Sentence:  Here is an embryo, or young form, which has just escaped from the egg, and is hurrying off seawards to "see life," without doubt, and to begin life in earnest as well. You now behold a little body, which, roughly described, we shall say has a triangular shape. It has a tail behind, and the shield or "shell" with which the little body is covered, is prolonged in front and at its side-angles or corners into spines or horns. Three pairs of feet, or appendages that resemble these organs, are possessed by the infant barnacle, the two hinder pairs being forked at their tips and provided with long bristles. A single eye appears in front of the two foremost "feet;" and a mouth, stomach, and intestine are discovered within this little body. Thus provided within and without, this little Cyclopean creature swims merrily through the sea. In this stage it is universally named the <WSD>"Nauplius</WSD>". 
Meaning of the word marked with <WSD> tags:  A crustacean larva that has three pairs of locomotive organs (corresponding to antennules, antennae, and mandibles), a median eye, and little or no segmentation of the body. (from mid 19th c.)