Merostomata: General Characters

Merostomata is a class of sub-phylum Celicerata of Phylum Arthropoda. They include extant horseshoe crabs and extinct sea scropions.

Systematic Position

Kingdom: Animalia
Sub-kingdom: Eumetazoa
Super-phylum: Ecdysosoa
Phylum: Arthropoda
Sub-phylum: Chelicerata
Class: Merostomata

Merostomata Characteristics

Horseshoe Crab (source wikipdia)

Merostomata Characteristics

Ø  Includes extinct sea scorpions (Eurypterida) and extant Horseshoe crabs (Limulus)

Ø  Marine aquatic forms

Ø  Limulus is an example for a living fossil

Ø  Prosoma with six pairs of appendages

merostomata general characters

Hurypterus (extinct merostomata) source: wikipedia

Ø  One pair forms the chelicerae

Ø  Four pairs forms the walking legs

Ø  Last one pair forms the pusher legs

Ø  Eyes compound with flateral median ocellus

Ø  Genital operculum present, formed by the fusion of first pair of mesosomal appendages

Ø  Other five pairs of mesosomal appendages is modified to form the book gills

Ø  Respiration by book gills

Ø  Excretion by coxal glands

Ø  Development indirect (larval stage present)

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