Phylum Arthropoda: the Arthropods Arthropoda: Major Taxonomic Groups (Part II) Subphylum Chelicerata Class Merostomata (Horseshoe Crabs) Class Arachnida (Spiders, Mites, Ticks, Scorpions, Allies) Subphylum Crustacea Class Malacostraca (Shrimp, Crabs, Lobsters, Crayfish) Class Branchiopoda (Brine Shrimp, Cladocerans) Class Maxillopoda (Copepods and Barnacles) Subphylum Myriapoda Chapter 15 Class Diplopoda (Millipedes) Class Chilopoda (Centipedes) Subphylum Hexapoda Class Insecta (Insects)
Myriapoda, Class Diplopoda: Subphylum Myriapoda: Millipedes Millipedes, Centipedes, & Allies Usually 30 or more pairs of legs, 2 pairs per segment ~13,000 species Results from fusion of adjacent pairs of body segments during development All are terrestrial Body usually round in cross section Carnivorous (centipedes) Mandibles modified for chewing or herbivorous (remaining Many have repugnatorial glands that produce a foul- groups) smelling liquid for defense Two body regions ( head Often found in leaf litter or under decaying logs or other and trunk ) objects Slow-moving; diurnal or nocturnal Single pair of antennae Dioecious; females lay eggs Mandibles Males may transfer sperm via spermatophores or by 10 to >750 pairs of legs gonopods
1 Myriapoda, Class Chilopoda: Centipedes
Usually 15 or more pairs of legs, 1 pair per segment Body usually flattened in cross section First pair of appendages modified into forcipules , or poison claws Range in size from <5 mm to >30 cm Found in leaf litter and under debris House centipedes often found inside buildings Fast-moving; nocturnal Dioecious; females may brood eggs and young Males produce a spermatophore
2 Above left is a symphylan and above right are several pauropods, both representatives of smaller groups of myriapods. Symphylans and pauropods are small but often common members of the soil community.
Subphylum Hexapoda: Insects and Relatives >1 million describes species; estimates of 5-30 million total >60% of all animal species Most are terrestrial, but some are aquatic Many species are aquatic as juveniles and terrestrial as adults Three body regions: head , thorax , and abdomen Mandibulate mouthparts, often heavily modified May be carnivores, herbivores, omnivores, or parasites Three pairs of legs on thorax One pair of antennae Many have wings
3 Class Insecta: Flight
Insects are first animals to develop flight Allows them to (a) move more easily to new areas, (b) exploit new food sources, (c) escape predators more easily Wings have thickened, hollow veins for strength and for Clockwise from above left are nutrient transport to wings collembolans (springtails), a dipluran, and a proturan. All are Most can fold wings over the back small soil-dwelling hexapods, the Exceptions are mayflies (Order Ephemeroptera) and latter two lacking eyes and dragonflies and damselflies (Order Odonata) proturans lacking antennae. All are Many are very maneuverable, and some can hover referred to as entognathous, because their mouthparts emerge Wings may be modified (ex: forewings in beetles), from the front of the head rather reduced (ex: hind wings in flies), or absent than the ventral side as in insects. Wings occur only in adults
Insecta: Types of Flight Direct or synchronous flight – muscles attached to wings contract for downward thrust One nervous impulse per wing beat Butterflies, dragonflies, and grasshoppers Indirect or asynchronous flight – muscles change the shape of the exoskeleton to create thrust One nervous impulse for several wing beats Flies, beetles, and wasps Indirect flight muscles allow much faster wing beat frequency than do direct flight muscles
4 Insecta: Appendages Insects may walk, run, jump, swim, burrow, or skate on water surface Because of this, many have highly modified limbs Legs may also be modified for catching prey, such as raptorial legs in mantids
Insecta: Feeding and Digestion Four types of mouthparts: labrum ; mandibles ; maxillae ; labium Basic biting mouthparts may be heavily modified for chewing, piercing, licking (sponging), or sucking Long, straight digestive system typical of all arthropods Foregut (muscular pharnyx and crop), midgut (site of digestion and absorption), and hindgut (intestine, reabsorbs water) Foregut and hindgut are lined with cuticle, which is shed during molting Typical biting mouthparts, from a grasshopper
5 Insecta: Gas Exchange
Tracheae are branched chitin-lined tubes that open to the outside via spiracles They are most branched in metabolically active tissue (e.g., flight muscles)
