Monoplacophora, meaning "bearing one plate", is a polyphyletic superclass of molluscs with a cap-like shell now living at the bottom of the deep sea. Extant representatives were not recognized as such until 1952; previously they were known only from the fossil record.
Megalograptus is a genus of eurypterid recovered from deposits of Ordovician age. The genus is classified as part of the Megalograptidae family and contains five species, four from Ohio and one from Virginia.
The evolution of the molluscs is the way in which the Mollusca, one of the largest groups of invertebrate animals, evolved. This phylum includes gastropods, bivalves, scaphopods, cephalopods, and several other groups. The fossil record of mollusks is relatively complete, and they are well represented in most fossil-bearing marine strata. Very early organisms which have dubiously been compared to molluscs include Kimberella and Odontogriphus.
Choia is a genus of extinct demosponge ranging from the Cambrian until the Lower Ordovician periods. Fossils of Choia have been found in the Burgess Shale in British Columbia; the Maotianshan shales of China; the Wheeler Shale in Utah; and the Lower Ordovician Fezouata formation. It was first described in 1920 by Charles Doolittle Walcott.
In a zoological context, spines are hard, needle-like anatomical structures found in both vertebrate and invertebrate species.The spines of most spiny mammals are modified hairs, with a spongy center covered in a thick, hard layer of keratin and a sharp, sometimes barbed tip.
A calcite sea is one in which low-magnesium calcite is the primary inorganic marine calcium carbonate precipitate. An aragonite sea is the alternate seawater chemistry in which aragonite and high-magnesium calcite are the primary inorganic carbonate precipitates. The Early Paleozoic and the Middle to Late Mesozoic oceans were predominantly calcite seas, whereas the Middle Paleozoic through the Early Mesozoic and the Cenozoic are characterized by aragonite seas.
Chiton magnificus, the liquorice sea cradle, is a Southeast Pacific species of edible chiton, a marine polyplacophoran mollusk in the family Chitonidae, the typical chitons.
Mattheva is a class of fossil mollusc, which might be better incorporated in a different class. It was erected to accommodate chiton-like organisms such as Matthevia. Phosphatic fossils have been questionably included in this class even though molluscs do not use phosphate.
Matthevia is a genus of Cambrian molluscs, perhaps related to the chitons. It consists of repeated monoplacophoran-like shells; according to one hypothesis, chitons arose when these tall shells began to overlap over the generations. The tall element of the shell was retained and forms the tips of modern chiton plates. There are distinct head, 'centre', and tail valves, which occur approximately in the ratio 1:5:1 — suggesting a seven-plated configuration.
Hemithecella is a problematic genus of Ordovician mollusc proposed by Stinchcomb and Darrough in 1995. Hemithecella belongs to what are informally known as multiplated molluscs; it is found in the late Cambrian of the Ozarks and the Lower Ordovician of the same region as well as in Minnesota and the southern Appalachian Mountains. Hemithecella has muscle scars identical to a monoplacophoran and not the musculature of a chiton to which some authors have suggested the multiplated molluscs belong. It is therefore classified in the Mattheviidae.
Petroxestes is a shallow, elongate boring originally found excavated in carbonate skeletons and hardgrounds of the Upper Ordovician of North America. These Ordovician borings were likely made by the mytilacean bivalve Corallidomus as it ground a shallow groove in the substrate to maintain its feeding position. They are thus the earliest known bivalve borings. Petroxestes was later described from the Lower Silurian of Anticosti Island (Canada) by Tapanila and Copper (2002) and the Miocene of the Caribbean by Pickerill et al. (2001).
Panulirus pascuensis is a species of spiny lobster found around Easter Island and the Pitcairn Islands in the Pacific Ocean. It is known in English as the Easter Island spiny lobster and in Spanish as Langosta de Isla de Pascua. This lobster is fished on a small scale for local consumption.
Allochiton is a genus of upper Cambrian chitons with a circular head valve.
The Paleoloricata are valved polyplacophora without sutural laminae or insertion plates. The "order" probably represents a paraphyletic grouping.
Mattheviidae is an extinct taxonomic family of fossil chitons, marine polyplacophoran mollusks that are found in Upper Cambrian deposits.
Polysacos is an extinct genus of multiplacophorans (chitons) known from articulated Carboniferous fossils; its seventeen shell plates are arranged in three rows, with seven iterated units. It demonstrates that multiplacophora are related to modern polyplacophora. It was fringed with a ring of hollow spines resembling those of the Ordovician Echinochiton.
Cantharidus festivus is a species of sea snail, a marine gastropod mollusk in the family Trochidae, the top snails.
Echimyidae is the family of neotropical spiny rats and their fossil relatives. This is the most species-rich family of hystricognath rodents. It is probably also the most ecologically diverse, with members ranging from fully arboreal to terrestrial to fossorial habits. They presently exist mainly in South America; three members of the family also range into Central America. Species of the extinct subfamily Heteropsomyinae formerly lived on Cuba, Hispaniola, and Puerto Rico in the Antilles, probably until the arrival of Europeans. Some authorities consider the nutria from southern and central South America to be a part of this family.
Acanthopleura echinata is a Southeast Pacific species of edible chiton, a marine polyplacophoran mollusc in the family Chitonidae, the typical chitons.
