Thermosbaenaceans: Thermosbaenacea

Adult thermosbaenaceans (ther-mohs-bee-NAY-cee-ans) are small, blind, and have slender bodies measuring up to 0.20 inches (5.2 millimeters). Their short head does not have a beaklike projection, or rostrum. They may or may not have eyestalks, but they never have eyes. The first pair of antennae (antennules) is branched, or biramous (BY-ray-mus). The second pair of antennae are uniramous (YU-neh-RAY-mus) or not branched. A short, shieldlike carapace covers the head and segmented thorax. The carapace of adult females has a large, bulging area that forms a brood chamber inside for storing eggs until they hatch. The first thoracic segment of both males and females is tightly joined, or fused, to the head.

The thorax has five to seven pairs of leglike biramous limbs called pereopods (PAIR-ee-oh-pawds). The pereopods are usually used for walking and sometimes swimming. The abdomen has six segments, but only the first two have appendages. The abdominal appendages, called pleopods (PLEE-oh-pawds), are well developed, narrow and rounded, or very small. At the end of the abdomen is a pair of slender biramous appendages, the uropods (YUR-oh-pawds). In between the uropods is a taillike segment called the telson. The telson in this species is not tightly joined with, or fused to, the last abdominal segment. The telson and uropods do not join together to form a fanlike tail.