Skip to main content

Decorator and Sponge Crabs

Several types of crabs collectively known as the decorator and sponge crabs camouflage themselves from predators by carrying something on top of their shells. The toothed decorator crabs (Dehaanius) are small crustaceans with hooklike bristles on their backs where algae can be attached. Algae attached to a crab’s shell acts as excellent camouflage. Like all crabs, these have five pairs of walking legs. The first pair is modified as claws, which pick up algae and place the material onto the hooks.

Sponge crabs, members of the Dromiidae family, hold their camouflage in place with two pairs of posterior legs that have been modified for grasping. The legs are turned up and armed with points that the crab sticks through the sponges to hold them in place. Sponges give off noxious chemicals that can cause predators to think twice before attacking.

decorator crabs (Dehaanius)
Decorator crabs (Dehaanius)

When it is time to molt, a crab that is decorated in sponges lifts them off and sets them aside. When the new, larger shell is in place and hardened, the crab picks up the sponges and places them on its back again. Sponges do not grow as quickly as crabs, so after a few molts the crabs have outgrown the spongy hat. To solve this problem, crabs find new sponges, using their front claws to trim them for a proper fit. If a sponge is not available, the sponge crab will wear algae or anything else it can find.

Popular posts from this blog

Advantages and Disadvantages of an Exoskeleton

More than 80 percent of the animal species are equipped with a hard, outer covering called an exoskeleton. The functions of exoskeletons are similar to those of other types of skeletal systems. Like the internal skeletons (endoskeletons) of amphibians, reptiles, birds, and mammals, exoskeletons support the tissues and give shape to the bodies of invertebrates. Exoskeletons offer some other advantages. Serving as a suit of armor, they are excellent protection against predators. Also, because they completely cover an animal’s tissues, exoskeletons prevent them from drying out. In addition, exoskeletons serve as points of attachment for muscles, providing animals with more leverage and mechanical advantage than an endoskeleton can offer. That is why a tiny shrimp can cut a fish in half with its claw or lift an object 50 times heavier than its own body.
Despite all their good points, exoskeletons have some drawbacks. They are heavy, so the only animals that have been successful with them …

Differences in Terrestrial and Aquatic Plants

Even though plants that live in water look dramatically different from terrestrial plants, the two groups have a lot in common. Both types of plants capture the Sun’s energy and use it to make food from raw materials. In each case, the raw materials required include carbon dioxide, water, and minerals. The differences in these two types of plants are adaptations to their specific environments.
Land plants are highly specialized for their lifestyles. They get their nutrients from two sources: soil and air. It is the job of roots to absorb water and minerals from the soil, as well as hold the plant in place. Essential materials are transported to cells in leaves by a system of tubes called vascular tissue. Leaves are in charge of taking in carbon dioxide gas from the atmosphere for photosynthesis. Once photosynthesis is complete, a second set of vascular tissue carries the food made by the leaves to the rest of the plant. Land plants are also equipped with woody stems and branches that …

Prokaryotic Cell Structure

Prokaryotic cells are about 10 times smaller than eukaryotic cells. A typical E. coli cell is about 1 μm wide and 2 to 3μm long. Structurally, prokaryotes are very simple cells when compared with eukaryotic cells, and yet they are able to perform the necessary processes of life. Reproduction of prokaryotic cells is by binary fission—the simple division of one cell into two cells, after DNA replication and the formation of a separating membrane and cell wall. All bacteria are prokaryotes, as are the archaea.

Embedded within the cytoplasm of prokaryotic cells are a chromosome, ribosomes, and other cytoplasmic particles (Fig. 1). Unlike eukaryotic cells, the cytoplasm of prokaryotic cells is not filled with internal membranes. The cytoplasm is surrounded by a cell membrane, a cell wall (usually), and sometimes a capsule or slime layer. These latter three structures make up the bacterial cell envelope. Depending on the particular species of bacterium, flagella, pili (description follows)…