Feresa attenuata is very similar in appearance to melon-headed whales and to juvenile false killer whales. From a distance it is very difficult to tell these three apart. The shape of the head, the dorsal fin and the flippers of pygmy killer whales are different from the other two. The head of Feresa attenuata is rounded and lacks a beak. They have an underslung jaw and white lips, and usually a white patch on the tip of the lower jaw. The skull is asymmetrical and the right jaw is smaller and usually has one less tooth than the left jaw. The teeth are large and conical. There are usually 8 to 11 pairs of teeth in the upper jaw and 11 to 13 pairs of teeth in the lower jaw.
Pygmy killer whales have a sub-triangular, long based, high dorsal fin with a tip that points backward. The dorsal fin is located near the center of the body and lacks rigidity, often inclining to the side. The flippers of pygmy killer whales are moderate in length and have rounded tips.
The body of Feresa attenuata is slender, though the midsection forward is slightly more robust than the midsection back. Pygmy killer whales are not whale sized at all; rather, they are average sized dolphins and part of the family Delphinidae. An adult ranges in length from 2.1 to 2.6 meters and weighs between 110 and 170 kg. The coloring is dark gray to black with some paler markings on the underside, as well as some white on the belly. Feresa attenuata has a groove on the skin of its belly that extends from anterior to the umbilicus to the anus. In both males and females this groove contains the umbilicus, the anus and the genitals. (Balcomb, 1987; Ridgway, 1994; Tinker, 1988; http://www.cetacea.org/pkiller.htm, 1999; http://www.sci.tamucc.edu/tmmsn/29Species/pygmykiller.html, 1999; http://www.gomr.mms.gov/homepg/regulate/environ/marmam/pygmy.html, 1999; http://library.advanced.org/2605/pygkill.htm, 1999).
Range mass: 110 to 170 kg.
Range length: 2.1 to 2.6 m.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: sexes alike