Crustacean

Crustaceans (Crustacea /krʌˈsteɪʃə/) form a large, diverse arthropod taxon which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill, woodlice, and barnacles.[1] The crustacean group is usually treated as a subphylum, and because of recent molecular studies it is now well accepted that the crustacean group is paraphyletic, and comprises all animals in the Pancrustacea clade other than hexapods.[2] Some crustaceans are more closely related to insects and other hexapods than they are to certain other crustaceans.

The 67,000 described species range in size from Stygotantulus stocki at 0.1 mm (0.004 in), to the Japanese spider crab with a leg span of up to 3.8 m (12.5 ft) and a mass of 20 kg (44 lb). Like other arthropods, crustaceans have an exoskeleton, which they moult to grow. They are distinguished from other groups of arthropods, such as insects, myriapods and chelicerates, by the possession of biramous (two-parted) limbs, and by their larval forms, such as the nauplius stage of branchiopods and copepods.

Most crustaceans are free-living aquatic animals, but some are terrestrial (e.g. woodlice), some are parasitic (e.g. Rhizocephala, fish lice, tongue worms) and some are sessile (e.g. barnacles). The group has an extensive fossil record, reaching back to the Cambrian, and includes living fossils such as Triops cancriformis, which has existed apparently unchanged since the Triassic period. More than 10 million tons of crustaceans are produced by fishery or farming for human consumption, the majority of it being shrimp and prawns. Krill and copepods are not as widely fished, but may be the animals with the greatest biomass on the planet, and form a vital part of the food chain. The scientific study of crustaceans is known as carcinology (alternatively, malacostracology, crustaceology or crustalogy), and a scientist who works in carcinology is a carcinologist.

Crustaceans
Temporal range: 511–0 Ma
Cambrian to present
A segmented animal is seen from the side. It has a long antennae and small black eyes; one pair of legs is much more robust than the others; the body is slightly arched and each segment carries a pair of appendages. The whole animal is translucent or a pale brown colour.
Abludomelita obtusata, an amphipod
Scientific classification
Kingdom: Animalia
Phylum: Euarthropoda
Clade: Pancrustacea
Subphylum: Crustacea
Groups included

Thylacocephala? †
Branchiopoda

Phyllopoda
Sarsostraca

Remipedia
Cephalocarida
Maxillopoda

Thecostraca
Tantulocarida
Branchiura
Pentastomida
Mystacocarida
Copepoda

Ostracoda

Myodocopa
Podocopa

Malacostraca

Phyllocarida
Hoplocarida
Eumalacostraca
Cladistically included but traditionally excluded taxa

Hexapods

Structure

Crab from Long Island
A shed carapace of a lady crab, part of the hard exoskeleton
Krillanatomykils
Body structure of a typical crustacean – krill

The body of a crustacean is composed of segments, which are grouped into three regions: the cephalon or head,[3] the pereon or thorax,[4] and the pleon or abdomen.[5] The head and thorax may be fused together to form a cephalothorax,[6] which may be covered by a single large carapace.[7] The crustacean body is protected by the hard exoskeleton, which must be moulted for the animal to grow. The shell around each somite can be divided into a dorsal tergum, ventral sternum and a lateral pleuron. Various parts of the exoskeleton may be fused together.[8]:289

Each somite, or body segment can bear a pair of appendages: on the segments of the head, these include two pairs of antennae, the mandibles and maxillae;[3] the thoracic segments bear legs, which may be specialised as pereiopods (walking legs) and maxillipeds (feeding legs).[4] The abdomen bears pleopods,[5] and ends in a telson, which bears the anus, and is often flanked by uropods to form a tail fan.[9] The number and variety of appendages in different crustaceans may be partly responsible for the group's success.[10]

Crustacean appendages are typically biramous, meaning they are divided into two parts; this includes the second pair of antennae, but not the first, which is usually uniramous, the exception being in the Class Malacostraca where the antennules may be generally biramous or even triramous.[11][12] It is unclear whether the biramous condition is a derived state which evolved in crustaceans, or whether the second branch of the limb has been lost in all other groups. Trilobites, for instance, also possessed biramous appendages.[13]

