1. Chapter 33 An Introduction to Invertebrates

2. Overview: Life Without a Backbone
Invertebrates are animals that lack a backbone
They account for 95% of known animal species
They are morphologically diverse
For example, the Christmas tree worm (Spirobranchus giganteus) has tentacles for gas exchange and feeding

3. Figure 33.1
Figure 33.1 What function do the red whorls of this organism have?

4. Sponges are suspension feeders, capturing food particles suspended in the water that passes through their body
Water is drawn through pores into a cavity called the spongocoel and out through an opening called the osculum
Sponges lack true tissues and organs

5. Choanocyte Osculum Spongocoel Pore Spicules Epidermis Water flow
Figure 33.4b
Choanocyte
Osculum
Spongocoel
Pore
Spicules
Epidermis
Figure 33.4 Anatomy of a sponge.
Water
flow
Amoebocytes
Mesohyl

6. Choanocytes, flagellated collar cells, generate a water current through the sponge and ingest suspended food
Sponges consist of a gelatinous noncellular mesohyl layer between two cell layers
Amoebocytes are found in the mesohyl and play roles in digestion and structure
Most sponges are hermaphrodites: Each individual functions as both male and female

7. Annelids Annelids have bodies composed of a series of fused rings
Annelids are coelomates
The phylum Annelida is divided into two groups
Polychaeta (polychaetes)
Oligochaeta (earthworms and their relatives, and leeches)

8. Earthworms
Earthworms eat through soil, extracting nutrients as the soil moves through the alimentary canal
Earthworms are hermaphrodites but cross-fertilize
Some reproduce asexually by fragmentation

9. Leeches
Most species of leeches live in fresh water; some are marine or terrestrial
Leeches include predators of invertebrates, and parasites that suck blood
Leeches secrete a chemical called hirudin to prevent blood from coagulating

10. Figure 33.25
Figure A leech.

11. Arthropods
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

12. Arthropod Origins
The arthropod body plan consists of a segmented body, hard exoskeleton, and jointed appendages
This body plan dates to the Cambrian explosion (535–525 million years ago)
Early arthropods show little variation from segment to segment

13. Arthropod evolution is characterized by a decrease in the number of segments and an increase in appendage specialization
These changes may have been caused by changes in Hox gene sequence or regulation

14. General Characteristics of Arthropods
The appendages of some living arthropods are modified for functions such as walking, feeding, sensory reception, reproduction, and defense

15. Pincer (defense) Mouthparts (feeding)
Figure 33.30
Cephalothorax
Abdomen
Thorax
Antennae
(sensory
reception)
Head
Swimming appen-
dages (one pair per
abdominal segment
Figure External anatomy of an arthropod.
Walking legs
Pincer
(defense)
Mouthparts
(feeding)

16. 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

17. Arthropods have eyes, olfactory receptors, and antennae that function in touch and smell
Arthropods have an open circulatory system in which hemolymph is circulated into the spaces surrounding the tissues and organs
A variety of organs specialized for gas exchange have evolved in arthropods

18. Molecular evidence suggests that living arthropods consist of four major lineages that diverged early in the phylum’s evolution
Chelicerates (sea spiders, horseshoe crabs, scorpions, ticks, mites, and spiders)
Myriapods (centipedes and millipedes)
Hexapods (insects and relatives)
Crustaceans (crabs, lobsters, shrimps, barnacles, and many others)

19. Most modern cheliceriforms are arachnids, which include spiders, scorpions, ticks, and mites

20. Scorpion Dust mite Web-building spider 50 m Figure 33.32
Figure Arachnids.
Web-building
spider

21. Arachnids have an abdomen and a cephalothorax, which has six pairs of appendages: the chelicerae, the pedipalps, and four pairs of walking legs
Gas exchange in spiders occurs in respiratory organs called book lungs
Many spiders produce silk, a liquid protein, from specialized abdominal glands

22. Myriapods Myriapods are terrestrial, and have jaw-like mandibles
Subphylum Myriapoda includes millipedes and centipedes
Myriapods are terrestrial, and have jaw-like mandibles
Millipedes eat decaying leaves and plant matter
Millipedes have many legs, with two pairs per trunk segment

23. Figure 33.34
(a) Millipede
Figure Myriapods.
(b) Centipede

24. Centipedes are carnivores
Centipedes have one pair of legs per trunk segment

25. Insects
Subphylum Hexapoda, insects and relatives, has more species than all other forms of life combined
They live in almost every terrestrial habitat and in fresh water
The internal anatomy of an insect includes several complex organ systems

26. Abdomen Thorax Head Compound eye Antennae Heart Dorsal artery Crop
Figure 33.35
Abdomen
Thorax
Head
Compound eye
Antennae
Heart
Dorsal
artery
Crop
Cerebral
ganglion
Anus
Vagina
Figure Anatomy of a grasshopper, an insect.
Malpighian
tubules
Ovary
Tracheal tubes
Nerve cords
Mouthparts

27. 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 has been increasing in the 65 million years since

28. 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

29. 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

30. 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

31. (a) Larva (caterpillar) (b) Pupa (c) Later-stage pupa (d) Emerging
Figure 33.37
(a) Larva (caterpillar)
(b) Pupa
(c) Later-stage
pupa
Figure Complete metamorphosis of a butterfly.
(d) Emerging
adult
(e) Adult

32. 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

33. Crustaceans
While arachnids and insects thrive on land, crustaceans, for the most part, have remained in marine and freshwater environments
Crustaceans, subphylum Crustacea, typically have branched appendages that are extensively specialized for feeding and locomotion
Small crustaceans exchange gases through the cuticle; larger crustaceans have gills

34. Most crustaceans have separate males and females
Isopods include terrestrial, freshwater, and marine species
Pill bugs are a well known group of terrestrial isopods
Decapods are all relatively large crustaceans and include lobsters, crabs, crayfish, and shrimp

35. Figure 33.39a
Figure Crustaceans.
(a) Ghost crab