2Arthropod Taxonomy: Overview The arthropods evolved along four main lines, which most zoologists recognize as 4 distinct subphyla1. Trilobita - extinct trilobites2. Chelicerata - horseshoe crabs, spiders, ticks, mites, and some extinct groups3. Crustacea - crabs, lobsters, shrimps, barnacles4. Uniramia - insects, centipedes, millipedes
3Arthropod Respiratory Advances Special respiratory structures allow the arthropods to metabolize more efficiently and thus move rapidlyHigh metabolic rates require rapid oxygen delivery, and arthropods can accomplish this with respiratory organs that have a large surface area for collecting oxygen quickly
4Structure of the Exoskeleton Composed of the polysaccharide chitin and protein – glycoproteinSecreted by the HypodermisOuter surface called the epicuticle; contains waxesThe thicker portion is called the procuticle:exocuticleendocuticle
6MoltingIn order to grow the arthropod must shed its exoskeleton, and secrete a new and larger one - molting or ecdysis.
7Jointed AppendagesExoskeleton divided into a number of plates and cylindersAt the junction point between plates and cylinders, the exoskeleton remains thin and flexible; these are the jointsJointed appendages allows arthropods to move efficiently and quicklyMuscles are integral to arthropod movement; they attach to the inner side of the exoskeleton; they often function as a lever systemArthropod jointVertebrate joint
8Specialized Arthropod Segments: Reduction in Metamerism The evolution of the arthropods witnessed a reduction in metamerismThe arthropods evolved modified groups of segments (e.g., segments became lost, some fused togetherThe fusion of groups of segments into functional groups is called tagmatizationIn so doing, various appendages on segments became specialized for functions other than locomotion, e.g. prey capture, filter feeding, sensing various kinds of stimuli, gas exchange, copulation, etc.
9TracheaeGas exchange organs among terrestrial arthropods is usually internal; invaginations of the integumentInsects have tracheae, branching networks of hollow air conducting tubes such that air is sent to every cell in every tissue
10Acute SensesArthropods have a well-developed nervous system that is of the same overall design as the annelids; anterior brain and a double, ventral hollow nerve cord.The sensory receptors of arthropods are usually associated with modifications of the chitinous exoskeletonThe head usually bears various kinds of sense organs (e.g. antennae) with extreme sensitivity
11Acute Senses cont.Many arthropods have compound eyes - eyes that are composed of many visual units called facets (ommatidia); capable of color vision and detecting the slightest movements of prey or predatorsSome eyes are simple eyes with only a few photoreceptors; however, they are capable of forming crude images
12Reproduction Circulatory System Dioecious; fertilization is external in aquatic forms, internal among the terrestrial forms. Most are oviparous (external development of young from eggs)Circulatory SystemOpen circulatory system
14Subphylum Trilobita A group of extinct marine arthropods. Ranged in size from a few millimeters up to 75 centimeters.Body divided into three longitudinal regions:Compound eye, composed of radially arranged visual unitsThey would have curled up like a woodlouse for protection against predators.Two-lobed appendages
15Subphylum Chelicerata Lack antennaeBody is usually composed of two regions: cephalothorax (prosoma) and abdomenCephalothorax is usually covered dorsally by the carapaceSix pairs of appendages: first pair are modified feeding structures - cheliceraeSecond pair are called pedipalpsFour additional pairs of appendages are walking legsNo abdominal appendagesSome have compound eyes, usually have simple eyes capable of forming crude images.
