UNSEGMENTEO SCHIZOCOELS 



215 



pseudocoelomates do not. The coelom is considered 

 a true body cavity because it is completely lined by 

 cells derived from embryonic mesoderm. 



Almost all ectoprocts are attached, as colonies, 

 on objects in shallow water. These moss animals are 

 usually hermaphroditic, individuals containing both 

 male and female sex organs, but some are male or fe- 

 male. The fertilized egg develops into a motile larva 

 which soon attaches to a suitable substrate. The 

 larva then transforms to an adult which asexually 

 buds into a colony. Fresh-water species produce an 

 internal asexual bud which is released upon death of 

 the adult colony; the bud will grow into a colony only 

 if environmental conditions are suitable for adult 

 growth and survival. The internal bud is thus the 

 ectoproct's means of surviving freezing or drying of 

 their fresh-water habitat. For example, drying of a 

 pond kills the adults and releases the internal buds; 

 if and when rains replace the pond waters, each bud 

 grows into an adult colony. 



PHORONIDA (Horseshoe Worms) 



Diagnosis: symmetry bilateral; unsegmented; 

 schizocoelomates with a lophophore; red, orange, 

 or green animals from under 0.1 inch to 15 inches 

 long (tubes to 18 inches); live in self-secreted, leath- 

 ery, membranous, or calcareous tubes containing ce- 

 mented sand grains, shells, and other materials; 

 superficially resemble some of the annelids (feather 

 worms), but the "fan" (lophophore) is usually a 

 double spiral of horseshoe shape, and the body is 



§^; 



smooth and unsegmented; all are sedentary and 

 marine (Figure 13.2). 



The phoronids are tube-dwelling, worm-like ani- 

 mals, of shallow marine waters. They use their 

 lophophores to filter microscopic organisms from 

 the water, the microorganisms being trapped upon a 

 sticky mucous secretion. Frequently they can be 

 observed in the shallow waters of bays during low 

 tides, but only the lophophore tentacles will be ex- 

 tended from within the tube — the characteristic 

 feeding position. 



Adults are hermaphroditic. Like most marine 

 animals, they shed sperm and eggs into the sea water, 

 the site of fertilization. The fertilized egg, or zygote, 

 develops into a motile trochophore-like larve that may 

 wander some distance. Soon the larva becomes sed- 

 entary and assumes the adult form. 



BRACHIOPODA ( Lamp Shells) 



Diagnosis: symmetry bilateral; unsegmented; 

 schizocoelomates with a lophophore; bear a super- 

 ficial resemblance to bivalve mollusks in having an 

 external shell of two valves, but these are top (dorsal) 

 and bottom (ventral) rather than right and left; a 

 flexible attachment stalk emerges through a hole in 

 the ventral valve near the hinge (no such structure 

 in bivalve mollusks); also possess internal skeletons, 

 something very rare in bivalves; sexes separate, re- 



Figure 13.2 Phofonis, a horseshoe worm. The tube, a structure often 

 formed of sand, silt, or other debris plus body secretions, is about twice 

 the length of the worm. 



Figure 13.3 Lamp shell types; A, Magellania; B, Terebratatia; C, 

 Lingula with tube found at its burrow bottom. The open port of the shell 

 is at or facing the mouth of the burrow. 



