Metamorphosis is a biological process by which an animal physically develops including birth transformation or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some insects, fish, amphibians, mollusks, crustaceans, cnidarians, echinoderms, and tunicates undergo metamorphosis, which is often accompanied by a change of nutrition source or behavior. Animals can be divided into species that undergo complete metamorphosis ("holometaboly"), incomplete metamorphosis ("hemimetaboly"), or no metamorphosis ("ametaboly").
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle.
Leptocephalus is the flat and transparent larva of the eel, marine eels, and other members of the superorder Elopomorpha. This is one of the most diverse groups of teleosts, containing 801 species in 4 orders, 24 families, and 156 genera. This group is thought to have arisen in the Cretaceous period over 140 million years ago.
The eel is a long, thin bony fish of the order Anguilliformes. The species has a catadromous life cycle, that is: at different stages of development migrating between inland waterways and the deep ocean. Because fishermen never caught anything they recognized as young eels, the life cycle of the eel was a mystery for a very long period of scientific history.
The saccopharyngiformes are a derived lineage of unusual eels within the order Anguilliformes, and includes families Cyematidae, Monognathidae, Eurypharyngidae, Saccopharyngidae, and the proposed family Neocyematidae. Most of the fish in this group are deep-dwelling and rarely seen, typically known from only a handful of specimens. Species include recognizable fish such as pelican eels and bobtail eels. Some can live deep in the ocean, well into the aphotic zone, approximately 500 to 1,800 meters deep. Extensive research has not been conducted on them due to being indirectly observed, with some species known only from their larvae. All families except for the exceptionally rare individuals of proposed family Neoceymatidae are found in all major oceans.
The pelican eel is a deep-sea eel. It is the only known member of the genus Eurypharynx and the family Eurypharyngidae. It belongs to the "saccopharyngiforms", members of which were historically placed in their own order, but are now considered true eels in the order Anguilliformes. The pelican eel has been described by many synonyms, yet nobody has been able to demonstrate that more than one species of pelican eel exists. It is also referred to as the gulper eel, pelican gulper, and umbrella-mouth gulper. The specific epithet pelecanoides refers to the pelican, as the fish's large mouth is reminiscent to that of the pelican.
The Anguillidae are a family of ray-finned fish that contains the freshwater eels. Eighteen of the 19 extant species and six subspecies in this family are in the genus Anguilla. They are elongated fish with snake-like bodies, their long dorsal, caudal and anal fins forming a continuous fringe. They are catadromous fish, spending their adult lives in freshwater, but migrating to the ocean to spawn. Eels are an important food fish and some species are now farm-raised, but not bred in captivity. Many populations in the wild are now threatened, and Seafood Watch recommend consumers avoid eating anguillid eels.
Snipe eels are a family, Nemichthyidae, of eels that consists of nine species in three genera. They are pelagic fishes, found in every ocean, mostly at depths of 300–600 m (980–1,970 ft) but sometimes as deep as 4,000 m (13,000 ft). Depending on the species, adults may reach 1–2 m (39–79 in) in length, yet they weigh only 80–400 g (2.8–14.1 oz). They are distinguished by their very slender jaws that separate toward the tips as the upper jaw curves upward. The jaws appear similar to the beak of the bird called the snipe. Snipe eels are oviparous, and the juveniles, called Leptocephali, do not resemble the adults but have oval, leaf-shaped and transparent bodies. Different species of snipe eel have different shapes, sizes and colors. The similarly named bobtail snipe eel is actually in a different family and represented by two species, the black Cyema atrum and the bright red Neocyema erythrosoma.
Slickheads, also known as nakedheads or smoothheads, are deep water fishes that belong to the family Alepocephalidae. They are most commonly found in the bathypelagic layer, which is approximately 3000m below the surface. They get their name from the lack of scales on their heads. Similarly, the scientific name is from the Greek ᾰ̓- (a-, "not"); λέπος (lepos, "scale"); and κεφαλή (kephalē, "head"). It has about 22 genera with ca. 96 species. In Japanese they are known as Sekitori Iwashi (関取鰯, "Massive Sardine").
