Cincta

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Cincta
Temporal range: Miaolingian
Trochocystites bohemicus with stem.jpg
Trochocystites bohemicus from the Czech Republic with a length of 15 millimetres (0.59 in)
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Superphylum: Deuterostomia
Clade: Ambulacraria
Phylum: Echinodermata
Class: Cincta
Jaekel, 1918
Families
  • Trochocystitidae
  • Gyrocystidae
  • Sucocystidae

Cincta is an extinct class of echinoderms that lived only in the Middle Cambrian epoch. [1] Homostelea is a junior synonym. [2] The classification of cinctans is controversial, but they are probably part of the echinoderm stem group. [1] [3]

Contents

Cinctans were sessile, asymmetrical animals with a skeleton made of stereom plates and a racquet-shaped body composed of a theca and stele. They may have had a lifestyle similar to modern tunicates, filter-feeding by pumping water through gill slits in their pharynx.

Description

Cinctans were asymmetrical animals, though some species were nearly bilaterally symmetrical. [1] Like all echinoderms, cinctans have a skeleton made of plates of stereom. The body of cinctans was divided into two sections, the main body, called the theca, and a posterior appendage called a stele. The overall shape of cinctans has been compared to a tennis racquet. [4] The theca of cinctans was surrounded on its margins by a frame of large stereom plates called a cinctus, and the dorsal and ventral surfaces were covered in a tessellated arrangement of small plates. The stele was essentially an extension of the cinctus, rather than a discrete appendage, and would have been fairly stiff side-to-side but possibly more flexible up and down. [4] The stele was not a holdfast, but may have served to stabilize the animal. [5] In most cinctans, the overall shape of the theca was only mildly asymmetrical, but in the unusual genus Lignanicystis the theca was highly asymmetrical, convergent on the stylophorans in some respects. [6] The species Graciacystis could reach a theca length of 14.5 millimetres (0.57 in). [7]

The theca of cinctans contained three major openings. The mouth was located on the right side of the anterior end, in the cinctus, and was associated with marginal grooves. All species had a left marginal groove, but the right marginal groove was sometimes absent and always shorter than the left one. The anus was located near the anterior end, on the right side, indicating that the gut was U-shaped. It was surrounded by a cone of plates equivalent to the periproct of modern echinoderms. [5] The largest opening, called the porta, was located at the anterior end and was covered by an operculum. It was likely an atrial opening like that of tunicates.

The asymmetry of the marginal groove likely indicates that cinctans had a water vascular system comprising two hydrocoels, with the left hydrocoel larger than the right. [1] In species with only a left marginal groove, the right hydrocoel may have been absent as in modern echinoderms.

Biology

Cinctans have been hypothesized to be epibenthic suspension feeders, with a lifestyle similar to modern tunicates. [1] They likely rested on the seafloor parallel to the current, with their mouth and porta oriented downstream. [3] They likely fed by actively pumping water through their pharynx.

Cinctans grew largely by the expansion of the plates. [7] A small number of plates were added to the stele, and somewhat more to the dorsal and ventral surfaces, during growth, but the number of plates making up the cinctus remained constant throughout growth. Because of the asymmetric anatomy of cinctans, they likely underwent torsion when metamorphosing from a larva into an adult. [1]

Classification

Chordata

Hemichordata
Echinodermata

Ctenocystoidea

Cincta

Soluta

Helicoplacus

Camptostroma

Stromatocystites

Kinzercystis

Gogia

Akadocrinus

Pleurocystites

Ubaghsicystis

Macrocystella

Aethocrinus

Phylogenetic position of Cincta within Deuterostomia [8] [9]

The classification of cinctans, like that of other carpoid echinoderms, is contentious. They have been hypothesized to be blastozoans, stem-group hemichordates, and stem-group echinoderms. [1]

Phylogenetic analyses have found cinctans to be stem-group echinoderms, intermediate between ctenocystoids and solutans. [8]

Asturicystis

Trochocystitidae

Trochocystites

Trochocystoides

Sotocinctus

Graciacystis

Protocinctus

Gyrocystidae

Progyrocystis

Gyrocystis

Sucocystidae

Ludwigicinctus

Undatacinctus

Sucocystis

Lignanicystis

Elliptocinctus

Phylogenetic relationships within Cincta [10] [7]

The internal phylogenetic relationships within cinctans have been difficult to study, due in part to their highly specialized anatomy making it difficult to determine their ancestral anatomy. [10] However, three families are recognized, the Trochocystidae, Gyrocystidae, and Sucocystidae, as well as some basal genera which do not fit into any of the families.

