68, k), absent in Chondrophorida and Cystophorida; they are contractile and resemble, both in appearance, structure and function, the umbrella of a medusa, with radial canals, ring-canal and velum; but they are without manubrium, tentacles or sense-organs, and are always bilaterally symmetrical, a peculiarity of form related with the fact that they are attached on one side to the stem.
In all other Siphonophores, the ancestral form was a Siphonula, a bilaterally symmetrical Anthomedusa After Haeckel, from Lankester's Treatise on Zoology.
- The Chaetopoda are with but few exceptions (Myzostomida in part, Sternaspis) elongated worms, flattened or, more usually, cylindrical, and bilaterally symmetrical.
Apart from the asymmetry of the intestine caused by the lateral position of the anus in the two genera just named, Brachiopods are bilaterally symmetrical animals.
The scolex is biradially constructed, the proglottides flattened, quadrangular and bilaterally symmetrical.
How would you define bilaterally? Add your definition here.