176 



HYDROIDA II 



Branchiocerianthus imperator (1909, p. 71) states: "Da im iibrigen die Familie 1 ganz kosmopolitisch ist 

 so diirfen wir wohj annehmen, dass Branehiocerianthus-Arten audi im Atlantisehen Ozean vorkommen, 

 bisher aber nur wegen ihres Lebens in grosserer Tiefe uoch nicht gefunden worden sind". 



Excellent proof as to the correctness of this supposition has now been furnished by the finding 

 of a Branchiocerianthus in the deep part of Davis Strait, where it occurs together with other repre- 

 sentatives of a southerly deep-sea fauna. Stechow's characterisation of the habitat of the genus as 

 "Kaltwassergebiet" however, is biogeographically erroneous; Branchiocerianthus has not vet been met 

 with in the cold area, and is hardly likely to prove a characteristic element in the fauna of that region. 

 The genus belongs to the abyssal region of the warmer seas, or strictly speaking, that portion of the 

 same which makes the home of the "intermediate fauna". The temperature here may certainly fall 

 pretty low in certain places, but is never below o°. The "Kaltwassergebiet" would include the cold 

 area, where the temperature is constantly below o°. 



Branchiocerianthus reniformis n. sp. 



(PI. I, figs. 2-5). 



The hydranth, viewed from below, has a distinctly kidney-shaped appearance, with a deep 

 (ventral) sinus reaching right in to the stalk. Owing to the depth of this incision, the stalk appears 

 comparatively centrally situated, the distance to the dorsal edge (6 mm) being slightly more than 

 that between the stalk and the margin of the disc perpendicular to the dorso-ventral axis (4,5 mm). 

 The oral aperture seems to be somewhat more excentrically placed, being distant between a fourth 

 and a third of the diameter of the disc from the dorsal margin of the disc. The oral aperture is 

 very large, and in the present specimen it is curved over, revealing the highly folded gastral endo- 

 derm (PL I, fig. 3). It would almost seem as if the margin of the oral aperture were divided into 

 lobes; from the single specimen here available, however, it is impossible to decide with certainty, 

 whether this is natural, or due to accidental damage. The margin of the oral aperture is curled, with 

 a closely packed tentacle crown, showing indications of multiserial arrangement. The oral tentacles 

 are everywhere round in transverse section, and are strongly built. The basal tentacles form a single 

 circle; they are very long, with exception of the ventral ones, which are placed along the margin of 

 the disc in the incision. In the incision itself, the tentacles decrease rapidly in length in towards 

 the stalk, at its base are the youngest tentacles, which are epiite small. The basal tentacles are later- 

 ally compressed at the base, where they easily fall off; in the present specimen, only the tentacles in 

 the incision and a pair beside it are intact, the remaining ones having fallen away. The stalk of the 

 polyp is thin, longitudinally striped. The short basal part is covered with numerous fine root hairs 

 extremely closely set, forming a tangled mass round the end of the stalk and entirely covering it 

 there. There is no zone of incipient root hair formation discernible above the developed part. 



The blastostyles form a crown, interrupted ventrally, about the hydranth between the tentacle 

 crowns, nearer the basal. The blastostyles are closely set in a crown which may be up to triple- 

 rowed. The large blastostyles divide near the base at once into two or three main branches of equal 

 size, which later (PI. I, fig. 5) again divide dichotomously at intervals two or three times. The top of 



1 I. e. Corymorpha and Branchiocerianthus, 



