ECTOPROCTA 



THROUGH 



ECHIUROIDEA 



Unsegmented Schizocoels 



The next eight "higher" phyla in the animal king- 

 dom are the schizocoels. The schizocoels (Gr. 

 schizo, cleave + koilos, hollow) are characterized 

 by a true body cavity, the coelom, of a type formed by a 

 cleavage, or split, in the middle germ layer, the 

 mesoderm. The marine members of these phyla share a 

 particular kind of larval stage, the trochophore. Ac- 

 tually larvae of these phyla show some variation and 

 some are referred to by different names; therefore, it 

 would be more accurate to say they share a "trocho- 

 phore-like" larval stage. The schizocoelous phyla 

 are grouped into the Lophophorata (Ectoprocta, 

 Phoronida, and Brachiopoda) and the Schizocoela 

 (unsegmented Sipunculoidea, Moliusca, and 

 Echiuroidea plus segmented Annelida and Arthro- 

 poda). All of these phyla are believed to have de- 

 veloped from an ancestral trochophore that was, in 

 turn, derived from an ancestral ciliated flatworm. 



LOPHOPHORATA: ECTOPROCTA, 

 PHORONIDA, AND BRACHIOPODA 



The phyla Ectoprocta, Phoronida, and Brachio- 

 poda probably followed similar lines of evolution. 

 This similarity is implied by their all having a tent- 

 acle-like structure, the lophophore, surrounding their 

 mouths. The lophophore is mainly a device for creat- 

 ing a current that directs microscopic food to the 



animal's mouth. This tentacle-like structure is the 

 basis for the three phyla being called the Lophopho- 

 rata, but rotifers, pterobranchs and certain other 

 animals have a similar structure also called a lopho- 

 phore. 



ECTOPROCTA (Moss Animals) 



Diagnosis: symmetry bilateral; body unseg- 

 mented; schizocoelomates with a lophophore; co- 

 lonial, some as tufts or branches less than 14-inch 

 high, others resembling colonial hydroids and corals 

 or seaweeds; a few are mat-like and some form thin 

 crusts on rocks, seaweeds, shells, or other objects; 

 difficult to observe, because most are small and in- 

 conspicuous, but some attain considerable size; most 

 colonies are attached, but some are free floating; a 

 few are not colonial but will not be seen; few are 

 truly moss-like; fresh-water forms are mostly jelly- 

 like or gelatinous; mostly marine, one fresh-water 

 order (Figure 13.1 ). 



The ectoprocts and entoprocts are called "moss 

 animals," a common name referring to their similar- 

 ity in external form and reflecting early confusion 

 about the true relationships of the two groups. This 

 confusion should not exist because, despite super- 

 ficial similarities, ectoprocts are schizocoelomates 

 and entoprocts are pseudocoelomates. Schizocoelo- 

 mates possess a true body cavity, the coelom, and 



213 