The main body cavity is an open circulatory system, where blood is pumped into the haemocoel by a heart located near the dorsum.[14] Malacostraca have haemocyanin as the oxygen-carrying pigment, while copepods, ostracods, barnacles and branchiopods have haemoglobins.[15] The alimentary canal consists of a straight tube that often has a gizzard-like "gastric mill" for grinding food and a pair of digestive glands that absorb food; this structure goes in a spiral format.[16] Structures that function as kidneys are located near the antennae. A brain exists in the form of ganglia close to the antennae, and a collection of major ganglia is found below the gut.[17]

In many decapods, the first (and sometimes the second) pair of pleopods are specialised in the male for sperm transfer. Many terrestrial crustaceans (such as the Christmas Island red crab) mate seasonally and return to the sea to release the eggs. Others, such as woodlice, lay their eggs on land, albeit in damp conditions. In most decapods, the females retain the eggs until they hatch into free-swimming larvae.[18]

Ecology

The majority of crustaceans are aquatic, living in either marine or freshwater environments, but a few groups have adapted to life on land, such as terrestrial crabs, terrestrial hermit crabs, and woodlice. Marine crustaceans are as ubiquitous in the oceans as insects are on land.[19][20] The majority of crustaceans are also motile, moving about independently, although a few taxonomic units are parasitic and live attached to their hosts (including sea lice, fish lice, whale lice, tongue worms, and Cymothoa exigua, all of which may be referred to as "crustacean lice"), and adult barnacles live a sessile life – they are attached headfirst to the substrate and cannot move independently. Some branchiurans are able to withstand rapid changes of salinity and will also switch hosts from marine to non-marine species.[21]:672 Krill are the bottom layer and the most important part of the food chain in Antarctic animal communities.[22]:64 Some crustaceans are significant invasive species, such as the Chinese mitten crab, Eriocheir sinensis,[23] and the Asian shore crab, Hemigrapsus sanguineus.[24]

Life cycle

Potamon fluviatile9
Eggs of Potamon fluviatile, a freshwater crab
Homarus gammarus zoea
Zoea larva of the European lobster, Homarus gammarus

Mating system

The majority of crustaceans have separate sexes, and reproduce sexually.[25] A small number are hermaphrodites, including barnacles, remipedes,[26] and Cephalocarida.[27] Some may even change sex during the course of their life.[27] Parthenogenesis is also widespread among crustaceans, where viable eggs are produced by a female without needing fertilisation by a male.[25] This occurs in many branchiopods, some ostracods, some isopods, and certain "higher" crustaceans, such as the Marmorkrebs crayfish.

Eggs

In many groups of crustaceans, the fertilised eggs are simply released into the water column, while others have developed a number of mechanisms for holding on to the eggs until they are ready to hatch. Most decapods carry the eggs attached to the pleopods, while peracarids, notostracans, anostracans, and many isopods form a brood pouch from the carapace and thoracic limbs.[25] Female Branchiura do not carry eggs in external ovisacs but attach them in rows to rocks and other objects.[28]:788 Most leptostracans and krill carry the eggs between their thoracic limbs; some copepods carry their eggs in special thin-walled sacs, while others have them attached together in long, tangled strings.[25]

Larvae

Crustaceans exhibit a number of larval forms, of which the earliest and most characteristic is the nauplius. This has three pairs of appendages, all emerging from the young animal's head, and a single naupliar eye. In most groups, there are further larval stages, including the zoea (pl. zoeæ or zoeas[29]). This name was given to it when naturalists believed it to be a separate species.[30] It follows the nauplius stage and precedes the post-larva. Zoea larvae swim with their thoracic appendages, as opposed to nauplii, which use cephalic appendages, and megalopa, which use abdominal appendages for swimming. It often has spikes on its carapace, which may assist these small organisms in maintaining directional swimming.[31] In many decapods, due to their accelerated development, the zoea is the first larval stage. In some cases, the zoea stage is followed by the mysis stage, and in others, by the megalopa stage, depending on the crustacean group involved.

Classification

The name "crustacean" dates from the earliest works to describe the animals, including those of Pierre Belon and Guillaume Rondelet, but the name was not used by some later authors, including Carl Linnaeus, who included crustaceans among the "Aptera" in his Systema Naturae.[32] The earliest nomenclaturally valid work to use the name "Crustacea" was Morten Thrane Brünnich's Zoologiæ Fundamenta in 1772,[33] although he also included chelicerates in the group.[32]

The subphylum Crustacea comprises almost 67,000 described species,[34] which is thought to be just ​110 to ​1100 of the total number as the majority of species remain as yet undiscovered.[35] Although most crustaceans are small, their morphology varies greatly and includes both the largest arthropod in the world – the Japanese spider crab with a leg span of 3.7 metres (12 ft)[36] – and the smallest, the 100-micrometre-long (0.00004 in) Stygotantulus stocki.[37] Despite their diversity of form, crustaceans are united by the special larval form known as the nauplius.

