Chapter 33. Invertebrates. Overview: Life Without a Backbone. Invertebrates are animals that lack a backbone They account for 95% of known animal species. LE 33-2. Cnidaria. Echinodermata. Chordata. Porifera. Other bilaterians (including Nematoda, Arthropoda, Mollusca, and Annelida).
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Other bilaterians (including
Mollusca, and Annelida)
A placozoan (LM)
A kinorhynch (LM)
A rotifer (LM)
A marine flatworm
A ribbon worm
A ctenophore, or comb jelly
A marine annelid
A loriciferan (LM)
Tardigrades (colorized SEM)
A cycliophoran (colorized SEM)
An acorn worm
A sea urchin
Azure vase sponge
Video: Hydra Eating Daphnia (time lapse)
Video: Hydra Budding
Video: Hydra Releasing Sperm
Cubozoan (sea wasp)
Video: Jelly Swimming
Video: Thimble Jellies
Video: Clownfish and Anemone
Video: Coral Reef
Ventral nerve cords
Mature flukes live in the blood vessels
of the human intestine
Larvae penetrate skin and blood vessels of humans.
Blood flukes reproduce sexually in the human host. Fertilized eggs exit host in feces.
Eggs develop in water into ciliated larvae. Larvae infect snails.
Asexual reproduction within snail results in another type of motile larva.
A land snail
A sea slug. Nudibranchs, or sea slugs,
lost their shell during their evolution.
Octopuses are considered among the most intelligent invertebrates.
Squids are speedy carnivores with beaklike jaws and well-developed eyes.
Chambered nautiluses are the only living cephalopods with an external shell.
Video: Earthworm Locomotion
Giant Australian earthworm
Ventral nerve cords
Video: C. elegans Crawling
Video: C. elegans Embryo Development (time lapse)
Video: Lobster Mouth Parts
Scorpions have pedipalps that are pincers specialized for defense and the capture of food. The tip of the tail bears a poisonous stinger.
Dust mites are ubiquitous scavengers in human dwellings but are harmless except to those people who are allergic to them (colorized SEM).
Web-building spiders are generally most active during the daytime.
(exit for eggs)
Video: Butterfly Emerging
Video: Bee Pollinating
Cockroaches have a dorsoventrally flattened body, with legs modified for rapid running. Forewings, when present, are leathery, whereas hind wings are fanlike. Fewer than 40 cockroach species live in houses; the rest exploit habitats ranging from tropical forest floors to caves and deserts.
Beetles comprise the most species-rich order of insects. They have two pairs of wings, one of which is thick and leathery, the other membranous. They have an armored exoskeleton and mouthparts adapted for biting and chewing. Beetles undergo complete metamorphosis.
Earwigs are generally nocturnal scavengers. While some species are wingless, others have two pairs of wings, one of which is thick and leathery, the other membranous. Earwigs have biting mouthparts and large posterior pincers. They undergo incomplete metamorphosis.
Dipterans have one pair of wings; the second pair has become modified into balancing organs called halteres. Their head is large and mobile; their mouthparts are adapted for sucking, piercing, or lapping. Dipterans undergo complete metamorphosis. Flies and mosquitoes are among the best-known dipterans, which live as scavengers, predetors, and parasites.
Hemipterans are so-called “true bugs,” including bed bugs, assassin bugs, and chinch bugs. (Insects in other orders are sometimes erroneously called bugs.) Hemipterans have two pairs of wings, one pair partly leathery, the other membranous. They have piercing or sucking mouthparts and undergo incomplete metamorphosis.
Ants, bees, and wasps are generally highly social insects. They have two pairs of membranous wings, a mobile head, and chewing or sucking mouthparts. The females of many species have a posterior stinging organ. Hymenopterans undergo complete metamorphosis.
Termites are widespread social insects that produce enormous colonies. It had been estimated that there are 700 kg of termites for every person on Earth! Some termites have two pairs of membranous wings, while others are wingless. They feed on wood with the aid of microbial symbionts carried in specialized chambers in their hindgut.
Butterflies and moths are among the best-known insects. They have two pairs of wings covered with tiny scales. To feed, they uncoil a long proboscis. Most feed on nectar, but some species feed on other substances, including animal blood or tears.
Dragonflies and damselflies have two pairs of large, membranous wings. They have an elongated abdomen, large, compound eyes, and chewing mouthparts. They undergo incomplete metamorphosis and are active predators.
Grasshoppers, crickets, and their relatives are mostly herbivorous. They have large hind legs adapted for jumping, two pairs of wings (one leathery, one membranous), and biting or chewing mouthparts. Males commonly make courtship sounds by rubbing together body parts, such as a ridge of their hind leg. Orthopterans undergo incomplete metamorphosis.
Stick insects and leaf insects are exquisite mimics of plants. The eggs of some species even mimic seeds of the plants on which the insects live. Their body is cylindrical or flattened dorsoventrally. They lack forewings but have fanlike hind wings. Their mouthparts are adapted for biting or chewing.
Commonly called sucking lice, these insects spend their entire life as an ectoparasite feeding on the hair or feathers of a single host. Their legs, equipped with clawlike tarsi, are adapted for clinging to their hosts. They lack wings and have reduced eyes. Sucking lice undergo incomplete metamorphosis.
Fleas are bloodsucking ectoparasites on birds and mammals. Their body is wingless and laterally compressed. Their legs are modified for clinging to their hosts and for long-distance jumping. They undergo complete metamorphosis.
Silverfish are small, wingless insects with a flattened body and reduced eyes. They live in leaf litter or under bark. They can also infest buildings, where they can become pests.
The larvae of caddisflies live in streams, where they make houses from sand grains, wood fragments, or other material held together by silk, Adults have two pairs of hairy wings and chewing or lapping mouthparts. They undergo complete metamorphosis.
Video: Echinoderm Tube Feet
A sea star (class Asteroidea)
A brittle star (class Ophiuroidea)
A sea urchin (class Echinoidea)
A feather star (class Crinoidea)
A sea cucumber (class Holothuroidea)
A sea daisy (class Concentricycloidea)