INVERTEBRATE EUCOEIOMATES 



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TAXONOMIC SUMMARY- 



Kingdom Animalia (L. ammalis, animate) — animals 



Subkingdom Eumetazoa (Gr. «/ — , true + m«(a, among + <:oon, animal) — eumetazoans 



Grade Bilateria (L. bi-, two + lateralis, side) 



Eucoelomata (Gr. eu- + koilos, hollow) 



Enterocoela (Gr. enteron, gut + koilos) 

 Phylum Echinodermata (Gr. echinos, spiny + derma, skin) — spiny-skinned animals 

 Subphylum Pelmatozoa (Gr. /)c/mato, stalk + zoon) — pelmatozoans 

 Class Crinoidea (Gr. cnnon, lily + oideos, form or type of) — sea lilies and feather 

 stars 

 Subphylum Eleutherozoa {Gr. eleutheros, free + zoon) — eleutherozoans 

 Class Holothuroidea (Gr. holothunon, sea cucumber + oideos) — sea cucumbers 

 Class Echinoidea (Gr. echinos + oideos) — sea and heart urchins, sand dollars 

 Class Asteroidea (Gr. QiZfr, star + oideos) — sea stars or starfish 

 Class Ophiuroidea (Gr. o/)A!j, snake + owra, tail + oideos) — brittle and basket stars 

 Phylum Chaetognatha (Gr. chaeton, bristle + gnathos,]3.w) — arrow worms 

 Phylum Hemichordata (Gr. hemi, half + chorde, string) — hemichordates 

 Class Enteropneusta (Gr. enleron, gut + pneuslos, breathed) — acorn worms 

 Class Pterobranchia (Gr. pteron, feather + branchion, gill) — pterobranchs 

 Class Planctosphaeroidea (Gr. planktos, wandering + sphaira, ball + oideos) — plancto- 



sphaeroids 

 Phylum Pogonophora (Gr. pogon, beard + phoros, bearing) — beard worms 

 Phylum Chordata (Gr. chorde) — chordates 

 Subphylum Tunicata (L. (unicaiui, clothed with a tunic) — tunicates 

 Class Larvaceae (L. larva, immature animal undergoing metamorphosis) — larvaceans 

 Class Thaliacea (Gr. Ihalia, abundance) — chain or pelagic tunicates 

 Class Ascidiaceae (Gr. askidion, a little leather bag) — ascidians 

 Subphylum Cephalochordata (Gr. A:e/»Aa/?, head + chorde) — lancets 



dipleurula, and perhaps its adult stage, the pentactula 

 may have had the five tentacles that provide the basis 

 of the five-rayed, or -armed, construction of this 

 phylum and of an ancestral feeding habit that used 

 the arms. Also, it is assumed that the tentacles gave 

 rise to the echinoderm water-vascular system. 



In the development of pentactula from the di- 

 pleurula, which probably was not an echinoderm and 

 may have been the ancestor of the echinoderm- 

 chordate line, there probably was first a bilateral 

 pentactula stage. The bilateral pentactula perhaps 

 already had tentacles and some development of the 

 water-vascular system. Then, torsion, or twisting 

 of the body mass would have had to occur for a radi- 

 ally symmetrical pentactula stage to result. From 

 such a radial animal further evolution of the echi- 

 noderms would have been fairly easy. 



We can learn more about echinoderms by studying 

 the crinoids (sea lilies and feather stars), the most 

 primitive living class. At the time of metamorphosis 



of crinoids and asteroids (starfish), the larva develops 

 an attachment apparatus from the portion anterior 

 to the mouth and becomes fixed to some object. The 

 strictly fossil classes and their contemporary sea lilies 

 seem to have had only attached organisms, suggesting 

 that the earliest echinoderms were stalked, attached 

 creatures. This idea is given a bit more weight by the 

 fact that some living crinoids (feather stars) must first 

 lose their attachment before becoming free-swimming 

 organisms. 



Another point of interest is the present develop- 

 mental change from bilateral larva to the radial adult. 

 Radial structure is typical of attached or floating 

 forms. The coelenterates are, perhaps, the best ex- 

 ample of this. The floating or attached radial or- 

 ganism does not seek its food but allows the environ- 

 ment to come to it. Therefore, we may again take 

 radial symmetry as evidence of an attached echino- 

 derm ancestor. 



Summing up, we might hypothesize a basically bi- 



