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Sponges have an irregular body form with many openings, and only three
main types of cell, which are not rigidly organized into layers. They are
long-lived and often abundant in aquatic habitats where all but a few are
filter feeders.
Summary of Section 1.2
Cnidarian cells are arranged in two layers separated by a largely acellular
mesogloea, which is deformable but also resilient. The mouth opens into a
sac-like gut. Most cnidarians are predators, catching prey with tentacles
armed with cnidocytes that contain poison. They have organized muscles and
medusae can swim strongly. Some have bioluminescent proteins that have
recently been used for research purposes.
Summary of Section 1.2
The body plan of ctenophores resembles that of cnidarians, but they lack
cnidocytes. All are marine and some species often become very abundant in
certain places.
Summary of Section 1.2
Worm-like animals with soft, extensible bodies are classified into several
different phyla.
Summary of Section 1.3
Platyhelminths lack a coelom and the gut has only one opening. They creep
using cilia as well as muscles. Only one group, the planarians, are free-living,
but some are very successful predators.
Summary of Section 1.3
Annelids have an anus as well as a mouth, paired appendages and a coelom
divided into segments, that serves as a hydrostatic skeleton for burrowing
and crawling. Polychaetes are marine predators or filter feeders and have
small ciliated larvae. Oligochaetes and leeches are mainly terrestrial or
freshwater; the former are mostly detritus feeders while leeches are predators
or bloodsuckers.
Summary of Section 1.3
Nematodes secrete a stiff cuticle, which is replaced by moulting during
growth. Although structurally uniform, they live in a wide range of habitats
and are often abundant.
Summary of Section 1.3
Several contrasting groups of invertebrates have hard skeletons.
Summary of Section 1.4
Unique features of molluscs include the mantle, shell, radula and a muscular
foot, which is usually expanded by the haemocoel acting as a hydrostatic
skeleton, and is not partitioned into segments.
Summary of Section 1.4
The molluscan shell is secreted by the mantle and grows from the edges. It
consists of protein and crystals of calcium carbonate. Pearls are formed
around foreign objects or wounds and consist mainly of protein.
Summary of Section 1.4
All bivalves collect particulate food on their greatly enlarged gills. Most are
sedentary, living in or on sand, rock or other substrate, protected by their hinged, usually symmetrical shell. The main bases for diversity are the
manner of attachment or burrowing, and the mechanism of food collection
and selection.
Summary of Section 1.4
Gastropods have a single shell, often coiled but sometimes reduced or absent;
the foot is usually muscular and locomotion often involves secretion of
mucus. The form of the tongue-like horny radula is diverse, reflecting the
wide range of diets in gastropod species. In pulmonates, the gills are absent
and the lining of the mantle acts as a lung. Many are terrestrial herbivores.
Summary of Section 1.4
In most living cephalopods, the shell is reduced or absent and the mantle is
very muscular. Many can swim by jet propulsion, and seize prey with long,
muscular tentacles. Their behaviour is complex and parallels that of fishes in
a remarkable variety of ways. The structure and properties of cephalopod
eyes and blood vessels closely resemble those of vertebrates.
Summary of Section 1.4
Most living cephalopods are oceanic, and live in middle or deep waters, so
many species, including some of the largest have never been seen alive. Their
physiological capacities must be estimated indirectly from the comparative
study of isolated tissues.
Summary of Section 1.4
Echinoderms are all marine and have pentamerous symmetry and an internal
skeleton. Tube-feet operated by muscles and a coelomic hydrostatic skeleton
serve for locomotion and food collection. The internal skeleton is much
reduced in holothurians, which move more like worms.
Summary of Section 1.4
Crinoids are filter-feeders that usually live attached to the substratum. Many
asteroids are active predators or filter-feeders. Most holothurians are detritus
Summary of Section 1.4
Echinoids rasp algae and other encrusting organisms with the Aristotle’s
lantern containing hard teeth. Others are detritus feeders living in or on sand.
Many deter predation by sharp and/or poisonous spines, hard shells, or living
in burrows.
Summary of Section 1.4
Nearly all echinoderms produce numerous eggs that are fertilized externally
and develop into free-swimming larvae.
Summary of Section 1.4
The Arthropoda is the most structurally diverse of the animal phyla and many
members of the phylum have a substantial impact on human life.
Summary of Section 2.1
The diversity of arthropod body forms is apparent from very early in the
fossil record, as exemplified by the assemblage of fossils of the Cambrian
period in the Burgess Shale formation in British Columbia.
Summary of Section 2.1
There is conservation of the segmental organization of the body across the
whole phylum through geological time, but the body plan and form of the
appendages also show a great deal of flexibility.
Summary of Section 2.1
The taxonomic status of the Arthropoda is controversial, but the majority of
researchers would agree that the Arthropoda is a polyphyletic group.
