The place that the Bridgeworms or Starworms ( Gephyrei ) should occupy in the system has been subject to a great difference of opinion. By some zoologists they were counted among the Echinoderms, others among the Worms, either among the Annelids or the Acanthocephalus.

Bonellia viridis, recognizable by its two-winged snout, lives in the Mediterranean Sea and on the Canadian coast, hidden between gravel and rock crevices. A green dye penetrates both the muzzle and the other body. This is covered with many warts and can constrict and contract in many ways. The snout is, if possible, suitable for even greater shape changes, since it is large in size of about 8 cm. body length, more than 50 cM. can be extended far and only when contracted[ 637 ]a few cM. is long. The mouth opening is a cervical longitudinal groove at the root of the snout. Occasionally the Bonellia leaves her hiding corner and crawls over the bottom with the help of her snout, the front horns of which act as sutures. The great flexibility of the body allows it to use very narrow crevices for shelter; she is averse to full daylight, likes the twilight of the morning better. The males, which have only recently become known as such, have a completely different appearance than the females, are tiny and resemble Turbellaria.