Distribution

All cinctan fossils are from the Middle Cambrian. The earliest cinctan is Protocinctus, which dates to Cambrian Stage 5, [1] now known as the Wuliuan. Their diversity peaked during the Drumian. The youngest cinctans are in the genera Undatacinctus and Sucocystis. [11] Cinctans died out just prior to the beginning of the Furongian epoch, during the Guzhangian age. [12] [11] The decline of cinctans was associated with a marine regression, and cinctans may have struggled to migrate as sea levels changed or run out of habitat due to the regression and cooling. [12]

Cinctan fossils are found in the former continents of Siberia, Avalonia, and western Gondwana. [10] They have been found in the Czech Republic, France, Germany, Italy, Morocco, Russia, Spain, and the United Kingdom. [11]

History

The first cinctan named, Trochocystites, was described in 1887. [10] Cinctans were originally considered to be cystoids, but in the early 20th century they were recognized as a distinct group. Because Cincta was originally described as an order, they were later assigned to their own subclass Homostelea, but Homostelea is now considered a junior synonym of Cincta. [13] [2]

Under the calcichordate interpretation of carpoids, cinctans were initially interpreted as basal stem-group echinoderms. [4] Later, however, they, as well as ctenocystoids, were interpreted as possible stem-group hemichordates under the calcichordate interpretation. [14]

Related Research Articles

<span class="mw-page-title-main">Chordate</span> Phylum of animals having a dorsal nerve cord

A chordate is a deuterostomic animal belonging to the phylum Chordata. All chordates possess, at some point during their larval or adult stages, five distinctive physical characteristics (synapomorphies) that distinguish them from other taxa. These five synapomorphies are a notochord, a hollow dorsal nerve cord, an endostyle or thyroid, pharyngeal slits, and a post-anal tail. The name "chordate" comes from the first of these synapomorphies, the notochord, which plays a significant role in chordate body plan structuring and movements. Chordates are also bilaterally symmetric, have a coelom, possess a closed circulatory system, and exhibit metameric segmentation.

<span class="mw-page-title-main">Vetulicolia</span> Extinct Cambrian group of animals

Vetulicolia is a phylum of bilaterian animals encompassing several extinct species belonging to the Cambrian period. The phylum was created by Degan Shu and his research team in 2001, and named after Vetulicola cuneata, the first species of the phylum described in 1987.

<span class="mw-page-title-main">Crinoid</span> Class of echinoderms

Crinoids are marine invertebrates that make up the class Crinoidea. Crinoids that remain attached to the sea floor by a stalk in their adult form are commonly called sea lilies, while the unstalked forms, called feather stars or comatulids, are members of the largest crinoid order, Comatulida. Crinoids are echinoderms in the phylum Echinodermata, which also includes the starfish, brittle stars, sea urchins and sea cucumbers. They live in both shallow water and in depths as great as 9,000 meters (30,000 ft).

<i>Helicoplacus</i> Extinct genus of marine invertebrates

Helicoplacus is the earliest well-studied fossil echinoderm. Fossil plates are known from several regions. Complete specimens were found in Lower Cambrian strata of the White Mountains of California.

<i>Cothurnocystis</i> Extinct genus of marine invertebrates

Cothurnocystis is a genus of small enigmatic echinoderms that lived during the Ordovician. Individual animals had a flat boot-shaped body and a thin rod-shaped appendage that may be a stem, or analogous to a foot or a tail. Fossils of Cothurnocystis species have been found in Nevada, Scotland, Czech Republic, France and Morocco.

<span class="mw-page-title-main">Edrioasteroidea</span> Extinct class of marine invertebrates

Edrioasteroidea is an extinct class of echinoderms. The living animal would have resembled a pentamerously symmetrical disc or cushion. They were obligate encrusters and attached themselves to inorganic or biologic hard substrates. A 507 million years old species, Totiglobus spencensis, is actually the first known echinoderm adapted to live on a hard surface after the soft microbial mats that covered the seafloor were destroyed in the Cambrian substrate revolution.

<span class="mw-page-title-main">Stylophora</span> Extinct group of marine invertebrates

The stylophorans are an extinct, possibly polyphyletic group allied to the Paleozoic Era echinoderms, comprising the prehistoric cornutes and mitrates. It is synonymous with the subphylum Calcichordata. Their unusual appearances have led to a variety of very different reconstructions of their anatomy, how they lived, and their relationships to other organisms.

<span class="mw-page-title-main">Ambulacraria</span> Clade of deuterostomes containing echinoderms and hemichordates

Ambulacraria, or Coelomopora, is a clade of invertebrate phyla that includes echinoderms and hemichordates; a member of this group is called an ambulacrarian. Phylogenetic analysis suggests the echinoderms and hemichordates separated around 533 million years ago. The Ambulacraria are part of the deuterostomes, a clade that also includes the many Chordata, and the few extinct species belonging to the Vetulicolia.

