Pachycerianthus torreyi n. sp. — A rai 
207 
sition; the irregular diminution gives them, 
rather, a biseptal arrangement. 
3. All the mesenteries, except those which 
occupy exactly the dorsal region, possess some 
"craspedes” in the zone placed immediately 
below the enterostome. Some mesenteries have 
"fils mesenteriques” on their "craspedes,” and 
alternating ones do not carry them. The mesen- 
teries deprived of "fils mesenteriques” are fer- 
til and possess "aconties” on a rather large part 
of their inferior extremity; their series begins 
with the S 3 and continues with the uneven 
numbered mesenteries S5, S 7 , S 9 , etc. 
As Torelli ( 1961:25-27) pointed out, this 
description is extremely incomplete, and hence 
it is very difficult to place the genus in the 
modern classification of the order. Some of her 
comments (1960:374-375; 1961:25) about 
the lack of clarity can be discounted, however, 
since she has translated incorrectly the term 
"fils mesenteriques” in the third item above as 
mesenterial filaments. As noted earlier the term 
was used by van Beneden ( 1897:33) and other 
French authors to refer rather to the "Mesen- 
terialfaden” or craspedonemes. Correctly trans- 
lated, the third passage states that some mesen- 
teries have- craspedonemes on their "craspedes” 
or mesenterial filaments and alternate mesen- 
teries have "aconties” on them. 
It is the interpretation of the term "acon- 
ties” in the third passage above that is most 
problematical. McMurrich (1910:10-14, 22- 
24), in his classification of the order, placed 
the genus in a family characterized by the 
presence in the larva of "acontia” or, as they 
were later called, acontioids, but included adult 
species both with and without acontioids. Carl- 
gren (1912^:37-48) believed that the struc- 
tures must be ordinary craspedonemes since 
acontioids in all the better known species are 
single, rather than scattered over a large part 
of the lower end of the mesentery. He placed 
the genus in the family Cerianthidae character- 
ized by the lack of both acontioids and cnid- 
orages. Although Carlgren is probably correct, 
the question can only be resolved definitely by 
reference to the type specimen; unfortunately 
the location of this material is at present un- 
known. In the' meantime we may assume, as 
I Torelli ( 1961 : 26 ) also does, although for the 
wrong reason, that these appendages are ordi- 
nary craspedonemes. Pachycerianthus is there- 
fore retained in the Cerianthidae. 
Without re-examination of the original mate- 
rial, Carlgren ( 1912^:40-48) defined the genus 
Pachycerianthus as "Cerianthidae whose second 
couple of protocnemes are short, sterile, and 
provided with an extremely well-developed re- 
gion of the cnido-glandular tract. Arrangement 
of the metacnemes ( = deuterocnemes McMur- 
rich) in each quartette M,B,m,b ( 1 , 3 , 2 , 4) 
more or less distinct.” He originally included 
eight species in the genus and later ( 1924^: 
182-186; 1940:15; and 1951:435-436) added 
three more. All of these species (even P. hene- 
deni, if we are considering the first quartette) 
have M,B,m,b metamesenterial arrangement. 
All except P. henedeni are known to have 
short, sterile second protomesenteries, and it 
is probable that in that species they are also 
sterile since very small mesenteries are rarely 
fertile. However, Carlgren has placed in the 
genus several species (including P. henedeni) 
in which the extent of the cnido-glandular tract 
is unknown, and also others, such as P. maua, 
in which it is very short. In addition, as Torelli 
( I960: 375-376) has indicated, the distinctness 
of the histological demarcation by Carlgren 
( 1912 ^: 59 - 67 ) of the mononeme into the 
cnido-glandular tract and the craspedion is 
questionable. (The mononeme is the aboral 
monofilar portion of the mesenterial filament.) 
It seems desirable therefore that this character 
be eliminated as a differential one not only in 
this but in all genera of cerianthids. 
The 10 species (other than P. henedeni ) 
placed in the genus by Carlgren comprise a 
distinct taxonomic entity with the remaining 
characters with which Carlgren defined Pachy- 
cerianthus and with no acontioids. C. hicyclus 
Torelli, 1961 and P. torreyi n.sp. of the present 
work may also be added. This group is sep- 
arated from the genera Cerianthus, Cerianthe- 
opsis, and Ceriantheomorphe by the possession 
of short, sterile second protomesenteries, and 
from Ceriantheopsis by the MBmb arrange- 
ment of the metamesenteries in Pachycerian- 
thus. Torelli (1961:27) does not believe that 
the properties of the second protomesenteries 
