| Helicocystis Temporal range: | |
|---|---|
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Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Stem group: | Echinodermata |
| Family: | † Helicocystitidae |
| Genus: | † Helicocystis |
| Species: | †H. moroccoensis |
| Binomial name | |
| †Helicocystis moroccoensis Smith & Zamora, 2013 [1] | |
Helicocystis is a stalked, spiralling pentaradial echinoderm known from the Cambrian Jbel Wawrmast Formation.
A chordate is a deuterostomic bilaterial 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.
An echinoderm is any deuterostomal animal of the phylum Echinodermata, which includes starfish, brittle stars, sea urchins, sand dollars and sea cucumbers, as well as the sessile sea lilies or "stone lilies". While bilaterally symmetrical as larvae, as adults echinoderms are recognisable by their usually five-pointed radial symmetry, and are found on the sea bed at every ocean depth from the intertidal zone to the abyssal zone. The phylum contains about 7,600 living species, making it the second-largest group of deuterostomes after the chordates, as well as the largest marine-only phylum. The first definitive echinoderms appeared near the start of the Cambrian.
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.
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.
Helicoplacoidea is an extinct class within the Echinodermata. All known taxa were discovered in sediments dating back to the Cambrian.
The Eocrinoidea are an extinct class of echinoderms that lived between the Early Cambrian and Late Silurian periods. They are the earliest known group of stalked, arm-bearing echinoderms, and were the most common echinoderms during the Cambrian.
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 four phyla: Chordata, Echinodermata, Hemichordata, and the extinct Vetulicolia known from Cambrian fossils. The extinct clade Cambroernida is thought to be a member of Deuterostomia.
Camptostroma roddyi is an extinct echinoderm from the Bonnia-Olenellus Zone of the Early Cambrian Kinzers Formation near York and Lancaster, Southeastern Pennsylvania. It is the only known species in the genus Camptostroma, as other species referred to this genus "do not appear to be cogeneric."
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.
Dibrachicystis is an extinct genus of rhombiferan echinoderm from the early Middle Cambrian. It is a stalked echinoderm within the family Dibrachicystidae which lived in what is now northernmost Iberian Chains, northern Spain. It is known from the holotype MPZ2009/1230 and from the paratypes MPZ2011/2–6. It was found in the uppermost part of the Murero Formation at Purujosa, Moncayo Natural Park, dating to the Lower Languedocian and referred to the Solenopleuropsis thorali Zone. It was first named by Samuel Zamora and A. B. Smith in 2011 and the type species is Dibrachicystis purujoensis.
Vizcainoia is an extinct genus of rhombiferan echinoderms from the early Middle Cambrian. It is a stalked echinoderm within the family Dibrachicystidae which lived in what is now France and Spain.
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.
Cotyledion tylodes is an extinct, stalked filter-feeder known from the Chengjiang lagerstatten. The living animal reached a couple of centimetres in height, and bore a loose scleritome of ovoid sclerites. Its interpretation has been controversial, and it has been previously identified as a carpoid echinoderm, or as a stem group echinoderm. C. tylodes is now classified as a stem group entoprocta based on new fossils that clearly show a U-shaped gut and a crown of tentacles. This entoproct interpretation of Cotyledion, however, has been questioned by Mark McMenamin, who considers it best interpreted as a stem group echinoderm based on the morphology of its stem sclerites.
Cincta is an extinct class of echinoderms that lived only in the Middle Cambrian epoch. Homostelea is a junior synonym. The classification of cinctans is controversial, but they are probably part of the echinoderm stem group.
Olivooides is an extinct, sphere-shaped microfossil from Cambrian strata. Fossils are currently known only from China. Olivooides was approximately 600‐870 μm in diameter. It was an egg with a large yolk content. Fossils from Shaanxi, China can be found in the cleavage, gastrulation, organogenesis, cuticularization, pre‐hatching, post‐hatching and subsequent growth stages of development. This fossil is a result of soft-bodied preservation. Olivooides has pentaradial symmetry and is usually preserved by calcium phosphate endocast. The internal structure is rarely preserved. It has no larval stage, so it likely had a quick and direct development.
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.
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.
Yanjiahella biscarpa is an extinct species of Early Cambrian deuterostome which may represent the earliest stem group echinoderm.
Yorkicystis is a genus of edrioasteroid echinoderm that lived 510 million years ago in the Cambrian aged Kinzers Formation in what is now Pennsylvania. This genus is important as it provides some of the oldest evidence of echinoderms losing their hard mineralized outer skeletons. Yorkicystis also shows that some echinoderms lost their skeletons during the Cambrian, which is a greatly different time as to when most other species lost theirs.
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.
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