• WordNet 3.6
    • n Belemnoidea order of extinct dibranchiate cephalopods related to the surviving spirulas
    • ***
Century Dictionary and Cyclopedia
    • belemnoidea An order or suborder of the dibranchiate cephalopods, now almost extinct, but very abundant in the Mesozoic age. They have internal chambered shells with septa traversed by a siphuncle, the posterior part of the shell bearing a calcareous guard or sheath. The arms, 10 in number, are provided with hooklets. Some authors include in this suborder the coiled living Spirula. In several of the fossil species the head, arms, and ink-bag of the animal have not infrequently been preserved.
    • ***