Lepidocaris

Lepidocaris; Temporal range: Pragian PreꞒ Ꞓ O S D C P T J K Pg N ↓
	Artist's restoration
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Crustacea
Class:	Branchiopoda
Order:	† Lipostraca ; Scourfield, 1926
Family:	† Lepidocarididae ; Scourfield, 1926
Genus:	† Lepidocaris ; Scourfield, 1926
Species:	†L. rhyniensis
Binomial name
	†Lepidocaris rhyniensis; Scourfield, 1926

Last updated September 03, 2023

Lepidocaris rhyniensis is an extinct species of crustacean. It is the only species known from the order Lipostraca, and is the only abundant animal in the Pragian-aged Rhynie chert deposits. It resembles modern Anostraca, to which it is probably closely related, although its relationships to other orders remain unclear. The body is 3 mm (0.12 in) long, with 23 body segments and 19 pairs of appendages, but no carapace. It occurred chiefly among charophytes, probably in alkaline temporary pools.

Biostratigraphy and taxonomy

All the known specimens of Lepidocaris rhyniensis have been excavated from the Rhynie chert deposits in Aberdeenshire, Scotland, which is a famous Lagerstätte , or site of exceptional preservation. Lepidocaris is the only abundant animal in the deposits,^[1] and is likely to be responsible for many of the frequent coprolites found in the rocks.^[2]

Lepidocaris was first described by D. J. Scourfield in a 1926 paper in the Philosophical Transactions of the Royal Society B .^[3] Scourfield could not accommodate his new genus in the same order as its closest relatives – the Anostraca – so he erected a new family and order for Lepidocaris alone: Lepidocarididae and Lipostraca, respectively.^[4] Until 2003, when Castracollis was described, Lepidocaris was the only crustacean known from the Rhynie chert.^[5]^[6]

Description

Lepidocaris rhyniensis is a segmented animal with 23 body segments.^[7] The whole body measures around 3 millimetres (0.12 in) long.^[4] The head has two pairs of antennae, the second of which is used for swimming.^[7] As in Anostraca, there is no carapace.^[7] There are eleven pairs of appendages on the thorax and abdomen, of which the first three pairs are phyllopodia, or leaf-like limbs, as seen in other branchiopods such as Triops , while the last eight pairs are similar to the swimming limbs of copepods.^[7] The tail ends in a pair of caudal furcae.^[8]

Ecology

A modern Nitella meadow, seen from above; Lepidocaris is likely to have inhabited a similar habitat in the Devonian. NitellaMeadow.jpg — A modern *Nitella* meadow, seen from above; *Lepidocaris* is likely to have inhabited a similar habitat in the Devonian.

Lepidocaris is one of the earliest preserved freshwater crustaceans.^[8] It is frequently found in association with the charophyte Palaeonitella (Characeae); if the ecology of Palaeonitella resembled that of its modern relatives, the water would have been alkaline.^[8] Similarly, Lepidocaris is thought to have had a similar ecology to extant members of the Anostraca and the Notostraca such as Artemia and Triops, inhabiting shallow, temporary pools.^[8]

Relationships

The phylogenetic position of Lepidocaris in relation to other orders of crustaceans is uncertain.^[9] In his original description of the species, Scourfield noted that Lepidocaris could not be accommodated in the existing order Anostraca, and even suggested that a position outside the Branchiopoda was not unthinkable.^[4] In 1986, Frederick Schram considered Lipostraca to be the sister group to Brachypoda, with the two orders together making up the Cephalocarida.^[10] In 1997, Dieter Walossek considered Lepidocaris and Rehbachiella to be stem-group anostracans, outside the extant Euanostraca.^[9] In 2001, Schram and Koenemann considered Lepidocaris and Rehbachiella to be stem-group lineages basal to the whole Branchiopoda.^[9]

Related Research Articles

<span class="mw-page-title-main">Branchiopoda</span> Class of crustaceans

Branchiopoda is a class of crustaceans. It comprises fairy shrimp, clam shrimp, Diplostraca, Notostraca and the Devonian Lepidocaris. They are mostly small, freshwater animals that feed on plankton and detritus.

Malacostraca is the second largest of the six classes of crustaceans just behind hexapods, containing about 40,000 living species, divided among 16 orders. Its members, the malacostracans, display a great diversity of body forms and include crabs, lobsters, crayfish, shrimp, krill, prawns, woodlice, amphipods, mantis shrimp, tongue-eating lice and many other less familiar animals. They are abundant in all marine environments and have colonised freshwater and terrestrial habitats. They are segmented animals, united by a common body plan comprising 20 body segments, and divided into a head, thorax, and abdomen.

