''Pontobdella muricata'' is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of marine

leech 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 bodie ...

in the family

Piscicolidae 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 the ...

. It is a parasite of fishes and is native to the northeastern

Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...

, the

Baltic Sea The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden and the North and Central European Plain. The sea stretches from 53°N to 66°N latitude and from ...

, the

North Sea The North Sea lies between Great Britain, Norway, Denmark, Germany, the Netherlands and Belgium. An epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian S ...

, and the

Mediterranean Sea The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the ea ...

Description

''Pontobdella muricata'' is a long, cylindrical, somewhat flattened leech, narrowing at both ends. It has a number of annulations, which do not correspond to its internal segmentation, and is one of the largest sea leeches, with a length up to long when at rest, and double that length when stretched. The anterior end has a sucker with which it feeds, and the posterior end bears another sucker with which it adheres to its host. The skin is rough and covered with small warts; the colour varies, juveniles are usually black or dark green with small speckles, while adults are pale grey, tan, or olive-green.

Distribution and habitat

Native to the northeastern Atlantic Ocean, the species ranges from the Arctic, the Baltic Sea, and the

, to the Mediterranean Sea. It has also been reported from the United States, Canada, Namibia, and Pakistan, but some of these records may be due to misidentification. It is found on the seabed at depths down to about and attached to large

demersal The demersal zone is the part of the sea or ocean (or deep lake) consisting of the part of the water column near to (and significantly affected by) the seabed and the benthos. The demersal zone is just above the benthic zone and forms a layer of ...

fish.

Ecology

This leech is an external parasite of cartilagenous fishes such as the

marbled electric ray The marbled electric ray (''Torpedo marmorata'') is a species of electric ray in the family Torpedinidae found in the coastal waters of the eastern Atlantic Ocean from the North Sea to South Africa. This benthic fish inhabits rocky reefs, seagr ...

(''Torpedo marmorata''), the

common stingray The common stingray (''Dasyatis pastinaca'') is a species of stingray in the family Dasyatidae, found in the northeastern Atlantic Ocean and the Mediterranean and Black Seas. It typically inhabits sandy or muddy habitats in coastal waters shall ...

(''Dasyatis pastinaca''), and the

thornback ray The thornback ray (''Raja clavata''), or thornback skate, is a species of ray fish in the family Rajidae. Distribution The Thornback ray is found in the Atlantic coastal waters of Europe and western Africa. It is also present from south Afri ...

(''Raja clavata''), and less often of

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fishes, is a class of bony fish. They comprise over 50% of living vertebrate species. The ray-finned fishes are so called because their fins are webs of skin supported by bony or hor ...

such as the

European plaice The European plaice (''Pleuronectes platessa''), commonly referred to as simply plaice, is a species of marine flatfish in the genus Pleuronectes of the family Pleuronectidae. Description The European plaice is characterized, on their dorsal ...

(''Pleuronectes platessa''), the black scorpionfish (''Scorpaena porcus''), and the red scorpionfish (''S. scrofa''). It is found attached to the gills, the abdomen, and the bases of the fins of the host, where it feeds by sucking blood. It is quiescent during the day, holding itself motionless and partially coiled, attached by its posterior sucker, but becomes active at night, when it feeds. It can separate from its host and swim by flattening its body. It is the intermediate host for the

protozoa Protozoa (singular: protozoan or protozoon; alternative plural: protozoans) are a group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic tissues and debris. Histo ...

n '' Trypanosoma raiae'', which it carries in its gut and transmits to rays. Like all leeches, ''P. muricata'' is a

hermaphrodite In reproductive biology, a hermaphrodite () is an organism that has both kinds of reproductive organs and can produce both gametes associated with male and female sexes. Many Taxonomy (biology), taxonomic groups of animals (mostly invertebrate ...

, and fertilisation is internal. The eggs pass through the

clitellum The clitellum is a thickened glandular and non-segmented section of the body wall near the head in earthworms and leeches, that secretes a viscid sac in which eggs are stored. It is located near the anterior end of the body, between the fourteent ...

, where each is enclosed in a spherical cocoon. These are attached to empty bivalve or gastropod shells on the seabed and are pale at first, but darken with age. They are often irregularly grouped together, each with a slender, twisted stalk connecting it to a spreading, membranous holdfast. The sphere is filled with a thick, gelatinous material with the developing embryo spirally coiled within. When it is nearly long and ready to hatch, a pair of small, rounded protuberances at the side of the sphere fall off, allowing the juvenile leech to emerge, and search for a suitable host fish.

References

{{Taxonbar, from=Q5155311 Leeches Fauna of the Atlantic Ocean Fauna of the Mediterranean Sea Animal parasites of fish Ectoparasites Animals described in 1758 Taxa named by Carl Linnaeus