The bobtail snipe eels are two species of deep-sea eels in the family Cyematidae, one only in each of two genera. They are small elongate fishes, growing up to 16cm in length.
Neocyema erythrosoma is a species of pelagic fish, a deep-water bobtail snipe eel in the family Cyematidae. It is the only member of its genus, Neocyema. It was first described by Peter Castle in 1978 after two specimens were caught at great depths in the south Atlantic Ocean in 1971. Further specimens have since been caught in the North Atlantic.
Monacoa grimaldii, also known as the mirrorbelly, barreleye, Grimaldi's barreleye, and flatiron fish, is a species of fish in the family Opisthoproctidae. Different sources express different views on its distribution. According to Poulsen and colleagues, it is known with certainty only from the Atlantic Ocean, with records from the Pacific Ocean representing other Monacoa species. However, FishBase and Catalog of Fishes include the Pacific, and in the case of the latter, the Indian Ocean in its range. It is typically mesopelagic, but it has been recorded from depths of 0 to 4,750 metres. It has a body length of 8 cm (3.1 in) SL.
Monognathus, or onejaw, is the only genus of the family Monognathidae of deep-sea eels. The name comes from the Greek monos meaning “one” and gnathos meaning “jaw”, a reference to the large mouth in comparison with the rest of the fish, and also the absence of an upper jaw.
The Japanese eel is a species of anguillid eel found in Japan, Korea, China, and Vietnam, as well as the northern Philippines. There are three main species under the Anguilla genus, and all three share very similar characteristics. These species are so similar that it is believed that they spawned from the same species and then experienced a separation due to different environments in the ocean. Like all the eels of the genus Anguilla and the family Anguillidae, it is catadromous, meaning it spawns in the sea but lives parts of its life in freshwater. Raised in aquaculture ponds in most countries, the Japanese eel makes up 95% of the commercially sold eel in Japan, the other 5% is shipped over by air to the country from Europe. This food in Japan is called unagi; they are an essential part of the food culture, with many restaurants serving grilled eel called kabayaki. However, presumably due to a combination of overfishing and habitat loss or changing water conditions in the ocean interfering with spawning and the transport of their leptocephali this species is critically endangered.
Pterothrissus gissu, also known as the Japanese gissu, is a species of ray-finned fish in the family Albulidae. The Japanese gissu is a rare fish that is distributed in deep water off northwest Pacific Ocean. This fish is known to pass through a leptocephalus larval stage, but only metamorphosed specimens have been available. This species is the only member of its genus.
Marine larval ecology is the study of the factors influencing dispersing larvae, which many marine invertebrates and fishes have. Marine animals with a larva typically release many larvae into the water column, where the larvae develop before metamorphosing into adults.
Eels are ray-finned fish belonging to the order Anguilliformes, which consists of eight suborders, 19 families, 111 genera, and about 800 species. Eels undergo considerable development from the early larval stage to the eventual adult stage and are usually predators.
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, more-so than where the larvae are planktonic, and thereby easily caught.
Opisthoproctus soleatus is a species of fish in the family Opisthoproctidae. It was first described in 1888 by Léon Vaillant. The species lives in most tropical seas, but is more common in the eastern Atlantic, from western Ireland to Mauritania and from Sierra Leone to Angola, and also in the South China Sea. O. soleatus can grow to a standard length of 10.5 centimetres (4.1 in) and usually live from about 500 to 700 metres deep.
Monacoa is a genus of fish in the family Opisthoproctidae found in Atlantic and Pacific Oceans. They are also known as long-nosed mirrorbellies or simply mirrorbellies, in reference to the bioluminescent organ in their intestines. The largest species, Monacoa grimaldii, can grow to 8 cm (3.1 in) standard length.
