Dissected crab that had been preserved in formaldehyde, with pink latex injected into circulatory system , showing heart pink thing in center , gills sort of pink things on left and right , gastric mill the object below the heart in this photo. Note: the head region of crab is facing bottom of picture. A sampling of some of the major crustacean groups:. Class Branchiopoda - water fleas, brine shrimp, fairy shrimp, etc.
Class Diplopoda - 10, sp. Millipedes share the same habitat as centipedes, but they are mostly herbivorous, feeding on decaying vegetation in the leaf litter. Animals that feed on detritus are called detritivores. Each segment of the millipede is actually two segments fused together hence the double set of legs.
They can secrete a defensive fluid that smells bad, and a few species actually secrete tiny amounts of cyanide gas to protect themselves! Class Insecta - , sp. If we knew all the different insects on Earth, there could be as many as 30 million species. Insects evolved about mya, with cockroaches and dragonflies among the first to appear. Insects have a head, thorax, and abdomen, with three pair of legs 6 legs on the thorax. Crustaceans have legs on the abdomen as well as on the thorax. Most insects have one or two pairs of wings.
They are the only invertebrates that fly. Most have compound eyes , and can communicate by sound and scent, using powerful chemical hormones called pheromones. Insects have extremely elaborate mouthparts, consisting of pairs of appendages fused into a lower lip labium , and an upper lip labrum , with other appendages called maxillae aiding in chewing.
These mouthparts are highly modified in various groups for chewing, sucking, and piercing. Insects undergo metamorphosis as they develop, changing from one form to another as they mature. The juvenile stages look like tiny versions of the adults. Their larvae are often radically different from the mature adult like the butterfly and the caterpillar. They not only look different, they live in different places and eat different food. Observe the preserved arthropods on display.
How do the various groups use their legs to walk, swim, feed or mate? Watch the way the millipede moves. Look at the legs. See how the waves of muscle contraction pass down through the segments?
The polychaete worm Nereis moves in exactly the same way. Handle the millipedes very gently. They are someone's pets. They also make great pets for dorm rooms - they need little care, don't take up much room, and don't make noise or messes, unlike your roommate.
Disturb the centipedes to get them moving around. Can you see the poison fangs? Notice how flat the body is, and contrast the number of legs with those of the millipede. Why does each container hold only a single centipede? Don't open the jars unless you have a thing for extreme pain. Play around with the roly-polys.
Oh, go ahead, it's cool. They won't bite. Watch the way they roll up into a ball when disturbed. Not all isopods can do this, but rolling up into an armored ball is a great defensive tactic. Compare our teeny tiny terrestrial version with the enormous preserved marine isopods.
Look at the live brine shrimp, hermit crabs and fiddler crabs. Treat them gently more pets. Watch the way they use their legs, including the modified legs that form their mouthparts. You may see the male fiddler crabs raise their large claw and wave it about to claim a territory inside the tank, in the hopes of attracting a mate Can you blame them?
Observe the live crayfish. What does the crayfish do when it feels threatened? How does it use its swimmerets when it is stationary? Observe the diversity in insect mouthparts etc.
Don't worry about being able to identify the individual slides. Try to get a feel for the way modified legs are employed in these animals for a wide variety of sucking, sponging, piercing and biting.
Observe the insects on display. You should be familiar for lab and lecture with the common orders of insects listed in this guide. Crayfish are relatively easy to dissect. Many of you have had ample practice dissecting them at Jazz Fest. Your first task is to determine whether you have a male or female crayfish.
Turn the animal on its back, and examine the area of the thorax where the legs join the body. Female crayfish have a circular opening, like a tiny doughnut, which is their seminal receptacle. Male crayfish have a hardened pair of swimmerets legs on the abdomen that extends back towards the head, and fits neatly into the groove between the walking legs.
These modified legs are stiff, like hard plastic. They are curved like half a soda straw, and when they are joined together, they make a tiny tube through which the sperm travel during copulation.
Crayfish literally copulate with their legs. Observe their external anatomy. Identify the following structures: rostrum, antennae, eyes, thorax, carapace, chelae claws , cheliped, walking legs, abdomen, swimmerets, telson, and uropod. Examine the various appendages and modified appendages closely. Scientists separate crabs into two groups, the hermit crabs and the true crabs. Hermit crabs differ from true crabs in that only the anterior portion of the body in hermit crabs is protected by a hard exoskeleton.
Not only is their abdomen unprotected, it is soft. As soon as it molts for the first time, a juvenile hermit crab quickly begins to look for a vacant shell to call home. Described in the order Decopoda footed , all true crabs have 10 appendages with the forward two having been modified into pincers in most species. The pincers and claws vary markedly from one species to the next. An examination of these appendages provides valuable insight into the natural history of the various species.
