Powerful Tentacles

he eight-tentacled octopus is one of the few large ocean cephalopods to live in deep water. It is usually found on the rocky or sandy bottoms of shallow waters near the mouths of rivers. It generally moves slowly, sometimes moving in brief spurts, but it can reach great speeds when hunting or fleeing. Some are quite intelligent, having highly evolved brains.

4 miles per hour

For the octopus, taking on the color of the ocean floor is a camouflage strategy to hide from its prey. In deeper waters, another tactic is to become luminescent to attract the prey. But when the octopus changes colors while doing a certain dance, it is trying . to attract the opposite sex.

Maximum speed of a fleeing octopus. Its speed is comparable to that of a fast-walking human.

SKIN

The skin is a highly elastic membrane that completely covers the octopus. .

HEAD

The head compresses and expands, depending on the octopus's breathing and movements. The head contain; the brain but without a rigid protective structure.

Attack

^^ To attack, the octopus points its funnel in the direction opposite to its motion. The common octopus (Octopus vulgaris), a species that can grow up to 40 inches (1 m) long and inhabits the Mediterranean Sea and North Atlantic Ocean, moves among the rocks on the seafloor, preferably at night. It surprises its prey and makes skillful use of its tentacles and jaws, which can rotate.

The funnel muscles can act as a mechanism for fleeing. Rather than directing the funnel forward, though, the octopus directs it to advance toward its prey.

Large Predators

Depending on its size, an octopus (like other large cephalopods such as the nautilus, cuttlefish, and squid) is carnivorous and eats both fish and other invertebrates: mollusks and crustaceans, especially crabs. It secretes a venom with its saliva to finish killing the prey before swallowing it.

± The tentacles stretch "v- forward and outward as ..■■' the octopus advances.

MOUTH

The mouth of an octopus has hard, chitin-like jaws for breaking shells.

Using the wide area at the base of its tentacles, it envelops the prey.

BREATHING

PROPULSION

Funnel relaxed muscle contracted

When the ring-shaped muscles contract, they expel a jet of water that propels the octopus backward. r

Grasping Ability

Powerful and versatile, with self-controlled movements, an octopus can move the entire weight of its body.

Arranged in two rows on the lower surfaces for clinging to rocks and for grasping prey. i

^^ The flow of water into and out of the funnel is ^ regulated by alternately contracting and relaxing ring-shaped muscles and long muscles. By regulating the force at which the water is expelled, the octopus can flee at high speed through a kind of jet propulsion. The octopus moves in the direction its head is pointing, with its tentacles outstretched.

The ring-shaped muscles relax, and the long muscles contract. Water enters.

EYES

Are located on the head. The octopus's sense of sight is exceptionally well developed.

TENTACLES

All eight tentacles have the same length. In the male, one tentacle functions as a genital organ.

Speedy Escape

An octopus often crawls among the rocks. Using the system of suckers, or adhesive discs, on its tentacles, an octopus clings to the seafloor or supports itself by attaching the suckers to the surfaces it encounters. By grasping with its forward tentacles, it can drag the rest of its body in that direction.

SUCTION

The funnel is the exit from the octopus's respiratory cavity. It is also extremely important for the creature's movement. The gills, inside the mantle, absorb oxygen from the water. When the cavity fills, the gills exchange oxygen for carbon dioxide to be emptied from the cavity.

chitinous ring

SELF-DEFENSE WITH INK

A gland located near the anus contracts when the octopus senses danger, expelling a fluid that creates a dark cloud in the water.