Remipedia is a class of blind crustaceans, closely related to hexapods, found in coastal aquifers which contain saline groundwater, with populations identified in almost every ocean basin so far explored, including in Australia, the Caribbean Sea, and the Atlantic Ocean. The first described remipede was the fossil Tesnusocaris goldichi. Since 1979, at least seventeen living species have been identified in subtropical regions around the world.

<span class="mw-page-title-main">Ostracod</span> Class of crustaceans

Ostracods, or ostracodes, are a class of the Crustacea, sometimes known as seed shrimp. Some 70,000 species have been identified, grouped into several orders. They are small crustaceans, typically around 1 mm (0.04 in) in size, but varying from 0.2 to 30 mm in the case of the marine Gigantocypris. Their bodies are flattened from side to side and protected by a bivalve-like valve or "shell" made of chitin, calcium carbonate and protein. The hinge of the two valves is in the upper (dorsal) region of the body. Ostracods are grouped together based on gross morphology. While early work indicated the group may not be monophyletic and early molecular phylogeny was ambiguous on this front, recent combined analyses of molecular and morphological data found support for monophyly in analyses with broadest taxon sampling. They have a wide range of diets, and the class includes carnivores, herbivores, scavengers and filter feeders.

The order Notostraca, containing the single family Triopsidae, is a group of crustaceans known as tadpole shrimp or shield shrimp. The two genera, Triops and Lepidurus, are considered living fossils, with similar forms having existed since the end of the Devonian, around 360 million years ago. They have a broad, flat carapace, which conceals the head and bears a single pair of compound eyes. The abdomen is long, appears to be segmented and bears numerous pairs of flattened legs. The telson is flanked by a pair of long, thin caudal rami. Phenotypic plasticity within taxa makes species-level identification difficult, and is further compounded by variation in the mode of reproduction. Notostracans are omnivores living on the bottom of temporary pools and shallow lakes.

Clam shrimp are a group of bivalved branchiopod crustaceans that resemble the unrelated bivalved molluscs. They are extant and also known from the fossil record, from at least the Devonian period and perhaps before. They were originally classified in the former order Conchostraca, which later proved to be paraphyletic, due to the fact that water fleas are nested within clam shrimps. Clam shrimp are now divided into three orders, Cyclestherida, Laevicaudata, and Spinicaudata, in addition to the fossil family Leaiidae.

Anostraca is one of the four orders of crustaceans in the class Branchiopoda; its members are referred to as fairy shrimp. They live in vernal pools and hypersaline lakes across the world, and they have even been found in deserts, ice-covered mountain lakes and Antarctic ice. They are usually 6–25 mm (0.24–0.98 in) long. Most species have 20 body segments, bearing 11 pairs of leaf-like phyllopodia, and the body lacks a carapace. They swim "upside-down" and feed by filtering organic particles from the water or by scraping algae from surfaces, with the exception of Branchinecta gigas, or "giant fairy shrimp", which is itself a predator of other species of anostracans. They are an important food for many birds and fish, and some are cultured and harvested for use as fish food. There are 300 species spread across 8 families.

Leptostraca is an order of small, marine crustaceans. Its members, including the well-studied Nebalia, occur throughout the world's oceans and are usually considered to be filter-feeders. It is the only extant order in the subclass Phyllocarida. They are believed to represent the most primitive members of their class, the Malacostraca, and first appear in the fossil record during the Cambrian period.

Eucarida is a superorder of the Malacostraca, a class of the crustacean subphylum, comprising the decapods, krill, and Angustidontida. They are characterised by having the carapace fused to all thoracic segments, and by the possession of stalked eyes.

<span class="mw-page-title-main">Thylacocephala</span> Extinct group of arthropods

The Thylacocephala are group of extinct probable mandibulate arthropods, that have been considered by some researchers as having possible crustacean affinities. As a class they have a short research history, having been erected in the early 1980s.

<i>Triops longicaudatus</i> Species of small freshwater animal

Triops longicaudatus is a freshwater crustacean of the order Notostraca, resembling a miniature horseshoe crab. It is characterized by an elongated, segmented body, a flattened shield-like brownish carapace covering two thirds of the thorax, and two long filaments on the abdomen. The genus name Triops comes from Greek ὤψ or ṓps, meaning "eye" prefixed with Latin tri-, "three", in reference to its three eyes. Longicaudatus is an Latin neologism combining longus ("long") and caudatus ("tailed"), referring to its long tail structures. Triops longicaudatus is found in fresh water ponds and pools, often in places where few higher forms of life can exist.

Arthropods are invertebrate animals in the phylum Arthropoda. They possess an exoskeleton with a cuticle made of chitin, often mineralised with calcium carbonate, a segmented body, and paired jointed appendages. In order to keep growing, they must go through stages of moulting, a process by which they shed their exoskeleton to reveal a new one. They are an extremely diverse group, with up to 10 million species.

