Sentence:  Only <WSD>nauplii</WSD> that are attracted to the light at the top of the hatching tank should be collected, since these are the healthy ones. 
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.)