Pair-Legged Position

Limnoriids are highly mobile. The animal has a head, a segmented thorax and abdomen, with seven pairs of legs positioned ventrally under the thorax. Pleopods positioned under the abdomen function as gills and are used in swimming. The last two posterior segments of the animal - the fifth pleomer... 

The sulfur atom in SF4 is bonded to four other atoms and has one nonbonding electron lone pair. Because an electron lone pair spreads out and occupies more space than a bonding pair, the nonbonding electrons in SF4 occupy an equatorial position where they are close to (90° away from) only two charge clouds. Were they instead to occupy an axial position, they would be close to three charge clouds. As a result, SF4 has a shape often described as that of a seesaw. The two axial bonds form the board, and the two equatorial bonds form the legs of the seesaw. (You have to tilt your head 90° to see it.)... 

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