Chapter 28 Arthropods Section 1 Characteristics of Arthropods

What is an Arthropod? A segmented, coelomate invertebrate animal with bilateral symmetry, an exoskeleton, and jointed structures called appendages

What is an Appendage? An appendage is any structure that grows out of the body of an animal (such as a leg or an antenna) Arthropods are the earliest known invertebrates to exhibit jointed appendages These appendages are adapted for many purposes including: sensing, walking, feeding, and mating

Why are jointed appendages advantageous? Allow more flexibility in animals that have hard, rigid exoskeletons Allow powerful movements of appendages Allow an appendage to be used in many different ways

What is an exoskeleton? A hard, thick outer covering Made of protein and chitin Often reinforced with calcium carbonate in aquatic species Can be continuous over the body or can be made of separate plates held together by hinges

What does an exoskeleton do? Protects and supports inner tissues Provides places for muscle attachment Provides protection against water loss when covered by a waxy layer

What are the disadvantages of an exoskeleton? Heavy…weight of the exoskeleton limits the size arthropods Cannot grow…so they must be periodically shed through the process of molting

What happens during molting? Before molting occurs, a new soft exoskeleton is formed underneath the current one When the new exoskeleton is ready the animal contracts muscles and takes in water or air causing the animal’s body to swell until the old exoskeleton splits open The old exoskeleton is shed The animal’s body gets bigger due to increased blood circulation (and sometimes also due to the animal taking in air) The new exoskeleton hardens in a larger size leaving room for the animal to grow

What happens during molting? During molting arthropods are vulnerable to predators because they are soft and cannot use the exoskeleton for the bracing of muscles (can’t move) So, during molting, arthropods have to hide or remain motionless for a few hours or days until their new exoskeleton hardens

How often does molting occur? Most arthropods molt 4 to 7 times before they become adults

How are arthropods segmented? In most arthropods, segments are fused into three body sections – head, thorax, and abdomen Some arthropods have a head and a fused thorax and abdomen Some arthropods have an abdomen and a fused head and thorax (called a cephalothorax) Some arthropods have all three body sections fused together

Why are arthropod segments fused? Fusion of segments protect the arthropod better However, fusion of segments also limits the movement of the arthropod

What type of respiratory structures do arthropods have? Arthropods need to have efficient respiratory structures that ensure rapid oxygen delivery to cells because active lifestyle of an arthropod requires a high metabolism and a large oxygen demand

What type of respiratory structures do arthropods have? Three types of respiratory structures have evolved in arthropods: Gills Tracheal tubes Book lungs (*Some arthropods also diffuse air directly across the exoskeleton and body wall but this requires a very thin and permeable exoskeleton)

What type of respiratory structures do arthropods have? Tracheal tubes Found in most insects Consist of branching networks of hollow air passages that carry air throughout the body Details: Muscles pump air through the tracheal tubes Air enters and leaves the tracheal tubes through openings on the thorax and abdomen called spiracles

What type of respiratory structures do arthropods have? Book lungs Found in most spiders and spider relatives Consist of air-filled chambers that contain leaf-like plates that are stacked or arranged like the pages in a book

What type of respiratory structures do arthropods have? Gills Found in aquatic arthropods Extract oxygen from the water and release carbon dioxide into the water

What type of senses do arthropods have? Arthropods have antennae Stalk-like structures Detect changes in the environment (such as changes in chemicals, movement, or sound) Used for sound and odor communication Antennae sense the odors of pheromones (chemical odor signals) which signal the arthropod to behave in a certain manner

What type of senses do arthropods have? Most arthropods have one pair of large compound eyes and three to eight simple eyes A simple eye is a visual structure with only one lens that is used for detecting light A compound eye is a visual structure with many lenses Each lens contributes a tiny portion to the total image allowing the arthropod to easily detect movements and color

What type of nervous systems do arthropods have? Have well developed nervous systems that process information from sense organs The nervous system consists of a double ventral nerve cord, an anterior brain, and several fused ganglia that act as control centers for the body section in which they are located

What other body systems do arthropods have? Arthropods have an open circulatory system A heart pumps blood into vessels that carry the blood away from the heart Blood then leaves the vessels and goes directly into the tissues Blood returns to the heart through open body spaces

What other body systems do arthropods have? Arthropods have a complete digestive system with a mouth, stomach, intestine, anus, and various digestive enzyme producing glands The mouthparts of most arthropods include one pair of jaws called mandibles that are adapted for holding, chewing, sucking, or biting various types of food

What other body systems do arthropods have? Most terrestrial arthropods secrete wastes through Malpighian tubules that are located in the abdomen and empty into the intestine

What other body systems do arthropods have? Arthropods have well developed muscular systems Muscles are attached to the inner surface of the exoskeleton on both sides of joints

How do arthropods reproduce? Most arthropods have separate males and females and reproduce sexually Fertilization is usually internal in terrestrial species but is often external in aquatic species A few species (like barnacles) are hermaphrodites Some species (such as bees, ants, aphids, and wasps) can reproduce through parthenogenesis which is a type of asexual reproduction in which a new individual develops from an unfertilized egg Reproductive diversity is one reason there are more arthropod species than all other animal species combined