Summary of Section 2.1
Representatives of the three living subphyla, Crustacea, Chelicerata and
Uniramia, show variations of the arthropodan plan. For example, the limbs of
many of the crustaceans show substantial adaptation for different mechanical or
reproductive functions. Mouthparts of many different insect species show
adaptation to specific methods of feeding.
Summary of Section 2.1
Arthropods have an exoskeleton, a layer of chitinous cuticle covering the
epidermis, of variable stiffness and permeability.
Summary of Section 2.2
The cuticle is made up of several layers and is a complex of proteins, lipids
and chitin, secreted by the epidermal cells. In crustaceans, the cuticle is
hardened by deposition of calcium salts; in insects, the cuticle is hardened by
Summary of Section 2.2
The cuticle is thin and soft at joints, facilitating movement of the body and
Summary of Section 2.2
Moulting and replacement of old cuticle enables growth.
Summary of Section 2.2
The arthropodan exoskeleton is largely impermeable to water and gases. Gas
exchange for respiration is usually by means of specialized structures.
Crustaceans, aquatic arthropods, have gills. Insects, mostly air-breathers as
adults, have tracheae and tracheoles that carry air directly to the respiring
Summary of Section 2.2
The life cycles of most crustaceans, such as barnacles and prawns, include a
planktonic larval stage, with the larva being very different in structure from
the adult.
Summary of Section 2.3
Barnacles have a planktonic nauplius larva that provides a dispersal stage in
the life cycle, but the behaviour of the cypris larvae when settling out of the
plankton to metamorphose into adults is complex and appears to ensure that
aggregations of barnacles of the same species are formed.
Summary of Section 2.3
The life cycle of spiders does not include a free-living larval stage — eggs
hatch into nymphs, sexually immature miniature spiders. A single female may
lay thousands of eggs and the young spiders are quite vulnerable during the
dispersal phase.
Summary of Section 2.3
The newly hatched spiders disperse, often by ballooning (being carried aloft
on a few silken threads).
Summary of Section 2.3
There are two principal types of larval development in insects. Exopterygote
insects have larval stages that are similar in structure to the adult, although
lacking functional wings and reproductive organs. In the endopterygote
insects, the larvae are very different organisms from the adults. The winged
adults are the dispersal stage rather than the larvae or nymphs.
Summary of Section 2.3
An understanding of the detailed timings of the stages of the life cycle of
blowflies, e.g. Calliphora, has important applications in forensic science,
enabling estimation of the time of death of murder victims.
Summary of Section 2.3
Malaria is a devastating disease spread by an insect vector, the mosquito. The
female mosquito feeds on human blood and while doing so injects the
malaria parasite, Plasmodium sp., into the human host.
Summary of Section 2.3
The mouthparts of female mosquitoes show special adaptations that facilitate
feeding on blood.
Summary of Section 2.3
Understanding of the life cycle and habits of mosquitoes has helped in
development of methods of control. Destruction of mosquito larvae has
proved effective although there are problems with this method. To date the
most effective method of controlling malaria has been by preventing contact
between mosquitoes and humans.
Summary of Section 2.3
Spiders have simple eyes typically arranged in two rows on the
Summary of Section 2.4
While most species of spider have poor vision, the hunting and jumping
spiders have sophisticated eyes providing great visual acuity.
Summary of Section 2.4
Sensory hairs on the body of spiders detect small vibrations, both in the air
and the web.
Summary of Section 2.4
A few spiders are known to communicate by pheromones.
Summary of Section 2.4
Insects have compound eyes made up of multiple units, ommatidia. As each
ommatidium points in a slightly different direction, each looks at a slightly
different part of the environment, and it is likely that an insect sees a mosaic
Summary of Section 2.4
Sound reception organs, tympanic organs, are found in seven insect orders.
Their structure is very different from the vertebrate ear.
Summary of Section 2.4
Location of the tympanic organs is not the same in all groups of insects that
have them.
Summary of Section 2.4
The tympanic organs of moths are used to detect their predators, bats.
Summary of Section 2.4
Orthopteran insects use sound for communication as a means of bringing
males and females together for mating.
Summary of Section 2.4
Most of the terrestrial arachnids are predators. Predation has evolved
independently in several orders of insect.
Summary of Section 2.5
Hunting and jumping spiders use their eyes to detect prey — they stalk insects
and jump on them.
Summary of Section 2.5
Praying mantids and dragonfly nymphs remain motionless until a victim is
within reach and then strike rapidly.
Summary of Section 2.5
Praying mantids have stereoscopic vision and can measure distance very
accurately. They also appear to be able to compare distances, which implies
the existence of memory.
Summary of Section 2.5
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