1. Section 28.1 Summary – pages 741 - 746
What is an arthropod?
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.
Section 28.1 Summary – pages

2. Section 28.1 Summary – pages 741 - 746
What is an arthropod?
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.
Section 28.1 Summary – pages

3. Section 28.1 Summary – pages 741 - 746
Arthropod exoskeletons provide protection
The exoskeleton is a hard, thick, outer covering made of protein and chitin (KI tun).
Section 28.1 Summary – pages

4. Section 28.1 Summary – pages 741 - 746
Arthropod exoskeletons provide protection
The exoskeleton protects and supports internal tissues and provides places for attachment of muscles.
In many aquatic species, the exoskeletons are reinforced with calcium carbonate.
Section 28.1 Summary – pages

5. Section 28.1 Summary – pages 741 - 746
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

6. Section 28.1 Summary – pages 741 - 746
Why arthropods must molt
Most arthropods molt four to seven times in their lives before they become adults.
When the new exoskeleton is soft, arthropods cannot protect themselves from danger because they move by bracing muscles against the rigid exoskeleton.
Section 28.1 Summary – pages

7. Section 28.1 Summary – pages 741 - 746
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

8. Section 28.1 Summary – pages 741 - 746
Segmentation in arthropods
In other groups, even these segments may be fused.
Some arthropods have a head and a fused thorax and abdomen.
Section 28.1 Summary – pages

9. Section 28.1 Summary – pages 741 - 746
Segmentation in arthropods
In other groups, there is an abdomen and a fused head and thorax called a cephalothorax.
Fusion of the body segments is related to movement and protection.
Section 28.1 Summary – pages

10. Section 28.1 Summary – pages 741 - 746
Arthropods have efficient gas exchange
Three types of respiratory structures have evolved in arthropods: gills, tracheal tubes, and book lungs.
Section 28.1 Summary – pages

11. Section 28.1 Summary – pages 741 - 746
Arthropods have efficient gas exchange
Most insects have tracheal tubes, branching networks of hollow air passages that carry air throughout the body.
Section 28.1 Summary – pages

12. Section 28.1 Summary – pages 741 - 746
Arthropods have efficient gas exchange
Muscle activity helps pump the air through the tracheal tubes.
Air enters and leaves the tracheal tubes through openings on the thorax and abdomen called spiracles.
Section 28.1 Summary – pages

13. Section 28.1 Summary – pages 741 - 746
Arthropods have efficient gas exchange
Most spiders and their relatives have book lungs, air-filled chambers that contain leaflike plates.
Section 28.1 Summary – pages

14. Section 28.1 Summary – pages 741 - 746
Arthropods have efficient gas exchange
The stacked plates of a book lung are arranged like pages of a book.
Section 28.1 Summary – pages

15. Section 28.1 Summary – pages 741 - 746
Arthropods have acute senses
Antennae are also used for sound and odor communication among animals.
Section 28.1 Summary – pages

16. Section 28.1 Summary – pages 741 - 746
Arthropods have acute senses
Have you ever watched as a group of ants carried home a small piece of food?
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

17. Section 28.1 Summary – pages 741 - 746
Arthropods have acute senses
Antennae sense the odors of pheromones.
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.
Section 28.1 Summary – pages

18. Section 28.1 Summary – pages 741 - 746
Arthropods have acute senses
A compound eye is a visual structure with many lenses.
Section 28.1 Summary – pages

19. Section 28.1 Summary – pages 741 - 746
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

20. Section 28.1 Summary – pages 741 - 746
Arthropods have other complex body systems
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.
Section 28.1 Summary – pages

21. Section 28.1 Summary – pages 741 - 746
Arthropods have other complex body systems
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.
Section 28.1 Summary – pages

22. Section 28.1 Summary – pages 741 - 746
Arthropods have other complex body systems
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.
Section 28.1 Summary – pages

23. Section 28.1 Summary – pages 741 - 746
Arthropods reproduce sexually
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.
Section 28.1 Summary – pages

24. Section 28.1 Summary – pages 741 - 746
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.
Section 28.1 Summary – pages

25. 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.

26. Objective 2: Subphylums for Arthropods
-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.
-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

27. 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.

28. 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.

29. 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.

30. 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.

31. 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.