Neenchelys andamanensis: A new species of Worm Eel from the Andaman Sea.

Worm Eels of the genus Neenchelys are small burrowing Eels found in the Indian ans Pacific Oceans. There are currently about ten described species, with other undescribed species known in museum and university collections.

In a paper published in the journal Zootaxa on 24 December 2015, Yusuke Hibino of the Fisheries Research Laboratory at Mie University, Ukkrit Satapoomin of the Phuket Marine Biological Center and Seishi Kimura, also of the Fisheries Research Laboratory describe a new species of Worm Eel from the Andaman Sea.

The new species is named Neenchelys andamanensis, meaning 'from the Andaman'. It is described from a single specimen collected from a depth of between 520 and 531 m off the coast of Phucket in 1999, and held in the collection of the Phuket Marine Biological Center. The specimen is 336 mm in length, and is of uncertain sex. It can be differentiated from other species in the same genus by the number of ribs and tail vertebrae.

Neenchelys andamanensis, 336 mm TL, Andaman Sea. (A) position of anus, (D) origin of dorsal fin. Hibino et al. (2015).

See also...

Neenchelys gracilis: A new species of Worm Eel from Taiwan.                                         Worm Eels, Ophichthidae, are burrowing Eels found...

Japanese Eel classified as Endangered.        The International Union for the Conservation of Nature published its annual update of its Red List of Threatened Species on Thursday 12 June 2014, marking the 50th year of the list's existence, and revising the status of a number of Plant and Animal species from around...

The effect of parasitic Nematodes on European Eels.                                       European Eels, Anguilla anguilla, have a complex life-cycle; they hatch from eggs in the Sargasso Sea...

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Neenchelys gracilis: A new species of Worm Eel from Taiwan.

Worm Eels, Ophichthidae, are burrowing Eels found in tropical and temperate waters from the coastal shallows to depths of about 750 m, with some species found in freshwater ecosystems. They range from about 10 cm to about 3 m in length, and are highly adapted to their burrowing lifestyle, with many species having lost their fins completely, with larger species occasionally mistaken for Sea Snakes.

In a paper published in the journal Zootaxa on 24 December 2015 Hsuan-Ching Ho of the National Museum of Marine Biology & Aquarium and Institute of Marine Biology at the National Dong Hwa University and Kar-Hoe Loh of the Institute of Ocean and Earth Sciences at the University of Malaya describe a new species of Worm Eel from off the coast of Dong-gang on the southeast coast of Taiwan.

The new species is placed in the genus Neenchelys and given the specific name gracilis, meaning slender. The species is described from a single specimen caught in a otter trawl at a depth of about 400 m. The specimen is 429 mm in length, with a fringe of cirri around its nostrils; it has small gill openings and has almost completely lost its pectoral fins (paired fins behind the gills). It is a brownish grey colour.

 Neenchelys gracilis. Lateral view of whole fish. Bars indicate the locality of the dorsal-fin origin (left) and the anus (right). Ho & Loh (2015).

See also...

Japanese Eel classified as Endangered.        The International Union for the Conservation of Nature published its annual update of its Red List of Threatened Species on Thursday 12 June 2014, marking the 50th year of the list's existence, and revising the status of a number of Plant and Animal species from around...

The effect of parasitic Nematodes on European Eels.                                       European Eels, Anguilla anguilla, have a complex life-cycle; they hatch from eggs in the Sargasso Sea...

A living fossil eel discovered in Palau.            Eels first appear in the fossil record about 100 million years ago, in the Mid Cretaceous. These Cretaceous forms are primitive compared to modern forms, with incomplete fusion of the dorsal, caudal and anal fins, scales on their bodies and many of the bones lost or fused still present. However they are still clearly eels, with elongate bodies and the loss and fusion of...

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Japanese Eel classified as Endangered.

