Phylum Arthropoda Blueprint for Success Chapter 14 and

Phylum Arthropoda: Blueprint for Success Chapter 14 and 15

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Characteristics of Arthropods Modified segmentation – body regions specialized for specific functions (tagmatization). Chitinous exoskeleton used for support and protection Paired, jointed appendages Growth accompanied by molting (ecdysis)

Characteristics of Arthropods Ventral nervous system Reduced coelom Open circulatory system where blood is released into tissue spaces (hemocoel) Complete digestive tract Metamorphosis often present

Arthropods 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 http: //www. backyardnature. net/arthropd. htm

Metamerism 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.

The Exoskeleton 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

The Exoskeleton 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)

The Exoskeleton Epicuticle and Procuticle: epicuticle exocuticle procuticle endocuticle epidermis

The Hemocoel Provides an internal cavity for the open circulatory system of arthropods Allows for the exchange of nutrients, wastes, and (sometimes) gases

Metamorphosis Indirect metamorphosis a significant change in physiology as the immature form becomes an adult Reduces competition between adults and immature stages

Metamorphosis 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.

Indirect

Subphylum Trilobitomorpha- Trilobites (extinct) Subphylum Chelicerata o Class Merostomata- Horseshoe Crabs, giant water scorpions (extinct) o Class Arachnida • • Order Scorpionida- scorpions Order Araneae- spiders Order Opiliones- harvestmen (daddy longlegs) Order Acarina- ticks and mites o Class Pycnogonida- sea spiders Subphylum Crustacea o Class Malacostraca- crabs, lobsters, crayfish, shrimp, krill, isopods o Class Branchiopoda- fairy shrimp, brine shrimp, and water fleas o Class Maxillopoda- barnacles and copepods Subphylum Hexapoda- insects and relatives Subphylum Myriapoda- millipedes and centipedes

Subphylum Examples: Spiders, mites, ticks, Chelicerata scorpions, sea spiders Characteristics: o Have 2 tagmata- prosoma o o o (cephalothorax) and opisthosoma No antenna First pair of appendages are chelicerae-often pincer-like (chelate) and used for feeding (may be hollow fangs) Second pair are pedipalps-usually sensory or used in locomotion, feeding, or reproduction Paired walking legs follow Opisthosoma contains digestive, reproductive, excretory and respiratory organs

ta a m o t s o er Class M

Class Arachnida

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Subphylum Crustacea 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

Class Malacostraca “Hard Shelled” 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)

http: //news. sciencemag. org/sciencen ow/2012/06/mantis-shrimpsmash. html

Class Malacostraca 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 in swimming and escape responses

Paired appendages that can be seen include the antennules (1), antennae (2), mandibles (3) that are used to chew and crush food, one of the second maxillae (4) that along with the first maxillae (covered by these structures) are involved in food handling, the flagella-like tips of the first maxillipeds (5), most of which are covered by the carapace, one of the second maxillipeds (6), the third maxillipeds (7) and the first pair of walking legs, which are called

Name Region Function Comments Other names used Antennule head sensory 1 st antennae Antennae head sensory 2 nd antennae Mandible head crushing or grinding food items jaw Maxillae head chewing and shredding food items 1 or 2 pairs Maxilliped thorax manipulating food items 3 pairs Pereopod thorax walking, clinging as many as 5 pairs walking legs Pleopod abdomen respiration, swimming, holding offspring As many as 5 pairs swimmerettes Uropod telson (last abd. segment) swimming, escape acessory jaws tail fan

Class Malacostraca

Class Malacostraca Reproduction All crustaceans are dioecious Mating occurs after molting of the female In females, developing eggs attach to pleopods and are brooded until hatched In males, pleopods are modified into claspers and used for sperm transfer Crayfish have direct development

Class Malacostraca 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

Class Malacostraca Gas Exchange & Gills in. Circulation 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

Class Maxillopoda Includes Barnacles and 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