The exact relationships of the Crustacea to other taxa are not completely settled as of April 2012. Studies based on morphology led to the Pancrustacea hypothesis,[38] in which Crustacea and Hexapoda (insects and allies) are sister groups. More recent studies using DNA sequences suggest that Crustacea is paraphyletic, with the hexapods nested within a larger Pancrustacea clade.[39][40]

Although the classification of crustaceans has been quite variable, the system used by Martin and Davis[41] largely supersedes earlier works. Mystacocarida and Branchiura, here treated as part of Maxillopoda, are sometimes treated as their own classes. Six classes are usually recognised:

Haeckel Copepoda
Copepods, from Ernst Haeckel's 1904 work Kunstformen der Natur
Haeckel Decapoda
Decapods, from Ernst Haeckel's 1904 work Kunstformen der Natur
Class Members Orders Photo
Branchiopoda brine shrimp
fairy shrimp
water fleas
tadpole shrimp
clam shrimp
Anostraca
Lipostraca
Notostraca
Laevicaudata
Spinicaudata
Cyclestherida
Cladocera
Daphnia pulex
Daphnia pulex (Cladocera)
Remipedia Nectiopoda Speleonectes tanumekes unlabeled-rotated
Speleonectes tanumekes (Speleonectidae)
Cephalocarida horseshoe shrimp Brachypoda
Maxillopoda barnacles
copepods
Calanoida
Pedunculata
Sessilia
c. 20 others
Chthamalus stellatus
Chthamalus stellatus (Sessilia)
Ostracoda seed shrimp Myodocopida
Halocyprida
Platycopida
Podocopida
Ostracod
Cylindroleberididae
Malacostraca crabs
lobsters
crayfish
shrimp
krill
mantis shrimp
woodlice
hooded shrimp
scuds
sandhoppers
etc.
Decapoda
Isopoda
Amphipoda
Stomatopoda
c. 12 others
Gammarus roeselii
Gammarus roeseli (Amphipoda)

Fossil record

Crustaceans have a rich and extensive fossil record, which begins with animals such as Canadaspis and Perspicaris from the Middle Cambrian age Burgess Shale.[42][43] Most of the major groups of crustaceans appear in the fossil record before the end of the Cambrian, namely the Branchiopoda, Maxillopoda (including barnacles and tongue worms) and Malacostraca; there is some debate as to whether or not Cambrian animals assigned to Ostracoda are truly ostracods, which would otherwise start in the Ordovician.[44] The only classes to appear later are the Cephalocarida,[45] which have no fossil record, and the Remipedia, which were first described from the fossil Tesnusocaris goldichi, but do not appear until the Carboniferous.[46] Most of the early crustaceans are rare, but fossil crustaceans become abundant from the Carboniferous period onwards.[42]

Shrimps at market in Valencia
Norway lobsters on sale at a Spanish market

Within the Malacostraca, no fossils are known for krill,[47] while both Hoplocarida and Phyllopoda contain important groups that are now extinct as well as extant members (Hoplocarida: mantis shrimp are extant, while Aeschronectida are extinct;[48] Phyllopoda: Canadaspidida are extinct, while Leptostraca are extant[43]). Cumacea and Isopoda are both known from the Carboniferous,[49][50] as are the first true mantis shrimp.[51] In the Decapoda, prawns and polychelids appear in the Triassic,[52][53] and shrimp and crabs appear in the Jurassic;[54][55] . The fossil burrow Ophiomorpha is attributed to ghost shrimps, whereas the fossil burrow Camborygma is attributed to crayfishes.The Permian–Triassic deposits of Nurra preserve the oldest (Permian: Roadian) fluvial burrows ascribed to ghost shrimps (Decapoda: Axiidea, Gebiidea) and crayfishes (Decapoda: Astacidea, Parastacidea), respectively[56].

