Megalograptidae is a family of extinct eurypterid

Eurypterid

Eurypterids are an extinct group of arthropods related to arachnids which include the largest known arthropods that ever lived. They are members of the extinct order Eurypterida ; which is the most diverse Paleozoic chelicerate order in terms of species...

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Description

Megalograptids were characterized by large exoskeletons with ovate to triangular scales. The prosoma (head) was subquadrate, with a tonguelike anterior process bearing marginal spines, and compound eyes on the top front of the head. The chelicerae (claws in front of the mouth) were small and short. The first and third pairs of walking legs were short, with diverging or closely spaced spines. The second pair of walking legs was enormously developed, with long paired spines. The fourth pair of walking legs was nearly spineless. The preabdomen, the front portion of the body, was narrow with axial furrows, while the postabdomen was moderately narrow with broad, flat and curved appendages on the last body segment. The telson

Telson

The telson is the last division of the body of a crustacean. It is not considered a true segment because it does not arise in the embryo from teloblast areas as do real segments. It never carries any appendages, but a forked "tail" called the caudal furca is often present. Together with the...

 was short and lanceolate.

Genera

• Class Merostomata
  Merostomata
  Merostomata is the name given to a grouping of the extinct Eurypterida and the Xiphosura . The term was originally used by James Dwight Dana to refer to Xiphosura only, but was emended by Henry Woodward to cover both groups....
  
   Dana, 1852
• Order Eurypterida Burmeister, 1843
• Suborder Eurypterina Burmeister, 1845
• Superfamily Megalograptoidea Caster & Kjellesvig-Waering, 1955

  Family Megalograptidae Caster & Kjellesvig-Waering, 1955

  Genus Megalograptus

  Megalograptus

  Megalograptus is a Ordovician eurypterid , and was among the earliest known genera . The generic name is derived from the fact that its first fossils were of its very spiny legs, which were mistaken for massive graptolites. It lived from 460 to 445 mya...

  
  Miller, 1874

  Megalograptus alveolatus (Shuler, 1915)

  Megalograptus ohioensis Caster & Kjellesvig-Waering, 1955

  Megalograptus shideleri Caster & Kjellesvig-Waering, 1964

  Megalograptus welchi Miller, 1874

  Megalograptus williamsae Caster & Kjellesvig-Waering, 1964

  Genus Echinognathus

  Echinognathus

  Echinognathus is a genus of prehistoric eurypterid in the Family Megalograptidae. Echinognathus is known from the Ordovician.-Description:...

  
  Walcott, 1882

  Echinognathus clevelandi Walcott, 1882