ALCYONARIA PENNATULACEA 



Pcnnatula swimming freely " with iill its delicate transparent 

 polypi expanded, and emitting tlieir usual brilliant phosphorescent 

 light, sailing through the still and dark abyss by the regular and 

 synchronous pulsations of tlie minute fringed arms of the whole 

 polypi," appears to be based on a statement made by Bohadsch in 

 1761, and picturesque though it be, is undoubtedly erroneous. 



The brilliant pliosphorescence of many species of Pennatulacea 

 has been observed by many naturalists, and it is very probable 

 that they all exhibit this property to some degree. The phos- 

 phorescence appears to be emitted by the mesenteric filaments 

 of the autozooids, but it is not yet determined whether the 

 phenomenon is confined to these organs or is more generally 

 distributed. 



The Pennatulacea are usually devoid of epizoites, but occa- 

 sionally the parasitic or semi-parasitic Entomostracan Lamippe is 

 found in the zooids. A small crab is also frequently found 

 between the large leaves of species of Fteroeides. The most 

 remarkable case of symbiosis, however, has recently been observed 

 in the form of an encrusting Gymnoblastic Hydroid ^ living on 

 the free edge of the leaves of a species of Ptilosarcus. 



The order Pennatulacea is divided into four sections. 



Sect. 1. Pennatuleae. — In this section the colony is distinctly 

 liilaterally symmetrical, and the autozooids are arranged in rows 

 with their body-walls fused to form leaves. 



The genus Pteroeides, the representative genus of the family 

 Pteroeididae, is a fleshy Sea-pen found in shallow sea water in 

 the warm waters of the Pacific Ocean and in the Mediterranean. 

 It has large leaves with long spiny, projecting spicules, and the 

 siphonozooids are borne by the leaves. Pennatula, the represen- 

 tative genus of the family Pennatulidae, has a wider distribution 

 in area and in depth. Pennatula p]iosp)liorea is a common l)ritish 

 species, found in depths of 10 to 20 fathoms in many localities 

 off our coasts. It is about 5 inches in length. There are several 

 varieties of this species distributed in Atlantic waters. Penna- 

 tida grandis is a magnificent species found in Norwegian fjords, 

 in the Faeroe Channel, and off the northern coasts of K America, 

 in depths of from 50 to 1255 fathoms. Specimens have been 



' To be described in the forthcoming Report on the Pennatulidae of the 

 "Siboga" E.xpedition. 



