Pacific lamprey

The Pacific lamprey (Entosphenus tridentatus or Lampetra tridentata) is an anadromous parasitic lamprey from the Pacific Coast of North America, and Asia. It is also a member of the Petromyzontidae family. The Pacific lamprey is also known as the Three Tooth lamprey and the Tridentate lamprey.

Description

Pacific lamprey grow to about 80 centimetres (31 in) as adults. They are anadromous and semelparous. They have slender, elongate bodies with two dorsal fins arising far back on the body. The anal fins are rudimentary and the lower lobe of the caudal fin is larger than the upper lobe and both lobes are continuous with the dorsal fin and the anal fin. Adults living in the sea are a bluish-black or greenish colour above and pale below, but those in fresh water are brown. This species is distinguished by having three (or occasionally two) sharp teeth on the supraoral bar above the mouth and three sharp points on each lateral plate.

Biology

Lamprey

Lampreys (sometimes also called lamprey eels) are any jawless fish of the order Petromyzontiformes, placed in the superclass Cyclostomata. The adult lamprey may be characterized by a toothed, funnel-like sucking mouth. The common name "lamprey" is probably derived from Latin lampetra, which may mean "stone licker" (lambere "to lick" + petra "stone"), though the etymology is uncertain.

Currently there are about 38 known extant species of lampreys. Although they are well known for boring into the flesh of other fish to suck their blood, in fact only a minority do so; only 18 species of lampreys are actually parasitic. The lampreys are a very ancient lineage of vertebrates, though their exact relationship to hagfishes and jawed vertebrates is still a matter of dispute.

Characteristics

Basic external anatomy of a lamprey

Basic external anatomy of a lamprey

Adults physically resemble eels, in that they have no scales, and can range from 13 to 100 cm (5 to 40 inches) long. Lacking paired fins, adult lampreys have large eyes, one nostril on the top of the head, and seven gill pores on each side of the head. The unique morphological characteristics of lampreys, such as their cartilaginous skeleton, suggest they are the sister taxon (see cladistics) of all living jawed vertebrates (gnathostomes), and are usually considered the most basal group of the Vertebrata. Instead of true vertebrae, they have a series of cartilaginous structures called arcualia arranged above the notochord. Parasitic lampreys feed on prey as adults by attaching their mouthparts to the target animal's body, then using their teeth to cut through surface tissues until they reach blood and body fluid. Although attacks on humans do occur, they will generally not attack humans unless starved. Non-parasitic lampreys, which are usually freshwater species, do not feed as adults; they live off reserves acquired as ammocoetes (larvae), which they obtain through filter feeding.

Pacific Ocean

The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south and is bounded by Asia and Australia in the west and the Americas in the east.

At 165.25 million square kilometers (63.8 million square miles) in area, this largest division of the World Ocean—and, in turn, the hydrosphere—covers about 46% of the Earth's water surface and about one-third of its total surface area, making it larger than all of the Earth's land area combined.

The equator subdivides it into the North Pacific Ocean and South Pacific Ocean, with two exceptions: the Galápagos and Gilbert Islands, while straddling the equator, are deemed wholly within the South Pacific. The Mariana Trench in the western North Pacific is the deepest point in the world, reaching a depth of 10,911 metres (35,797 ft).

The eastern Pacific Ocean was first sighted by Europeans in the early 16th century when Spanish explorer Vasco Núñez de Balboa crossed the Isthmus of Panama in 1513 and discovered the great "southern sea" which he named Mar del Sur. The ocean's current name was coined by Portuguese explorer Ferdinand Magellan during the Spanish circumnavigation of the world in 1521, as he encountered favourable winds on reaching the ocean. He called it Mar Pacifico, which in both Portuguese and Spanish means "peaceful sea".