1. Noncoelomate Invertebrates
Chapter 33

2. Invertebrate Phylogeny Revolution
Scientists generally agree about the taxonomic classification of 36 animal phyla
-They do disagree, however, about how these are interrelated
Traditional reconstructions lump together phyla that share major features of body plan
New reconstructions employ molecular comparisons of rRNA and other genes

3. Invertebrate Phylogeny Revolution
Both old and new phylogenies agree that:
-Porifera first separated from Eumetazoa
-Among the eumetazoans, Cnidaria and Ctenophora branch out before Bilateria
-Bilateria are divided into two groups: protostomes and deuterostomes
Modern phylogeny differs radically from traditional phylogeny in construction of the protostome lineage

4. Invertebrate Phylogeny Revolution
Traditionally, the branches of animals are based on the nature of the body cavity:
-Acoelomates = Have no body cavity
-Pseudocoelomates = Have pseudocoel
-Coelomates = Have coelom
Acoelomates and pseudocoelomates are always protostomes
Coelomates are either protostomes or deuterostomes

5. Invertebrate Phylogeny Revolution

6. Invertebrate Phylogeny Revolution
Modern protostome phylogeny distinguishes between two major clades that have evolved independently:
-Spiralians
-Ecdysozoans

7. Invertebrate Phylogeny Revolution
Spiralians
-Grow by adding mass to an existing body
-Two main groups
-Lophotrochozoa: mostly coelomates
-Include the phyla Brachiopoda, Mollusca and Annelida
-Platyzoa: mostly acoelomates
-Include the phyla Platyhelminthes, and Micrognathozoa

8. Invertebrate Phylogeny Revolution
Ecdysozoans
-Increase in size by molting their external skeletons
-Two phyla have been particularly successful
-Nematoda: pseudocoelomates
-Roundworms
-Arthropoda: coelomates
-Insects, crustaceans, and others

9. Invertebrate Phylogeny Revolution

10. Parazoa Parazoans lack tissues, organs and a definite symmetry
-However, they have complex multicellularity
Sponges, phylum Porifera, are parazoans
-Include marine and freshwater species
-Larval sponges are free-swimming, but adults are anchored onto submerged objects

11. Parazoa Adult sponges are shaped like a vase
Walls of the “vase” have three functional layers

12. Parazoa
1. Inner layer = Specialized flagellate cells called choanocytes, or collar cells
2. Central layer = Gelatinous, protein-rich matrix called the mesohyl
3. Outer layer = Protective epithelium
Mesohyl may contain spicules and/or fibers of a tough protein called spongin
-These strengthen the body of the sponge

13. Parazoa

14. Parazoa Sponges are “filter-feeders”
-Beating of the choanocyte flagella draws water through numerous small pores
-Brings in food and oxygen and expels wastes
-Small organisms are filtered from the water, which flows through passageways
-Eventually exits from the osculum

15. Parazoa Sponge reproduction -Asexual = Fragmentation
-Sexual = Egg and sperm
-Larval sponges use cilia for swimming
-Settle down on a substrate
-Transform into adults

16. Eumetazoa Eumetazoans are animals with distinct tissues
Embryos have distinct layers
-Inner endoderm = Forms the gastrodermis
-Outer ectoderm = Forms the epidermis and nervous system
-Middle mesoderm (Only in bilateral animals)
-Forms the muscles

17. Eumetazoa Eumetazoans also evolved true body symmetry
-Radiata = Exhibit radial symmetry
-Phylum Cnidaria
-Phylum = Ctenophora
-Bilateria = Exhibit radial symmetry
-All other animals

18. Phylum Cnidaria Cnidarians are nearly all marine
-Bodies have distinct tissues but no organs
Cnidarians are diploblastic
-Ectoderm (epidermis) and endoderm (gastrodermis)
-In between, a layer of gelatinous material (mesoglea)

19. Phylum Cnidaria Cnidarians are carnivores
They have two basic body forms
-Polyps = Cylindrical and sessile
-Medusae = Umbrella-shaped and free-living

20. Phylum Cnidaria

21. Phylum Cnidaria
Some cnidarians exist as either medusae or polyps, while others alternate between the two phases
Polyps may reproduce sexually or asexually
-Asexual reproduction occurs by budding and may produce a new polyp or medusae
Medusae reproduce sexually
-Form free-swimming larvae called planulae

23. Phylum Cnidaria Cnidarians have internal extracellular digestion
-Digestion begins with extracellular fragmentation in the gastrovascular cavity
-This is followed by phagocytosis and intracellular digestion
Cnidarians have no circulatory, respiratory or excretory systems

24. Phylum Cnidaria
Cnidarians have unique specialized cells on their epidermis called cnidocytes
The nematocyst is a special type of cnidocyte
-Contains a small but powerful harpoon
-Used for food acquisition and defense

25. Phylum Cnidaria

26. Four Classes of Cnidarians
Hydrozoa (hydroids)
Scyphozoa (jellyfish)
Cubozoa (box jellyfish)
Anthozoa (corals and sea anemones)

27. Phylum Ctenophora
A small phylum whose members are known as comb jellies, sea walnuts or sea gooseberries
Structurally more complex than cnidarians
Capture prey with a colloblast
-Contains strong adhesive material

28. Phylum Ctenophora
Ctenophores propel themselves through water with eight rows of fused cilia
They are triploblastic
-Have true muscles cells derived from the mesoderm
Their mode of symmetry is not strictly radial as in cnidarians

