Download Squid Biology/Anatomy Notes, based on Loligo sp

Squid Biology/Anatomy Notes, based on Loligo sp.
Moving/Locomotion
Squid are among the fastest invertebrates on earth speeding
through the water at up to 40 km/h (24 mph). Very odd when
compared to other members of the phylum Mollusca like the snail,
slug, oyster, etc. When escaping predators, some squid can even
jump 3m (about 12ft) out of the water and glide like a flying fish.
They can move fast because they are naturally jet propelled. The
outside body of the squid is called the MANTLE which fits like a
hat over the real body and organs of the squid. By opening up the
mantle around the head squid suck water inside the mantle. Then
they squish the mantle closed. The water is let out in only one
place, the FUNNEL. Like a jet fighter engine nozzle, the squid can
open, close, twist, and turn the funnel to go where they want. Of
course they would fly around like a released balloon if they didn't
have FINLETS to act as rudders on the outside. Also like a
balloon they would flop and fold if they didn't have a strong
support beam, called the PEN inside the mantle to make it stiff.
Breathing/Respiration
Squid live in the ocean, therefore they need some type of gill(s) in
order to get oxygen from the water. Oxygen needs to pass from the
water into the blood. Squid do this by putting the blood next to the
water with only a thin wall, one cell thick, between water and
blood in a feathery structure called the CTENIDIUM (two are
called CTENIDIA). The ctenidia are found on either side of the
siphon. Oxygen-rich water is continually pushed past the ctenidia
by contraction of the MANTLE. Some rare, deep-water squid that
swim using webbed arms don't have gills, the webs are so thin that
they work as gills.
Eating
Squid are very successful predators. They feed on fish, shrimp, just about anything swimming that's
smaller than them. Squid have eight ARMS and two TENTACLES, unlike octopus which only have
eight arms. The arms are short. They rip-apart prey and stuff it into the mouth in the center of them.
The tentacles are much longer and have suckers only at the ends. Squid get close to prey, then shoot
out the extra-long tentacles to capture it and pull it in. The squid takes bites out of the prey with a
BEAK made out of the same stuff as human fingernails. The meat is ripped apart even more by the
RADULA, a conveyor belt of tiny teeth that nearly all molluscs have.
Food is swallowed and travels through the ESOPHAGUS into the small muscular STOMACH where
digetive juices from the LIVER and PANCREAS help break it down. The mushy food is then passed
into the big CECUM where it is absorbed into the squid's hemolymph (blood) and spread through the
body. Wastes are passed out the rectum, through the funnel, and into the water as the squid squirts
away.
Sex/Reproduction
Most squid live only a short time, one to three years. A male squid makes sperm with
a single TESTIS and then wraps it into a packet of sperm called a
SPERMATOPHORE with a gland called NEEDHAM'S SAC. He hands it off like
a football to the female using his long tentacles. The spermatophore is stuck to the
inside wall of the female's mantle so she can use it to fertilize her eggs when she lays
them. Often the female doesn't wait for the male to remove his tentacle and she rips it
off during her escape. This doesn't affect the male too much because he dies after
mating. Female Loligo sp. squid lay from 1000 to 5000 eggs in strings or 'fingers'
stuck to the bottom of the ocean. She has two glands, nidamental glands, that make a
hard, bad-tasting covering for the egg finger so that other animals won't eat the eggs.
After laying her eggs, the female usually dies. Squid usually swarm to shallow water
with sandy bottoms to reproduce so when they all die on the bottom seals, sea lions,
crabs, humans, and fish harvest the bodies for food. After several weeks baby squid,
about the size of a rice grain, hatch out and head to deep water to feed for one or two
years before returning to mate and die.
Blood/Circulation
Most molluscs (clams, oysters, scallops, snails, and slugs) have an open circulatory system, meaning
that the organs slosh around in a single pool of bluish 'blood' called HEMOLYMPH. The fast paced
life of a squid is possible partly because its hemolymph is pumped quickly around the body inside
veins, arteries, and capillaries; a closed circulatory system like humans have. Earth squid have three
hearts. One big SYSTEMIC HEART pumps hemolymph around the body and to the brain, while one
BRANCHIAL HEART on each gill helps push hemolymph through the little capillaries there.
Brain & Nerves
Squid have a fairly large brain between their big eyes. The largest parts of the brain are the parts
related to vision. Since squid have a soft body (not protected by shells like its relatives clams, oysters,
and snails) the brain is protected by a rubbery box almost like a skull made out of cartilage. Humans
studied squid brains and nerves for a long time because squid nerve cells are some of the largest on the
planet, much bigger than human nerve cells. Two really big ones called STELLATE GANGLIA
control the quick squeezing of the mantle. They are so big that humans were able to figure out how
nerves work by changing the chemicals and electrical impulses in these nerves. This research led
people to develop ways to fight some human diseases like muscular dystrophy, muscular sclerosis, and
Alzheimer's.
Senses
Research indicates that squid cannot smell, they have no noses.
They can feel different textures, but cannot tell one shape from
another. They 'hear' by sensing vibrations in the water. Their
eyes, however, are marvelous. Squid eyes are very similar to fish
eyes. Squid use their eyes to find and capture prey. They have no
eyelid, but control the amount of light coming into the eye by
opening and closing their slitted pupil. They focus on something
by moving a hard, clear LENS back and forth within the eye.
Some species of squid may be able to see color.
Changing Color/Camouflage
The color of a dead squid is very different from the changing colors of a live
squid. Color cells, called CHROMATOPHORES, in the squid's skin
contract and expand to produce different colors and patterns. Sometimes
squid use this ability to hide, but most times their color reflects their moods.
Squid can turn dark, squeeze ink out of their INK SAC, then turn light or
clear to confuse a predator and escape. Squid ink is made out of melanin
(the same stuff that produces human tans) and mucous (snot). Chemicals in
the ink also confuse fish noses to help squid get away. Some squid can even
glow in the dark, called BIOLUMINESCENCE. Glowing squid use
PHOTOPHORES to produce more or less light.