Draft:Evolution of spiralia

Spiralia are a morphologically diverse clade of protostome animals, including within their number the molluscs, annelids, platyhelminths and other taxa.The term Spiralia is applied to those phyla that exhibit canonical spiral cleavage, a pattern of early development found in most (but not all) members of the Lophotrochozoa.

list of spiralian animals

Fossil record

The first evidence of spiralia in the fossil record comes from trace fossils in Ediacaran sediments,and the first bona fide spiralia fossil is Kimberella

earlier fossils are controversial; the fossil Ikaria wariootia may be the earliest known spiralian Animal,but may also a early Bilaterian Animal. Fossils are known from around the time of Ikaria wariootia (571 million years ago) but none of these have spiralian affinities However, more recent evidence shows these fossils are actually late Paleozoic instead of Ediacaran.

Cambrian explosion

Diurodrilus is one of the first spiralian animal in the cambrian Diurdrilus is a genus of tiny marine animals that has traditionally been assigned to the annelid worms, although this affinity is not certain. With a maximum length of 0.45 mm, it has an unusual morphology with many traits not found in other annelids, including a ventral creeping foot.^[1][2] Analyses of DNA have both refuted and supported placement within the annelids,^[2][3] with the unusual morphology perhaps due to evolutionary progenesis, in which organisms develop sexual maturity while retaining the larval traits of their ancestors.^[3] and Lobatocerebrum a unknow genus of Annelid and also the first Molluscs and Brachiopods an complex phylum of Lopotrochozoa.

Ordovician-Permian

the first spiralian animal in the Ordovician was Tentaculita an extinct class of uncertain placement ranging from the Early Ordovician to the Middle Jurassic. They were suspension feeders with a near worldwide distribution. The presence of perforate septa and "septal necks" has been used to argue for a cephalopod affinity, whereas the shell microstructure, notably the presence of punctae, points to a brachiopod relationship.^[5]

And another spiralian animal from the Ordovician was Neocephalopoda a group of cephalopod mollusks that include the coleoids and all extinct species that are more closely related to extant coleoids than to the nautilus. In cladistic terms, it is the total group of Coleoidea. In contrast, the palcephalopoda are defined as the sister group to the neocephalopoda.^[1]

After the Late Ordovician mass extinction where there more spiralian animals like Actinoceras the principal and root genus of the Actinoceratidae, a major family in the Actinocerida, that lived during the Middle and Late Ordovician. It is an extinct genus of nautiloid cephalopod that thrived in the warm waters of the United States and England during the Paleozoic era.

And the first scolecodont is the jaw of a polychaete annelid, a common type of fossil-producing segmented worm useful in invertebrate paleontology. Scolecodonts are common and diverse microfossils, which range from the Cambrian period (around half a billion years ago at the start of the Paleozoic era) to the present. They diversified profusely in the Ordovician,^[1] and are most common in the Ordovician, Silurian and Devonian marine deposits of the Paleozoic era.

Relatedly, more problematic worm-like fossils have been described in even older, Neoproterozoic era deposits in the Ediacaran Hills of southern Australia and in mid-Cambrian deposits of Burgess shale in British Columbia.

Since the other classes of annelids (specifically, the earthworms and leeches) lack hard parts, only the sea-dwelling polychaetes are frequently represented in the fossil record. Polychaetes are commonly fossilized due to their chitinous teeth and their dwelling tubes made of durable calcite (a calcium carbonate), hardened mucus (a.k.a. parchment), and/or chitin-like cement.

And then there was the Devonian and there was the first famous spiralian animals and it was the Ammonoids a extinct spiral shelled cephalopods comprising the subclass Ammonoidea. They are more closely related to living coleoids (i.e., octopuses, squid and cuttlefish) than they are to shelled nautiloids (such as the living Nautilus).^[1] The earliest ammonoids appeared during the Devonian, with the last species vanishing during or soon after the Cretaceous–Paleogene extinction event. They are often called ammonites, which is most frequently used for members of the order Ammonitida, the only living group of ammonoids from the Jurassic up until their extinction.^[2]

And then there was the Carboniferous and many animals started going on the land most of the spiralian animals on land where Gastropods and Annelida but the climate maked the earth warmer and then was the permian began and the last spiralian animal of the paleozoic was