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Signal crayfish branchiobdellid crop 2.jpg
Branchiobdellids on the claw of a signal crayfish
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Annelida
Class: Clitellata
Order: Branchiobdellida

Branchiobdellida is an order of freshwater leech-like clitellates that are obligate ectosymbionts or ectoparasites, mostly of astacoidean crayfish. [1] They are found in the Northern Hemisphere and have a holarctic distribution in East Asia, the Euro-Mediterranean region and North and Central America, with the greatest species diversity being in North and Central America. [2]



The exact relationship of this group of clitellates with other groups has been the subject of debate for a century or more. The American zoologist Perry C. Holt wrote his doctoral thesis on branchiobdellids and devoted his 45 years of research to the taxon. With his colleague, the American zoologist Richard L. Hoffman, he described 8 new genera and 75 new species, and re-described various other species. In 1965, he came to the conclusion that the group should be raised from a family to an order, a sister group to the oligochaetes and leeches. Forty years later, molecular data from rDNA and mitochondrial DNA studies has shown that he was correct, and that Oligochaeta, Branchiobdellida, Acanthobdellida and Hirudinea form a monophyletic group and that each should be considered an order. [3] Branchiobdelida is now acknowledged to be sister to leeches and acanthobdellidans. [4]


Branchiobdellida vary in length between 1 mm (0.04 in) and 10 mm (0.4 in). The body is formed from fifteen segments. There is no prostomium, and the peristomium and next three segments are modified into a sucker, surrounded by small tentacles, with the mouth at its centre. The buccal cavity has a single dorsal and a single ventral tooth. Segment 14 has the anus on its dorsal surface, and segment 15 forms a sucker. [5]


The majority of branchiobdellida use crayfish as hosts, usually living on their heads, carapaces and chelae (claws), but in some instances living inside their gill cavities. [2] In East Asia, some species live on freshwater shrimp, and in Northern and Central America, freshwater crabs, shrimps and isopods host branchiobdellids, and some have even been found on Chesapeake blue crabs. In the Euro/Mediterranean region, however, crayfish are exclusively used as hosts. Some branchiobdellids are generalists, but a few are limited to association with a single host species. Several different species of branchiobdellid are sometimes found on a single crayfish. Their hosts include open-water crustaceans, cave-dwellers and burrowers, [2] but many branchiobdellida have a very limited range, occurring in a single river system or a single cave. An Appalachian brook crayfish was found to have one species of branchiobdellid in the gill chambers, one on the oral and ventral surfaces of the body and one on the chelae. [6]


Branchiobdellida feed on the micro-organisms and detritus that accumulate on their host; they will also feed on any soft tissues exposed where the host's exoskeleton is damaged. The relationship is generally symbiotic in that the host benefits from the cleaning activities of the branchiobdellids, and the latter benefit from a constant supply of food and a surface on which to deposit their cocoons; the worms have been maintained for months in the laboratory in the absence of a host, but the cocoons must be attached to a living host in order for normal development of the embryos to occur. [2]

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Malacostraca Largest class of crustaceans

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, and divided into a head, thorax, and abdomen.

Oligochaeta Subclass of annelids including earthworms

Oligochaeta is a subclass of animals in the phylum Annelida, which is made up of many types of aquatic and terrestrial worms, including all of the various earthworms. Specifically, oligochaetes comprise the terrestrial megadrile earthworms, and freshwater or semiterrestrial microdrile forms, including the tubificids, pot worms and ice worms (Enchytraeidae), blackworms (Lumbriculidae) and several interstitial marine worms.

Clitellata Class of annelid worms

The Clitellata are a class of annelid worms, characterized by having a clitellum - the 'collar' that forms a reproductive cocoon during part of their life cycles. The clitellates comprise around 8,000 species. Unlike the class of Polychaeta, they do not have parapodia and their heads are less developed.

Erpobdella obscura is a freshwater ribbon leech common in North America. It is a relatively large leech and is commonly used as bait by anglers for walleye and other sport fish. In Minnesota, live bait dealers annually harvest over 45,000 kg of bait-leeches, raising concerns of over-harvest.

Marine invertebrates

Marine invertebrates are the invertebrates that live in marine habitats. Invertebrate is a blanket term that includes all animals apart from the vertebrate members of the chordate phylum. Invertebrates lack a vertebral column, and some have evolved a shell or a hard exoskeleton. As on land and in the air, marine invertebrates have a large variety of body plans, and have been categorised into over 30 phyla. They make up most of the macroscopic life in the oceans.

Euhirudinea True leeches

Euhirudinea, the true leeches, are an infraclass of the Hirudinea. These clitellate annelids are of somewhat unclear relationships; namely the relationships of Hirudinea with oligochaetes are in need of revision. It may be that the presumed sister taxon of the Euhirudinea, the Acanthobdellidea, turns out to be more distantly related, as was already the case with the Branchiobdellida. Thus, eventually Euhirudinea might become a junior synonym of Hirudinea.

Arhynchobdellida Order of leeches

Arhynchobdellida, the proboscisless leeches, are classified as an order of the Hirudinea. More recently, this order has been rejected and replaced with a newer classification. Still, leech taxonomy and systematics may eventually need to be revised, not because of the many uncertainties exist about their phylogeny, but because the major clades of clitellate annelids - and whether the clitellates are themselves are a clade - have not been fully elucidated. For example, the "true leeches" (Euhirudinea) might actually be synonymous with the Hirudinea, as all other leech-like annelids might not be very closely related to the true leeches.

