CHAPTER 11 



OJI 



Phylum Ctenophora. 

 Comb Jellies 



HE phylum Ctenophora (comb bearers) 

 includes a small group of about 100 species 

 of exclusively marine animals that resemble 

 coelenterate jellyfishes. They are widely dis- 

 tributed, being especially abundant in warm 

 seas. Ctenophores are beautifully iridescent 

 in sunlight, and they glow like electric light 

 bulbs at night, due to their luminescence. 



Ctenophores are commonly called sea 

 gooseberries or sea walnuts (Fig. 67) be- 

 cause of their shape; or comb jellies because 

 of the comblike locomotor organs arranged 

 in 8 rows which extend as meridians from 

 pole to pole. They are biradially symmetri- 

 cal, since the parts, though in general radi- 

 ally disposed, lie half on one side and half 

 on the other side of a median longitudinal 

 plane (Fig. 67). The mouth is situated at 

 one end (oral), and a sense organ (stato- 

 cyst) at the opposite or aboral end. 



Most ctenophores possess two solid, con- 

 tractile tentacles which emerge from blind 

 pouches opposite each other; these are 

 covered with glue cells (colloblasts), which 

 produce a secretion of use in capturing the 

 small animals they eat. Their food consists 

 of fish eggs, molluscan larvae, and small 

 pelagic invertebrates. The Bureau of Fish- 

 eries reports that large numbers of oyster 

 larvae are killed by ctenophores. 



Ctenophores are hermaphroditic. The ova 

 and spermatozoa are formed on the walls of 

 the digestive canals just beneath the cili- 

 ated bands. The eggs and sperms pass to 

 the outside by way of the mouth. The fer- 

 tilized eggs usually develop directly into the 

 adult. 



As in coelenterate jellyfishes, the cellular 

 layers of ctenophores constitute a very small 

 part of the body, most of it being composed 

 of the transparent jellylike mesoglea. A 

 thin ciliated epidermis, derived from the 

 ectoderm, covers the exterior and lines the 

 pharynx (stomodaeum); and a gastrodermis 

 derived from the endoderm, also ciliated, 

 lines the stomach and the gastrovascular 

 canals associated with it. 



Scattered cells and muscle fibers lie in the 



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