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Invertebrates

Grace Atkins Biology Ms. Lecuyer June 7, 2010 Cellular organization

Invertebrates have no backbone and are part of the Kingdom Animalia. All invertebrates share common traits. Firstly, they are all multi-cellular. They also have no cell walls. Most invertebrates have tissues that construct the specific organization of cells. Also most organisms in this kingdom reproduce sexually. This is when two gametes combine to form a new organism. The cells work together for the survival of the organism. All cells have a specific responsibility. Out of the two million species on Earth, ninety-eight percent of them are invertebrates. Lastly, invertebrates range from one millimeter long to many meters long. Energy/Metabolism

Invertebrates cannot make their own food. They are heterotrophic. Heterotrophs eat other things to get energy. Invertebrates eat both plants and animals to obtain energy. Invertebrates are cold-blooded and warm their bodies by the heat in their surroundings. Most invertebrates live in water for some of their life. Aquatic invertebrates have thin external layers that are permeable to water. This allows for the exchange of gases that are needed to keep the animal alive. Aquatic invertebrates feed by ingesting their prey after capturing them. Some invertebrates live on land, such as earthworms or insects. Earthworms have strong muscles for crawling. They secrete mucous to keep their bodies moist.

Responsiveness

Soft-bodied marine invertebrates take advantage of the organic carbon in the environment. Larval forms can increase in biomass and in the absence of paniculate foods. Invertebrates adapt to live in water. They are protected from predators by camouflage and hard shells. Also, mayfly nymphs have external gills for breathing in water. Caddis fly larvae make a shell of sand to protect their soft bodies. Another example is that diving beetles are streamlined so they can move fast through the thick water. Growth/Reproduction

Invertebrates mostly reproduce sexually, but some reproduce asexually. An example of a invertebrate is a butterfly. A butterfly reproduces asexually. Butterflies go through metamorphosis, which means a change of body. The first stage is the egg stage. This is when the adult butterfly lays her eggs on the host plant. The second stage is the caterpillar stage. The caterpillar hatches from the egg. It then keeps eating. The third stage is the chrysalis stage. This is when the caterpillar goes in a "lovely" green box. People say that it is one of the most beautiful objects in the world. In this box the caterpillar changes into a butterfly. This takes about a week to ten days. The cells of the caterpillar transform into the cells of a butterfly's body. The fourth stage is the adult stage. This is when the butterfly comes out from its chrysalis, the chrysalis turns from green to clear so you can see the patterns of the butterfly.

Heredity

There are six different groups of invertebrates. They are sponges, coelenterates, echinoderms, worms, mollusks, and arthropods. Sponges live mostly in saltwater. They do not move from place to place and they filter tiny organisms out of the water for food. Stinging tentacles surround the mouths of coelenterates. Their mouths take in food and get rid of waste. Echinoderms live in seawater and have exoskeletons. Worms have many different varieties and habitats. They can live from the bottom of the ocean or inside other animals. Mollusks are soft-bodied. They often live in hard shells. Mollusks are the second-largest group of invertebrates. On the other hand, arthropods are the largest group of invertebrates. They have segmented bodies and an exoskeleton. Arthropods include insects, arachnids, centipedes, millipedes, and crustaceans. Adaptation/Evolution

All animals have a common ancestor that evolved over 600 million years ago from colonial protists. The nervous system, segmentation, body cavities, and bilateral symmetry are adaptations that are a big part of the evolution of invertebrates. By studying the embryonic development of invertebrates, their evolutionary history is revealed. A variety of body plans appear randomly in the fossil record about 550 million years ago. This is called the Cambrian explosion. Sponges and cnidarians were the first groups of animals to evolve over 650 million years ago. Roundworms and flatworms have evolved from different ancestors. Segmented worms and mollusks evolved in the ocean around 550 million years ago. The development of excretory systems and eyes evolved first in these groups. Eventually, lungs and other organs evolved independently in mollusks and arthropods. Arthropods developed from annelids in three distinct groups. Main adaptations are jointed appendages and an exoskeleton. Also based on fossil evidence, scientists have discovered that horseshoe crabs have stayed the same for 300 million years! Echinoderms evolved over 650 million years ago and share a recent common ancestor with vertebrates. Flight evolved around four different times, starting with arthropods.

Regulation/Homeostasis

Since invertebrates are cold-blooded animals they get their body heat from their surroundings. Their body temperature controls how fast or slow digestion occurs. In the cold, invertebrates move very slowly and thus digest slowly. When it is warmer invertebrates move more quickly and thus digest quickly. They do not have to spend much of their energy bank on keeping a constant temperature.