However, the great radiation of crustaceans occurred in the Cretaceous, particularly in crabs, and may have been driven by the adaptive radiation of their main predators, bony fish.[55] The first true lobsters also appear in the Cretaceous.[57]

Consumption by humans

Many crustaceans are consumed by humans, and nearly 10,700,000 tons were produced in 2007; the vast majority of this output is of decapod crustaceans: crabs, lobsters, shrimp, crawfish, and prawns.[58] Over 60% by weight of all crustaceans caught for consumption are shrimp and prawns, and nearly 80% is produced in Asia, with China alone producing nearly half the world's total.[58] Non-decapod crustaceans are not widely consumed, with only 118,000 tons of krill being caught,[58] despite krill having one of the greatest biomasses on the planet.[59]

See also

References

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Sources

External links

A White Sport Coat and a Pink Crustacean

A White Sport Coat and a Pink Crustacean is the third studio album by American singer-songwriter Jimmy Buffett and the first major-label album in Buffett's Don Gant-produced "Key West phase", although Buffett himself frequently refers to A White Sport Coat and a Pink Crustacean as his first album. It was initially released on June 4, 1973, as Dunhill DS-50150 and October 26, 1987, as MCA. It was the first album of his career to feature Buffett's trademark mustache, which would remain in use until Hot Water.

The title of the album is a play on the country song "A White Sport Coat and a Pink Carnation" by Marty Robbins, and it contains several of what later became Buffett's most popular songs. The album was recorded at outlaw country singer Tompall Glaser's studio in Nashville, Tennessee. It marks the first reference to Buffett's backup band as "The Coral Reefer Band" and is the first album on which long-time Reefers Michael Utley and Greg "Fingers" Taylor play.

Amphipoda

Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods range in size from 1 to 340 millimetres (0.039 to 13 in) and are mostly detritivores or scavengers. There are more than 9,900 amphipod species so far described. They are mostly marine animals, but are found in almost all aquatic environments. Some 1,900 species live in fresh water, and the order also includes terrestrial animals and sandhoppers such as Talitrus saltator.

Arthropod leg

The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments (called podomeres) are of Latin origin, and may be confused with terms for bones: coxa (meaning hip, plural coxae), trochanter (compare trochanter), femur (plural femora), tibia (plural tibiae), tarsus (plural tarsi), ischium (plural ischia), metatarsus, carpus, dactylus (meaning finger), patella (plural patellae).

Homologies of leg segments between groups are difficult to prove and are the source of much argument. Some authors posit up to eleven segments per leg for the most recent common ancestor of extant arthropods but modern arthropods have eight or fewer. It has been argued that the ancestral leg need not have been so complex, and that other events, such as successive loss of function of a Hox-gene, could result in parallel gains of leg segments.

Calanoida

Calanoida is an order of copepods, a kind of zooplankton. They include around 46 families with about 1800 species of both marine and freshwater copepods. Calanoid copepods are dominant in the plankton in many parts of the world's oceans, making up 55%–95% of plankton samples. They are therefore important in many food webs, taking in energy from phytoplankton and algae and 'repackaging' it for consumption by higher trophic level predators. Many commercial fish are dependent on calanoid copepods for diet in either their larval or adult forms. Baleen whales such as bowhead whales, sei whales, right whales and fin whales eat calanoid copepods.Calanoids can be distinguished from other planktonic copepods by having first antennae at least half the length of the body and biramous second antennae. Their key defining feature anatomically, however, is the presence of a joint between the fifth and sixth body segments. The largest specimens reach 18 millimetres (0.71 in) long, but most are 0.5–2.0 mm (0.02–0.08 in) long.

Chaceon fenneri

Chaceon fenneri, commonly known as the golden crab or golden deepsea crab, is one of several species of crab harvested for food by humans. It was formerly called Geryon fenneri. Like the blue crab, its common name comes from the color of its shell; it is usually cream to tan in color. Both parts of the binomen Chaceon fenneri commemorate Fenner A. Chace, Jr. It is found on the ocean floor at depths of 200 to 1,500 m (660–4,920 ft) in the tropical west Atlantic, ranging from the Gulf of Mexico to Brazil. It cannot swim. The carapace of this large crab measures up to 20 cm (7.9 in), making the entire animal similar in size to a dinner plate. Its diet includes benthic (bottom-dwelling) organisms like mollusks and worms.

Crustacean larva

Crustaceans may pass through a number of larval and immature stages between hatching from their eggs and reaching their adult form. Each of the stages is separated by a moult, in which the hard exoskeleton is shed to allow the animal to grow. The larvae of crustaceans often bear little resemblance to the adult, and there are still cases where it is not known what larvae will grow into what adults. This is especially true of crustaceans which live as benthic adults (on the sea bed), more so than where the larvae are planktonic and therefore more easily caught.

