Arachnida General Characters (Phylum: Arthropoda, Sub-phylum: Chelicerata)

Characteristics of Aracnids

Eight Legs of Arachnid (Spider) source: wikipedia

Arachnida is a class of sub-phylum Chelicerata of Phylum Arthropoda. They include Spiders, Scorpions and Mites.

Systematic Position:

Kingdom : Animalia
Sub-kingdom: Eumetazoa/ Bilateria
Superphylum: Ecdysosoa
Phylum: Arthropoda
Sub-phylum: Chelicerata
Class: Arachnida

Identifying characters of Arachnida

Ø.  Includes spiders, scorpions and mites

Ø.  They are terrestrial chelicerates

Ø.  Processes eight walking legs

Ø.  Differ from insects in the presence of eight legs (insects are with six legs) and absence of antennae and wings

Ø.  Prosoma (cephalothorax) bears a pair of pre-oral chelicerae and a pair of post-oral pedipalps

Ø.  Cephalothorax also bears four pairs of walking legs

Ø.  In spiders, each chelicerae bears a fang into which the poisonous glands opens

What is chelicerae

Chelicerae of a Spider (Green) (source Wikipedia)

Ø.  Abdominal appendages are modified into book lungs

Ø.  Spinnerets in spiders and pectines in scorpions are modified abdominal appendages

Ø.  Respiration by book lungs

Ø.  Excretion by coxal glands or by malpighian tubules

Ø.  Show direct development

Ø. Scorpions are viviparous

Ø.  Scorpions shows prolonged parental caring

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