Glossiphoniidae Family of annelid worms

Glossiphoniidae are a family of freshwater proboscis-bearing leeches. These leeches are generally flattened, and have a poorly defined anterior sucker. Most suck the blood of freshwater vertebrates like amphibians, crocodilians and aquatic turtles, but some feed on invertebrates like oligochaetes and freshwater snails instead. Although they prefer other hosts, blood-feeding species will opportunistically feed from humans.

Leech Parasitic or predatory annelid worms

Leeches are segmented parasitic or predatory worms that comprise the subclass Hirudinea within the phylum Annelida. They are closely related to the oligochaetes, which include the earthworm, and like them have soft, muscular, segmented bodies that can lengthen and contract. Both groups are hermaphrodites and have a clitellum, but leeches typically differ from the oligochaetes in having suckers at both ends and in having ring markings that do not correspond with their internal segmentation. The body is muscular and relatively solid, and the coelom, the spacious body cavity found in other annelids, is reduced to small channels.

Motobdella montezuma is a species of leech which is only found in Montezuma Well, central Arizona, United States. It is a nocturnal pelagic predator that feeds almost exclusively on the endemic amphipod Hyalella montezuma, which it detects using passive sonar and swallows whole.

Sucker (zoology) Specialised attachment organ of an animal

A sucker in zoology refers to specialised attachment organ of an animal. It acts as an adhesion device in parasitic worms, several flatworms, cephalopods, certain fishes, amphibians, and bats. It is a muscular structure for suction on a host or substrate. In parasitic annelids, flatworms and roundworms, suckers are the organs of attachment to the host tissues. In tapeworms and flukes, they are a parasitic adaptation for attachment on the internal tissues of the host, such as intestines and blood vessels. In roundworms and flatworms they serve as attachment between individuals particularly during mating. In annelids, a sucker can be both a functional mouth and a locomotory organ. The structure and number of suckers are often used as basic taxonomic diagnosis between different species, since they are unique in each species. In tapeworms there are two distinct classes of suckers, namely "bothridia" for true suckers, and "bothria" for false suckers. In digeneal flukes there are usually an oral sucker at the mouth and a ventral sucker posterior to the mouth. Roundworms have their sucker just in front of the anus; hence it is often called a pre-anal sucker.

<i>Haemopis sanguisuga</i> Species of annelid

Haemopis sanguisuga is a species of freshwater leech in the family Haemopidae. It is commonly called the horse-leech, but that is due to the similarity of its appearance to the leech Limnatis nilotica, which sometimes enters the nasal cavities of livestock. Haemopis sanguisuga does not behave in this way. Another synonym for this leech is Aulastomum gulo.

Crustacean Subphylum of arthropods

Crustaceans form a large, diverse arthropod taxon which includes such animals as crabs, lobsters, crayfish, shrimps, prawns, krill, woodlice, and barnacles. The crustacean group can be treated as a subphylum under the clade Mandibulata; because of recent molecular studies it is now well accepted that the crustacean group is paraphyletic, and comprises all animals in the clade Pancrustacea other than hexapods. Some crustaceans are more closely related to insects and the other hexapods than they are to certain other crustaceans.

Annelid Phylum of segmented worms

The annelids, also known as the ringed worms or segmented worms, are a large phylum, with over 22,000 extant species including ragworms, earthworms, and leeches. The species exist in and have adapted to various ecologies – some in marine environments as distinct as tidal zones and hydrothermal vents, others in fresh water, and yet others in moist terrestrial environments.

Hirudo orientalis is a species of medicinal leech. It has been confused with Hirudo medicinalis, but has recently been recognized as a different species. This Asian species is associated with mountainous areas in the subboreal eremial zone and occurs in Azerbaijan, Iran, Uzbekistan and Kazakhstan. It occurs also in Georgia, and probably in Armenia.

Erpobdella punctata is a leech in the family Erpobdellidae. It is found in freshwater streams and ponds in many parts of North America.

Piscicolidae Family of annelid worms

The Piscicolidae are a family of jawless leeches in the order Rhynchobdellida that are parasitic on fish. They occur in both freshwater and seawater, have cylindrical bodies, and typically have a large, bell-shaped, anterior sucker with which they cling to their host. Some of the leeches in this family have external gills, outgrowths of the body wall projecting laterally, the only group of leeches to exchange gases in this way.

<i>Acanthobdella peledina</i> Species of annelid worm

Acanthobdella peledina is a species of leech-like clitellate in the order Acanthobdellida. It feeds on the skin and blood of freshwater fishes in the boreal regions of northern Europe, Asia and North America.

<i>Barbronia weberi</i> Species of annelid worm

Barbronia weberi is a species of predatory freshwater leech in the family Salifidae. It is native to southeastern Asia but has spread to other parts of the world, including Australia, South America, southern Europe and the United States.

Nectonema is a genus of marine horsehair worms first described by Addison E. Verrill in 1879. It is the only genus in the family Nectonematidae described by Henry B. Ward in 1892, in the order Nectonematoidea, and in the class Nectonematoida. The genus contains five species; all species have a parasitic larval stage inhabiting crustacean hosts and a free-living adult stage that swims in open water.


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