Harpetida is one of the eleven
orders of the
extinct arthropod
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...
class
Class or The Class may refer to:
Common uses not otherwise categorized
* Class (biology), a taxonomic rank
* Class (knowledge representation), a collection of individuals or objects
* Class (philosophy), an analytical concept used differentl ...
Trilobita
Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the At ...
. The first harpetid trilobites appear in the Upper
Cambrian, and the last species die out at the end of the
Devonian period.
Harpetid trilobites are characterized among trilobites by bearing a comparatively large, semicircular brim around the
cephalon (head) which is often perforated by small pores. This brim is thought to serve as a filter-feeding apparatus. The brim stretches backward on either side of the cephalon (head) and typically has a pronounced suture along the outside.
The compound eyes are typically reduced to small tubercles, though they have strong ridges stretching to the glabella (central region of the cephalon). They also typically have 12 or more thoracic segments. The
pygidia are usually small.
The families of Harpetida were formerly included in the order
Ptychopariida
Ptychopariida is a large, heterogeneous order of trilobite containing some of the most primitive species known. The earliest species occurred in the second half of the Lower Cambrian, and the last species did not survive the Ordovician–Silurian ...
, but were recently given their own order (Ebach & McNamara 2002). The subclass Librostoma was erected in 1990 by
Richard Fortey
Richard Alan Fortey FRS FRSL (born 15 February 1946 in London) is a British palaeontologist, natural historian, writer and television presenter, who served as president of the Geological Society of London for its bicentennial year of 2007.
Ea ...
to cover the various orders originally placed within Ptychopariida. The name "Harpidae" was once used as the name for the trilobite family containing the type genus ''Harpes''. However, this is in conflict with the use of the same name for the family of
harp snails and that taxon had precedence.
Families and genera
*
Entomaspididae
Entomaspididae is a family of harpetid trilobites that ranges from the Upper Cambrian to Lower Ordovician of marine strata in China and the United States.
Description
Entomaspidids, as in other harpetid trilobites, have proportionally large, ...
**''
Baikadamaspis''
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Entomaspis
''Entomaspis'' is an extinct genus of harpetid trilobite from Upper Cambrian to Early Ordovician marine strata of the United States. Species are typified by their proportionally large, vaulted, croissant-shaped or bonnet-shaped cephalons that ...
'' (=''Hypothetica'')
*
Harpetidae
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Arraphus''
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Bohemoharpes'' (=Declivoharpes; =Unguloharpes)
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Bowmania''
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Brachyhipposiderus''
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Conococheaguea''
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Dolichoharpes''
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Dubhglasina'' (=''Australoharpes''; ''Sinoharpes'')
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Eoharpes'' (/''Harpina'')
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Eotrinucleus''
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Harpes'' (=''Helioharpes''; ''Reticuloharpes'')
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Heterocaryon''
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Hibbertia
''Hibbertia'', commonly known as guinea flowers, is a genus of flowering plants in the family Dilleniaceae. They are usually shrubs with simple leaves and usually yellow flowers with five sepals and five petals. There are about 400 species, mo ...
'' (/''Platyharpes''; ''Harpesoides''; ''Metaharpes''; ''Paraharpes''; ''Thorslundops''; ''Wegelinia'')
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Kathrynia''
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Kielania'' (=''Lowtheria'')
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Lioharpes'' (=''Fritchaspis'')
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Paleoharpes''
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Scotoharpes'' (=''Aristoharpes''; ''Selenoharpes'').
*
Harpididae
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Chencunia''
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Dictyocephalites''
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Fissocephalus''
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Harpides''
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Harpidoides''
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Kitatella''
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Loganopeltis''
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Loganopeltoides''
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Metaharpides''
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Paraharpides''
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Pscemiaspis''
External links
Order Harpetida- from A Guide to the Orders of Trilobites by Sam Gon III
Trilobite orders
Cambrian first appearances
Late Devonian animals
Late Devonian extinctions
{{harpetida-stub