43 Veligers and Polyps-High

Veligers and Polyps FOCUS Question How do ocean invertebrates develop?

海洋无脊椎动物是如何发展的?

Life in the Sea When you think of animals, what do you picture? Dogs, cats, fish, and birds? These animals all have backbones. They are called vertebrates. But most animals on Earth are invertebrates. These animals do not have backbones. They include everything from insects to snails to octopuses. Many invertebrates live in the sea. Two examples are bivalves and sea jellies. These animals have strange and fascinating life cycles!

当你想到动物的时候，你会想到什么? 狗、猫、鱼和鸟? 这些动物都有脊椎。 它们被称为脊椎动物。 但是地球上的大多数动物都是无脊椎动物。 这些动物没有脊骨。 它们包括昆虫、蜗牛、章鱼等各种生物。 许多无脊椎动物生活在海里。 两个例子是双壳类动物和海水母。 这些动物有着奇怪而迷人的生命周期!

Bivalves If you eat seafood, you have probably seen bivalves. Clams, oysters, mussels, and scallops are all bivalves. An adult bivalve has a two-part shell. The shell protects the animal's soft body. Most of the time, the bivalve keeps its shell slightly open. A tube on its body sticks out of the shell. This tube, called a siphon, pulls water inside the shell and across the animal's gills. The siphon also pulls in tiny bits of food and moves them into the mouth. Many adult bivalves attach themselves to rocks or coral. Others bury themselves in soft sand or mud. Word Wise The prefix bi- means "two." Valve means "door." Bivalves can close their two shells like a pair of doors.

如果你吃海鲜，你可能见过双壳类动物。 蛤蜊、牡蛎、贻贝和扇贝都是双壳类。 成年双壳类动物的壳由两部分组成。 外壳保护着动物柔软的身体。 大多数时候，双壳类动物的壳都是微微张开的。 它身上的一根管子从壳里伸出来。 这个管子被称为虹吸，将水吸进贝壳内并穿过动物的鳃。 虹吸还会吸入微小的食物碎片，并将它们送入口中。 许多成年双壳类动物附着在岩石或珊瑚上。 有的则把自己埋在软沙或泥里。 前缀bi-的意思是“两个”。 Valve的意思是“门”。双壳类动物可以把它们的两个壳像一对门一样合上。

Baby Bivalves Young bivalves live different lives than adult bivalves. Bivalves hatch from eggs laid in the water. A young bivalve starts as a larva called a veliger. The veliger swims freely in the water. Veligers are tiny. They have only a single shell. They also have a body part called a velum (see photo). The veliger flaps its velum to swim and grab food such as tiny plants. As the veliger grows, its shell gets bigger and heavier. Eventually, the veliger sinks toward the bottom. It develops a strong foot that helps it crawl along the seafloor.

幼小的双壳动物与成年双壳动物的生活方式不同。 双壳类动物在水中产卵孵化。 一个年轻的双壳类动物开始时是一种被称为膜壳的幼虫。 鱼在水里自由地游动。 Veligers很小。它们只有一个壳。 它们还有一个身体部位叫做“膜”(见图)。 它拍打着它的膜游泳和抓取食物，比如小植物。 随着膜层的生长，它的壳变得越来越大，越来越重。 最终，外膜会沉到底部。 它长出了强壮的脚，帮助它在海底爬行。

Changing Shape Once the veliger is on the seafloor, it goes through metamorphosis. It changes shape as it becomes an adult. The veliger shell grows into two halves that can open and close. Most adult bivalves become sessile, or stationary. They stay in one spot for the rest of their lives. Clams use their foot to dig a hole in the seafloor. Mussels and oysters make a powerful cement to attach themselves to a hard surface. They stick to such things as rocks, coral, or wood. Do You Know? Not all adult bivalves stay in one spot. Scallops can swim, even as adults! They use strong muscles to "flap" their shells together.

一旦膜层在海底，它就会发生变形。 它长大后会改变形状。 外膜壳长成两半，可以打开和关闭。 大多数成年双壳类变得无梗或静止不动。 它们一辈子都待在一个地方。 蛤蜊用脚在海底挖洞。 贻贝和牡蛎能产生一种强大的水泥，将自己附着在坚硬的表面上。 它们会粘在岩石、珊瑚或木头上。 你知道吗?并不是所有的成年双壳动物都呆在一个地方。 扇贝成年后也会游泳!它们用强壮的肌肉将壳“拍打”在一起。

Aquaculture In many places, people farm and harvest bivalves. Several kinds of bivalves are raised as food sources. Oysters are raised for food and for the beautiful pearls they make, which can be used in jewelry. Ocean farming is known as aquaculture. Aquaculture involves several steps: 1. Farmers collect adult bivalves from the ocean. 2. Bivalves lay eggs in tanks of warm water. The veligers hatch. 3. The farmers feed and care for the veligers until they are ready for metamorphosis. 4. The farmers set up ropes, nets, or wood in a shallow seashore area or in the mouth of a river. 5. They release the veligers in this area. 6. The veligers attach to the structures set up by the farmers. There, they change into adult bivalves. 7. Bivalves are collected and sold to stores and restaurants.

在许多地方，人们种植和收获双壳类动物。 几种双壳类动物被饲养作为食物来源。 人们饲养牡蛎既是为了食用，也是为了生产可以用来制作珠宝的美丽珍珠。 海洋养殖被称为水产养殖。 水产养殖涉及几个步骤:1。 农民们从海里收集成年双壳类动物。 2. 双壳类在温水罐中产卵。 绒毛孵化。3.农民们喂养和照顾这些绒毛，直到它们准备好蜕变。 4. 农民们在浅海地区或河口架起绳索、网或木头。 5. 他们在这片区域释放了外皮。 6. 这些绒毛附着在农民搭建的结构上。 在那里，它们变成成年双壳类动物。 7. 双壳类动物被收集并出售给商店和餐馆。