The Hexapods and Myriapods: Terrestrial Triumphs Chapter 15 Zoology

The Insects 750,000 + species insects described, but may be 30 million species undescribed. Many adaptations make insects one of the most successful terrestrial animals. Exoskeleton for water conservation Tracheal System for gas exchange Metamorphosis Many types of mouth parts Flight

Subphylum Myriapoda Myriad, ten thousand + podus, foot; millipedes and centipedes. Two tagmata (head and trunk) All are terrestrial

Class Diplopoda – The Millipedes Have 11 – 100 trunk segments, each with two pairs of appendages. Each segment is actually the fusion of two segments; internally there are two ganglia, two pairs of ostia, etc. in each segment. Most are round. Feed on decaying plant matter. Roll into a ball for defense. Some excrete hydrogen cyanide as a deterrent to predators.

Giant African Millipede See it move!

Class Chilopoda – The Centipedes 15+ trunk segments, each with a pair of legs. Flattened body Last pair of legs is modified into long sensory appendages. Nocturnal predators Poison claws (maxillipeds) on first segment capture other invertebrates and small vertebrates. Males lay down a silk web and places a spermatophore for female.

Predatory Centipede vs. Mouse

Subphylum Hexapoda Class Insecta three tagmata (head, thorax, and abdomen) Five pair of head appendages Three pairs of legs on thorax

Fig. 20.8

Fig. 20.4a

Specialized Mouthparts Modified mouthparts have allowed insects to diversify and take advantage of many different food sources. Modify generic structures for various food sources. Generalized Insect Mouthparts

Fig. 20.19a Chewing Mouthparts

Fig. 20.19b Piercing Mouthparts

Fig. 20.19d Siphoning Mouthparts

Fig. 20.19e Sponging Mouthparts

Antennae Modifications Fig. 20.5

Insect Flight Direct or Synchronous Flight – muscles attach at the base of wings contract for downward thrust and muscles attach to the exoskeleton contract for upward thrust. Requires two nerve impulses for upward and downward strokes. Ex. Butterflies, dragonflies, grasshoppers. Indirect or Asynchronous Flight – muscles act to change the shape of the exoskeleton for both strokes. Only one nerve impulse for 50 cycles. Ex. Flies and wasps.

Indirect Insect Flight Indirect flight muscles allow wings to beat faster than neural transmission. Dorsoventral and longitudinal muscles. Flexible thorax.

Review of Insect Physiology Digestion – three part tract. Respiration – most use a tracheal system Circulation – open circulatory system Nervous – ventral nerve cord with some segmental ganglion. Excretion – Malpighian tubules with uric acid.

Fig. 20.14

Fig. 20.Fig. 20a

Fig. 20.Fig. 20b

Tracheal Systems in Insects The tracheal system of insects Consists of tiny branching tubes that penetrate the body Tracheae Air sacs Spiracle (a) The respiratory system of an insect consists of branched internal tubes that deliver air directly to body cells. Rings of chitin reinforce the largest tubes, called tracheae, keeping them from collapsing. Enlarged portions of tracheae form air sacs near organs that require a large supply of oxygen. Air enters the tracheae through openings called spiracles on the insect’s body surface and passes into smaller tubes called tracheoles. The tracheoles are closed and contain fluid (blue-gray). When the animal is active and is using more O2, most of the fluid is withdrawn into the body. This increases the surface area of air in contact with cells.

The tracheal tubes Supply O2 directly to body cells. Body cell Air sac Tracheole Tracheoles Mitochondria Myofibrils Body wall (b) This micrograph shows cross sections of tracheoles in a tiny piece of insect flight muscle (TEM). Each of the numerous mitochondria in the muscle cells lies within about 5 µm of a tracheole. 2.5 µm Air

Tracheal System Limits Size See the Giant Weta

Copyright © The McGraw-Hill Companies, Inc Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Insect Excretion

3 Kinds of Insect Metamorphosis Ametabolous Metamorphosis – only difference between larvae and adult are size; both are wingless. Silverfish, Order Thysanura. After Flight… Hemimetabolous Metamorphosis – develop from egg to adult has several stages (instars) with smaller versions of adults called nymphs. Immature nymphs have no wings or genitalia until adult.

3 Kinds of Insect Metamorphosis Holometabolous Metamorphosis – after hatching from egg, immatures are called larvae (very different body form than adult). After several instars, the last larval molt forms a pupa – undergoes radical body form change. Protective case may enclose pupal stage: Moths use silk to make a cocoon. Butterflies use the larval exoskeleton to make a chrysalis. Adult emerges from case very different in body form – eclosion.

Incomplete or Hemimetabolous Metamorphosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Incomplete or Hemimetabolous Metamorphosis From Hickman/Roberts/Larson, Integrated Principles of Zoology, 11th ed., Copyright © 2001 The McGraw-Hill Companies.

Complete or Holometabolous Metamorphosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Complete or Holometabolous Metamorphosis From Raven/Johnson, Biology, 3rd ed., Copyright © 1999 The McGraw-Hill Companies.

You Decide? Fig. 20.24

Hemimetabolous - insects hatch looking much like adults Hemimetabolous - insects hatch looking much like adults. Nymphs gradually attain adult form and wings. Holometabolous - young very different from adults. Pupal stage metamorhosis into adult.

Insect Orders

Order Collembela Antennae with 4-6 segements No compound eyes Six segments in abdomen Furcula for jumping No wings Springtails

Order Thysanura Tapering abdomen Long antennae, scaled on body No wings Silverfish

Order Odonota Elongate, membraneous wings. Long, slender abdomen Large compound eyes Dragonflies,damselflies

Order Mantodea Long prothorax Legs armed with spine for grasping prey Mantids Missouri Native –Chinese mantis, Tenodera aridifolia

Blattaria Oval, flattened body Head concealed by an extension of prothorax Cockroaches

Order Orthoptera Long, narrow forewing Hindwing is broader Chewing mouthparts Grasshopper

Order Dermaptera Elongate, chewing pouthparts Abdomen with unsegmented forcepslike cerci Short wings Earwigs

Order Isoptera Workers are white and wingless Abdomen broadly joins thorax Reproductive forms with wings Termites

Order Hemiptera Cicadas, leafhoppers, aphids Piercing-sucking mouthparts Wings membraneous Basal portion is leathery Apical portion of wing is membranous Cicadas, leafhoppers, aphids

Order Coleoptera Hard front wings meet midline to form a cover (elytra) Hindwings membranous Chewing mouthparts Beetles, largest insect order; 350,000+ species

Order Lepidoptera Wings are broad and covered in scales Mouthparts form a sucking tube Butterflies and moths

Order Diptera One pair of well-developed wings, other pair reduced to knoblike halteres Mouthparts variously modified, but never chewing. Flies

Order Hymenoptera Four membranous wings Well-developed ovipositor,sometimes modified into a sting Mouthparts for biting and lapping. Social and solitary forms Bees, wasps, ants

Order Phthiraptera Small, wingless, ectoparasites Dorsoventrally flattened Sucking/chewing mouth parts Lice

Order Siphonaptera Flattened laterally Sucking mouthparts, ectoparasites Jumping legs Fleas

The End What order am I?