Mollusks-Segmented worms- Arthropods

Transcription

1 Mollusks-Segmented worms- Arthropods

2 Mollusks-Segmented worms- Arthropods Organ systems Triploblastic Bilateral True coelom

3 Mollusca 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 shell

4 All molluscs have a similar body plan with three main parts: Muscular foot Visceral mass Mantle Many molluscs also have a water-filled mantle cavity, and feed using a rasplike radula

5 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

6 There are four major classes of molluscs: Polyplacophora (chitons) Gastropoda (snails and slugs) Bivalvia (clams, oysters, and other bivalves) Cephalopoda (squids, octopuses, cuttlefish, and chambered nautiluses)

7 Table 33-3

8 Chitons Class Polyplacophora consists of the chitons, ovalshaped marine animals encased in an armor of eight dorsal plates

9 Fig

10 Gastropods About three-quarters of all living species of molluscs are gastropods

11 Fig (a) A land snail (b) A sea slug

12 Most gastropods are marine, but many are freshwater and terrestrial species Most have a single, spiraled shell Slugs lack a shell or have a reduced shell The most distinctive characteristic of gastropods is torsion, which causes the animal s anus and mantle to end up above its head

13 Fig Anus Mantle cavity Stomach Intestine Mouth

14 Bivalves Molluscs of class Bivalvia include many species of clams, oysters, mussels, and scallops They have a shell divided into two halves

15 Fig

16 The mantle cavity of a bivalve contains gills that are used for feeding as well as gas exchange

17 Fig Mantle Digestive gland Hinge area Gut Coelom Heart Adductor muscle Anus Mouth Excurrent siphon Shell Palp Foot Mantle cavity Gonad Gill Water flow Incurrent siphon

18 Cephalopods Class Cephalopoda includes squids and octopuses, carnivores with beak-like jaws surrounded by tentacles of their modified foot Most octopuses creep along the sea floor in search of prey

19 Fig Octopus Squid Chambered nautilus

20 Squids use their siphon to fire a jet of water, which allows them to swim very quickly

21 One small group of shelled cephalopods, the nautiluses, survives today

22 Cephalopods have a closed circulatory system, welldeveloped sense organs, and a complex brain

23 Annelida Annelids have bodies composed of a series of fused rings The phylum Annelida is divided into three classes: Oligochaeta (earthworms and their relatives) Polychaeta (polychaetes) Hirudinea (leeches)

24 Table 33-4

25 Oligochaetes Oligochaetes (class Oligochaeta) are named for relatively sparse chaetae, bristles made of chitin They include the earthworms and a variety of aquatic species Earthworms eat through soil, extracting nutrients as the soil moves through the alimentary canal Earthworms are hermaphrodites but cross-fertilize

26 Fig Epidermis Circular muscle Cuticle Coelom Septum (partition between segments) Longitudinal muscle Metanephridium Anus Dorsal vessel Chaetae Intestine Nephrostome Fused nerve cords Clitellum Ventral vessel Metanephridium Esophagus Crop Giant Australian earthworm Pharynx Intestine Cerebral ganglia Mouth Subpharyngeal ganglion Blood vessels Gizzard Ventral nerve cord with segmental ganglia

27 Polychaetes Members of class Polychaetes have paddle-like parapodia that work as gills and aid in locomotion

28 Fig Parapodia

29 Leeches Members of class Hirudinea are blood-sucking parasites, such as leeches Leeches secrete a chemical called hirudin to prevent blood from coagulating

30 Fig

31 Arthropoda Two out of every three known species of animals are arthropods Members of the phylum Arthropoda are found in nearly all habitats of the biosphere

32 Arthropod Origins The arthropod body plan consists of a segmented body, hard exoskeleton, and jointed appendages, and dates to the Cambrian explosion ( million years ago) Early arthropods show little variation from segment to segment

33 General Characteristics of Arthropods The appendages of some living arthropods are modified for many different functions

34 Fig Cephalothorax Abdomen Antennae (sensory reception) Head Thorax Swimming appendages (one pair located under each abdominal segment) Walking legs Pincer (defense) Mouthparts (feeding)

35 The body of an arthropod is completely covered by the cuticle, an exoskeleton made of layers of protein and the polysaccharide chitin When an arthropod grows, it molts its exoskeleton

36 Arthropods have an open circulatory system in which fluid called hemolymph is circulated into the spaces surrounding the tissues and organs A variety of organs specialized for gas exchange have evolved in arthropods

37 CLASS ARACHNIDA Spiders-Scorpion-Tick Cephalothorax and Abdomen 4 pairs of legs Simple eyes No antennae

38 Fig Scorpion 50 µm Dust mite Web-building spider

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40 Class Crustaceans While arachnids and insects thrive on land, crustaceans, for the most part, have remained in marine and freshwater environments Crustaceans typically have branched appendages that are extensively specialized for feeding and locomotion Most crustaceans have separate males and females Cephalothorax and abdomen-compound eyes-tow pair of antennae-5 pairs of legs-mostly marine and freshwater

41 Fig a (a) Ghost crab

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43 Class Diplopoda Millipedes terrestrial, and have jaw-like mandibles Each trunk segment has two pairs of legs Elogate---dorsal convexed body many segments one pair of antennae simple eyes---terrestrial Scavengers

44 Fig

45 Centipedes, class Chilopoda, are carnivores They have one pair of legs per trunk segment Flattened body Simple-eyes One pair of antennae

46 Fig

47 Class Insecta more species than all other forms of life combined They live in almost every terrestrial habitat and in fresh water Head thorax and abdomen Three pairs of walking legs Often with wins on thorax Simple and compound eyes One pair of antennae

48 Fig Abdomen Thorax Head Compound eye Antennae Anus Heart Dorsal artery Crop Cerebral ganglion Vagina Malpighian tubules Ovary Tracheal tubes Nerve cords Mouthparts

49 Insects diversified several times following the evolution of flight, adaptation to feeding on gymnosperms, and the expansion of angiosperms Insect and plant diversity declined during the Cretaceous extinction, but have been increasing in the 65 million years since

50 Flight is one key to the great success of insects An animal that can fly can escape predators, find food, and disperse to new habitats much faster than organisms that can only crawl

51 Many insects undergo metamorphosis during their development In incomplete metamorphosis, the young, called nymphs, resemble adults but are smaller and go through a series of molts until they reach full size

52 Insects with complete metamorphosis have larval stages known by such names as maggot, grub, or caterpillar The larval stage looks entirely different from the adult stage

53 Most insects have separate males and females and reproduce sexually Individuals find and recognize members of their own species by bright colors, sound, or odors Some insects are beneficial as pollinators, while others are harmful as carriers of diseases, or pests of crops Insects are classified into more than 30 orders

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