Invertebrates

Invertebrates are animals that lack a vertebral column. They make up 98% of all
animal species - all animals except fish, reptiles, amphibians, birds, and mammals.
Initially separated into only two groups, they have gradually been divided into
10 groups, all of whom are marvellously adapted to their individual living situations.

Annelida

The Annelids, from Latin anellus meaning "little ring", is a group that includes animals
such as segmented worms and is comprised of 15,000 modern species including the
well-known earthworms and leeches. They are found in most wet environments, and
include many terrestrial, freshwater, and especially marine species (such as the
polychaetes), as well as some which are parasitic or mutualistic. They range in length
from under a millimeter to over 3 meters (the seep tube worm Lamellibrachia luymesi).
Although perhaps not the most attractive group, the worms of the world have a very
deep, intense impact on the world around them.

Arthropoda - insects, arachnids, crustaceans
Cnidaria - jellyfishes, corals, sea anemones, hydras
Echinodermata - starfish, sea urchins, sea cucumbers
Mollusca - squid, snails, bivalves
Nematoda - round worms
Nematomorpha - horsehair worm or gordian worms
Platyhelminthes - flat worms Porifera - sponges

Spiders

  
Chilean rose hair & Costa-Rican tiger rump tarantulas


The study of spiders is called arachnology. Spiders are awesome in so many ways - their silk is
stronger than steel of the same thickness, some can jump many times their own body length,
and still others can fly as spiderlings by spinning parachute-like silk strands behind them
and riding on the winds! We hope you enjoy this exciting information and if you encounter any terms
that you don't recognize, please be sure to check out our glossary for their meanings.

You can tell a spider from an insect in that it has only two body segments and not three. They also
have eight legs instead of six, no chewing mouth parts and no wings. They are classified in the
order Araneae, one of several orders within the larger class of arachnids, and a group that also
contains scorpions, whip scorpions, mites, ticks, and opiliones (harvestmen).

All spiders produce silk; a thin, strong protein strand produced by the spider from spinnerets most
commonly found on the end of the abdomen. Not all spiders use their silk to trap their prey in webs
the way you might commonly see in your garden. Many use it to aid in climbing, form smooth walls
for burrows, build egg sacs, wrap prey, and temporarily hold sperm, among other applications.
Some spiders spin a silk sac under water and bring air from the surface to trap inside it. Then the
spider lives inside the dome safe from birds and other non-aquatic predators! Spiders are found all
over the world, from the tropics to the Arctic.

Spiders can only eat their food in liquid form. For this purpose predigestion is carried out both
internally and externally to liquefy the tissues of their prey. Some spiders do this by injecting
digestive juices onto prey while piercing it with their chelicerae. The resulting liquefied "soup" is
then sucked up by the spider. Dense combs of hairs around the mouth filter out solids while the
spider ingests the liquids. Many spiders will store prey temporarily. Web-building spiders that have
made shrouds to wrap their prey in will store them to consume later. Spiders are capable of
digesting their own silk, so some spiders may eat their used webs and recycle the used protein!

Just about all spiders can inject venom to protect themselves or to kill prey. Only about 200
species, however, have bites that can pose health problems to humans. Many larger species' bites
may be quite painful, but will not produce lasting health concerns. Their eyes are single lenses
rather than compound eyes. Spiders usually have eight eyes in various arrangements. Some have
six eyes, although some have four, or even two eyes. Sometimes one pair of eyes is better
developed than the rest, or even, in some cave species, there are no eyes at all. Several families
of hunting spiders, such as jumping spiders and wolf spiders, have fair to excellent vision. The
main pair of eyes in jumping spiders even see in color!

Spiders have an open circulatory system which means they do not have true blood, or veins
like we do. Rather, their bodies are filled with haemolymph, which is pumped through arteries by a
heart into spaces called sinuses surrounding their internal organs.

Insects

    
Dragonfly, Insect Diagram, and Praying Mantis

"If all mankind were to disappear, the world would regenerate back to the rich state of equilibrium
that existed 10 000 years ago. If insects were to vanish, the environment would collapse into chaos." - Asaac Asimov

The insects have proven to be the most successful creatures on earth. These amazingly diverse
critters have conquered the entire planet except for the frozen polar environments at the highest
altitudes and in the immediate vicinity of active volcanoes. 70% of all the species on earth are insects.

Insects play a very important role in the web of life in every environment. Some of their jobs
include pollinating flowering plants, being a source of food for insectivorous animals and assisting
in the decomposition of plants and animals. Modern insect classification divides the Insecta into 29 orders.

Unlike spiders, insects have three body parts, called segments. The three segments are
referred to as the head, thorax and abdomen, and each part serves the insect in its own
way. The head holds the eyes, if the animal has any, as well as the mouthparts. The thorax
is where the legs are attached, and the abdomen contains all the organs the insect needs to
live. Most insects actually breathe through their abdomens and not through their mouths at all!

They have no internal skeleton the way mammals do, and so all their guts
are held in place with an external shell called an exoskeleton. Without this, an insect would
just be a puddle of mush on the ground! Insects always have three pairs of legs, though some
immature forms can have many more, such as caterpillars. Insects typically have a pair of lower
jaws called the maxillae and upper jaws called mandibles. Some of the variations on mouth parts
include the tubular sucking ones of butterflies and some moths, and stabbing mouth parts such
as we might find on mosquitos. Some adult insects don't have mouths at all! All insects have
one pair of antennae on the head which are used for a variety of purposes, not the least of
which is being able to pick up the scent of pheromones from receptive females for mating. Most
insects have one or two pairs of wings although some insects such as lice, fleas, bristletails
and silverfish are completely wingless.

There are 300 000 species of beetle in the world. Scarab or dung beetle fossils have been
found to be 40 million years old and were considered sacred in ancient Egypt. There are over
780 species of dung beetle found in South America alone, and over 600 species of longhorn beetle.
Rhinoceros beetles, unlike dung beetles, live on rotting vegetation and their wings are fused
together so they can no longer fly. They are too heavy and flight would require too much energy,
so they walk everywhere they want to go. Beetles have no auditory organs so they can't hear
anything, but crickets have sound receptors on the knee joints that pick up the sounds of other
crickets. Tiger beetles are the fastest running insects int he world. By comparison, humans would
have to run 720 miles per hour just to keep up to them! They are nocturnal and are very effective insect hunters.

Often insects are mistakenly called bugs, but true bugs look very different from other insects.
They have a needle-like mouthpart that is used as both a syringe to inject and a straw to
suck out the juices of insects or plants, depending on their diet.