Octopuses - search.credoreference.com fileTopic Page: Invertebrates Definition: invertebrate from The Penguin Dictionary of Science General term of convenience given to an …

Topic Page: Invertebrates

Definition: invertebrate from The Penguin Dictionary of Science

General term of convenience given to an animal species that is not a member of the ➤chordate

subphylum Vertebrata. In modern classification systems the term has no taxonomic status. ➤➤Appendix

table 8.

Summary Article: What is an Invertebrate? from Animals: A Visual Encyclopedia

Invertebrates are animals that have neither a backbone nor a bony

internal skeleton. This group makes up more than 95 percent of the

animal kingdom. It is incredibly varied. Some invertebrates are little

known, like the microscopic rotifers (animals that may be smaller than

bacteria). Others are more familiar. Snails and spiders, fleas and

flatworms, centipedes and corals: these are all invertebrates. There are

simple invertebrates, such as sponges, that have no brain or internal

organs. And there are complex ones, like the highly intelligent octopus.

Factf ile

An estimated five million species of invertebrates exist today. This could double as we learn more about

the habitats of invertebrates.

Nematodes, or roundworms, are possibly the most numerous creatures on Earth. Some are so

tiny that as many as 90,000 can be counted on one rotting apple.

Invertebrates sometimes gather together in huge numbers. One of the biggest locust swarms on

record contained 72,000,000,000 insects and covered 463 sq miles (1,200 km2).

Image from: Selection of

shell ornaments from... in

Encyclopedia of Archaeology

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Octopuses have shown that they are brainy. A female octopus in a German zoo watched

keepers unscrewing the lids of jars of shrimps—and learned how to do it herself.



Arthropoda—Insects, arachnids, crustaceans (1,000,000 species)Arthropoda—Insects, arachnids, crustaceans (1,000,000 species)

Arthropods, as these animals are known as a group, have a hard outer covering. This covering, called an exoskeleton,

is divided into sections. Examples of an exoskeleton are the shell of a crab and the casing of a beetle. Arthropods

also have jointed limbs, which are arranged in pairs.



Mollusca—Squid, snails, bivalves (60,000 species).Mollusca—Squid, snails, bivalves (60,000 species).

Most mollusks live inside a hardened shell of some sort. This may be a single shell, like that of a snail, or in two

halves joined by a hinge, like that of a clam or a mussel. However, molluks also include animals, such as the octopus

and the cuttlefish, that have either no shell or an internal one.

Cnidaria—Jellyf ish, corals, hydras (11,000 species).Cnidaria—Jellyf ish, corals, hydras (11,000 species).

This group contains various aquatic animals, including jellyfish, sea anemones, and corals. Cnidarians, as they are

called, all possess tentacles that bear stinging cells (cnidae). Some cnidarians can swim, others are attached to the

seabed.



Annelida—Earthworms, leeches, polychaetes (12 ,000 species).Annelida—Earthworms, leeches, polychaetes (12 ,000 species).

These are called annelid worms and they all have bodies that are divided into segments. The common earthworm

belongs to this group. Polychaetes are also known as bristleworms. There are marine, freshwater, and land-dwelling

annelids.



Echinodermata—starf ish, sea urchins, sea cucumbers (7 ,000 species).Echinodermata—starf ish, sea urchins, sea cucumbers (7 ,000 species).

The common name of this group of marine animals is echinoderms. A key feature of many of them is an extremely

prickly body. Nearly all echinoderms live on the seafloor and most of them can move around to feed.



Porifera—Sponges (9 ,000 species).Porifera—Sponges (9 ,000 species).

Sponges may seem like plants but they are not. They are the simplest of all living animals. Their bodies are basically

a tube of fibers. Sponges live attached to rocks on the seafloor. Water currents carry food into their bodies.

Invertebrates f rom the past

One of the first invertebrate groups to appear on Earth were the sponges, some 600 million years ago.

Fossils of soft-bodied invertebrates, like jellyfish, are rare. However, fossils of trilobites, crustaceanlike

arthropods, are abundant. Trilobites survived for 300 million years, becoming extinct about 250 million

years ago. Other fossil finds include giant griffonflies with 30 in (75 cm) wingspans, water-scorpions 61/2

ft (2 m) long, and giant marine mollusks with shells 30 ft (9 m) long.



Living on others

Among the invertebrates are most of the world’s parasites. These are animals that live on the outside

or the inside of other animals, including humans. Many, though not all, are harmful. Common parasites

include worms of various kinds that live in their host’s intestines. Pests such as warble flies lay eggs in

the hair of mammals like horses and cattle. When the grubs hatch, they burrow into the skin, causing

sores. Some insects lay their eggs on other insects, and the emerging grubs eat their host.

Creat ing new life

Invertebrates reproduce in various ways. Not all of them need to find a mate. Sponges and starfish can

create new individuals from bits of their own bodies. In fact, if two sponges are put through a sieve and

mixed up, they clump together to form a single animal. Many insects lay unfertilized eggs that hatch and

develop into replicas of their parent. Stick insects, water fleas, and aphids all reproduce like this.



It takes twoIt takes two butterflies to produce eggs. All insects start off as eggs, then pass through various stages, such as

caterpillar and pupa, before becoming adult.



Single parentsS ingle parents such as aphids can produce young from unfertilized eggs. This is a quick way of building up

numbers.

Copyright © 2008 Dorling Kindersley Limited



APAWhat is an invertebrate? (2008). In C. Love, & C. Stamps (Eds.), Animals: a visual encyclopedia. London,

UK: Dorling Kindersley Publishing, Inc. Retrieved from


Chicago"What is an Invertebrate?" In Animals: A Visual Encyclopedia, edited by Carrie Love, and Caroline Stamps.

Dorling Kindersley Publishing, Inc., 2008. https://search.credoreference.com/content/topic/invertebrates

HarvardWhat is an invertebrate? (2008). In C. Love & C. Stamps (Eds.), Animals: a visual encyclopedia. [Online].

London: Dorling Kindersley Publishing, Inc. Available from:

https://search.credoreference.com/content/topic/invertebrates [Accessed 2 June 2018].

MLA"What is an Invertebrate?" Animals: A Visual Encyclopedia, edited by Carrie Love, and Caroline Stamps,

Dorling Kindersley Publishing, Inc., 1st edition, 2008. Credo Reference,

https://search.credoreference.com/content/topic/invertebrates. Accessed 02 Jun. 2018.



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Octopuses - search.credoreference.com fileTopic Page: Invertebrates Definition: invertebrate from The Penguin Dictionary of Science General term of convenience given to an …