<span class="mw-page-title-main">Deuterostome</span> Superphylum of bilateral animals

Deuterostomes are bilaterian animals of the superphylum Deuterostomia, typically characterized by their anus forming before the mouth during embryonic development. Deuterostomia is further divided into 4 phyla: Chordata, Echinodermata, Hemichordata, and the extinct Vetulicolia known from Cambrian fossils. The extinct clade Cambroernida is also thought to be a member of Deuterostomia.

<i>Camptostroma</i> Extinct genus of marine invertebrates

Camptostroma roddyi is an extinct echinoderm from the Bonnia-Olenellus Zone the Early Cambrian Kinzers Formation near York and Lancaster, Southeastern Pennsylvania. In life, it would have resembled a cupcake, with the axial skeleton forming a star pattern on the upper surface. It was originally thought, on the basis of its medusoid shape, to be a jellyfish-like organism, but the fossils themselves clearly rule out the possibility of a gelatinous body - the stereom plates are clearly preserved and possess the calcitic cleavage pattern diagnostic of echinoderms. It has been placed in a class of basal echinoderms, the Edrioasteroids.

<span class="mw-page-title-main">Homalozoa</span> Extinct historic group of marine invertebrates

Homalozoa is an obsolete extinct subphylum of Paleozoic era echinoderms, prehistoric marine invertebrates. They are also referred to as carpoids.

Pelmatozoa was once a clade of Phylum Echinodermata. It included stalked and sedentary echinoderms. The main class of Pelmatozoa were the Crinoidea which includes sea lily and feather star.

<span class="mw-page-title-main">Stereom</span>

Stereom is a calcium carbonate material that makes up the internal skeletons found in all echinoderms, both living and fossilized forms. It is a sponge-like porous structure which, in a sea urchin may be 50% by volume living cells, and the rest being a matrix of calcite crystals. The size of openings in stereom varies in different species and in different places within the same organism. When an echinoderm becomes a fossil, microscopic examination is used to reveal the structure and such examination is often an important tool to classify the fossil as an echinoderm or related creature.

Diploporita is an extinct class of blastozoan that ranged from the Ordovician to the Devonian. These echinoderms are identified by a specialized respiratory structure, called diplopores. Diplopores are a double pore system that sit within a depression on a single thecal (body) plate; each plate can contain numerous diplopore pairs.

Paleontology or palaeontology is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science. This article records significant discoveries and events related to paleontology that occurred or were published in the year 2018.

<span class="mw-page-title-main">Soluta (echinoderm)</span> Extinct clade of echinoderms

Soluta is an extinct class of echinoderms that lived from the Middle Cambrian to the Early Devonian. The class is also known by its junior synonym Homoiostelea. Soluta is one of the four "carpoid" classes, alongside Ctenocystoidea, Cincta, and Stylophora, which made up the obsolete subphylum Homalozoa. Solutes were asymmetric animals with a stereom skeleton and two appendages, an arm extending anteriorly and a posterior appendage called a homoiostele.

<span class="mw-page-title-main">Ctenocystoidea</span> Extinct clade of marine invertebrates

Ctenocystoidea is an extinct clade of echinoderms, which lived during the Cambrian and Ordovician periods. Unlike other echinoderms, ctenocystoids had bilateral symmetry, or were only very slightly asymmetrical. They are believed to be one of the earliest-diverging branches of echinoderms, with their bilateral symmetry a trait shared with other deuterostomes. Ctenocystoids were once classified in the taxon Homalozoa, also known as Carpoidea, alongside cinctans, solutes, and stylophorans. Homalozoa is now recognized as a polyphyletic group of echinoderms without radial symmetry. Ctenocystoids were geographically widespread during the Middle Cambrian, with one species surviving into the Late Ordovician.

<i>Ctenoimbricata</i> Extinct genus of marine invertebrates

Ctenoimbricata is an extinct genus of bilaterally symmetrical echinoderm, which lived during the early Middle Cambrian period of what is now Spain. It contains one species, Ctenoimbricata spinosa. It may be the most basal known echinoderm. It resembles the extinct ctenocystoids and cinctans, particularly the basal ctenocystoid Courtessolea. Ctenoimbricata is interpreted as a deposit-feeding pharyngeal basket feeder. It was relatively small, with a body 20 millimetres (0.79 in) long.

<i>Yanjiahella</i> Extinct genus of marine invertebrates

Yanjiahella biscarpa is an extinct species of Early Cambrian deuterostome which may represent the earliest stem group echinoderm.

<i>Lepidocystis</i> Extinct genus of echinoderms

Lepidocystis is a Palaeozoic genus of imbricate lepidocystoid eocrinoid, closely related to Kinzercystis, It bore a stalk, with which it attached to firm substrates; and brachioles arising as lateral branches from its arms.

References

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