Section 28.1 Summary – pages A typical arthropod is a segmented, coelomate invertebrate animal with bilateral symmetry, an exoskeleton, and jointed structures called appendages. An appendage is any structure, such as a leg or an antenna, that grows out of the body of an animal. What is an arthropod?

Section 28.1 Summary – pages Arthropods are the earliest known invertebrates to exhibit jointed appendages. Joints are advantageous because they allow more flexibility in animals that have hard, rigid exoskeletons. What is an arthropod?

Section 28.1 Summary – pages The exoskeleton is a hard, thick, outer covering made of protein and chitin (KI tun). Arthropod exoskeletons provide protection

Section 28.1 Summary – pages In many aquatic species, the exoskeletons are reinforced with calcium carbonate. The exoskeleton protects and supports internal tissues and provides places for attachment of muscles. Arthropod exoskeletons provide protection

Section 28.1 Summary – pages Why arthropods must molt A second and more important disadvantage is that exoskeletons cannot grow, so they must be shed periodically. Shedding the old exoskeleton is called molting.

Section 28.1 Summary – pages When the new exoskeleton is soft, arthropods cannot protect themselves from danger because they move by bracing muscles against the rigid exoskeleton. Most arthropods molt four to seven times in their lives before they become adults. Why arthropods must molt

Section 28.1 Summary – pages Segmentation in arthropods In most groups of arthropods, segments have become fused into three body sections—head, thorax, and abdomen.

Section 28.1 Summary – pages In other groups, even these segments may be fused. Segmentation in arthropods Some arthropods have a head and a fused thorax and abdomen.

Section 28.1 Summary – pages In other groups, there is an abdomen and a fused head and thorax called a cephalothorax. Segmentation in arthropods Fusion of the body segments is related to movement and protection.

Section 28.1 Summary – pages Three types of respiratory structures have evolved in arthropods: gills, tracheal tubes, and book lungs. Arthropods have efficient gas exchange

Section 28.1 Summary – pages Most insects have tracheal tubes, branching networks of hollow air passages that carry air throughout the body. Arthropods have efficient gas exchange

Section 28.1 Summary – pages Air enters and leaves the tracheal tubes through openings on the thorax and abdomen called spiracles. Muscle activity helps pump the air through the tracheal tubes. Arthropods have efficient gas exchange

Section 28.1 Summary – pages Most spiders and their relatives have book lungs, air-filled chambers that contain leaflike plates. Arthropods have efficient gas exchange

Section 28.1 Summary – pages The stacked plates of a book lung are arranged like pages of a book. Arthropods have efficient gas exchange

Section 28.1 Summary – pages Antennae are also used for sound and odor communication among animals. Arthropods have acute senses

The ants were able to work together as a group because they were communicating with each other by pheromones, chemical odor signals given off by animals. Section 28.1 Summary – pages Arthropods have acute senses Have you ever watched as a group of ants carried home a small piece of food?

Section 28.1 Summary – pages Accurate vision is also important to the active lives of arthropods. 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. Antennae sense the odors of pheromones. Arthropods have acute senses

Section 28.1 Summary – pages A compound eye is a visual structure with many lenses. Arthropods have acute senses

Section 28.1 Summary – pages Arthropod nervous systems are well developed. The nervous system consists of a double ventral nerve cord, an anterior brain, and several ganglia. Arthropods have ganglia that have become fused. These ganglia act as control centers for the body section in which they are located.

Section 28.1 Summary – pages Arthropod blood is pumped by a heart in an open circulatory system with vessels that carry blood away from the heart. The blood flows out of the vessels, bathes the tissues of the body, and returns to the heart through open body spaces. Arthropods have other complex body systems

Section 28.1 Summary – pages Arthropods have a complete digestive system with a mouth, stomach, intestine, and anus, together with various glands that produce digestive enzymes. The mouthparts of most arthropod groups include one pair of jaws called mandibles. Arthropods have other complex body systems

Section 28.1 Summary – pages Most terrestrial arthropods excrete wastes through Malpighian tubules. In insects, the tubules are all located in the abdomen rather than in each segment. Malpighian tubules are attached to and empty into the intestine. Arthropods have other complex body systems

Section 28.1 Summary – pages Most arthropod species have separate males and females and reproduce sexually. Fertilization is usually internal in land species but is often external in aquatic species. Arthropods reproduce sexually

Section 28.1 Summary – pages Arthropods reproduce sexually Some species, including bees, ants, aphids, and wasps, exhibit parthenogenesis, a form 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.

Objective 2: Subphylums for Arthropods -Subphylum Trilobita: Examples include trilobites. All extinct forms; Cambrian to Carboniferous; body divided by two longitudinal furrows into three lobes; distinct head, trunk, and abdomen, biramous (two- branched) appendages. -Subphylum Chelicerata: eurypterids, horseshoe crabs, spiders, ticks. First pair of appendages modified to form chelicerae; pair of pedipalps and four pairs of legs; no antennae; no mandibles; cephalothorax and abdomen usually unsegmented.

Objective 2: Subphylums for Arthropods -Subphylum Crustacea: crustaceans. Mostly aquatic, with gills; cephalothorax usually with dorsal carapace; biramous appendages, modified for various functions; head appendages consisting of two pairs of antennae, one pair of mandibles, and two pairs of maxillae; development primitively with Nauplius stage -Subphylum Uniramia: All appendages currently thought of as uniramous; head appendages consisting of one pair of antennae, one pair of mandibles, and one or two pairs or maxillae. Examples include: centipedes, millipedes, and insects.

Objective 3: Classes of Chelicerata -Class Merostomata: aquatic chelicerates. Cephalothorax and abdomen; compound lateral eyes; appendages with gills; sharp telson; subclass Eurypterida (all extinct) and Xiphosurida, horseshoe crabs. Examples include Limulus.

Objective 3: Classes of Chelicerata -Class Pycnogonida: Sea Spiders. Small (3 to 4 mm). Some reach 500mm; body chiefly cephalothorax; tiny abdomen; usually four pairs on long walking legs (some with five or six pairs); mouth on long proboscis; four simple eyes; no respiratory or excretory system. Example: Pycnogonum.

Objective 3: Classes of Chelicerata -Class Arachnida: scorpions, spiders, mites, ticks, harvestmen. Four pairs of legs; segmented or unsegmented abdomen with or without appendages and generally distinct from cephalothorax; respiration by gills, tracheae, or book lungs; excretion by Malpighian tubules and /or coxal glands; dorsal bi- lobed brain connected to ventral ganglionic mass with nerves, simple eyes; chiefly oviparous; no true metamorphosis. Examples Argiope, Centruroides.

Objective 4: Crustaceans Antennae: are also used for sound and odor communication among animals. Mandibles: The mandible of an arthropod is a pair of mouthparts used for either for biting, cutting and holding food. Mandibles are often simply referred to as jaws. Maxillae: Paired maxillae cut food and manipulate it during mastication. Maxillae can have hairs and "teeth" along their inner margins.

Objective 4: Crustaceans Cephalothorax: an abdomen and a fused head and thorax. Gills: respiratory structures for aquatic organisms which extract oxygen from the water. Rostrum: (beak) A snout like projection on the head of an arthropod. Carapace: A shield like plate covering the cephalothorax of certain crustaceans. Telson: A nonsegmented part of tail fan of arthropods. Uropod: The last abdominal segments which make up the tail fan of arthropods.