Phylum Arthropoda “arthro” = jointed “pod” = foot, appendage largest phylum of animals on Earth; 3 of 4 animals are some kind of arthropod chitinous exoskelton grow by molting exoskelton Most are small because shell limits size Somites fused or combined into functional groups or tagmata Most common arthropods are insects (on land) and crustaceans (in the ocean)

Why have arthropods achieved such great diversity and abundance? Versatile exoskeleton Segmentation and efficient locomotory appendages Efficient tracheal respiratory system Highly developed sensory organs Complex behavior patterns Reduced competition through metamorphosis

Figure 13_02

Ecdysis – process of an arthropod shedding its exoskeleton for reasons of growth and repair of injuries “soft-shelled crab”

Figure 13_03

Figure 13_04

Subphylum Crustacea                                                           Great variety of forms; most familiar are shrimp, crabs, lobster 2 pair of antennae, calcified exoskeleton, gills Some freshwater, but most are marine

Less familiar groups of crustaceans Copepods – abundant as zooplankton; use enlarged antennae for limited movement

Less familiar groups of crustaceans Barnacles – sessile filter feeders attach to any number of hard surfaces filter using feathery cirri Surrounded by plates forming a shell

Less familiar groups of crustaceans Amphipods – laterally compressed body Small; slightly larger than rice grain Many found on beaches in seaweed

Less familiar groups of crustaceans Isopods – dorsoventrally flattened Variable in size from rice to shoebox One kind eats wood (gribble), another is parasitic (fish lice)

Deep sea isopod – “big”                                                                   

Less familiar groups of crustaceans Krill – planktonic and shrimp-like up to about 2 inches long primarily in polar waters important food source for many whales, penguins, and fish

Decapods – “10 legs” shrimps, lobsters, crabs; largest group of crustaceans in numbers and physical size first pairs of legs usually claws shrimps typically scavengers; many are symbionts as cleaners with fish and anemones lobsters are mainly nocturnal and are either scavengers or predators of molluscs hermit crabs use snail shells to protect soft abdomen True crabs with abdomen tucked under shell; scavengers or predators; swimming crabs vs. walking crabs

Red-banded coral shrimp

Penaeid shrimp – “eatin’ shrimp”

male female

Giant hermit crab

Subphylum Trilobita Extinct for about 200 million years Larval horseshoe crabs closely resemble trilobites

Subphylum Chelicerata Ancient group; horseshoe crabs, sea spiders, spiders, ticks, scorpions Two tagmata (carapace and abdomen) Six pairs of appendages; 1 pair chelicerae, 1 pair pedipalps, 4 pairs of walking legs No mandibles or antennae Most suck liquified contents of prey

Class Merostomata horseshoe crabs only extant members of this group widespread; mainly found in shallow waters with soft bottoms forage in mud for worms or scavenge Possess a protective carapace and long spinelike telson Abdomen possesses layered book gills

Class Arachnida Possess six pairs of appendages, the most anterior of which are the chelicerae (fangs in spiders) Spiders with cephalothorax and abdomen unsegmented and connected by slender pedicel; possess poison and spin silk; have book lungs Scorpions with short cephalothorax that bears the appendages and a segmented abdomen ending in a stinging apparatus Ticks and mites with fused cephalothorax and abdomen; most abundant arachnids; many are disease vectors and plant pests

Scorpion Dust mite Web-building spider 50 µm Fig. 33-31 Figure 33.31 Arachnids Web-building spider

Stomach Intestine Heart Brain Digestive gland Eyes Ovary Poison gland Fig. 33-32 Stomach Intestine Heart Brain Digestive gland Eyes Ovary Poison gland Figure 33.32 Anatomy of a spider Book lung Anus Gonopore (exit for eggs) Chelicera Pedipalp Spinnerets Sperm receptacle Silk gland

Subphyla Myriapoda and Hexapoda (formerly Uniramia) The myriapods include centipedes and millipedes The hexapods include the insects

Subphylum Myriapoda The myriapods pods consist of a head and an elongated, segmented trunk Possess many uniramous appendages Single pair of antennae, mandibles, and one or two pair of maxillae Consists of the Classes Chilopoda (centipedes) and Diplopoda (millipedes)

Class Chilopoda - Centipedes Centipedes are active predators with fangs that inject venom Possess one pair of appendages per segment Prefer hiding under logs or rocks in moist environments

Class Diplopoda - millipedes Harmless and herbivorous or detritivorous, prefer same environments as centipedes Possess two pair of legs per trunk segment For defense may release toxic fumes or taste bad

Insects Subphylum Hexapoda, insects and relatives, has more species than all other forms of life combined They live in almost every terrestrial habitat and in fresh water The internal anatomy of an insect includes several complex organ systems

Abdomen Thorax Head Compound eye Antennae Heart Cerebral ganglion Fig. 33-35 Abdomen Thorax Head Compound eye Antennae Heart Cerebral ganglion Dorsal artery Crop Anus Vagina Figure 33.35 Anatomy of a grasshopper, an insect Malpighian tubules Ovary Tracheal tubes Mouthparts Nerve cords

Insects diversified several times following the evolution of flight, adaptation to feeding on gymnosperms, and the expansion of angiosperms Insect and plant diversity declined during the Cretaceous extinction, but have been increasing in the 65 million years since

Flight is one key to the great success of insects An animal that can fly can escape predators, find food, and disperse to new habitats much faster than organisms that can only crawl

Many insects undergo metamorphosis during their development In hemimetabolous (incomplete) metamorphosis, the young, called nymphs, resemble adults but are smaller and go through a series of molts until they reach full size

Insects with holometabolous (complete) metamorphosis have larval stages known by such names as maggot, grub, or caterpillar The larval stage looks entirely different from the adult stage

(a) Larva (caterpillar) (b) Pupa (c) Later-stage pupa (d) Emerging Fig. 33-36 (a) Larva (caterpillar) (b) Pupa (c) Later-stage pupa Figure 33.36 Metamorphosis of a butterfly (d) Emerging adult (e) Adult

Most insects have separate males and females and reproduce sexually Individuals find and recognize members of their own species by bright colors, sound, or odors Some insects are beneficial as pollinators, while others are harmful as carriers of diseases, or pests of crops Insects are classified into more than 30 orders

Fig. 33-37a Figure 33.37 Insect diversity

Fig. 33-37b Figure 33.37 Insect diversity

Fig. 33-37c Figure 33.37 Insect diversity

Fig. 33-37d Figure 33.37 Insect diversity

Fig. 33-37e Figure 33.37 Insect diversity