16Class Meristomata (e.g., Horeshoe crabs) Marine chelicerates, common off of the Atlantic and Gulf coastsLarge dorsal carapace bearing compound eyesPossess chelicerae, pedipalps, and 4 pair of walking legs (all but the last pair are chelateAbdomen terminates in a long tail called the telson; used to turn the animal right side upPossess a series of gill plates called book gills
18Class ArachnidaRespiration is accomplished via book lungs, tracheae, or bothMost are harmless or very beneficial to humansUsually have 8 simple eyes; at the very least they detect motion; for some of the predatory forms, they are capable of forming crude imagesMany species have evolved poison glands associated with the cheliceraeUsually food is PREDIGESTEDBlack widowBrown recluse
19ORDER SCORPIONIDA (Scorpions) About 2000 species worldwide. Nocturnal animals, all relatively large. Associated with deserts, but also common in tropics.Fluoresce under UV light.Small cheliceraTwo segments, prosoma and opisthosomaMost stings are harmless, similar to a wasp
23ORDER Araneae (Spiders) Largest Group of Arachnids. Eight-eyed!Prosoma have chelicerae with large fangs and poison glandsPedipalps are leg-like; in males modified for sperm transferCephalothorax and abdomen shows no external segmentation; tagma are joined by a narrow pedicel
25Respiration and Circulation Arachnids have book lungs, chambers with leaf-like plates for exchanging gases; air flows over the plates and blood flows through themBlood contains hemocyanin and has ameoboid cells that are similar to human immune cells and platelets
26Prey capture among the spiders Some species are cursorial predators, those that stalk and ambush their prey; they usually have well-developed eyesJumping spiderOthers are web building spiders, those that construct various kinds of webs made of silk to trap their preyEyes are not as well developed as cursorial predators, but they have a battery of sensory hairs for detecting vibrationsGrass spider
27Sensory StructuresMost spiders are predaceous and have all kinds of sensory hairs and relatively well-developed eyes for motion detection; chemoreceptors are also used
32Other Relatives Class Acarina – Ticks and Mites Herbivores, scavengers or ectoparasitesCan transmit diseaseClass Pycnogonida – Sea SpidersMales protect the young, “stuck together”
33Class MalacostracaPossess 2 pair of antennae: First pair is homologous to those of insects; second pair is unique to the crustaceansSecond antennae have various functions, including sensory, locomotion or feeding.The head bears a pair of compound eyes and 3 pairs of mouthparts: a pair of mandibles (chewing/grinding) and 2 pairs of maxillae (food handling)Primitively, the first three pairs of thoracic segments are maxillipeds; (handling food/sensory)Also, there are usually 5 pairs of appendages strengthened for walking (walking legs) and protection (chelipeds, pincer-like claws)
34Abdomen is also highly variable, but it is primitively large SubPhylum Crustacea cont.Abdomen is also highly variable, but it is primitively largeGroups with a well-developed abdomen usually possess six pairs of appendages: Five pairs of structures called swimmerets (=pleopods); one pair of structures called uropods,Uropods together with the terminal telson form a tail fan than can serve as rudders during locomotion
35GillsMany aquatic arthropods (crabs and lobsters) have gills, which are typically modifications of appendages or outgrowths of the body wall - folds of tissue with a large surface area
36Sensory StructuresCompound eyes on moveable eyestalksCrayfish have statocysts present for balanceTactile receptors on the appendages and at jointsMouthparts and Antennae lined with chemoreceptors (setae)ReproductionMale turns female on back and deposits sperm; after fertilization, eggs are shed; they are sticky and attach to the pleopods
37SubPhylum Crustacea cont. Primitively many of the appendages of the crustaceans are biramous: there is an outer exopod and an inner endopodThey usually have an extremely hardened exoskeleton, which is impregnated with calcium carbonate - carapace
38The primitive larva of the crustaceans is called the nauplius larva SubPhylum Crustacea cont.The primitive larva of the crustaceans is called the nauplius larvaIt has an unsegmented body, a frontal eye, and 3 pairs of appendages, representing the 2 pairs of antennae and the mandiblesCrabs and their relatives have a second larval stage called a zoea. They have Postlarva is a sexually immature miniadult.
39Crustacean Diversity Ostracod Water flea Copepod Fairy shrimp Fish louse
40Barnacles are Crustaceans! The only members of this class that are monoecious