Hagfish

From Wikipedia, the free encyclopedia

(Redirected from Hyperotreti)
Jump to: navigation, search
 Sections should be added to this article, to conform with Wikipedia's Manual of Style.
Please discuss this issue on the talk page.
Hagfish
Pacific hagfish resting on bottom280 m depth off Oregon coast
Pacific hagfish resting on bottom
280 m depth off Oregon coast
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Subphylum: Craniata
Class: Myxini
Order: Myxiniformes
Family: Myxinidae
Genera

Eptatretus
Myxine
Nemamyxine
Neomyxine
Notomyxine
Paramyxine
Quadratus

Hagfish are marine craniates of the class Myxini, also known as Hyperotreti. Myxini is the only class in the clade Craniata that does not also belong to the subphylum Vertebrata[1]. Despite their name, there is some debate about whether they are strictly fish (as there is for lampreys), since they belong to a much more primitive lineage than any other group that is commonly defined fish (Chondrichthyes and Osteichthyes). Their unusual feeding habits and slime-producing capabilities have led members of the scientific and popular media to dub the hagfish as the most "disgusting" of all sea creatures.[1][2][3]

Contents

Hagfish are long, vermiform and can exude copious quantities of a sticky slime or mucus (from which the typical species Myxine glutinosa was named). When captured and held by the tail, they escape by secreting the fibrous slime, which turns into a thick and sticky gel when combined with water, and then cleaning off by tying themselves in an overhand knot which works its way from the head to the tail of the animal, scraping off the slime as it goes. Some authorities conjecture that this singular behavior may assist them in extricating themselves from the jaws of predatory fish. However, the "sliming" also seems to act as a distraction to predators, and free-swimming hagfish are seen to "slime" when agitated and will later clear the mucus off by way of the same travelling-knot behavior.

Hagfish have elongated, 'eel-like' bodies, and paddle-like tails. Colours depend on the species, ranging from pink to blue-grey, and may have black or white mottling. Eyes may be vestigial or absent. The hagfish has no true fins or jaws, and has six barbels around its mouth and a single nostril. Instead of vertically articulating jaws like Gnathostomata (vertebrates with jaws), they have a pair of horizontally moving structures with toothlike projections for pulling off food. There are typically short tentacle-like protrusions around the mouth.

Hagfish enter both living and dead fish, feeding on the insides (polychaete marine worms are also prey). While having no ability to enter through skin, they will often enter through current openings such as the mouth, gills or anus. They tend to be quite common in their range, sometimes becoming a nuisance to fishermen by devouring the catch before it can be pulled to the surface. Not unlike leeches, they have a sluggish metabolism and can go months between feedings.

Hagfish average about half a metre (18 inches) in length; Eptatretus goliath is the largest known, with a specimen recorded at 127 cm, while Myxine kuoi and Myxine pequenoi seem to reach no more than 18 cm. An adult hagfish can secrete enough slime to turn a large bucket of water into gel in a matter of minutes.

There has been long discussion in scientific literature about the hagfish being non-vertebrate. Given their classification as Agnatha, Hagfish are seen as an elementary vertebrate in between Prevertebrate and Gnathostome. Thus, their classification is as an invertebrate within subphylum Craniata.

  • They are part of the subphylum Craniata but, taxonomically speaking, they are not vertebrates.
  • They do not have vertebrae so, anatomically, they're not vertebrates.

Recent molecular biology analyses tend to classify hagfish as invertebrates (see references) within subphylum Craniata, their molecular evolutive distance from Vertebrata (sensu stricto) being short. A single fossil of hagfish shows that there has been little evolutionary change in the last 300 million years. [4]

The circulatory system of the hagfish has both closed and open blood vessels, with a heart system that is the most primitive of all vertebrates, bearing some resemblance to that of some worms. This system comprises a "brachial heart", which functions as the main pump, and three types of accessory hearts: the "portal" heart(s) which carry blood from intestines to liver; the "cardinal" heart(s) which move blood from the head to the body, and the "caudal" heart(s) which pump blood from the trunk and kidneys to the body. None of these hearts are innervated, so their function is probably modulated, if at all, by hormones.