Many crustacean larvae were not immediately recognised as larvae when they were discovered, and were described as new genera and species. The names of these genera have become generalised to cover specific larval stages across wide groups of crustaceans, such as zoea and nauplius. Other terms described forms which are only found in particular groups, such as the glaucothoe of hermit crabs, or the phyllosoma of slipper lobsters and spiny lobsters.

Decapoda

The Decapoda or decapods (literally "ten-footed") are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crayfish, crabs, lobsters, prawns, and shrimp. Most decapods are scavengers. The order is estimated to contain nearly 15,000 species in around 2,700 genera, with around 3,300 fossil species. Nearly half of these species are crabs, with the shrimp (about 3000 species) and Anomura including hermit crabs, porcelain crabs, squat lobsters (about 2500 species) making up the bulk of the remainder. The earliest fossil decapod is the Devonian Palaeopalaemon.

Hematodinium

Hematodinium is a genus of dinoflagellates. Species in this genus, such as Hematodinium perezi, the type species, are internal parasites of the hemolymph of crustaceans such as the Atlantic blue crab (Callinectes sapidus) and Norway lobster (Nephrops norvegicus). Species in the genus are economically damaging to commercial crab fisheries, including causing bitter crab disease in the large Tanner or snow crab fisheries of the Bering Sea.Introduction

Hematodinium is a harmful parasitic dinoflagellate in marine decapod crustaceans, often dwelling in the hemolymph of host organisms (Gornik 2013). Drastic changes in the host’s vital organs, tissues, and hemolymph lead to the degeneration of the organism (Stentiford & Shields 2005). Previous studies indicate that species in genus Hematodium affect many organisms in Order Decapoda, and may also affect Order Amphipoda (Lohan 2012) and subclass Copepoda (Manier et al, 1971). These crustacean taxa include crabs, lobsters, crayfish, prawns, and shrimp – all commercially important food sources for many countries. The effects of Hematodinium parasites are aggressive and can be lethal, thus capable of eradicating entire crab populations. Discoveries of Hematodinium pathogens in decapods span from western Atlantic Ocean (Lohan 2012) to southern Australia (Gornik 2013). As a result of the prevalence of Hematodinium in many ocean waters, significant damage is done for many fishery industries around the globe.

History of knowledge

Hematodinium perezi is one of the first species to have been studied in genus Hematodinium (Stentiford & Shields 2005). This organism is well-known and is consequently used as the main study subject for this genus. The first declaration of H. perezi was made in 1931 by Chatton and Poisson off the coasts of Normandy and France. They were discovered in swimming crabs Carcinus maenas and Liocarcinus depurator. At that time, Chatton and Poisson’s studies were not successful in generating reliable data on Hematodinium. This was because only a small percentage of tested crabs showed indication that they carried the H. perezi parasite. Nonetheless, future discoveries of similar diseases in other crabs have been linked back to H. perezi since Chatton and Poisson’s first sighting. Later affected crabs include Cancer pagurus (Latrouite et al., 1988; Stentiford et al., 2002) and Necora puber (Wilhelm and Boulo, 1988; Wilhelm and Mialhe, 1996).

In 1994, a second species Hematodinium australis found in Australia has been distinguished from H. perezi. Hudson and Shields (1994) point out that besides its southern hemispheric location, the trophont size as well as the presence of rounded plasmodial stages differed between parasitic groups. Molecular research later confirmed the separation of H. australis from H. perezi (Stentiford & Shields 2005).

Up until now, there are only a few determining characteristics between Hematodinium species (Stentiford & Shields 2005). All known species are found in crustacean hosts, have hemolymph-dwelling filamentous plasmodial stages, intrusive amoeboid trophont infections, and a dinokaryon.

Species in speculation of belonging to genus Hematodinium are currently in need of further research. Lack of comparative work between the type species and the latest species discoveries prevent exploration of the diversity of genus Hematodinium (Stentiford & Shields 2005). Difficulties arise due to the inaccessibility of representative type materials to use for comparative studies, and only a meager list of useful physical characteristics available between the type species and potential Hematodinium parasites (Small 2012). Therefore, newly discovered taxa are designated the general classification of Hematodinium sp. or are referred to being Hematodinium-like. In some cases, new parasite discoveries are incorrectly identified as H. perezi due to close resemblance to the type species.

