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
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
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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