Those that possess small, almost delicate-looking claws such as arrow crabs are likely to graze on a variety of algae to acquire nutrition. Crabs such as spider crabs and king crabs that have at least one large, powerful-looking claw that is heavily armored are far more likely to be carnivorous, feeding on a variety of snails, clams, fishes and other animals that must be crushed to be eaten. Many carnivorous species are also quick to scavenge when the opportunity presents itself.
In turn, crabs are heavily preyed upon by octopuses and many fishes, including moray eels and bottom-dwelling sharks and rays. Crabs display a remarkable variety of adaptations.
For instance, the species known as porcelain crabs, which can be recognized by their flat, smooth bodies and single pair of antennae between their eyes, have the ability to detach their own claws during conflict to facilitate a wise retreat.
But that is not all. The detached claws keep pinching while the crab makes its getaway. For many years barnacles were mistakenly classified as members of the phylum Mollusca mollusks instead of Arthropoda. However, in a British biologist recognized the many similarities that barnacles share with other arthropods.
Barnacles develop from an egg into a larval stage in a manner similar to lobsters, shrimps and crabs. Barnacles also possess the jointed appendages found in other crustaceans. But barnacles only display some of these characteristics as larvae.
Once they become adults, barnacles remain hidden within a shelled fortress of their own making. Barnacles live in habitats that range from the intertidal zones to the skin of whales. The feet are repeatedly drawn through the water in a mesmerizing, sweeping motion to catch food particles. The food is then drawn into the shell where it can be ingested.
Being permanently attached to the reef as an adult also presents problems where reproduction is involved. Often the pod in question was attached to a fish or some other creature, but that is not always the case. Copepods, for example, fill an important slot in many food chains being a major component in the plankton supply. Some copepods and isopods live their lives attached to the bodies of larger animals including bony fishes, sharks and rays, dolphins, whales and turtles.
Copepods burrow into the skin of their host while isopods hold on by clinging. While some species of copepods and isopods are parasitic, their presence tends to be more of an irritant than life-threatening. Many species primarily acquire nutrition by eating away at the skin and body of their host; many feed by removing food from the water that flows past them.
While they are certainly not limited to these species, copepods can often be seen in the mouths and on the dorsal fin of mako sharks in the waters off southern California, while isopods are often observed attached to the head of soldierfishes and squirrelfishes in tropical seas.
Some species of isopods can be seen in many areas with rocky beaches before you ever enter the water. Isopods bear some resemblance to the terrestrial crustaceans known as pill bugs. They can be seen scurrying around rocks and other structures as they hide in cracks and crevices along shorelines in the tidal zones where they make their livings by scavenging on a variety of algae and organic debris.
The name amphipod refers to myriad species of crustaceans known as sand fleas, beach hoppers and water fleas. While they are relatively small creatures, they, too, often occur in numbers too high to count, and collectively they serve as a valuable food source for many larger creatures. Amphipods are common from the shoreline to the deep sea.
Beach dwelling amphipods tend to bury themselves in the sand by day and emerge as the sun gets low on the horizon. Their bites are irritating and can itch for several days.
Having a hard shell has its downside. Growth is difficult and it can be especially dangerous. In order to grow, crustaceans must discard their existing shell in an act known as molting and then create a newer, larger shell. During this time, their soft body parts are exposed to predators. Creating a newly hardened shell requires time.
Molting is controlled by hormones that are produced by glands in the elongated eye stalks. Before shedding their existing skeleton but as part of the molting process, crustaceans undergo a period in which they feed heavily and store fat reserves. Once sufficient fat has been stored, the animal begins to form the foundation of a new shell underneath the existing shell. Hormonal changes cause the old shell to fracture and split in strategic places.
Once the old shell has sufficiently deteriorated, the animal climbs out of the remains and the new shell begins to expand and harden. In some instances the old shell is simply abandoned, but in others the molting animal will eat some of the old shell in order to reacquire calcium that will help the new shell harden. Once the old shell has been shed, the animal is quick to seek cover in a hiding place where it can wait safely as the new shell takes shape and hardens. However, in many crustaceans it is only during this soft-shelled period that females can be mated.
During the period while the shell is soft, important hormonal processes prevent the loss of body fluids and encourage body tissues to swell and growth to occur. In time, the newly created shell hardens over the enlarged body. As the hardening occurs, another hormonally triggered event causes excess body fluids to be expelled and the soft body of the animal inside shrinks, leaving ample room for body growth before a new shell is needed again.
Larval crustaceans often molt as many as a dozen times in one year. Once they have settled out of the water column and become members of reef communities, the frequency of molts tends to lessen, but the animals tend to molt several times annually with the number of events continuing to slow as they age.
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