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Squid Biology/Anatomy Notes, based onLoligo 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 whencompared 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 themantle 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. Ofcourse 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 thewater 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 thesiphon. Oxygen-rich water is continually pushed past the ctenidia

by contraction of the MANTLE. Some rare, deep-water squid thatswim using webbed arms don't have gills, the webs are so thin thatthey 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 haveeight 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

BEAKmade out of the same stuff as human fingernails. The meat is ripped apart even more by theRADULA, a conveyor belt of tiny teeth that nearly all molluscs have.

Food is swallowed and travels through the ESOPHAGUS into the small muscularSTOMACH where

digetive juices from the LIVERand PANCREAS help break it down. The mushy food is then passedinto 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.

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Sex/Reproduction

Most squid live only a short time, one to three years. A male squid makes sperm witha 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 laysthem. 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 aftermating. 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 waterwith 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 twoyears 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 insideveins, 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 GANGLIAcontrol 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, andAlzheimer's.

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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 noeyelid, but control the amount of light coming into the eye by

opening and closing their slitted pupil. They focus on somethingby moving a hard, clearLENS 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 skincontract 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 theirINK 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.