other deuterostomes are the result of convergent evolution, so it seems that through the course of evolution the echinoerms have lost a number of ancestral characters retained in the other phyla

6. Characters retained: • Embryonic development & Gastrulation • Triploblastic • Complete digestive tract • Body Cavity • Eucoelomate • Symmetry • Bilateral during larval stages

7. Characters lost or diminished: • Segmentation • Cephalization • No head, brain or specialized sense organs • Sensory apparatus are not centralized • Bilateral symmetry in the adult form • The bilateral symmetry in the larvae goes through a dramatic metamorphosis, reorganizing the body into a Pentaradially Symmetrical adult

8. Metamorphosis • The coelom forms as a U shape, which pinches off into 3 distinct cavities, 2 of which will become diminished • The digestive tract becomes reorganized, with the formation of new mouth and anal openings and a new orientation (mouth on the left and anus on the right) • The left and right sides of the larvae undergo differential development, with the left side forming the oral surface and the right side forming the aboral surface

9. Derived characters special to the Echinoderms • Water-vascular system • Consisting of a madroporite, a system of canals (stone canal, ring canal, radial canals and lateral canals) and sucker tipped tube feet • Dermal endoskeleton • Consisting of calcified plates called ossicles and a variety of spines and pedicellaria • Hemal system • Poorly understood, it appears to function for distribution of materials • Pentaradial symmetry • Organs radiate from a central disc, characteristically in a pattern of fives

10. Water Vascular System

11. Tube Feet

12. Crinoids (Sea Lilies)

13. Sea Stars

14. Brittle Stars

15. Sea Cucumbers

16. Sea Urchins

17. Echinoderms - Video • Sea Stars • https://www.youtube.com/watch?v=A100m5EpfFI • https://www.youtube.com/watch?v=rE8l-KFQlhY • Sea Urchins • https://www.youtube.com/watch?v=nD7_0obUm0o • https://www.youtube.com/watch?v=D3W4OCnHyCs • Sand Dollars • https://www.youtube.com/watch?v=bSsgDhWpPq0 • https://www.youtube.com/watch?v=gLK71-vsi2E

18. Phylum Hemichordata • Hemichordates are deuterostomes, a characteristic they share with both echinoderms and chordates • As the name suggests, hemichordates have some derived characteristics that are ancestral to the phylum chordata • Dorsal, hollow nerve cord • Gill slits in the pharynx • These traits are shared with all chordates, but are absent in the echinoderms

19. Hemichordate Diversity • The phylum Hemichordata consists of two classes • The Acorn Worms (Enteropneusta) • The Pterobranchs • The Acorn Worms and the Pterobranchs are similar in body form, but vary with regard to feeding structures • Feeding structures in both are ciliated to collect food particles and direct them to the mouth

20. Acorn Worms – Feeding • The acorn worms have a muscular proboscis used for food gathering located anterior to the mouth opening • The mouth is ventrally located • A collar is associated with the mouth, and is used both to direct food into the mouth and to redirect particles too large to ingest • Acorn worms are free living and burrow actively to search for food

21. Pterobranchs - Feeding • The proboscis itself is shield shaped • The base of the proboscis bears several tentacles which extend into the water to create a food gathering surface for filter feeding • Pterobranchs move freely inside of a collagenous tube, but are sessile in that they are restricted to life within that tube

22. Gill Slits in the Pharynx • Hemichordates have one or more pairs of gill slits that allow water from the pharynx to pass out of the animal, rather than being ingested • Cilia maintain water flow through the gill pouches • Aside from providing a mechanism for filtering and concentrating food particles, the gill pouches create a surface for gas exchange.

23. Central Nervous System • A point of emphasis in our discussion of the evolution of the central nervous system has been the presence in many invertebrate phyla of ventral nerve cords • A ventral nerve cord persists in the hemichordates, but is accompanied by a dorsal nerve cord • The dorsal nerve cord is hollow because it is formed by an invagination of ectodermal embryonic tissue, as is the “spinal cord” associated with the chordates

24. Phylum Chordata • The chordates are deuterostomes – they possess a complete digestive tract with the mouth forming from the 2nd opening of the gastrula • Chordates, like the hemichordates, have a dorsal hollow nerve cord. Unlike hemichordates they do not have a persistent ventral nerve cord • All chordates, at some time in their development, have pairs of pharyngeal gill slits

25. The Notochord • The distinguishing characteristic of phylum Chordata is an endoskeleton centered around the formation of a notochord • The notochord is a rod of mesodermal tissue located on the dorsal side of the animal that extends almost the full length of the body • The notochord lies just ventral to the nerve cord that forms the central nervous system

26. More notochord stuff • In the simplest of the chordates, the notochord is a simple rod of tissue with a fibrous sheath that provides some level of longitudinal rigidity • In other chordates, the notochord may exhibit pronounced segmentation, and may or may not become ossified (impregnated with calcium, forming bone)

