Invertebrates
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' INVERTEBRATES Braconid wasp Invertebrates are animals without a backbone or skeleton mussels. Indirectly, humans benefit from invertebrates that containing bones. Invertebrates range in size from are essential food for fish, birds, and other vertebrates microscopic to 59 feet long and weighing nearly a ton, like that we harvest or simply enjoy watching. As pollinators the giant or colossal squids. While vertebrates – animals and decomposers, invertebrates are necessary for plant with a backbone – are better known, they are greatly reproduction and growth, and therefore provide food and outnumbered by invertebrates in species diversity and sheer sources of shelter, fuel, and medicine that we need to survive. abundance. Most living things are invertebrates with more than 1.25 million species globally. In Iowa, for example, ARTHROPODS there are more than 2,000 species of moths, while the most Arthropods have the greatest number of species among diverse group of Iowa vertebrates, birds, have only 300-400 all groups of invertebrates. Included in the arthropods species that live or migrate through our state. Invertebrates are several classes of familiar animals, including insects, are an incredibly diverse group of animals that can be found arachnids (spiders, mites, and ticks), crustaceans (lobsters, everywhere you might look in Iowa. crayfish, and shrimps), millipedes, and centipedes, all of Invertebrates are also important to our survival; we depend which have many species living in Iowa. Despite their on services these animals provide. Humans consume diversity, arthropods all share common characteristics that some invertebrates directly as food, like crayfish and distinguish them from other major groups of animals. Table 1: Five major taxonomic groups of invertebrates found in Iowa. GROUP (PHYLUM) EXAMPLES ENVIRONMENT PHYSICAL CHARACTERISTICS Body is segmented and covered Insects, spiders, mites, ticks, Arthropods (Arthropoda) Freshwater, terrestrial by an exoskeleton made of chitin; crustaceans, millipedes, centipedes paired, jointed appendages. Wormlike body is soft and Segmented worms (Annelida) Earthworms, leeches freshwater, terrestrial segmented Body is soft and unsegmented with a muscular foot; snails and Mollusks (Mollusca) Snails, slugs, bivalves (ex. mussels) Freshwater, terrestrial slugs have tentacles on their head; mussel body is enclosed in a shell Freshwater, terrestrial, inside a host Wormlike body is smooth, round, Roundworms (Nematoda) Nematodes, hookworms body and unsegmented Flatworms, flukes, tapeworms, Freshwater, terrestrial, inside a host Wormlike body is flat, and usually Flatworms (Platyhelmintha) planarians, or turbellarians body unsegmented Invertebrate taxonomic tree. Table 2: Five major classes of Arthoropods found in Iowa. Plants Animals INSECT CLASS ARACHNID CLASS CRUSTACEAN GROUP MILLIPEDE CLASS CENTIPEDE CLASS Insects Spiders, mites, ticks Crayfish, sowbugs (isopods), Millipedes Centipedes cladocerans Vertebrates Invertebrates Protozoa Flatworms Mollusks 3 body parts: Head, thorax, 2 body regions: 2 body regions: Cylindrical or flattened, Flattened, elongated body, abdomen Cephalothorax, abdomen Cephalothorax, abdomen elongated body, 20+ body 15+ body segments segments 3 pairs of segmented legs 4 pairs of segmented legs At least 5 pairs of segmented 2 pairs of legs per 1 pair of legs per segment legs segment Annelids Amoeba Arthropods Nematodes 1 pair of antennae no antennae 2 pairs of antennae 1 pair of short antennae 1 pair of large antennae Planarian 0, 2, or 4 wings no wings no wings no wings no wings >1,000,000 species globally 75,500 species globally 67,000 species globally 10,000 species globally 8,000 species globally Millipedes and Arachnids Crustaceans Insects Centipedes Land snail Soil nematodes Earthworm Crayfish Common eastern American giant Zebra jumping spider bumble bee millipede Arthropods have pairs of jointed appendages, resembling There are 15 groups or classes in the arthropod phylum, human legs and arms. It is the jointed legs that gives this but only the five major classes commonly observed in Iowa group their name; arthro is Greek for joint and pod refers are presented here. Classes differ based on a few key to feet and legs. Arthropods also have an exoskeleton, characteristics listed in Table 2, including: made of a special material called chitin, which covers the 1. Number of body regions outside of their body. They have an open circulatory system 2. Number of legs with no network of veins, arteries, and capillaries, and a 3. Number of antennae simple heart completely unlike a human heart. Rather than having a spinal cord like humans, they have a nerve cord that runs down the front of their bodies which serves a similar role as our nervous system. Arthropod breathing is accomplished either with gills or through a system of holes in the exoskeleton called spiracles and tubes that move air from spiracles to organs called tracheae. These differences from vertebrates might lead to the mistaken conclusion that this is a small, exclusive group of