Introduction

Ostracoda is a class of the Crustacea, sometimes known as the seed shrimp because of their appearance. Some 50,000 extinct and extant species have been identified, grouped into several orders. Scientific classification or biological classification refers to how biologists group and categorize extinct and living species of organisms. ... Classes Remipedia Cephalocarida Branchiopoda Ostracoda Maxillopoda Malacostraca The crustaceans (Crustacea) are a large group of arthropods (55,000 species), usually treated as a subphylum. ...

Ostracods are small crustaceans, typically around one mm in size, but varying between 0,2 to 30 mm, laterally compressed and protected by a bivalve-like, chitinous or calcareous valve or "shell". The hinge of the two valves is in the upper, dorsal region of the body. Orders Subclass Protobranchia Solemyoida Nuculoida Subclass Pteriomorphia - oysters Arcoida Mytiloida Pterioida Subclass Paleoheterodonta - mussels Trigoinoida Unionoida Subclass Heterodonta - clams, zebra mussels Veneroida Myoida Subclass Anomalosdesmata Pholadomyoida Animals of the Class Bivalvia are known as bivalves because they typically have two-part shells, with both parts being more or less symmetrical. ... In biology, chitin is one of the main components in the cell walls of fungi, the exoskeletons of insects and other arthropods, and in some other animals. ...

Ecologically ostracods can be part of the zooplankton, or (most commonly) they are part of the benthos, living on or inside the upper layer of the sea floor. Many ostracods are also found in fresh waters and some are known from humid continental forest soils. Photomontage of plankton organisms Plankton is the aggregate community of weakly swimming but mostly drifting small organisms that inhabit the water column of the ocean, seas, and bodies of freshwater. ... In marine geology and biology, benthos are the organisms and habitats of the sea floor; in freshwater biology they are the organisms and habitats of the bottoms of lakes, rivers, and creeks. ...

Ostracodes have a long and well-documented fossil record from the Cambrian to the present day. An outline microfaunal zonal scheme based on both foraminifera and ostracoda was compiled by M.B. Hart (1972). FOSSIL is a standard for allowing serial communication for telecommunications programs under DOS. FOSSIL stands for Fido Opus SEAdog Standard Interface Layer and was made by a group of Fidonet sysops to make their software work on different machines. ... The Cambrian is a major division of the geologic timescale that begins about 542 million years before the present (BP) at the end of the Proterozoic eon_geology and ended about 490 million years BP with the beginning of the Ordovician period. ... Orders Allogromiida Carterinida Fusulinida - extinct Globigerinida Involutinida Lagenida Miliolida Robertinida Rotaliida Silicolocunida Spirillinida Textulariida The Foraminifera, or forams for short, are a large group of amoeboid protists with reticulating pseudopods, fine strands that branch and merge to form a dynamic net. ...

Ostracods have been particularly useful for the biozonation of marine strata on a local or regional scale, and they are invaluable indicators of paleo-environments because of their widespread occurence, small size, easily-preservable generally-moulted calcified bivalve carapaces, the valves are a commonly found microfossil.

Morphology

The body of an ostracod is encased by two valves, which together form the duplicature. A distinction is made between the valve (hard parts) and the body with its appendages (soft parts).

Soft parts and ontogeny

The body consists of a cephalon (head), separated from the thorax by a slight constriction. The segmentation is unclear. The abdomen is regressed or absent whereas the adult gonads are relatively large. There are 5-8 pairs of appendages. The branchial plates are responsible for oxygenation. The cephalon is the foremost portion of the segmented body of a trilobite. ... Diagram of a tsetse fly, showing the head, thorax and abdomen The thorax is a division of an animals body, that lies between the head and the abdomen. ... Segmentation is a general term for the division or partition of something into separate pieces or segments. ... This article is in need of attention. ... A sex organ, or primary sexual characteristic, narrowly defined, is any of those parts of the body (which are not always bodily organs according to the strict definition) which are involved in sexual reproduction and constitute the reproductive system in an complex organism; namely: Male: penis (notably the glans penis...

During the ontogeny the epidermis (containing mesodermal tissue) is invaginated ventrolaterally near the cephalon/thorax area. This invagination proceeds upwards and tailwards, until the whole animal is enveloped by lamellae on both sides: the duplicature is formed. The dorsal region never becomes invaginated, and is called the istmus. The mesodermal tissue in the duplicature develops into the vestibulum. The vestibulum makes contact with the body near the istmus. The vestibulum plays a role in oxygenation. The two lamellae surrounding the animal each have an inner and an outer lamella. Ontogeny (also ontogenesis or morphogenesis) describes the origin and the development of an organism from the fertilized egg to its mature form. ... Epidermis could refer to: In plants, the outermost layer of cells covering the leaves and young parts of a plant, see plant dermal tissue system. ... Mesoderm is one of the three germ layers in the early developing embryo, the other two layers being the ectoderm and the endoderm. ... Invagination is one of the morphogenetic processes by which an embryo takes form, and is the initial step of gastrulation, the massive reorganization of the embryo from a simple spherical ball of cells, the blastula, into a multi-layered organism, with a differentiated endoderm, mesoderm, and ectoderm. ... Vestibule can have the following meanings: A large entrance, reception area, antechamber, or room A small room or passage that connects the outer door of a building to the interior of the building An area in a train where people get on and off. ...

Hard parts

External link

• Introduction to Ostracoda (http://www.gre.ac.uk/schools/nri/earth/ostracod/introduction.htm)