104 



CLASSIFICATION, PHYLOGENY, AND EVOLUTION: 



SEGMENTATION 



Segmentation is the linear repetition of body parts. 

 True segmentation is conspicuous externally and in- 

 ternally in most Annelida; it is visible mainly ex- 

 ternally in the Arthropoda, and internally in the 

 Chordata. Especially in chordates, segmentation 

 may be seen clearly only during development. 



MISCELLANEOUS CHARACTERS 



The nature of other features, such as skeleton, ap- 

 pendages, and sexual status, are also important in 

 diagnosing phyla. These biological aspects are de- 

 scribed very briefly as they are used in the following 

 classification of animals. 



ANIMAL CLASSIFICATION 



The principles of animal complexity permit the 

 separation of the animal phyla in different ways. A 

 widely used classification (Hyman's) is that given be- 

 low. 



Kingdom Animalia — cellular, tissue, or organ system 

 organization; multicellular animals 

 suBKiNGDOM MESozoA — composcd of an outer layer of 

 body cells and an inner layer of 

 reproductive cells; cellular 

 organization 

 PHI LUM MESOZOA (Mesozoans) 

 SUBKINGDOM PARAZOA — ccUular Organization, but almost 

 at the tissue level of organization 



PHYLUM PORIFERA (SpOnges) 



SUBKINGDOM EUMETAZOA — tissuc or Organ system grade 

 of organization 

 GRADE RADiATA — primarily of radial symmetry; tissue 

 grade of organization with incipient 

 organ systems and mesoderm 



A. Symmetry radial, biradial, or essentially bilateral; 



mouth usually encircled by tentacles; no rows 

 of ciliated plates 



PHYLUM COELENTERATA (= CNIDARIa) (Coclenter- 



ates) 



B. Symmetry biradial; tentacles, if present, not en- 



circling mouth; 8 rows of ciliated paddle-plates 

 PHYLUM cTENOPHORA (Comb Jellies) 

 GRADE BiLATERiA — Symmetry bilateral or secondarily 

 radial; organ system grade of con- 

 struction; mostly with mesoderm of 

 ectodermal origin and usually with 

 a body cavity other than the diges- 

 tive cavity 



A. Acoelomata — region between digestive cavity and 



body wall filled with cells; no body cavity 



1. Anus absent, poorly developed organ systems, 



often considered tissue-organ organization 



PHYLUM PLATYHELMINTHES (FlatWOrms) 



2. Anus present, organ systems present 



PHYLUM NEMERTiNEA (= rhy.nchocoela) (Rib- 

 bon Worms) 



B. Pseudocoelomata — space between digestive tract 



and body wall incompletely lined by cells of 

 mesodermal origin; space is a remnant of a de- 

 velopmental cavity, the blastocoel 



1 . Digestive tract absent 



PHYLUM acanthocephala (Spiny-headed 

 Worms) 



2. Intestine essentially straight; anus posterior 

 PHYLUM aschelminthes (Cavity Worms) 



3. Intestine looped; anus near mouth 

 PHYLUM entgprocta (Moss Animals) 



C. Eucoelomata — body cavity a true coelom 



1. Lophophorata — with a circular, crescent- 



shaped or double spiraled, coiled ridge (the 

 lophophore) bearing ciliated tentacles; intestine 

 looped, bringing mouth near anus; body 

 cavity a schizocoel. 



a. Colonial, with gelatinous, chitinous, or 



calcareous encasements 



PHYLUM ECTOPROCTA (= BRYOZOA Or 



polyzoa) (Moss Animals) 



b. Solitary 



(1) Worm-like 



PHYLUM phoronida (Fan Worms) 



(2) With a bivalve shell 



PHYLUM BRACHiopoDA (Lamp Shells) 



2. Schizocoela — coelom originates as a space in 



the mesoderm; no lophophore 



a. Unsegmented 



(1) Visceral mass covered by a body fold, 



the mantle, which secretes a shell; 

 contains a small group having true 

 segmentation. 



PHYLUM MOLLUSCA (Mollusks) 



(2) No mantle; naked; worm-like 



(a) With an eversible proboscis 

 PHYLUM sipunculoidea (Peanut 



Worms) 



(b) No proboscis; mouth ventral 

 PHYLUM echiuroidea (Echiurids) 



b. Segmented 



(1) No jointed appendages 



PHYLUM ANNELIDA (Segmented Worms) 



(2) With jointed appendages 



pinxuM ARTHROPODA (Joint-legged 

 Animals) 



