574 
THE VOYAGE OF H.M.S. CHALLENGER. 
diate surface layer, there was a large quantity of the algae -like branching Rhizopod 
described by Mr. H. B. Brady, F.R.S., under the name of Rhizammina algceformis, and in 
addition many deep-sea animals. A Ceplialopod was found here which does not seem 
to be specifically distinct from Enoploteuthis margaritifera, Rupp., hitherto known 
only from the Mediterranean. Mr. Moseley described from this trawling a new genus 
and species of Actiniaria, Corallimorphus rigidus, full particulars regarding which are 
given by Professor Richard Hertwig in his Report 1 on this group. Professor Hertwig has 
summed up the principal peculiarities of the deep-sea Actiniaria in the following notes : — 
The Actiniaria. — “ The soft-bodied Zoantharia (Actiniae, or Malacodermata) are among 
the groups which are represented in the depths of the sea by a relatively considerable 
number of members. The Challenger Expedition discovered at depths varying from 280 
to 2300 fathoms some twenty species, many of them in great numbers. In most cases 
the species and genera are new, and not unfrequent! y they belong to new families, so 
that it has been demonstrated by the Expedition that the organisation of these animals 
is much more varied than was previously known. 
“ All Anthozoa, whether solitary or colonial, agree with one another in certain general 
features of structure. The body of the individual polyp is a hollow cylinder, which is 
enclosed by a membrane called the ‘ wall.’ The ends of this cylinder are constituted 
above by the ‘ pedal disk ’ or ‘ base,’ below by the ‘ oral disk both of which are 
intimately connected with the wall, and for the most part abut at right angles against 
it. Along the margin of the oral disk arise the tentacles, hollow evaginations, into which 
the lumen of the hollow cylinder is produced. 
“ In the centre of the oral disk lies the mouth, which has the form of a narrow slit, 
always placed in a certain definite direction, the sagittal axis of the body of the Actinia 
being always indicated by the length of the slit, whilst its shortest diameter indicates 
the transverse axis (fig. 189). 
“ A tube open below, which is compressed transversely in accordance with the form of 
the mouth, and must be regarded as an invaginated portion of the oral disk, hangs 
down from the mouth into the body cavity. This tube, formerly called stomach, now 
more correctly oesophagus, is held in position by radial septa, which arise from the body 
wall as well as from the oral and pedal disks, and are inserted into the oesophagus. 
The number and arrangement of the septa are of morphological significance ; in most 
Actiniae they are united in pairs ; the number of such pairs is at least 6, and increases 
in multiples of 6, so that 12, 24, 48, &c., pairs of septa are met with. Exceptions to 
this arrangement, which also occurs in the hexamerous skeleton-forming corals, were 
previously known, in the case of the Edwardsiae, Zoantheae, and Ceriantheae, but by the 
Challenger Expedition the number of exceptions has been increased. Thus, although in 
1 Zool. Chall. Exp., part xv., 1882. 