The International Union for the Conservation of Nature published its annual update of its Red List of Threatened Species on Thursday 12 June 2014, marking the 50th year of the list's existence, and revising the status of a number of Plant and Animal species from around the world. The Japanese Eel, Anguilla japonica, has been included on the list for the first time, being believed to have lost over half its spawning population in the last 30 years, primarily due to overfishing. 

A Japanese Eel, Anguilla japoonica, in Hong Kong. HT Cheng/iNaturalist.

While named for Japan, the species is quite widespread, being found from Korea and Japan in the north, along the coasts of China, Taiwan and Hong Kong to the Philippines in the south, as well as sometimes being found in Thailand, Vietnam and Cambodia. However recent studies have shown that all the Eels across this range form a single population with a common breeding ground, to the west of the Mariana Islands. The Eel is also widely bred in captivity, with waterways stocked from captive-bred Eels across much of its range. However it is far from clear if these captive-bred Eels are capable of returning to the wild spawning grounds, and thereby contributing to the future of the species. 

The known range of the Japanese Eel, Anguilla japonica. ICUN Species Survival Commission.

Like most Eels the Japanese Eel has a complex life cycle, with adults migrating to breed at an oceanic breeding site remote from the land, and an ocean-going larval stage that migrates back to estuarine waters before metamorphosing into a juvenile that takes several years to mature to a full adult. Unusually the Japanese Eel seems to have two separate post-metamorphic lifestyles, with some juveniles migrating into rivers and other fresh water ecosystems to mature, while others remain in shallow marine waters around the coast. However all these Eels appear to be a single breeding population. 

The single breeding site for the species, combined with heavy levels of human consumption of all life-stages across its range, and uncertainty as to the extent to which each adult population contributes to the breeding population, together with the risk of the breeding cycle being disrupted by climate-change driven changes in ocean current, lead to a considerable degree of concern about the future of this species.

See also...

 The effect of parasitic Nematodes on European Eels.

European Eels, Anguilla anguilla, have...

 A living fossil eel discovered in Palau.

Eels first appear in the fossil record about 100 million years ago, in the Mid Cretaceous. These Cretaceous forms are primitive compared to modern forms, with incomplete fusion of the dorsal, caudal and anal fins, scales on their bodies and many of the bones lost or fused still present. However they are still clearly eels, with elongate bodies and the loss and fusion of some bones associated with the group, in...

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The effect of parasitic Nematodes on European Eels.

European Eels, Anguilla anguilla, have a complex life-cycle; they hatch from eggs in the Sargasso Sea in the southwest North Atlantic, then migrate to European inland waterways where they grow for up to 25 years before returning to the Sargasso to breed. This life-cycle exposes leaves them exposed to a number of human-related threats, including overfishing, habitat loss and pollutants, and the species has suffered a dramatic decline in numbers since the 1970s, to the alarm of conservationists. Since the 1980s the species is also known to be widely suffering from infection from an invasive parasitic Nematode worm, Anguillicoloides crassus, which probably entered Europe with imported Eels from Southeast Asia, and against which the European Eel apparently has no natural defenses. 

The European Eel, Anguilla anguilla. Animal Base/Staats-und Universitätbibliothek Göttingen.

Anguillicoloides crassus infects the swim-bladders of Eels, and from where it drains blood. The Nematode has a much shorter life-cycle than the Eel, and an infection will purge itself since eggs are laid outside the host, but multiple infections can damage or even destroy the swim-bladder, removing the Eels ability to control its own buoyancy and killing it. Anguillicoloides crassus is not reliant on the Eels to survive, it can use a variety of hosts including many types of Fish and Crustaceans, so a reserve of Nematodes is likely to remain in the environment even if the Eels become locally extinct, so that new Eels recolonizing an area will be infected immediately.

The parasitic Nematode Worm, Anguillicoloides crassus. AquaNIS.

Eels raised in the laboratory and infected with Anguillicoloides crassus, tend to be underweight compared to other Eels of the same age. Such infected Eels are approximately the same length as uninfected Eels, but are notably thinner. Based upon this studies of Eels in the field have tended to use weight-to-length ratio as a proxy for Nematode infection, though this has never actually been tested in wild Eels.

