270 



PHORONIDEA 



SUBPHYLUM 6. PHORONIDEA.* 



Sessile, marine worms living in chitinous tubes in shallow water, which 

 have at the anterior end of the body a horseshoe-shaped tentacular crown 

 or lophophore. The animals are gregareous, their tubes being often 

 twisted together, but without, however, communicating with one another. 

 The tubes are also covered with sand, pieces of shell, etc., which give them 

 a characteristic appearance. The lophophore consists of a double ridge, 

 each part of which bears a single row of tentacles, its lateral extremities 

 forming a spiral coil on each side. The mouth and the anus are near 

 together in the middle of the lophophore, but are 

 separated by a long projection of the body wall 

 called the epistome. Near the anus are the paired 

 orifices of the kidneys. The body cavity is large and 

 is divided by a diaphragm into two parts, an upper 

 or anterior, which is continuous with the cavities of 

 the epistome and the tentacles, and a lower, which 

 contains the viscera: the diaphragm is pierced by 

 blood vessels and the oesophagus. The digestive tract 

 is U-shaped, consisting of the oesophagus, stomach, 

 and intestine, and is supported by longitudinal mesen- 

 teries. Two circulatory fluids are present, a colorless 

 fluid in the body cavity and a red fluid in a system 

 of closed vessels which lie along the two limbs of the 

 digestive tube and are distributed to the tentacles 

 and other organs. The kidneys are a pair of tubes 

 which communicate between the body cavity and the 

 outside. The nervous system is subepithelial in posi- 

 tion and consists of a nerve ring surrounding the mouth and nerves 

 going from it to the tentacles. The animals are hermaphroditic, the 

 gonads lying near the stomach and discharging their products into the 

 coelom, whence they find their way to the outside through the kidney 

 pores. The development is a metamorphosis, the characteristic larva 

 being known as the actinotrocha. 



The systematic position of the animals has long been a matter of 

 dispute, but they are now usually placed near the Bryozoa and Brachio- 

 poda. The subphylum contains a single genus and about a dozen species, 

 of which two are American. 



PHORONIS Wright. With the characters of the subphylum: 11 

 species. 



Fig. 442 Phoro- 

 nis architecta 

 young individual 

 with about 30 ten- 

 tacles (Cowles). 1, 

 epistome ; 2, lopho- 

 phore ; 3, digestive 

 tract. 



* See "Phoronis architecta," by R. P. Cowles, Mem. Nat. Acad., Vol. 10, p. 76, 

 1905. "On Phoronis pacifica sp. nov.," by H. B. Torrey, Biol. Bull., Vol. 2, p. 283, 1901. 



