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