Subphylum Chelicerata

Body Structure

Two tagmata

Prosoma

Opisthosoma

No distinct head NO ANTENNAE

mostly Uniramous

Chelicerae

Pedipalps

Tagmatization

Cuticle = non living outer covering

Segments, tagmata, divide labor -- results from fusion of somites

Always contains chitin, sometimes with calcium carbonate

usually rigid due to sclerotization but joints are flexible due to the protein reslin

Benefits: Hard and tough,light, waterproof

  • muscle attachment

Pitfalls: joints are vulnerable and ecdysis

5 Layers of exoskeleton secreted by epidermis

Procuticle - mostly composed of chitin and associated proteins

Endocuticle- thickest layer near epidermis

Exocuticle - attaches to the outermost layer

Epicuticle - waxy layer on outermost layer (little to no chitin)

Setae - or sensory structures may project from epidermis through cuticle

Joints - areas of thin cuticle for movement --- specialized on different regions for different functions

Head - feeding and sensory

Thorax - locomotion

Abdomen - visceral and reproduction

Body Systems

Digestion and feeding

Complete digestion (alimentary canal) with specialized regions

Circulation

Open circulatory system

Hemocoel with hemolymph formed by fusion of coelom and blastocoel during development

Tubular heart, arteries, and sinuses

Heart has ostia through which hemolymph enters/exits

Respiration

Excretion

Book gills, book lungs, or tracheae

Malpighian tubules

Nervous and Sensory Systems

Dorsal brain, which may be separated into supra and subesophageal ganglia

Double ventral nerve cord with regional ganglia

Compound eyes for vision

Composed of many ommatidia

produces a mosaic image

good for detecting movement

Setae (tactile) all over the body

Reproduction and Development

Mostly sexual but some asexual by parthenogensis

Mostly dioecious but some monoecious exceptions

Mostly internal fertilization with penis or spermatophore

Female may have an ovipositor for laying eggs

Most go through metamorphosis a series of stages that look different and occupy different habitats --> reduces copetition

Ecdysis required to transition between stages, and to grow after reaching the adult stage

Taxonomic Divisions

Class Merostomata

Large, hardened carapace covering ventral appendages; book gills on the ventral opisthosoma for respiration; pedipalps and four subsequent appendages serve as walking legs; so technically five pairs of walking legs; which are all chelate except for last pair

Class Pycnogonida

Long legs and a highly reduced body with a specialized wet of legs (ovigers) for repro.

Class Arachnida

Prosoma has six pairs of appendages: a pair of pedipalps, 4 walking legs, strong sucking pharynx for liquid

Order Scorpiones

Chelate pedipalps and a long metasoma terminating in a sting

Order Pseudoscorpiones

Chelate pedipalps, but lack stinger and book lungs

Order Araneae

Prosoma and opisthosoma connected by a narrow-waisted pedicel; have spinnerets

Order Opiliones

broadly joined prosoma and opisthosoma lacking a pedicel; raised on long legs

Order Acari

Complete fusion of prosoma and opisthosoma with mouthparts on a capitulum