Harpetida
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Harpetida is one of the eleven
order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...
s of the
extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...
arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...
class Class, Classes, 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 d ...
Trilobita Trilobites (; meaning "three-lobed entities") are extinction, extinct marine arthropods that form the class (biology), class Trilobita. One of the earliest groups of arthropods to appear in the fossil record, trilobites were among the most succ ...
. The first harpetid trilobites appear in the Upper
Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...
, and the last species die out in the late
Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...
period. Harpetid trilobites are characterized among trilobites by bearing a comparatively large, semicircular brim around the
cephalon Cephalon, Inc. was an American biopharmaceutical company co-founded in 1987 by pharmacologist Frank Baldino Jr., Frank Baldino, Jr., neuroscientist Michael Lewis, and organic chemist James C. Kauer—all three former scientists with the DuPont ...
(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–Siluria ...
, but were recently given their own order in 2002. The subclass Librostoma was erected in 1990 by Richard Fortey 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 **'' Baikadamaspis'' **'' Entomaspis'' (=''Hypothetica'') * Harpetidae **'' Arraphus'' **'' Bohemoharpes'' (=''Declivoharpes''; =''Unguloharpes'') **'' Bowmania'' **'' Brachyhipposiderus'' **'' Conococheaguea'' **'' Dolichoharpes'' **'' Dubhglasina'' (=''Australoharpes''; ''Sinoharpes'') **'' Eoharpes'' (/''Harpina'') **'' Eotrinucleus'' **'' Eskoharpes'' (='' Globoharpes''?) **'' Globoharpes''(?) **'' Harpes'' (=''Helioharpes''; ''Reticuloharpes'') **'' Heterocaryon'' **'' Hibbertia'' (/''Platyharpes''; ''Harpesoides''; ''Metaharpes''; ''Paraharpes''; ''Thorslundops''; ''Wegelinia'') **'' Kathrynia'' **'' Kielania'' (=''Lowtheria'') **'' Lioharpes'' (='' Fritchapsis'') **'' Paleoharpes'' **'' Scotoharpes'' (=''Aristoharpes''; ''Selenoharpes''). * Harpididae **'' Chencunia'' **'' Dictyocephalites'' **'' Fissocephalus'' **'' Harpides'' **'' Harpidoides'' **'' Kitatella'' **'' Loganopeltis'' **'' Loganopeltoides'' **'' Metaharpides'' **'' Paraharpides'' **'' Pscemiaspis''


References


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 Librostoma {{harpetida-stub