Agnostida
Peronopsis interstrictus
Scientific classification
Kingdom: Animalia Phylum: Arthropoda Class: Trilobita Order: Agnostida Salter, 1864
Families
Suborder Agnostina Scientific classification or biological classification is a method by which biologists group and categorize species of organisms. ... Animalia redirects here. ... Subphyla and Classes Subphylum Trilobitomorpha Trilobita - trilobites (extinct) Subphylum Chelicerata Arachnida - spiders,scorpions, etc. ... Orders Agnostida Redlichiida Corynexochida Lichida Nektaspida? Phacopida Proetida Asaphida Harpetida Ptychopariida Trilobites are extinct arthropods in the class Trilobita. ... John William Salter (December 15, 1820 - August 2, 1869) was an English naturalist and palaeontologist. ... Superfamily Agnostoidea Agnostidae Ammagnostidae Clavagnostidae Diplagnostidae Doryagnostidae Glyptagnostidae Metagnostidae Peronopsidae Ptychagnostidae Superfamily Condylopygoidea Condylopygidae Suborder Eodiscina Superfamily Eodiscoidea Calodiscidae Eodiscidae Hebediscidae Tsunyidiscidae Weymouthiidae Yukoniidae

Agnostida (the agnostids) is an order of trilobite. These small trilobites first appeared toward the end of the Early Cambrian and thrived in the Middle Cambrian. The last agnostids held out until the Late Ordovician. Scientific classification or biological classification refers to how biologists group and categorize extinct and living species of organisms. ... Orders Agnostida Redlichiida Corynexochida Lichida Phacopida Proetida Asaphida Harpetida Ptychopariida Nektaspida (doubtful order) Trilobites are extinct arthropods in the class Trilobita. ... The Cambrian is a major division of the geologic timescale that begins about 542 ± 1. ... The Ordovician period is the second of the six (seven in North America) periods of the Paleozoic era. ...

The Agnostida are divided into two suborders -- Agnostina and Eodiscina -- that are then divided into a number of families. The Eodiscina appear to be "normal" trilobites with only two or three segments in the thorax; some resemble trilobites of the order Ptychopariida. As a group, agnostids have pygidia (tails) that are similar in size and shape to their cephalons (heads). Neither looks much like the corresponding regions of other trilobites. There has been more than one argument about which end is the "head". In biological classification, family (Latin: familia, plural familiae) is 1) a rank or 2) a taxon in that rank. ... Suborders Suborder Ptychopariina Superfamily Ellipsocephaloidea Superfamily Ptychoparioidea Suborder Olenina Ptychopariida is a large, heterogenous order of trilobite containing some of the most primative species known. ... The pygidium is the posterior body part or shield of crustaceans, some insects, and trilobites. ... The cephalon is the foremost portion of the segmented body of a trilobite. ...

Agnostids were probably benthic (bottom-dwelling) creatures. Most agnostid species have no eyes. They likely lived on areas of the ocean floor that received little or no light and fed on detritus that descended from upper layers of the sea to the bottom.

Unfortunately, the appendages are known only for one genus of agnostid. The legs of that genus look much more like crustacean legs than the legs of other trilobites with preserved appendages. This has caused many taxonomists to question whether the agnostids are truly trilobites. Another view is that the agnostids represent the first line to have diverged from the trilobites. However, four orders of trilobites (Redlichiida, Corynexochida, Naraoidia, Ptychopariida) considerably predate the earliest Agnostids in the fossil record. For other uses of the word, please see Genus (disambiguation). ... Classes & Subclasses Branchiopoda Phyllopoda Sarsostraca Remipedia Cephalocarida Maxillopoda Thecostraca Tantulocarida Branchiura Pentastomida Mystacocarida Copepoda Ostracoda Myodocopa Podocopa Malacostraca Phyllocarida Hoplocarida Eumalacostraca The crustaceans (Crustacea) are a large group of arthropods, comprising approximately 52,000 described species [1], and are usually treated as a subphylum [2].They include various familiar animals... Taxonomy, sometimes alpha taxonomy, is the science of finding, describing and naming organisms, thus giving rise to taxa. ... Suborders Olenellina Redlichiina Redlichiida is an order within the major extinct arthropod class Trilobita. ... Suborders Suborder Corynexochina Suborder Illaenina Suborder Leiostegiina Corynexochida is an order of trilobite that lived from the Lower Cambrian to the Middle Devonian. ... Families Liwiidae Naraoiidae The Nectaspida (also Nectaspia and Nektaspida) is an extinct order of soft-bodied arthropods proposed by Raymond in 1920; its taxonomic status is uncertain. ... Suborders Suborder Ptychopariina Superfamily Ellipsocephaloidea Superfamily Ptychoparioidea Suborder Olenina Ptychopariida is a large, heterogenous order of trilobite containing some of the most primative species known. ... Three small ammonite fossils, each approximately 1. ...

Agnostina are generally referred to simply as "agnostids" even though they probably should be called "agnostines".

External links

• Agnostida fact sheet
• A Guide to the 8 Orders of Trilobites By Sam Gon III