///. ASTIIOZOA : nEXACORALLA. 



259 



In the Alcyoniid.e {Ah-yoniuui,* AntTiomastus) an axial skeleton is 

 lacking, but the flesh contains numerous calcareous particles, the scleroder- 

 mites. The sea pens, Pennatulid*, have the basal part buried in the 

 mud, the rest, expanded like a disc or feather, bears the polyps. An axial 

 skeleton usually occurs in the stalk. Pennahda* colder waters ; Ren ilia,* 

 warmer seas. The Gorgoniid.e (sea fans, sea whips) have an axis of more 

 firmness, which may be calcareous, and the colony may branch and the 

 branches anastomose. Here belong, besides many tropical genera whose 

 names end in ' goi'gia,' Frimnoa* of our colder waters; Isis oi tropical 

 seas, with skeleton of alternating calcareous and horny parts, and the pre- 

 cious coral (Coraliium ruhrutn, fig. 206) of the Mediterranean, the fishing 

 for which at Naples amounts yearly to half a million dollars. In the Tubi- 

 PORiD^E, or organ-pipe corals, the separate polyps are enclosed in parallel 

 tubes united at intervals by horizontal plates. The HeliOpoi'ce were long 

 regarded as Hexacoralla because of their massive skeletons with six sclero- 

 septa. The paleozoic Syriiigopora belongs near Tubipora, while the 

 Favositid^ resemble the Alcyoniidaj. 



Order III. Hexacoralla (Zoantharia). 

 The simple tubular tentacles are liiglily characteristic of the 

 Hexacoralla, as is the arrangement of the jtaired septa in sixes as 

 described above. Yet there are excep)tions to this rule. On the 

 one liaud is Edicardsia (common in our colder waters), in which 

 there are sixteen or more tentacles and only eight septa (fig. 205), 

 but which exhibits a condition through which the young actinians 

 pass ; on the other hand in the Zoantharia, Cerianthia?, and 

 Antipatharia the rule of six has undergone extensive modification. 

 Sub Order I. ACTINAPJA (Malacoderma). The sea-anemones are 

 mostly solitary, without skeleton; with numerous septa and tentacles. 



They occur in all seas from tide marks 

 to the greatest depth. A few are 

 free, but most are sessile. Except the 

 colonial Zoantheaj all can creep by 

 the pedal disc. Represented in our 

 seas by Metridium, Bunodes, Sagar- 

 tia, Bicidinm (parasitic on Cyanea)^ 

 Halcampa, etc. The Zoanthese have 

 two kinds of alternating mesenteries 

 and the individuals of the colonies 

 are usually incrusted with foreign 

 matter. Bi<izoantlms lives symbi- 

 oticallv witli hermit crabs (fig. 113). 



Sub Order II. ANTIPATHAPJA. 

 Six pairs of septa and six {Antijiatlies) 

 or twenty-four ((?era?-(Z/(/) simple ten- 

 tacles; colony with a black liorny axis 

 son, IS, Bicidliuii^ parasiticum (after ^^^^ ^^ calcarcous skeleton. Simu- 



Edimn'dsiella sipuiiculoidex latter Stimp- 



Verrill), C, Bunodes 

 rill). 



stdla (after 



late the Gorgonids. 



