Phylum Arthropoda1

Phylum Arthropoda

Arthropoda Overview

Subphylum Chelicerata

Class Merostomata

Class Pycnogonida

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Phylum Arthropoda

Defining Characteristics– Epidermis produces a segmented, jointed and

hardened chitinous exoskeleton with musculature between individual joints of appendages

– Complete loss of motile cilia in adult larval stages

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Phylum Arthropoda

Phylum includes crustaceans, insects, and chelicerates

Chelicerates – Primarily terrestrial– Also horseshoe crabs and sea spiders

Crustaceans – Marine and freshwater, absent from land

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Arthropod Characters

Arthropods have segmented bodies with some or all of the segments bearing jointed appendages

Appendages are specialized for:

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The Wonders of Chitin

All arthropods have a chitinous jointed exoskeleton

How is this detrimental and beneficial?

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Molting (Ecdysis)

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Arthropod Segments

Arthropod segments are grouped into body regions

Some have two regions – Cephalothorax, and abdomen

Some have three regions– Head, thorax, abdomen

Many regions have multiple appendages– Appendages are modified for a particular function

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Arthropod Appendages

The head usually contains pairs of joint appendages, which are sensory and used in feeding – Antenna’s or feelers are first – Followed by the jaws and mandibles which are

used for biting and chewingMandible and accessory mouth parts aid in

handling the food and moving it towards the mouth

Arthropod Appendages

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Arthropod Vision

Simple eyes – Light sensitive cells

share a common lens Compound eyes

– Thousand of closely packed units called ommatidia

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Compound & Simple Eyes

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Digestive system

Most arthropods have three main regions: foregut, midgut and hindgut

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Respiration and Circulatory System

Extensive surface areas are needed to supply the large oxygen demands of most arthropods– Gills can occur both inside and outside of the of the

carapace Circulatory System

– Open circulatory system as in molluscs, hearts vary in structure but do exist

– Blood is pumped into empty spaces bathing the tissues in blood

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Nervous System and Reproduction