The FUnnel

Crustaceans and Arachnids piders, snakes, ticks, and mites naked eye. In Greek mythology, Arachne all belong to the same class, was a woman who challenged the goddess

Arachnida. They are covered Athena to weave faster than she herself with sensory hairs so tiny that could. This angered the goddess, who they cannot be seen by the turned Arachne into a spider, forcing her

COLORFUL ARMOR | CHANGING OUTFITS SHARP FRONT LEGS IN THE MIDDLE OF THE CHAIN

A SPECIAL FAMILY QUALITY SILK SIXTH SENSE POISONOUS STING

COLORFUL ARACHNID

Some species of the family Trombidiidae catch our attention because of their intense red color and the velvet-like appearance of their hair.

to weave forever. That is where these creatures get their name. Within the world of crustaceans, well-known animals such as the shrimp, lobster, and crab are also discussed in this chapter. You will find details about their anatomy, their differences and similarities, and the way in which they live that will surprise you. Some species breathe through gills and also breathe through their skin. J

Colorful Armor

Even though they inhabit all known environments, crustaceans are most closely identified with the aquatic environment. That environment is where they were transformed into arthropods with the most evolutionary success. Their bodies are divided into three parts: the cephalothorax, with antennae and strong mandibles; the abdomen, or pleon; and the back (telson). Some crustaceans are very small: sea lice, for instance, are no larger than one hundredth of an inch (a quarter of a millimeter). The Japanese spider crab, on the other hand, is more than 9 feet (3 m) long with outstretched legs, as it has legs in both the abdomen and the thorax in addition to two pairs of antennae. •

Wood Louse

(Armacfillicfium vulgare)

This invertebrate, belonging to the order Isopoda, is one of the few terrestrial crustaceans, and it is probably the one best adapted to life outside the water. When it feels threatened, it rolls itself up, leaving only its exoskeleton exposed. Even though it can reproduce and develop away from the water, it breathes through gills. The gills are found in its abdominal appendages and for this reason must be kept at specific humidity levels. That is also why the wood louse seeks dark and humid environments, such as under rocks, on dead or fallen leaves, and in fallen tree trunks.

EXOSKELETON

Divided into independent parts

Malacostraca

is the name given to the class of crustaceans that groups crabs together with sea lobsters, shrimp, wood lice, and sea lice. The term comes from Greek, and it means "soft-shelled." Sea and river crabs have 10 legs, and one pair of these legs is modified in a pincer form. Malacostraca are omnivorous and have adapted to a great variety of environments; the number of segments of their exoskeleton can vary from a minimum of 16 to more than 60.

APPENDAGES

EXOSKELETON

Divided into independent parts

consist of a lower region from which two segmented branches grow, one internal (endopod) and the other external (exopod).

SEGMENTS

The back segments are smaller, and when they bend, they help enclose the animal completely.

Together Forever

THE PACIFIC SPIDER CRAB CAN WEIGH UP TO

45 pounds

BARNACLE TRANSVERSAL CUT

APPENDAGES

BARNACLES WITHOUT A SHELL

At birth, barnacles (Pollicipes cornucopia) are microscopic larvae that travel through the sea until they reach a rocky coast. Then they attach themselves to the shore by means of a stalk, which they develop by the modification of their antennae, and then form a shell. Once they are attached, they remain in one spot for the rest of their lives, absorbing food from the water. Barnacles are edible.

Segmented legs

Mouth

Legs extended to catch food

Segmented legs

Mouth

Legs extended to catch food

Spawning

The female lays her eggs in deep-water beds.

PINCERS

are the front pair of legs. They are used to catch food.

SHELL -

The shell is hard and measures about 2.5 inches (6.0 cm) across.

EUROPEAN GREEN CRAB

Carcinus maenas is a littoral crab that lives on most continents and that has become a plague. It comes in a variety of colors.

FRONT LATERAL MANDIBLE

THREE-LAYERED SKELETON

Its interior part can contain up to 80 percent chitin.

MOVABLE FINGER

FIXED FINGER

and migrates to less saline waters.

ABDOMEN (PLEON)

Evolution

THE FEWER THE SEGMENTS FORMED BY ITS BODY, THE MORE HIGHLY EVOLVED THE CRUSTACEAN.

THE CRAB'S LIFE CYCLE

Even though it is well adapted to variations in the salinity of the water, the female crab, after mating, always moves to saltier waters and lays her eggs there. The larvae will go through different stages before becoming crabs.

