Artemia - Brine shrimp

A small aquatic animal belonging to the family Artemiidae, order Anostraca, class Crustacea, phylum Arthropoda. Its English name is sometimes read as it is and called brine shrimp. Its nauplius larvae are often used as food for young tropical fish, and are also known by the product name Sea Monkey. Immediately after hatching, the nauplius larvae are about 0.4 mm long, and when they become adults, they reach about 1 cm. Their bodies are long and slender, with 11 thoracic segments and 9 abdominal segments, and they do not have a carapace. They have swimming legs on their thorax, which they move in sequence to swim on their backs. There is only one species in one genus, but there are many regional varieties, some of which reproduce sexually and some that reproduce parthenogenetically. There are also ovoviviparous species that directly produce nauplius larvae, and oviparous species that produce dauber eggs. Dauber eggs do not hatch until they have dried out once. When dried eggs are placed in seawater, nauplii hatch in 10 to 20 hours, and after feeding on tiny algae and protozoa, they molt 12 times to become adults. They live in salt lakes all over the world, and were once seen in salt fields along the Seto Inland Sea coast of Japan.

[Masamichi Takeda]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

節足動物門甲殻綱無甲目アルテミア科に属する水生小動物。英名をそのまま読んでブラインシュリンプとよぶこともある。また、ノープリウス幼生を熱帯魚の稚魚の餌(えさ)として使うことが多く、シーモンキーという商品名もある。孵化(ふか)直後のノープリウス幼生は体長0.4ミリメートルほどで、成体は約1センチメートルになる。体は細長くて11胸節、9腹節からなり、背甲をもたない。胸部には遊泳肢(ゆうえいし)があり、順次動かして、あおむけになって泳ぐ。1属1種であるが、多くの地方的品種に分かれ、有性生殖をするものと単為生殖をするものとがある。また、直接ノープリウス幼生を産む卵胎生(らんたいせい)と、耐久卵を産む卵生のものがある。耐久卵は一度乾燥しないと孵化しない。乾燥した卵を海水につけると10～20時間でノープリウス幼生が孵化し、微小な藻類や原生動物を食べて12回脱皮すると成体になる。全世界の塩湖に生息し、日本でもかつては瀬戸内海沿岸の塩田でみられた。

［武田正倫］

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