116 INVERTEBRATE MORPHOLOGY. 



II. Subtype CNIDARIA. Without pores in walls and with nematocysts. 

 I. Class HYDROMEDUSiE. — Ectoderm and endoderm meet at mouth. Be- 

 productive organs develop in ectoderm. Medusa with vehim ; sense- 

 organs not modified tentacles. 



1. Order Hydrarim. — No medusa form ; tentacles hollow. Hydra. 



2. Order Narcomedusce. —No hydroid form ; sense-organs otocysts 



of endodermal origin ; radiating canals represented by broad 

 pouches. Cunoctantha, Cunina. 



3. Order Trachymedusce. — No hydroid form ; sense-organs otocysts 



of endodermal origin ; radiating canals narrow. Liriope, Ger- 

 yonia, Rhopalonema. 



4. Order LeptomediiseB or Campanularice. — With both hydroid and 



medusoid forms, the latter frequently degenerate. Hydranths 

 with hydrotheciB ; gonangia present. Medusa with otocysts of 

 ectodermal origin ; reproductive organs on radial canals. 



(a) Hydroid and medusoid forms both well developed. Eu- 



cope, Obelia. 

 (6) Hydroid form not well developed. JEquorea, Rhegma- 



todes. 

 (c) Medusoid form degenerate. Sertularia, Halecium, Aglao- 

 phenia. 



5. Order Anthomedusoe or Tubularim. With both hydroid and me- 



dusoid forms, the latter frequently degenerate. Hydroid forms 

 without hydrothecsB or gonangia. Medusoid forms with eye- 

 spots ; reproductive organs developed in wall of manubrium. 

 (a) Medusoid form well developed. Margelis, Ooryne, Pen- 



naria. 

 (6) Medusoid form degenerate. Clava, Hydractinia, Tubu- 

 laria, Eudendrium. 



6. Order HydrocorallincE. — Hydroid forms polymorphic ; secreting 



calcareous skeleton by ectoderm. Medusoid forms usually de- 

 generate. Millepora, Stylaster. 



7. Order Siphonophora. — Free-swimming, pelagic, polymorphic col- 



onies. 



(a) Nectocalyces present, without pneumatophore. Diphyes. 

 (6) With both nectocalyces and pneumatophore. Agalina. 



(c) With pneumatophore only. Caravella. 



(d) Discoidal forms without nectocalyces. Velella, Poipita. 

 II. Class ScYPHOMEDUs^. — With medusoid form only in adult stage. 



"Velum not present ; sense-organs are modified tentacles. Kepro- 

 ductive organs develop in endoderm. 



1. Order Stauromedusa. — With the eight primary tentacles not at 



all or but slightly modified. Tessera, Luceriiaria. 



2. Order Peromedusce. — With the four interradial primary tentacles 



transformed into sense-organs. 