Aeschronectida is an extinct order of mantis shrimp-like crustaceans which lived in the Mississippian subperiod in what is now Montana. They exclusively lived in the Carboniferous, or the age of amphibians. They have been found mostly in the U.S. and in the British Isles, in 1979 species were found in the Madera Formation in New Mexico. Aeschronectida was first identified appearing in Continental Europe in around 2014. While sharing similar characteristics to Stomatopoda, they lack certain physical characteristics of that taxon. The first species of Aeschronectida is accredited to Frederick R. Schram. They diverge substantially from typical hoplocaridan morphology by having more unmodified thoracopods. It's theorized that these thoracopods evolved to become more specialized, making them potential ancestors to Stomatopoda.

Cyclida is an extinct order of crab-like fossil arthropods that lived from the Carboniferous to the Jurassic and possibly Cretaceous. Their classification is uncertain, but they are generally interpreted as crustaceans, likely belonging to the superclass Multicrustacea.

Wingertshellicus is an extinct genus of arthropod that has been found in Hunsrück Slate, that is located in the Rhenish Massif in Germany, and lived about 405 million years ago, during the Lower Emsian.

The subphylum Hexapoda or hexapods comprises the largest clade of arthropods and includes most of the extant arthropod species. It includes the crown group Insecta, as well as three much smaller groups of wingless arthropods that were once considered insects: Collembola (springtails), Protura (coneheads) and Diplura. The insects and springtails are very abundant and are some of the most important pollinators, basal consumers, scavengers/detritivores and micropredators in terrestrial environments.

Crustaceans belong to the subphylum Crustacea, and form a large, diverse group of arthropods including decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group can be treated as a subphylum under the clade Mandibulata. It is now well accepted that the hexapods emerged deep in the Crustacean group, with the completed group referred to as Pancrustacea. The three classes Cephalocarida, Branchiopoda and Remipedia are more closely related to the hexapods than they are to any of the other crustaceans.

Phosphatocopina is an extinct group of bivalved arthropods known from the Cambrian period. They are generally sub-milimetric to a few millimetres in size. They are typically only known from isolated carapaces, but some found in Orsten-type phosphatized preservation have their bodies preserved in high fidelity in three dimensions.

References

↑ "Introduction to Branchiopoda". University of California, Berkeley . Retrieved August 5, 2011.
↑ Nigel H Trewin, Stephen R Fayers & Ruth Kelman (2003). "Subaqueous silicification of the contents of small ponds in an Early Devonian hot-spring complex, Rhynie, Scotland". Canadian Journal of Earth Sciences . 40 (11): 1697–1712. Bibcode:2003CaJES..40.1697T. doi:10.1139/e03-065.
↑ Paul Selden & John R. Nudds (2004). "The Rhynie Chert". Evolution of Fossil Ecosystems (2nd ed.). Manson Publishing. pp. 47–58. ISBN 978-1-84076-041-5.
1 2 3 D. J. Scourfield (1926). "On a new type of crustacean from the old Red Sandstone (Rhynie chert Bed, Aberdeenshire) – Lepidocaris rhyniensis, gen. et sp. nov". Philosophical Transactions of the Royal Society B: Biological Sciences . 214 (411–420): 153–187. Bibcode:1926RSPTB.214..153S. doi: 10.1098/rstb.1926.0005 . JSTOR 92140.
↑ Jørgen Olesen (2009). "Phylogeny of Branchiopoda (Crustacea) – character evolution and contribution of uniquely preserved fossils" (PDF). Arthropod Systematics & Phylogeny . 67 (1): 3–39. Archived from the original (PDF) on 2012-03-21. Retrieved 2011-08-06.
↑ "Castracollis". University of Aberdeen . Retrieved 2020-05-26. This is the first new crustacean described from the chert since Lepidocaris rhyniensis (Scourfield 1926, 1940c).
1 2 3 4 D. R. Khanna (2004). "Segmentation in arthropods". Biology of Arthropoda. Discovery Publishing House. pp. 316–394. ISBN 978-81-7141-897-8.
1 2 3 4 "Lepidocaris". The Rhynie Chert Crustaceans. University of Aberdeen . Retrieved August 5, 2011.
1 2 3 Frederick R. Schram & Stefan Koenemann (2001). "Developmental genetics and arthropod evolution: part I, on legs". Evolution & Development . 3 (5): 343–354. doi:10.1046/j.1525-142X.2001.01038.x. PMID 11710766. S2CID 25997101.
↑ M. A. Wills (1998). "A phylogeny of recent and fossil Crustacea derived from morphological characters". In Richard A. Fortey & Richard H. Thomas (ed.). Arthropod Relationships. Systematics Association special volume. Vol. 55. Springer. pp. 189–209. ISBN 978-0-412-75420-3.