Mysids: Mysida

The bodies of mysids are usually glassy and transparent, although deep-sea species are often red. Many species have dark, star-shaped patterns made up of clusters of special cells. These clusters of cells give some mysids the ability to change colors to match their background. They can turn dark against a black background or a dark olive green if they are living among green algae (AL-jee).

Most mysids resemble wormlike shrimp and measure between 0.39 to 1.18 inches (10 to 30 millimeters) long. Both pairs of antennae are branched, or biramous (BY-ray-mus). Males have bristles on the bases of the second pair of antennae. The compound eyes are black and mounted on flexible stalks. Each compound eye has multiple lenses. The head and segmented thorax are tightly joined together in a single body region called the cephalothorax (SEH-feh-lo-THOR-acks). A shieldlike carapace covers the head and most of the cephalothorax and is tightly attached with, or fused to, the first 3 or 4 thoracic (thuh-RAE-sik) segments.

The thorax has eight pairs of biramous thoracic limbs, or pereopods (PAIR-ee-oh-pawds). The first and sometimes second pairs of pereopods have pincherlike claws and are used for feeding. The bases of some pereopods in females have plates that form a brooding chamber called the marsupium (mar-SUE-pee-uhm).

The abdomen has six segments. All segments are similar in appearance except for the last, which is twice as long as the others. Each of the first five abdominal segments has a pair of biramous appendages, or pleopods (PLEE-oh-pawds), underneath. The pleopods are usually smaller in the female and sometimes in the male. Males have specialized pleopods that are used for mating. At the tip of the abdomen is a flaplike tail, or telson. On either side of the telson is a biramous uropod (YUR-oh-pawd). Together the telson and uropods form a fanlike tail.