Habitat and ecology

At the time of Small’s (2012) studies, 38 host crustacean species have been affected by Hematodinium parasites. Some of the economically-important infected hosts include tanner and snow crabs from the Northeast Pacific and Atlantic Oceans, blue crabs in the Atlantic and Gulf coasts of the United States, Norwegian lobsters, and Edible crabs from Europe. It is anticipated that the geographical spread of Hematodinium will grow and reach various other aquatic regions globally due to oceanic currents, host movements and habitat expansions, as well as transportation vessels. Furthermore, as new crustacean species are targeted and fished as commercial seafood, new species of pathogens may be discovered. This was the case in a recent finding in multiple Asian crustacean farm facilities. (Small 2012) notes that only aquaculture species from southern and eastern China have been documented, which include swimming crab P. trituberculatus, the mud crab S. serrata, and the ridgetail white prawn Exopalaemon carinicauda. In addition, a small new finding of Hematodinium parasites in crustaceans was also recently discovered in Russian waters.

Recent findings from infected Chinese crustacean farms

In 2004, swimming crabs P. trituberculatus from Zhoushan were diagnosed with “milky disease” (Small 2012). They showed signs of lethargy due to the development of white muscle tissues and milky hemolymph. In addition, these crabs had a deficiency in cellular hemolymph and developed discoloured shells. Over 3000 acres of coastal aquatic culture was affected, with death rates as high as 60%. This was the first noted outbreak of its kind in China.

In 2005, mud crabs S. serrata were infected with “yellow water disease” in Zhejiang Province (Small 2012). Hematodinium trophonts, prespores, and dinospore stages were present in studied individuals. Affected mud crabs were thinner than usual, had white muscle mass, and had abnormal milky liquids below the carapace. Other mud crab culture regions in that same year were also hit with Hematodinium infections. During transit in between shipments, affected crabs had a ‘cooked’ orange appearance and died shortly after.

In 2008, a disastrous Hematodinium infection epidemic shook ridgetail white prawn (E. carinicauda) aquacultures in Zhoushan (Small 2012). Shrimp were languid and had white muscles in their appendages. Most notable is the white colour of their hemolymph, giving the illness the name “milky shrimp disease.” Mortality rates reached 100%, completely wiping out many aquafarms.

Research on the aforementioned epidemics show that the same parasite is able to infect multiple crustacean hosts, as amplified partial SSU gene and ITS1 rDNA regions from the parasite infecting ridgetail white prawn were exceedingly similar to the sequences from parasites infecting swimming crabs and mud crabs (Xu et al., 2010). Xu et al. (2010) were the first to report a Hematodinium infection in shrimp.

Recent findings from infected Russian crustacean farms

Red king crabs P. camtschaticus and blue king crabs P. platypus from the Sea of Okhotsk in Russia studied in late 2006 had a tiny percentage of individuals that showed symptoms of a Hematodinium infection (Ryazanova, 2008). Scientists found that king crab hemolymphs developed a cream colour following parasite acquisition. Furthermore, prepared crab meat was unpalatable and was reminiscent of “bitter crab disease” described in Tanner crabs (Meyers et al., 1987). Vast numbers of Hematodinium parasites ranging from different vegetative life stages were present in all sampled crab tissues (Ryazanova, 2008).

Description of the organism

Species belonging to genus Hematodinium bear the key identifying characteristics of dinoflagellates. These include a dinokaryon, a pellicle, naked gymnodinoid dinospores, and dinomitosis (Stentiford & Shields 2005). Because only a handful of species in this genus have been studied, there is a poor understanding of their life cycle.

Scientists speculate that spore ingestion is the main transmission pathway in which crustacean hosts acquire Hematodinium parasites (Shields, 1994). However, cannibalism with the ingestion of trophonts is another possibility. Vegetative cells known as trophonts are usually located in the host’s hemolymph and quickly multiply via schizogony. Plasmodia containing 2 to 8 nuclei are motile in H. perezi. Sporulation follows, leading to the formation of prespores then of dinospores. Dinospores supposedly exit the host through small openings in the carapace or through antennal glands. Macrospores are slightly larger than microspores by a few micrometers, and both are able to withstand ocean water conditions for several days.

