Coelomate Invertebrates

1. Coelomate Invertebrates Chapter 33

2. Coelomates • Coelomates have a new body design that allows for the development of complex tissues and organs. • allows wider array of body architectures and increased body size

3. Mollusks • Mollusks (Mollusca) • extremely diverse • characterized by a coelom • great economic significance • pearls • mother of pearl • economic / environmental costs • zebra mussel invasion • intermediate hosts for parasites

4. Body Plan of the Mollusks • Distinct bilateral symmetry • Digestive, excretory, and reproductive organs are all concentrated in a visceral mass and a muscular foot. • May have differentiated head • Folds constituting a mantle • gills - increased surface area for gas exchange

5. Body Plan of the Mollusks • Shells serve primarily for protection • Radula - rasping tongue-like organ used for feeding • Circulatory system (except cephalopods) consists of a heart and an open circulatory system. • Nitrogenous wasted removed by nephridia • nephrostome lined with cilia

6. Mollusk Body Plans

7. Body Plan of the Mollusks • Reproduction in mollusks • most have distinct male and female individuals • most engage in external fertilization • many have free-swimming larvae (trochophores) which closely resemble larval stage of many marine annelids • veliger stage follows trochophore stage

8. Classes of Mollusks • Polyplacophora: chitons • oval bodies with eight overlapping calcareous plates • Gastropoda: snails and slugs • heads of most have pair of tentacles with eyes at the ends • undergo torsion during embryological development.

9. Classes of Mollusks • Bivalvia: bivalves • clams, scallops, mussels and oysters • two lateral shells hinged together dorsally • mantle secretes shell and ligaments • most are sessile filter-feeders

10. Classes of Mollusks • Cephalopoda: octopuses, squids, nautilus • most intelligent of the invertebrates • active marine predators • foot evolved into a series of tentacles equipped with structures to capture prey • highly developed nervous systems

11. Segmented Animals • Building of body from series of similar segments • small change in existing segment can produce new kind of segment with different function • Annelids • three characteristics: • repeated segments • specialized segments • connections

12. Segmented Animals • Body plan of the annelid • tube within a tube • internal digestive tract within the coelom • specialized for different functions • hydrostatic skeleton for locomotion • each segment typically possesses setae, that help anchor during locomotion • most have closed circulatory system • nephridia collect and transport wastes

13. Classes of Annelids • Polychaeta: polychaetes • well developed head with specialized sense organs • parapodia on most segments • usually lack permanent gonads • Oligochaeta: earthworms • hermaphroditic

14. Classes of Annelids • Hirudinea: leeches • occur mostly in fresh water • hermaphroditic • develop clitellum during breeding season • unable to self-fertilize • secrete anticoagulant into wounds

15. Lophophorates • Lophophore - circular or U-shaped ridge around the mouth bearing one or two rows of ciliated, hollow tentacles • functions as surface for gas exchange and as food-collection organs • use cilia to capture food

16. Jointed Appendages and Exoskeleton • All arthropods have jointed appendages. • Rigid external skeleton (exoskeleton) • protects animal and provides sites for muscle attachment • brittle, thus arthropod body size limited due to exoskeleton thickness • estimates of a quintillion insects alive at any one time • 1,000,000 species

17. Arthropod Body Plan • Exoskeleton • tough outer covering that also serves to anchor muscles • Molting (ecdysis) • shedding of outer cuticular layer

18. Arthropod Body Plan • Compound eye • composed of many ommatidia • each covered with a lens and linked to a complex of eight retinal cells and a light sensitive core rhabdom • Simple eyes (ocelli) have single lenses. • function in distinguishing light from darkness

19. The Compound Eye

20. General Characteristics of Arthropods • Circulatory system • greatly reduced coelom • open circulatory system • Nervous system • double chain of segmented ganglia running along the animal’s ventral surface • brain appears to be inhibitor rather than stimulator

21. General Characteristics of Arthropods • Respiratory system • no single major respiratory organ • small branched air ducts - tracheae • branch into tracheoles • air passes into trachea through spiracles • Excretory system • Malpighian tubules

22. Crustaceans • Most crustaceans have two pairs of antennae, three types of chewing appendages, and various numbers of leg pairs. • all pass through nauplius larval stage • mandibles likely originated from a pair of limbs that took on chewing function during course of evolution

23. Crustaceans • Decapod crustaceans • “ten footed” • exoskeleton usually reinforced with calcium carbonate • most body segments are fused into cephalothorax covered by carapace • Lobsters and crayfish have swimmerets and uropods to aid in swimming, and may have a telson (tail spine).

24. Decapod Crustacean

25. Crustaceans • Terrestrial and freshwater crustaceans • about half of estimated 4,500 species are terrestrial and live in moist habitats • pillbugs • sowbugs • isopods • Sessile crustaceans • barnacles • free-swimming larvae

26. Class Arachnida • Largest of three classes • have a pair of chelicerae, a pair of pedipalps, and four pairs of walking legs • most are carnivorous, except for mites • many spiders have book lungs

27. Class Arachnida • Order Araneae: spiders • about 35,000 named species of spiders • many do not spin webs, but actively hunt • have poison glands leading through their chelicerae • used to bite and paralyze prey

28. Class Arachnida • Order Acari: mites and ticks • largest in terms of number of species and most diverse of arachnids • about 30,000 named species • diverse in structure and habitat • found in virtually every habitat known • ticks can carry many diseases

29. Class Chilopoda and Diplopoda • Centipedes and millipedes • both have bodies that consist of a head region followed by numerous segments • centipedes have 30+ legs • carnivorous • millipedes have 60+ legs • herbivorous

30. Class Insecta • Largest group of organisms on earth • More than half of all named species on earth are insects. • hectare of lowland tropical rainforest is estimated to be inhabited by as many as 41,000 insect species

31. Class Insecta • External features • three body segments • head, thorax, and abdomen • three pairs of legs • one pair of antennae • modified mouthparts • solid wings

32. Class Insecta • Internal organization • tubular digestive system • dilute digestive enzymes • trachea extends throughout body • fat body for food storage • Sense receptors • sensory hairs - linked to nerve cells • tympanum - found with tracheal air sacs • pheromones – communication signals

33. Insect Life Histories • Metamorphosis • simple • immature stages • complete • larvae • pupa (chrysalis)

34. Deuterostome Development • Echinoderms • ancient group of marine animals consisting of about 6,000 living species • name refers to hard, calcium-rich endoskeleton beneath the skin • unique water-vascular system is a fluid-filled system used to aid in movement and feeding

35. Echinoderm Body Plan • Secondary radial symmetry • bilaterally symmetrical during larval development, but become radially symmetrical as adults. • Five part body plan • Nervous system - nerve ring

36. Echinoderm Body Plan • Endoskeleton • delicate epidermis containing thousands of neurosensory cells • continuous growth • body plates often pierced to allow tube foot extension

37. Echinoderm Body Plan • Water vascular system • radiated from a ring canal that encircles esophagus • five radial canals extend into each of the five body parts • water enters through madreporite • radial canals extend into the hollow tube feet • ampulla located at base

38. Echinoderm Water-Vascular System

39. Echinoderm Body Plan • Body cavity • coelom connects with tubular systems and helps provide circulation and respiration • Reproduction • many echinoderms have the ability to regenerate • most reproduction is sexual and external

40. Class Asteroidea • Sea stars • abundant in intertidal zone • important marine predators • body composed of central disc that merges gradually with the arms