In a paper published in the Proceedings of the Royal Society Series B Biological Sciences on 16 January 2013, a team of scientists led by François Lefebvre of Station Biologique de la Tour du Vala, describe the results of a study of Eels in a complex of brackish lagoons in the Rhône River delta, in which Eels were actively checked for Nematode infection and signs of past infection (scarring of the swim bladder), and the rate of infection was compared to the weigh-to-length ratio of the Eels.

Surprisingly this study found that the relationship between infection rate and age appeared to be reversed in wild Eels compared to laboratory-raised Eels; fatter Eels showed signs of bearing a heavier parasite load that thinner Eels, suggesting that the model used in many previous studies is completely wrong and must be reassessed. Lefebvre et al. suggest that while infection in the laboratory is deliberate and not influenced by diet, this is not the case with wild Eels, which become infected by consuming Nematode eggs, thus making more voracious Eels more likely to become infected, while giving Eels that consume less, either through more selective feeding or for other reasons, a better chance of avoiding the Nematodes.

See also An invasive Serpulid Worm in the La Encrucijada Biosphere Reserve, Mexico, Blue Flatworms invade Menorca and A living fossil eel discovered in Palau.

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A living fossil eel discovered in Palau.

Eels first appear in the fossil record about 100 million years ago, in the Mid Cretaceous. These Cretaceous forms are primitive compared to modern forms, with incomplete fusion of the dorsal, caudal and anal fins, scales on their bodies and many of the bones lost or fused still present. However they are still clearly eels, with elongate bodies and the loss and fusion of some bones associated with the group, in particular the gill rakers and the pectoral fins.

Volume 279 of the Proceedings of the Royal Society B (Biological Sciences) contains a paper by a team lead by David Johnson of the Division of Fishes at the National Museum of Natural History at the Smithsonian Institution, describing the discovery of a remarkable living fossil eel from a submarine cave in a coral reef fringing Ngemelis Island, part of the Pacific Ocean Republic of Palau. This eel shows many features in common with Cretaceous eels, and has been named Protanguilla palau (the first/earliest eel from Palau).

Protanguila palau. Top, adult female named as the Holotype, 176 mm in length. All other pictures of juvenile specimen named as Paratype. Top centre, whole specimen, 65 mm in length, scale bar is 5 mm. Left centre, head in lateral view, scale bar is 5 mm. Right centre, head in ventral view, scale bar is 2 mm. Bottom left, close up of left gill opening in ventral view, scale bar is o.5 mm. Bottom centre, stained scales on lateral body-line, scale bar is 0.5 mm. Bottom right, close up of scales, scale bar is 0.5 mm. From Johnson et al. (2012).

Protoanguila palau shows many similarities to Cretaceous eels, it has an unfused palette, incompletely fused fins, and retains its scales and some bones lost in modern eels. In addition it shows some features lost in even Cretaceous eels, it retains its gill rakers, and whilst clearly an eel, lacks the elongate form found in all other eels. Gene sequencing of P. palau confirms that while it is more closely related to eels than any other fish, all other eels are more closely related to one-another than they are to P. palau.

Based upon this Johnson et al. suggest that P. palau is a living fossil, which branched off from other eels at some time around the boundary between the Triassic and the Jurassic, and has been living in isolation ever since. Whilst this seems fairly reasonable (the date is suspiciously precise, 'before the Mid Cretaceous' would have been more defensible), Ngemelis Island is a coraline limestone platform on top of an extinct submarine volcano - a feature that is unlikely to have remained unaltered since the Mesozoic. This implies that P. palau must have migrated here some time in the more recent past, and may well have relatives elsewhere in the West Pacific.

See also New Mouse Lemur discovered in Madagascar and Boney Fish on Sciency Thoughts YouTube.