Discrepancies in life stages can occur due to the timing of parasite acquisition as well as due to varying maturation rates of parasites in different hosts (Shields, 1994). For example, in host C. bairdi, sporulation can occur in more or less than a year. In contrast, studies concerning hosts Portunus pelagicus and Scylla serrata suggest a faster development rate of Hematodinium parasites.

Life cycle of Hematodinium sp. in host Nephrops norvegicus

One particular species with a known life cycle is the unnamed Hematodinium parasite taken from host Nephrops norvegicus. Appleton and Vickerman’s (1998) in vitro experiments describe the fusion of macrodinospores and microdinospores to produce filamentous trophonts that form colonies known as ‘Gorgonlocks.’ Next, these Gorgonlocks either progress into ‘clump’ colonies, or they become an interconnected plasmodial colony known as an arachnoid trophont. The arachnoid trophont enlarges to form an arachnoid sporont, which enters sporogony to produce sporoblasts. Sporogenesis follows in which sporoblasts develop into macro- and microspores, coming full circle with the life cycle. Appleton and Vickerman (1998) suggest that the life stage that scientists often encounter Hematodinium sp. is sporogony. However, other researchers oppose their proposition as trophic stages have been found in other hosts (Meyers et al., 1987).

Two examples of partial life cycles of Hematodinium sp.

An incomplete life cycle of a Hematodinium species in the hemolymph of host Chionoecetes bairdi was also documented by Eaton et al. (1991). The plasmodial trophont produced amoeboid trophonts, which then morphed into prespores and dinospores (Meyers et al., 1987). Both Meyers et al. (1987) and Eaton et al. (1991) described macrodinospores measuring between 12 and 14 mm long and microspores between 7 and 9 mm long.

Additionally, a partial life cycle of Hematodinium sp. is made available by Shields and Squyars’ (2000) observations in host Callinectes sapidus. This life history contrasts that of the parasite found in N. norvegicus described earlier. The vermiform plasmodium either buds to create more plasmodia, or it enters merogony. The vegetative amoeboid trophonts detach during segmentation, in which fission processes follow. Eventually, the amoeboid trophonts stop for a final fission division, as a result of high cellular densities. They proceed to a final sporogonal division to produce four dinospores.

Practical importance

Crustaceans make up a significant fraction of globally imported marine shellfish. They are economically important worldwide, therefore a single epidemic can result in a monetary loss starting at hundreds of thousands of dollars (Stentiford & Shields 2005). Parasites belonging to genus Hematodinium contribute to the mortality rates of commercial crustaceans, thus able to initiate the decline of the crustacean market. A notable example is the economic effect of the “bitter crab disease” caused by Hematodinium sp. on southeast Alaskan crabs. This infection alters the biochemical composition of crustacean flesh, resulting in an unpleasant change in taste (Stentiford & Shields 2005). It takes only one affected host for the disease to sweep an entire shipment of crabs (Meyers et al., 1987). More than $250,000 was lost as a result of higher-than-normal crab mortality rates, as described by Meyers et al. (1987). Moreover, the state of Virginia faces an annual $500k to $1 million deficit as a result of unlisted declines in crustacean Callinectes sapidus populations during summer and autumn in highly saline waters (Stentiford & Shields 2005).

A complete assessment of the impact of Hematodinium sp. on commercialized shellfish is not possible due to the nature of living goods (Stentiford & Shields 2005). Dead and/or distant crustaceans cannot be analyzed for parasitic infections. Young crabs and mature female crabs are often overlooked as well.

Scientists have used several methods in the diagnosis of Hematodinium sp. in crustacean hosts. These include visual examination, wet smears, neutral red staining, histology, and molecular detection (Stentiford & Shields 2005). Funding for further research on the impact of Hematodinium sp. on fisheries can be justified by the possible development of more versatile scientific methods to identify other ‘at risk’ crustacean populations.

List of species

Hematodinium perezi

Hematodinium australis

External links

General Genus Overview:

http://www.vims.edu/research/departments/eaah/programs/crustacean/research/hematodinium/

Bitter Crab Disease:

http://www.dfo-mpo.gc.ca/science/aah-saa/diseases-maladies/hematcb-eng.html

Ibacus peronii

Ibacus peronii, the Balmain bug or butterfly fan lobster, is a species of slipper lobster. It lives in shallow waters around Australia and is the subject of small-scale fishery. It is a flattened, reddish brown animal, up to 23 cm (9 in) long and 14 cm (6 in) wide, with flattened antennae and no claws.