Very little is known about Hagfish reproduction. In some species, sex ratio can be as high as 100:1 in favour of females. In other species, individual hagfish which are hermaphroditic, with both ovaries and testes, but the female gonads remain non-functional until the individual has reached a particular stage in the hagfish lifecycle, are not uncommon. Females typically lay 20-30 yolky eggs, that tend to aggregate due to the presence of Velcro-like tufts at either end. Hagfish do not have a larval stage, in contrast to lampreys, which have a long larval phase.

Hagfish are eaten in Japan and South Korea, and their skin is made into "eel leather" (used for so-called "eelskin" products ) in Korea.

In recent years hagfish have become of special interest for genetic analysis investigating the relationships among chordates. It has also recently been discovered that the mucus excreted by the hagfish is unique in that it includes strong, threadlike fibres similar to spider silk. What is interesting about hagfish slime is that it is fibre-reinforced. No other slime secretion known is reinforced with fibres in the way Hagfish slime is. The fibres are about as fine as spider silk (averaging two micrometres), but can be twelve centimetres long. When the coiled fibres leave the Hagfishes' 'slime' gland, they unravel quickly to their full length without tangling. Research continues into potential uses for this or a similar synthetic gel or of the included fibres. Some possibilities include new biodegradable polymers, space-filling gels, and as a means of stopping blood flow in accident victims and surgery patients.

In December of 2003, an article was published by University of Queensland claiming the Hagfish's eye as being significant to evolution of more complex eyes. [2]

About 65 species are known, in 7 genera. A number of the species have only been recently discovered, living at depths of several hundred metres. Some of the species are listed here:

  1. ^ N. A. Campbell and J. B. Reece (2005). Biology Seventh Edition. Benjamin Cummings, San Francisco CA.
  2. ^ Keeping an eye on evolution. PhysOrg.com (2007-12-03). Retrieved on 2007-12-04.
  • New species Eptatretus goliath
  • J.M. Jørgensen, J.P. Lomholt, R.E. Weber and H. Malte (eds.) (1997). The biology of hagfishes. London: Chapman & Hall. 
  • Delarbre et al (2002). "Complete Mitochondrial DNA of the Hagfish, Eptatretus burgeri: The Comparative Analysis of Mitochondrial DNA Sequences Strongly Supports the Cyclostome Monophyly". Molecular Phylogenetics and Evolution 22 (2): 184-192. 
  • Bondareva and Schmidt (2003). "Early Vertebrate Evolution of the TATA-Binding Protein, TBP". Molecular Biology and Evolution 20 (11): 1932-1939. 
  • Fudge, D. (2001). Hagfishes: Champions of Slime Nature Australia, Spring 2001 ed., Australian Museum Trust, Sydney. pp. 61-69.

Wikimedia Commons has media related to:
 The subject of this article has been identified by the Missing Encyclopedic Articles project as being a high priority for expansion.

Retrieved from "http://en.wikipedia.org/wiki/Hagfish"
Advanced Search
Included Web Search Engines


Safe Search

close

Top Matching Results

Occasionally Search.com will highlight specialized results that are based on the context of your query. Examples of specialized results include specific links to news, images, or video.

Top Matching Results may highlight information from other Search.com pages, content from the CNET Network of sites, or third party content. The listings are based purely on relevance. Search.com does not receive payment for listings in this section but our partners that provide this data may get paid for listing these products.

Sponsored Links

This section contains paid listings which have been purchased by companies that want to have their sites appear for specific search terms and related content. These listings are administered, sorted and maintained by a third party and are not endorsed by Search.com.

Search Results

Search.com sends your search query to several search engines at one time and integrates the results into one list which has been sorted by relevance using Search.com's proprietary algorithm. You can customize the list of search engines included in your metasearch from the preferences.

The search engines that are used in your metasearch may allow companies to pay to have their Web sites included within the results. To view the Paid Inclusion policy for a specific search engine, please visit their Web site. Search.com does not accept payment or share revenue with any search engine partner for listings in this section.