Jayson Lab 8: The Arthropods (Part 1) PDF

The Arthropods Lab#8 Introduction to the Arthropods 85% of all metazoans are Arthropods. Defining characteristics: 1. Segmented, jointed, and sclerotized chitinous exoskeleton with musculature between individual joints of appendages 2. Loss of cilia in adults & larvae Ar...

The Arthropods Lab#8 Introduction to the Arthropods 85% of all metazoans are Arthropods. Defining characteristics: 1. Segmented, jointed, and sclerotized chitinous exoskeleton with musculature between individual joints of appendages 2. Loss of cilia in adults & larvae Are metameric (segmented) with new segments that arise during development from a specific budding zone at the rear of the animal. Regions of the body are masked by fusions of segments and modified for specialized features called tagmatization. Have a hard protecting called the cuticle made of chitin. Exoskeleton is secreted over whole body by epidermal cells. Cuticle is water-impermeable which means that it can’t be used for gas exchange. One advantage of this is that Arthropods are highly resistant to dehydration. Cuticle is thin and flexible in certain regions forming joints, in many regions. Introduction to the Arthropods Exoskeleton is shed and regrown, increasing the animal’s size in a process called ecdysis. This process is under hormonal and neural control. In muscles, strength of contractions depend on rate at which nerve impulses are delivered to the fibers. Have striated muscles which allow for contraction faster than smooth muscles. Have an open circulatory system and heart with ostia. Their Vision is possible due to ocelli or compound eyes. Ocelli are light sensitive and not image forming. Compound eyes are image forming. Made up of units called Ommatilda, which give them a wide visual range. Major Arthropod Groups Subphylum Trilobitomorpha Subphylum Crustacea Class Trilobita (trilobites) Class Malacostraca Subphylum Chelicerata Order Isopoda (pillbugs, woodlice) Order Amphipoda (sand fleas) Class Merostomata (horseshoe crabs) Order Euphausiacea (euphausiids/ krill) Class Arachnida (spiders, mites, ticks, Order Stomatopoda (stomatopods) scorpions) Order Decopoda (crabs, lobsters, shrimp, hermit Class Pycnogonida (sea spiders) crabs) Class Branchiopoda (brine/ fairy shrimp, Subphylum Myriapoda clam shrimp, water fleas) Order Chilopoda (centipedes) Class Ostracoda (ostracods) Order Diplopoda (millipedes) Class Copepoda (copepods) Pancrustacea Class Pentastomida Subphylum Hexapoda (Pancrustacea) Class Cirripeda (barnacles) Class Entognatha Class Insecta (Ectognatha) Subphylum Crustacea (next column) Trilobitomorpha Defining characteristics: 2 anterior furrows divide the body into 2 lateral & 1 central region Extinct Flattened dorsoventrally, covered by a carapace Compound eyes with ommatidia Biramous appendages Chelicerata Defining characteristics: 1. Lack antennae 2. Body divided into two tagmata: the prosoma & opisthosoma (no distinct head) 3. First pair of appendages (chelicerae) adapted for feeding Includes the classes merostomata, arachnida, and pycnogonida Chelicerae for biting & shredding food Lack mandibles  Class Merostomata (Horseshoe Crabs) Defining characteristics: 1. Flattened appendages on the opisthosoma, modified into book gills 2. Telson drawn out into elongated spike Prosoma/ cephalothroax covered with a carapace: Composed of chelicerae & 5 pairs of walking legs: first pair are the pedipalps, last pair contain chilaria Opisthosoma: 6 pairs of appendages & book gills Class Pycnogonida (Sea Spiders) Defining characteristics: 1. Body without tagmata 2. Proboscis with opening 3. Varied number of walking legs Ovigers for grooming & carrying eggs Parasitic larvae A: head; B: thorax; C: abdom en 1: proboscis; 2: chelifores; 3: palps; 4: ovigers; 5: egg sacs;  Class Arachnida (spiders, mites, ticks, scorpions) Prosoma & opisthosoma are the tagmata Appendages include chelicerae, pedipalps, maxilla, walking legs Book lungs with spiracles & tracheae Spinnerets in Spiders. Mandibulata vs. Pancrustacea Defining characteristics for Mandibulata subphylum: Mandibles on the third head segment for chewing/ grinding food Retinula of compound eyes: 8 cells Includes subphylums myriapoda, insecta & crustacea Defining Characteristics for Pancrustacea subphylum: Recent Molecular data Morphological characteristics Shows close relationship to myriapoda and chelicerates  New organization Hexapods are a subgroup of Pancrustacea Old Crustacea paraphyletic Many traits shared by Hexapods and Myriapods are convergent Single pair of antennae Tracheal system Mandibulates are a good group Mandibles vs Chelicerate mouthparts New organization – ‘Pancrustacea’  Myriapoda Includes the classes of chilopoda (centipedes) & diplopoda (millipedes) Unwaxed cuticle Lack compound eyes, have ocelli Chilopoda Carnivorous Tracheae with open spiracles Nocturnal to conserve water Repugnatorial glands to discourage predation Diplopoda Detritovores Pairs of segments fuse to have 2 pairs of legs per diplosegment Calcium salts on integument to discourage predation Crustacea Defining characteristics: 1. Head bearing 5 pairs of appendages (including 2 pairs of antennae) 2. Larval form (nauplius) bearing 3 pairs of appendages & medial eye Includes the classes malacostraca, branchiopoda ostracoda, copepoda, pentastomida, & cirripeda Branchiopoda (brine/ fairy shrimp, clam shrimp, water fleas) Coxa (first segment of leg) modified to form a flattened paddle for gas exchange & locomotion Filter feeders Some lack a carapace Microscopic Cirripeda (Barnacles) Defining characteristics: 1. Highly modified to attach to hard substrates (including other animals), or for parasitic life 2. Thoracic limbs modified as filtering cirri 3. Lack abdomen Shell: carina, rostrum, scuta, terga Cirri: feeding appendages Lack abdominal segments, gills, and heart Reduced head for nonmotile lifestyle Malacostraca (Class) Defining characteristics: 1. Thorax with 8 segments, abdomen with 6-7 segments plus a telson 2. Appendages on 6th abdominal segment flattened to form uropods Includes the orders of decapods, euphausiids, stomatopods, isopods, and amphipods Head, thorax, abdomen Rostrum – a beaklike projection on the anterior of the head Compound eyes Antennae, mandibles, maxillae, maxillipeds, walking legs (pereopods), uropods Chromatophores Cambarus sp.- A Malacostraca Cambarus sp.- A Malacostraca External Anatomy Internal Anatomy Identifying the Sex of a Crayfish