27. Ancestral and Derived Characters • Aside from the shared ancestral characteristics that Chordates share with their closest relatives (deuterostome development, notochord, dorsal hollow nerve cord & pharyngeal gill slits) the Chordates share 2 derived characteristic only with other Chordates: • An endostyle (from which the thyroid gland is derived) • A post-anal tail

28. The Endostyle • The endostyle is a specialized organ associated with the pharynx • In some of the invertebrate chordates the endostyle functions largely as a filter-feeding apparatus, secreting mucus for trapping food particles in the pharynx • The endostyle persists in Chordates that do not filter feed. The thyroid gland is derived from the embryonic endostyle, and retains a function related to feeding and metabolism

29. Chordate Diversity • The Chordates are a diverse phylum, including both invertebrate and vertebrate classes • The Protochordates are invertebrate filter feeders, and consist of the Urochordates (tunicates) and the Cephalochordates (lancelets) • The Agnatha are the jawless fish. They are the simplest bodied vertebrates, with a cranium and a well developed tripartite brain (three regions: forebrain, midbrain, hindbrain)

30. Protochordates: Tunicates

31. Tunicate Anatomy • Tunicates are filter feeders • Water enters the mouth, filters through the gill slits in the pharynx, and passes out through the atrial siphon • Food passes through a complete digestive tract

32. Protochordates: Lancelets

33. Lancelet Anatomy • Lancelets are filter feeders like the tunicates, but they have more fully developed musculature, notochord and dorsal nerve cord

34. Vertebrates with Jaws • The most familiar Chordates are the Vertebrates. • Aside from the Agnatha, the remaining vertebrate Chordates have jaws derived from the first 2 pairs of gill arches • The ability to process food has evolved independently in many different phyla. Any level of processing has the potential to improve digestion and thus increase the chances of survival

35. Vertebrate Diversity - Fish • Agnatha – jawless fish (hagfish and lampreys) • Chondrichthyes – jawed fish with cartilage skeletons (sharks and rays) • The Chondrichthyes lack a swim bladder, and maintain bouyancy through a large, oily liver • Osteichthyes – jawed fish with bony, calcified skeletons (most familiar fish) • The bony fish offset the density of their heavy skeleton with an air filled swim bladder on the dorsal side of their body cavity

36. Class Agnatha – Jawless Fish

37. Chondrichthyes – Cartilage Fish

38. Osteichthyes – Bony Fish

39. Poikilothermy vs. Homeothermy • Poikilothermic • Temperature varies • “Cold Blooded” • Ectothermic • Body temperature is a function of the outside environment • All invertebrates, as well as fish, amphibians and reptiles • Homeothermic • Temperature is relatively constant • “Warm Blooded” • Endothermic • Body temperature results from within • Body heat derived from metabolism • Dinosaurs (theoretically), birds and mammals

40. Vertebrate Diversity – PoikilothermicTetrapods • Class Amphibia • Includes frogs, toads, salamanders and newts. • Moist, vascular skin functions for gas exchange • The earliest terrestrial vertebrates • Amphibians are tied to moist environments by the need to keep their skin and their eggs moist • Class Reptilia • Includes lizards, turtles, crocodilians & snakes • Dry, scaly skin is well adapted for life on land • Shelled, amniotic egg frees reptiles from the need to return to the water to lay eggs

41. Amphibians

42. Reptiles

43. Vertebrate Diversity – HomeothermicTetrapods • Class Mammalia • Mammals are distinguished by a variety of skin gland variations • Hair glands • Milk glands • Class Aves (Birds) • Birds possess a number of adaptations unique to the class Aves, including • Feathers (derived from epidermal scale pouches) • Bipedalism, with Forelimbs adapted for flight • Sternum with a broad “keel” for pectoral muscle attachment

44. Mammals

45. Birds (Class Aves)

46. Mammalian Diversity • Class Mammalia is divided into 3 groups due to variations in reproductive behavior and anatomy • Monotremes • Include the platypus and the echidna • Marsupials • Include the kangaroo, koala and opossum • Placentals • Include most familiar mammals, including humans

47. Monotremes • Monotremes have reproductive systems and behaviors almost identical to reptiles. They are oviparous (egg layers) and their eggs have leathery shells

48. Marsupials • Marsupials are viviparous. Their young are born live, but immature and poorly developed • Marsupial young continue their development through prolonged lactation within a protective pouch

49. Placental Mammals • Placental mammals are live born after a long gestation period • The young are nourished through the placenta, which imbeds in the wall of the uterus and allows exchange of nutrients and waste

50. Marc Kirschner, Harvard: How the chordate got its cord • https://www.youtube.com/watch?v=232wtCuLsoI • https://www.youtube.com/watch?v=Y0xfpGdh1_Y • https://www.youtube.com/watch?v=I1yqkSuTwrU