Megathura crenulata

Megathura crenulata
Megathura crenulata on the right, and the warty sea cucumber Parastichopus parvimensis on the left
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Gastropoda
Order:	Archaeogastropoda
Superfamily:	Fissurelloidea
Family:	Fissurellidae
Genus:	Megathura
Species:	M. crenulata
Binomial name
Megathura crenulata G. B. Sowerby I, 1825

Living specimen of Megathura crenulata with mantle extended over much of its shell.

Megathura crenulata, common name the great keyhole limpet or giant keyhole limpet, is a northeast Pacific species of limpet in the family Fissurellidae.^[1] Megathura is a monotypic genus, in other words, this is the only species in that genus.

Description

These keyhole limpets are large, growing up to 60–132 mm (2.4–5.2 in), and unusually have a shell largely concealed in the tough fleshy mantle.^[2]

Megathura crenulata, the giant keyhole limpet, is a gastropod (close relative of snails and slugs) in the phylum Mollusca. This limpet is found on rocky shores (where rocks serve as protection from potential predators) from low intertidal zones to subtidal waters. The limpets are present from Northern California (coast of Monterey Bay) to lower Baja California (coast of Isla Asuncion). The shell of this species is covered by the mantle and has a large apical, oval opening, just forward of the center. This opening allows water and waste to exit their mantle cavity. The water enters the mantle cavity under the shell near the head and passes over the paired gills, where gas exchange takes place. The shell has concentric growth lines and fine ribs that extend radially. The exposed mantle of this limpet is either black or a pale, grayish white (edge is dark purple or black). The diet of M. crenulata includes seaweeds, colonial ascidians (sea squirts) and algae. They eat by scrapping them from surfaces with a radula. The radula is a belt with several chains of small teeth and is mostly composed of chitin, a highly resistant carbohydrate. Their way of locomotion is by the pale yellow muscular foot, which is found on their ventral side. M. crenulata has been used for experimental studies on gamete agglutination. Their blood (as in other molluscs) appears bluish when oxygenated! This is due to the presence of hemocyanin, a copper-containing protein analogous to hemoglobin. However, unlike hemoglobin, this oxygen-carrying molecule is not bound to cells, but simply dissolved in the hemolymph (fluid part of their blood). ^{[3] [4]}

Distribution

They are native to rocky coasts of Southern California, United States to Baja California, Mexico and are found at shallow depths below the low tide line.^[5]

Keyhole limpet hemocyanin

Keyhole limpet hemocyanin from Megathura crenulata is used as vaccine carrier protein. Keyhole Limpet hemocyanin, or KLH, is a copper containing respiratory protein, similar to hemoglobin in humans. KLH is a large protein that acts as the hapten carrier part of the vaccine component, and is so far thought to be non-toxic. The major potential use of KLH is for bladder carcinoma by stimulating a specific immune response, but there are many other medical uses such as stress assessment, understanding inflammatory conditions, and treating drug addition. Vaccines and other KLH uses are in the research or trial phases. A liter of blood from a keyhole limpet will produce 20 grams of protein, which can be worth as much as $100,000.^[6][7][8]

^{[9] [10] [11]}

References

External links

• Gastropods.com: Megathura crenulata

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