Spiomenia spiculata has a curved body that tapers slightly toward the posterior end; it is usually widest at its midsection. It has a dorsofrontal sensory pit, dorsoterminal sense organ, and a mantle cavity opening partly closed off by spicules. The longest epidermal spicules on S. spiculata are found toward the rear of the organism near the opening to the mantle cavity. There are nine different types of spicules, including two types of copulatory spicules that occur in paired groups protruding through the mantle cavity. Several accessory copulatory spicules are grouped near the opening to the mantle cavity. The pedal groove contains three types of solid spicules. The radula of S. spiculata makes a single turn into paired anteroven-tral radular pockets; there are 22-25 teeth with 22-23 denticles per tooth. In addition, this aplacophoran has unusually large paired salivary glands on its upper surface that empty into the esophagus where it joins the radular sac.
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