Evolution of the Animal Phyla

Transcription

1 Evolution of the Animal Phyla

2 Fig Evolutionary trends among the animals

3 21.6 Roundworms: The Evolution of a Body Cavity The evolution of an internal body cavity was important for three reasons Circulation Rapid passage of material Movement Muscle-driven body movement Organ function Little deformation by surrounding muscles

4 Three kinds of body plans Fig Acoelomates Have no body cavity Pseudocoelomates Have body cavity between mesoderm and endoderm Pseudocoel Coelomates Have body cavity entirely within mesoderm Coelom

5 Phylum Nematoda Nematodes are bilaterally symmetrical, cylindrical, unsegmented worms The pseudocoel serves as a hydrostatic skeleton Gains rigidity from being filled with fluid under pressure Therefore muscles can work against this skeleton Lack a defined circulatory system Covered by a thick, flexible cuticle Rotifera Food passes through the mouth by the sucking action of the pharynx Nematoda Reproduction is sexual Fig

6 Fig

7 21.7 Mollusks: Coelomates The bulk of the animal kingdom consists of coelomates Development of specialized tissues in animals involves primary induction In this process one of the three primary tissues interacts with another A major advantage of the coelomate body plan is that it allows mesoderm endoderm contact

8 The three major groups of mollusks Gastropods Snails and slugs Fig Bivalves Clams, oysters and scallops Cephalopods Octopuses and squids

9 21.8 Annelids: The Rise of Segmentation Segmentation is the building of a body from a series of similar segments It offers evolutionary flexibility Small change in existing segment can produce a new segment with a different function The first segmented animals to evolve were the annelid worms, phylum Annelida

10 Most annelid species are marine About one-third are terrestrial Fig Earthworm Shiny bristle worm

11 The basic body plan is a tube within a tube Three characteristics Repeated segments Separate segments able to expand or contract independently Specialized segments Front segments contain the worm s sensory organs Connections Materials and information pass through partitions in the segments Segmentation underlies the body organization of all complex coelomate animals Fig

12 Fig Evolutionary trends among the animals

13 21.9 Arthropods: Advent of Jointed Appendages Arthropods belong to the phylum Arthropoda The most successful of all animal groups 2/3 rd of all named species 80% of all arthropods are insects Scientists estimate that a quintillion insects are alive at any one time Fig

14 All arthropods have jointed appendages They have a rigid external skeleton made up of chitin This exoskeleton protects the animals and provides sites for muscle attachment It is brittle, so its thickness limits arthropod body size Arthropod bodies are segmented Most larval stages have many segments These fuse into functional groups in the adult Fig

15 Chelicerates Arthropods that lack jaws, or mandibles Their mouthparts, called chelicerae, are the foremost appendages of the body Mandibulates are arthropods that have mandibles Fig Jumping spider Bullfrog ant

16 Chelicerates Arachnida is the largest class of chelicerates 57,000 named species Largely terrestrial organisms Spiders, ticks, mites, scorpions Brown recluse Black widow Fig Poisonous spiders

17 Mandibulates Crustaceans Large, diverse group of primarily aquatic organisms Differ from insects, but resemble millipedes and centipedes, in having legs on their abdomen and thorax Fig Body of a lobster

18 Mandibulates Crustaceans Three general types Fig Edible crab 1. Decapods Crabs, shrimp, lobsters 2. Pillbugs and sowbugs Terrestrial crustaceans 3. Barnacles Sessile as adults Sowbug

19 Mandibulates Millipedes and Centipedes Consist of a head region followed by numerous similar segments Centipedes have one pair of legs on each segment Millipedes have two pairs of legs on each segment Active carnivores Fig Sedentary herbivores

20 Mandibulates Insects The largest group of arthropods by far ~ 1 million species identified Fig Beetle Flea Honeybee Grasshoppers Dragonfly Moth

21 21.10 Protostomes and Deuterostomes In the coelomates there are two different developmental patterns In protostomes, the mouth develops from or near the blastopore The anus (if present) develops later from another region of the embryo In deuterostomes, the anus develops from or near the blastopore The mouth develops later from another region of the embryo

22 Fig