29. The Bilaterian Acoelomates
The Bilateria are characterized by bilateral symmetry
-Allowed for high levels of specialization
Bilaterians are traditionally classified by the condition of their coelom
-Acoelomates
-Pseudoceolomates
-Coelomates

30. Phylum Platyhelminthes
The flatworms are soft-bodied animals
-Many species are parasitic
-Others are free-living
Move by ciliated epithelial cells
Have developed musculature

31. Phylum Platyhelminthes
Flatworms have an incomplete digestive cavity with only one opening
-Therefore, they cannot feed continuously
Muscular contractions in the pharynx allows food to be ingested and torn into small bits
Tapeworms (parasitic flatworms) lack digestive systems
-Absorb food directly through body walls

32. Phylum Platyhelminthes
Flatworms have an excretory and osmoregulatory system
-Network of fine tubules runs through body
-Flame cells located on the side branches
-Primary function = water balance
-Secondary function = excretion
Metabolic wastes are excreted into the gut and eliminated through the mouth

33. Phylum Platyhelminthes
Flatworms lack a circulatory system
-Flattened body shape and highly-branched gut utilize diffusion
They have a simple nervous system
-Eyespot can distinguish light from dark
Most are hermaphroditic
-Undergo sexual reproduction
-Also have capacity for asexual regeneration

34. Phylum Platyhelminthes

35. Phylum Platyhelminthes

36. Phylum Platyhelminthes
Flatworms have been traditionally grouped into four major classes
-Turbellaria
-Monogenea
-Trematoda
-Cestoda
Free-living
Parasitic
New studies group all three parasitic classes into a single group, Neodermata

37. Phylum Platyhelminthes
Class Turbellaria
-Free-living flatworms
-Recently shown to be polyphyletic
-Found in freshwater, marine and even terrestrial environments

38. Phylum Platyhelminthes
Classes Monogenea and Trematoda
-Flukes
-Live as ectoparasites or endo-parasites in the bodies of other animals
-Attach by suckers, anchors or hooks
-Most have a life cycle that involves two or more hosts

39. Phylum Platyhelminthes
Clonorchis sinensis: Oriental liver fluke
-Complex life cycle
-Miracidium – Ciliated stage in egg
-Rediae – Nonciliated larvae produced within sporocyst
-Cercaria – Tadpole-like larval stage
-Metacercaria – Adult stage produced within cysts

41. Phylum Platyhelminthes
Other important flukes are the blood flukes of the genus Schistosoma
-Three species cause the disease schistosomiasis, or bilharzia
-Worms coat themselves with host’s own antigens
-Thus, are immunologically invisible

42. Phylum Platyhelminthes
Class Cestoda
-Tapeworms
-Live as parasites within the bodies of other animals
-Most species occur in the intestines of vertebrates

43. Phylum Platyhelminthes
Class Cestoda
-Long flat bodies divided into three zones
-Scolex = Attachment organ
-Neck = Unsegmented portion
-Proglottids = Repetitive sections
-Each a complex hermaphroditic unit
-Taenia saginata is the beef tapeworm

44. Phylum Platyhelminthes

45. Phylum Platyhelminthes
Acoel flatworms were once considered basal members of the phylum Platyhelminthes
-Have a primitive nervous system and lack a digestive cavity
Are now classified in their own phyla, Acoela

46. Phylum Nemertea
Nemerteans are often called ribbon worms or proboscis worms
Are long animals that can stretch to several meters

47. Phylum Nemertea
Nemerteans possess a fluid-filled sac, the rhynchocoel: a true coelomic cavity
Are the simplest animals with a complete digestive system (mouth and anus)
Have a closed circulatory system
They are not related to flatworms
-Are now classified with other coelomate protostomes in the Lophotrochozoa

48. Phylum Cycliophora Discovered in 1995
Acoelomates that live on the mouthparts of claw lobsters
Have unique anatomy and form of sexual reproduction

49. The Pseudocoelomates
Possess a pseudocoel, which is a cavity between the mesoderm and endoderm
-Serves as a hydrostatic skeleton, against which the animal’s muscles can work
Pseudocoelomates lack a defined circulatory system
-Role is performed by fluids that move within the pseudocoel

50. Phylum Nematoda Nematodes are roundworms comprising many species
-Found in marine, freshwater and soil habitats
Are bilaterally symmetrical and unsegmented

51. Phylum Nematoda Nematodes are covered with a flexible, thick cuticle
Are ecdysozoans
-Molt cuticle four times
Lack specialized respiratory organs and exchange oxygen through their cuticles

52. Phylum Nematoda Mouth is equipped with piercing organs called stylets
Food passes through the mouth by the sucking action of the pharynx
Undigested material is eliminated through the anus

53. Phylum Nematoda

54. Phylum Nematoda Nematodes usually reproduce sexually
-Sexes are separate
Adults of some species exhibit eutely
-Have a fixed number of cells
-Caenorhabditis elegans has only 959 cells

55. Phylum Nematoda
Many nematodes are active hunters, preying on protists and other small animals
Others are parasites of plants
Still others live within the bodies of larger animals

56. Phylum Nematoda Nematodes can cause diseases in humans
-Trichinella causes trichinosis
-Forms cysts in muscles
-Ascaris lumbricoides – Intestinal roundworm

57. Phylum Rotifera
Rotifers are bilaterally symmetrical unsegmented pseudocoelomates
-They have complex internal organs
They propel themselves through water by rapidly beating thick cilia at their heads
-“Wheel animals”
They gather food via a conspicuous organ called the corona

58. Phylum Rotifera