Most insects have methods for ventilating the gills tracheae in order to move air May use muscle contractions or create biochemical vacuums Aquatic insects have gills or diffuse gas across body walls (some carry bubbles underwater)
6 Insecta: Circulation and Excretion Circulatory system similar to other arthropods but less developed (blood not used in gas exchange) Circulatory fluid called hemolymph Gases carried dissolved in hemolymph Some insects (e.g., moths) generate heat by rapid contraction of flight muscles (shivering thermogenesis ) Excrete uric acid via Malpighian tubules (like spiders)
Insecta: Nervous System Similar in structure to nervous system of annelids and other arthropods Many have two enlarged ganglia in head: the brain and the subesophageal ganglion Subesophageal ganglion is associated with sensory organs tied to the mouthparts Segmental ganglia occur along the ventral nerve cord Some insects are capable of learning and memory
7 Insecta: Sensory Organs
Excellent chemoreceptors and touch ocelli receptors (numerous hair-like setae)
Many insects can hear with Johnston’s Compound eye organs (at base of antennae) or tympanal organs (in legs, abdomen, or thorax) Light-detecting organs include ocelli (for light/dark perception) and compound eyes (used for forming images)
In the katydid at right, the tympani are on the legs. In the grasshopper below left, it’s on the side of the abdomen. In the parasitic fly Ormia below right, the tympani are on the anterior thorax.
8 Insecta: Chemical Regulation Insecta: Reproduction Like other arthropods, insects have endocrine glands that release hormones Most have complex mating behaviors which control many biological processes and internal fertilization Some examples are molting, growth, Pheromones (e.g., moths), visual reproduction, alarm signaling signals (e.g., fireflies), or auditory Pheromones are released chemicals that cause behavioral changes in other signals (e.g., cicadas) may be individuals involved in male courtship displays Sex pheromones attract mates Females of many species deposit Alarm pheromones warn others of eggs with an ovipositor danger
Ametabolous Development
Immature stages look like small adults; no metamorphosis Only change is development of adult reproductive structures Found only in the more primitive wingless hexapods
9 Holometabolous Development Hemimetabolous Development Immature stages ( larvae ) Immature stages do not resemble adults Larvae often worm- or (nymphs ) look grub-like, often missing generally like legs, antennae, or other small adults adult parts Prior to reaching As juveniles age, adulthood, larvae go through a “resting” stage they develop adult called a pupa reproductive Pupa often, but not structures and always, encased in a wings cocoon Inside pupa, larva is This is sometimes retransformed into the called simple adult form This process is called metamorphosis complete metamorphosis
Insecta: Social Insects Eusocial Ants
Certain insects (some bees and wasps; all ants and termites) have highly developed social systems Referred to as eusocial insects Individuals form large colonies, almost entirely female, with castes , or division of labor One or perhaps a few individuals can breed; these are the queens Remaining females are sterile, and may be workers , soldiers , foragers Males are called drones , and functionally primarily in mating Colony acts as a “superorganism” Evolutionary origin has caused much debate
10 Eusocial Bees & Eusocial Termites wasps
Insecta: Major Insects and Humans Orders Insects are both enormously beneficial and Order Blattaria – costly to humans cockroaches Order Hemiptera – “true” They are essential to many ecological functions bugs, cicadas, aphids Food web dynamics Pollination of plants Order Isoptera – termites Soil aeration and decay processes Order Odonata - They produce products humans use (honey, silk, dragonflies, damselflies wax) Order Orthoptera - grasshoppers, crickets, Some cause damage to crops and livestock while katydids others help prevent this damage Order Ephemeroptera - Some spread diseases (e.g., mosquitoes) mayflies
11 Insecta: Major Arthropoda: Evolutionary Orders Relationships Order Coleoptera – beetles There is Order Diptera – flies currently a lot Order Hymenoptera - of debate and ants, bees, wasps disagreement Order Lepidoptera - about the moths, butterflies relationships Order Siphonaptera – among the fleas various Order Neuroptera – subphyla of lacewings & allies arthropods
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