creatures. However, arthropods contain approximately three-fourths of all the world's species, numbering in the millions compared to the roughly 60,000 vertebrate species. Soldier fly Table 2: Five major classes of Arthoropods found in Iowa. INSECT CLASS ARACHNID CLASS CRUSTACEAN GROUP MILLIPEDE CLASS CENTIPEDE CLASS Insects Spiders, mites, ticks Crayfish, sowbugs (isopods), Millipedes Centipedes cladocerans 3 body parts: Head, thorax, 2 body regions: 2 body regions: Cylindrical or flattened, Flattened, elongated body, abdomen Cephalothorax, abdomen Cephalothorax, abdomen elongated body, 20+ body 15+ body segments segments 3 pairs of segmented legs 4 pairs of segmented legs At least 5 pairs of segmented 2 pairs of legs per 1 pair of legs per segment legs segment 1 pair of antennae no antennae 2 pairs of antennae 1 pair of short antennae 1 pair of large antennae 0, 2, or 4 wings no wings no wings no wings no wings >1,000,000 species globally 75,500 species globally 67,000 species globally 10,000 species globally 8,000 species globally Class Insecta Insecta is the largest class of arthropods and they all have Iowa insects, like this worker an exoskeleton and jointed legs. In Iowa, insects come in ant, all have three body Antennae all shapes and sizes, from tiny gnats to the 6-inch cecropia segments–a head with antennae and eyes, a thorax to which moth, but they all have the following combination of specific attaches three pairs of legs and characteristics that have specialized functions. The head has an abdomen. Head the mouth parts, eyes, antennae, and other sense organs, and the brain. The antennae are used primarily to detect odors and chemicals in the environment and to physically feel their Thorax environment for navigation purposes. The thorax carries the means of travel: three pairs of legs and the wings, if present. Insects that possess wings most often have two pairs There are 15 groups or classes in the arthropod phylum, although some, like flies, have only one pair of wings. Some but only the five major classes commonly observed in Iowa insects such as fleas and worker ants don’t have wings at Abdomen are presented here. Classes differ based on a few key all. Finally, the abdomen contains the internal organ systems characteristics listed in Table 2, including: necessary for digestion, breathing, and reproduction. 1. Number of body regions Class Arachnida Arachnids, like this zebra jumping spider (Salticus 2. Number of legs The class Arachnida includes spiders, mites, ticks, scorpions, scenicus), have their head 3. Number of antennae and related organisms and is a diverse and well-known group. and thorax fused into a There are no estimates for the number of species that can cephalothorax. They also have an abdomen and four be found in Iowa, but more than 75,000 have been recorded pairs of legs. globally. Abdomen Arachnids have only two body parts. The first body region consists of the head and thorax fused into a single structure called the cephalothorax, where four pairs of legs are attached. The second body region of the Arachnida is the abdomen. The two body regions are obvious in large spiders Cephalothorax such as the garden spider found all over Iowa. Arachnids do not have antennae or wings. Daddy-longlegs are technically separate from spiders (they are a separate order in the arachnid class). Daddy-longlegs, also called harvestmen, have the cephalothorax and abdomen fused into what appears to be a single segment. There are four pairs of segmented legs attached to the cephalothorax. Eight legs Crustaceans Although the most recognizable crustaceans are important foods for humans such as shrimp, crab, and lobster. Iowa Two pair of antennaeTwo pairs has its own diverse set of crustaceans including crayfish, of antennae sowbugs or isopods, amphipods, cladocerans, copepods, and ostracods. Like the Arachnida, crustaceans have Crustaceans, like this sowbug, have two body regions like the archanids two body regions; a cephalothorax and an abdomen. Cephalothorax but at least five pairs of legs and Cephalothorax Unlike arachnids, however, crustaceans have two pairs of two pairs of antennae (one pair is antennae and at least five pairs of legs. Crustaceans have very short on the sowbug). one pair of appendages per abdominal segment. What AbdomenAbdomen we generally call legs, also known as walking legs, are attached to the thorax region. Class Diplopoda Members of the class Diplopoda are called millipedes. Each body segment has four legs (two pairs) per segment. 20+ body segments Their numerous legs are close together and short, making 20+ body segments their movements relatively slow and occurring by waves of leg movement down the body. Millipedes have many body segments with two pairs of Class Chilopoda legs per segment. Members of the class Chilopoda are called centipedes and their name translates to mean "one hundred legs," Two pairsTwo of pair s of legs though this can be an exaggeration. In fact, the number legs per segmentper segment of legs a centipede has actually varies with the number of body segments, but they always have two legs (one pair) per segment.