The Chaetognatha or chaetognaths are a phylum of predatory marine worms that are a major component of plankton worldwide. Commonly known as arrow worms, they are mostly nektonic; however about 20% of the known species are benthic, and can attach to algae and rocks. They are found in all marine waters, from surface tropical waters and shallow tide pools to the deep sea and polar regions. Most chaetognaths are transparent and are torpedo shaped, but some deep-sea species are orange. They range in size from 2 to 120 millimetres.
Aurelia aurita is a species of the family Ulmaridae. All species in the genus are very similar, and it is difficult to identify Aurelia medusae without genetic sampling; most of what follows applies equally to all species of the genus.
The European sprat, also known as brisling, brisling sardine, bristling, garvie, garvock, Russian sardine, russlet, skipper or whitebait, is a species of small marine fish in the herring family Clupeidae. Found in European, West Asian and North African waters, it has silver grey scales and white-grey flesh. Specific seas in which the species occurs include the Irish Sea, Black Sea, Baltic Sea and Sea of the Hebrides. The fish is the subject of fisheries, particularly in Scandinavia, and is made into fish meal, as well as being used for human consumption. When used for food it can be canned, salted, breaded, fried, boiled, grilled, baked, deep fried, marinated, broiled, and smoked.
Pelagic fish live in the pelagic zone of ocean or lake waters—being neither close to the bottom nor near the shore—in contrast with demersal fish that live on or near the bottom, and reef fish that are associated with coral reefs.
Mnemiopsis leidyi, the warty comb jelly or sea walnut, is a species of tentaculate ctenophore. It is native to western Atlantic coastal waters, but has become established as an invasive species in European and western Asian regions. Three species have been named in the genus Mnemiopsis, but they are now believed to be different ecological forms of a single species M. leidyi by most zoologists.
The nursehound, also known as the large-spotted dogfish, greater spotted dogfish or bull huss, is a species of catshark, belonging to the family Scyliorhinidae, found in the northeastern Atlantic Ocean. It is generally found among rocks or algae at a depth of 20–60 m (66–197 ft). Growing up to 1.6 m (5.2 ft) long, the nursehound has a robust body with a broad, rounded head and two dorsal fins placed far back. It shares its range with the more common and closely related small-spotted catshark, which it resembles in appearance but can be distinguished from, in having larger spots and nasal skin flaps that do not extend to the mouth.
The European pilchard is a species of ray-finned fish in the monotypic genus Sardina. The young of the species are among the many fish that are sometimes called sardines. This common species is found in the northeast Atlantic, the Mediterranean, and the Black Sea at depths of 10–100 m (33–328 ft). It reaches up to 27.5 cm (10.8 in) in length and mostly feeds on planktonic crustaceans. This schooling species is a batch spawner where each female lays 50,000–60,000 eggs.
Merluccius merluccius, the European hake, is a merluccid hake of the genus Merluccius. Other vernacular names include Cornish salmon and herring hake. It is a predatory species which was often netted alongside one of its favoured prey, the Atlantic herring, thus the latter common name. It is found in the eastern Atlantic from the Norway and Iceland south to Mauritania and into the Mediterranean Sea. It is an important species in European fisheries and is heavily exploited with some populations thought to be being fished unsustainably.
Mertensia ovum, also known as the Arctic comb jelly or sea nut, is a cydippid comb jelly or ctenophore first described as Beroe ovum by Johan Christian Fabricius in 1780. It is the only species in the genus Mertensia. Unusually among ctenophores, which normally prefer warmer waters, it is found in the Arctic and adjacent polar seas, mostly in surface waters down to 50 metres (160 ft).
Sagitta is a genus of Chaetognatha, a phylum commonly known as arrowworms or arrow worms. Phylum Chaetognatha comprises small marine worms.
The leaping mullet is a species of fish in the family Mugilidae. It is found in coastal waters and estuaries in the northeast Atlantic, ranging from Morocco to France, and including the Mediterranean and Black Sea. It has been introduced to the Caspian Sea.
Parasagitta elegans, the elegant arrow worm, is a small arrow worm in the family Sagittidae, previously named Sagitta elegans
Beroe ovata is a comb jelly in the family Beroidae. It is found in the South Atlantic Ocean and the Mediterranean Sea and has been introduced into the Black Sea, the Aegean Sea, the Sea of Azov and the Caspian Sea. It was first described by the French physician and zoologist Jean Guillaume Bruguière in 1789.
Beroe cucumis is a species of comb jelly in the family Beroidae. It is found in the Atlantic Ocean. It was first described by the Danish missionary and naturalist Otto Fabricius in 1780.
Bolinopsis infundibulum, commonly known as the common northern comb jelly, is a species of comb jelly in the family Bolinopsidae. It is found in the northern Atlantic Ocean and was first described by the Danish naturalist Otto Friedrich Müller in 1776.
Pleurobrachia pileus is a species of comb jelly, commonly known as a sea gooseberry. It is found in open water in the northern Atlantic Ocean, the North Sea, the Baltic Sea and the Black Sea, and was first described by the Danish zoologist Otto Friedrich Müller in 1776.
Parasagitta is a genus of arrow worms in the family Sagittidae. At one time these arrow worms were classified in the genus Sagitta.
The dispersal of invasive species by ballast water refers to the unintentional introduction of invasive species to new habitats via the ballast water carried by commercial shipping vessels. Ballast water spreads an estimated 7000 living species to new habitats across the globe. These species can affect the ecological balance of their new regions by outcompeting native species or otherwise impacting native ecosystems.
Beroe gracilis is a species of comb jelly in the family Beroidae. It is a free-swimming species found in the North Sea, the Atlantic Ocean and the Mediterranean Sea.
Eukrohnia hamata is a species of arrow worm, transparent marine invertebrates belonging to the phylum Chaetognatha. Characterized by its unique morphology and adaptation for life in the deep-sea environment, this planktonic predator is widely distributed throughout the world's oceans, and plays an important role in marine ecosystems.
