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Blueprint for Success Chapter 14 and 15 Modified segmentation – body regions specialized for specific functions (tagmatization). Chitinous exoskeleton used for support and protection Paired, jointed appendages Growth accompanied by molting (ecdysis) Ventral nervous system Reduced coelom Open circulatory system where blood is released into tissue spaces (hemocoel) Complete digestive tract Metamorphosis often present Successful in almost all habitats on the earth. Most abundant animals – Several million species identified o 30 to 50 million species may yet be undescribed Triploblastic, protostome development Exhibit bilateral symmetry Four aspects contribute to arthropod success. o 1. Metamerism o 2. Exoskeleton o 3. The Hemocoel o 4. Metamorphosis Segmentation, most evident externally Each external segment bears a pair of appendages Body cavity not divided internally Permits the specialization of regions of the body for specific functions Regional specialization = Tagmatization o Body regions (tagmata) specialized for: feeding, sensory perception, locomotion, visceral functions. External, jointed skeleton which encloses arthropods Provides support, protection, and prevents water loss System of levers for muscle attachment and movement Secreted by epidermal cells o Epidermis covered by exoskeleton on outside Consists of two layers: o 1. Epicuticle = outermost, waxy lipoprotein layer o 2. Procuticle/Endocuticle = bulky inner layer made of chitin Hardening of the procuticle provides armor-like protection Modifications of the exoskeleton o Formation of joints o Sensory receptors (bristles, lenses, etc) o Gas exchange Must be periodically shed for growth (ecdysis) Epicuticle and Procuticle: epicuticle exocuticle procuticle endocuticle epidermis Provides an internal cavity for the open circulatory system of arthropods Allows for the exchange of nutrients, wastes, and (sometimes) gases Indirect development, a significant change in physiology as the immature form becomes an adult Reduces competition between adults and immature stages Evolution of arthropods has resulted in an increasing divergence of body forms, behaviors, and habitats between immature and adult stages. o Ex: Larval crabs feed on plankton, adult crabs prowl sandy bottoms for live prey. o Ex: Caterpillar feeds on leafy vegetables, adult butterfly feeds on nectar from flowers. Examples: o Crayfish, crabs, lobster, shrimp, barnacles and copepods. Two unique characteristics: o 1. Two pairs of antennae o 2. Biramous appendages Five classes of crustaceans and numerous orders o Class Malacostraca** o Class Maxillopoda** o Class Branchiopoda o Class Remipedia o Class Cephalocarida “Soft Shell” Largest class of crustaceans: o crabs, lobsters, crayfish, shrimp, krill, isopods Body divided into two regions o 1. Cephalothorax (fusion of sensory/feeding and locomotion tagmata) o 2. Abdomen (a muscular tail) Paired, biramous appendages in both body regions Appendages on Cephalothorax: o Pairs 1 and 2 – Antennae (TWO pairs!) o Pairs 3 through 5 – Mouth appendages • Mandible Pair (Chewing) • Maxillae (Food handling) o Pairs 6 through 8 – Maxillipeds • Accessory sensory and food handling appendages o Pairs 9 through 13 – Pereopods (Walking legs) • Cheliped (Pincher-like) Appendages on Abdomen o Pleopods (Swimmerets) o Telson used Reproduction All crustaceans are dioecious Mating occurs after molting of the female In females, developing eggs attach to pleopods and are brooded until hatached In males, pleopods are modified into claspers and used for sperm transfer Crayfish have direct development Feeding Predators, herbivores, scavengers Foregut includes an enlarged stomach, specialized for grinding Midgut = “intestine” Short hindgut ends in anus and used for water and salt regulation Gas Exchange & Circulation Gills in gill chamber o Between the carapace and body wall Muscular Heart Dorsal, anterior, and posterior arteries empty into sinuses of hemocoel Sensory & Regulation Ventral nervous system Compound eyes Crayfish: Excretion organs are called “green glands” Other crustaceans: maxillary glands Includes Barnacles and Copepods Copepods are most abundant crustacean o Marine and Freshwater Barnacles are sessile o Marine only o Most monoecious o Attach to various substrates o Some are parasitic