CEPHALOTHORAX

□ Egg needs a saline environment for its development.

At first, the crab is a swimming larva.

In the sea or river bed, the larva grows seven to eight times its original size..

and migrates to less saline waters.

The prawn is a 10-leggetl crustacean that lives in deep waters and is able to withstand great variations in the salinity of its living environment.

MOVABLE FINGER

FIXED FINGER

ABDOMEN (PLEON)

Evolution

THE FEWER THE SEGMENTS FORMED BY ITS BODY, THE MORE HIGHLY EVOLVED THE CRUSTACEAN.

CEPHALOTHORAX

PINCERS

are the front pair of legs. They are used to catch food.

MULTIPLE FUNCTIONS

All crustaceans have a number of appendages that are modified for different and varied functions, depending on the species..

THE CRAB'S LIFE CYCLE

Even though it is well adapted to variations in the salinity of the water, the female crab, after mating, always moves to saltier waters and lays her eggs there. The larvae will go through different stages before becoming crabs.

SHELL -

The shell is hard and measures about 2.5 inches (6.0 cm) across.

EUROPEAN GREEN CRAB

Carcinus maenas is a littoral crab that lives on most continents and that has become a plague. It comes in a variety of colors.

FRONT LATERAL MANDIBLE

THREE-LAYERED SKELETON

Its interior part can contain up to 80 percent chitin.

Spawning

The female lays her eggs in deep-water beds.

EXOSKELETON

The greater its number of segments, the less highly evolved the species.

SEA LICE

SEA LICE

Copepoda are tiny crustaceans that form part of plankton. Copepoda play a very important ecological role because they are a source of food for many marine animals. There are more than 10,000 species of copepoda. Most are marine species, though there are also some freshwater species. The majority measure between 0.02 and 0.1 inch (0.5-2 mm) long; the smallest ones (Sphaeivnellopsis monothrix) reach only 0.004 inch (0.11 mm) in length, and the largest (Pennella balaenopterae) are 13 inches (32 cm) long.

Changing Outfits

The lobster belongs to the crustaceans, which are characterized by, among other things, an exoskeleton that supports and protects the body of the animal. The exoskeleton has both advantages and disadvantages. The stiffness of the structure prevents growth, which is why the animal grows only when the shell is renewed. This process is called molting. During molting the layers of the new cuticle harden, and minerals and materials from the old exoskeleton are reabsorbed to create a new exoskeleton. •

CEPHALOTHORAX

is formed by the abdomen and the fused segments of the head and the thorax, all of which are covered P by the shell.

EXOSKELETON

is made of a substance called chitin, which is strengthened by calcium salts. In the exoskeleton molting process, the new layers are formed in the cuticle; they then detach from the epidermis and form a new shell. This process uses a large amount of metabolic energy.

A LOBSTER CAN LIVE

100 years

AND NOT STOP GROWING IN ALL THAT TIME.

SEGMENTED ABDOMEN

The lobster is made of segments with appendages that give its body its hardness.

Palinuridae argus

ANTENNAE

4 vu yr

m vv ffe

TELSON SEGMENT

DOLPHIN-LIKE TAIL-

The tail is used for swimming. The bending of the tail and the abdomen propel the lobster backward and forward.

Chitinous Exoskeleton

The hard pincers help the lobster get food, and the segmented body allows for movement. However, the exoskeleton is a disadvantage in small places, because it cannot change shape. Even though the exoskeleton protects the lobster from abrasive contact, it can harm it once it breaks, because the fissure will not mend until the next molting.

WALKING LEGS

Five pairs of legs, of which one or more pairs are modified into pincers.

Jit.

WALKING LEGS

Five pairs of legs, of which one or more pairs are modified into pincers.

Jit.

THE LOBSTER MOLTS

once a

NEW TAIL SEGMENT

COLOR

Its color varies from gray to green and yellow, including even shadings of red and black.

heno es. D

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