Journal of Crustacean Biology

The Journal of Crustacean Biology is a quarterly peer-reviewed scientific journal in the field of carcinology (crustacean research). It is published by The Crustacean Society and Oxford University Press (formerly by Brill Publishers and Allen Press), and since 2015 the editor-in-chief has been Peter Castro. According to the Journal Citation Reports, its 2016 impact factor is 1.064.The journal has a mandatory publication fee of US$ 115 per printed page for non-members of the Society and an optional open access fee of $1830 minimum.

Malacostraca

Malacostraca is the largest of the six classes of crustaceans, 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, woodlice, amphipods, mantis shrimp 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 (rarely 21), and divided into a head, thorax, and abdomen.

Maxillopoda

Maxillopoda is a diverse class of crustaceans including barnacles, copepods and a number of related animals. It does not appear to be a monophyletic group, and no single character unites all the members.

Peracarida

The superorder Peracarida is a large group of malacostracan crustaceans, having members in marine, freshwater, and terrestrial habitats. They are chiefly defined by the presence of a brood pouch, or marsupium, formed from thin flattened plates (oostegites) borne on the basalmost segments of the legs. Peracarida is one of the largest crustacean taxa and includes about 12,000 species. Most members are less than 2 cm (0.8 in) in length, but the largest is probably the giant isopod (Bathynomus giganteus) which can reach 76 cm (30 in).

Pygidium

The pygidium (plural pygidia) is the posterior body part or shield of crustaceans and some other arthropods, such as insects and the extinct trilobites. It contains the anus and, in females, the ovipositor. It is composed of fused body segments, sometimes with a tail, and separated from thoracic segments by an articulation.

Sessilia

Sessilia is an order of barnacles, comprising the barnacles without stalks, or acorn barnacles. They form a monophyletic group and are probably derived from stalked barnacles. The order is divided into three suborders. Brachylepadomorpha contains a single family, Neobrachylepadidae, while Verrucomorpha contains two families, Verrucidae and Neoverrucidae. The remaining twelve families are in the suborder Balanomorpha.

SpongeBob SquarePants (season 3)

The third season of the American animated television series SpongeBob SquarePants, created by Stephen Hillenburg, aired on Nickelodeon from October 5, 2001 to October 11, 2004, and consists of 20 episodes. The series chronicles the exploits and adventures of the title character and his various friends in the fictional underwater city of Bikini Bottom. The season was executive produced by series creator Hillenburg, who also acted as the showrunner. Hillenburg halted production on the show to work on the 2004 film adaptation of the series, The SpongeBob SquarePants Movie. After production on the film, Hillenburg resigned from the show as its showrunner, and appointed staff writer Paul Tibbitt to overtake the position. Season 3 was originally set to end the series after the release of the film, but the success prevented the series from ending, leading to a fourth season.

The season received critical acclaim from media critics and fans. During its run, SpongeBob SquarePants became (and remains) the highest rated children's show on cable, with over 50 million viewers a month. The show received several recognitions, including its nomination at the Primetime Emmy Awards for Outstanding Children's Program. The episodes "New Student Starfish" and "Clams" were nominated for Outstanding Animated Program (for Programming Less Than One Hour) category, while the entry "SpongeBob B.C. (Ugh)" won the same category. The season was also the first time the show received a nomination at the Kids' Choice Awards and won. It won the 2003 Kids' Choice Awards for Favorite Cartoon, and also won the following year's Kids' Choice Award for the same category. Celebrities—including Justin Timberlake, Kelly Osbourne, Britney Spears, Bruce Willis, Noel Gallagher, rapper Dr. Dre, and Mike Myers—have been reported to be fans of the show.Several compilation DVDs that contained episodes from the season were released. The SpongeBob SquarePants: The Complete 3rd Season DVD was released in Region 1 on September 27, 2005, Region 2 on December 3, 2007, and Region 4 on November 8, 2007.

Telson

The telson is the posterior-most division of the body of an arthropod. It is not considered a true segment because it does not arise in the embryo from teloblast areas as do real segments. It never carries any appendages, but a forked "tail" called the caudal furca may be present. The shape and composition of the telson differs between arthropod groups.

Uropod

Uropods are posterior appendages found on a wide variety of crustaceans. They typically have functions in locomotion.

Extant Arthropoda classes by subphylum
Chelicerata
Myriapoda
Pancrustacea
(Crustacea +
+ Hexapoda)

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