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PACIFIC SCIENCE, Vol. XIX, April 1965 
measurements given in this section were ob- 
tained from portions of five of the paratypes 
of the species sectioned and stained with Hei- 
denhain’s iron hematoxylin and eosin, Mallory’s 
triple stain, and acid haernaium and light 
green. Ten nematocysts of each type were meas- 
ured in each portion of each animal examined. 
RESULTS AND DISCUSSION 
Family CERIANTHIDAE 
DIAGNOSIS: Ceriantharia without acontioids 
or cnidorages. 
Genus Pachycerianthus Roule, 1904. 
DIAGNOSIS: Cerianthidae with the second 
couple of protomesenteries short and sterile. 
Arrangement of metamesenteries in each quar- 
tette M,B,m,b (1,3,2,4) more or less distinct. 
DISCUSSION 
Torelli ( 1961 : 25—27 ) claims that the genus 
Pachycerianthus proposed by Roule ( 1904^: 
792-793) is invalid since it is not clearly dis- 
tinguished from the genus Cerianthus. Her 
opinion is partly based on an incorrect inter- 
pretation of the terms in the literature. It is 
therefore first necessary to trace briefly the 
history of some of the terms used to describe 
the mesenterial filaments and their appendages. 
Haime (1854:374) noted the presence of 
"cordons pelotonnes” along the edge of some 
of the mesenteries of Cerianthus membrana- 
ceus. Von Heider (1879:216-217) and Hert- 
wig and Hertwig (1879:578-580) described 
the "Mesenterial-filamente” of the same species 
in more detail. The mesenteries of this species 
have numerous branching appendages, the 
"Mesenterialfaden,” which are not homologous 
to the acontia of the Actiniaria (as von Heider 
thought), since they possess ascending and 
descending limbs of the mesenterial filament 
separated by a portion of endoderm. Van Bene- 
den (1897:27-37) further investigated the 
structure of the "filaments mesenteriques,” or 
"craspedes” of Gosse (1860:xxiii) in speci- 
mens of several adult and larval species. He 
found "fils mesenterique” with a structure simi- 
lar to Hertwig and Her twig’s "Mesenterial- 
faden” and also, in several larval species, much 
longer and rounder appendages near the pos- 
terior end of the mesentery which he believed 
to be true "acontie.” McMurrich (1910:19) 
used the term "craspedoneme” to distinguish 
Hertwig and Hertwig’s "Mesenterialfaden” 
from these "acontia.” 
Carlgren (1912^:68-72; 1912$: 383-385), 
re-investigating the same species examined by 
van Beneden, showed that true acontia were 
not present even there but rather structures 
homologous with the craspedonemes were pres- 
ent in which the endoderm was reduced so as 
to be surrounded by the two limbs of the fila- 
ment. Bourne (1919:60-61) also noted differ- 
ences between the "acontia” of Ceriantharia 
and those of the Actiniaria. In some portions 
of the collected works of van Beneden pub- 
lished posthumously in 1923, the term "acon- 
tie” is used. However, in another portion he, 
in agreement with the above authors, also states 
that the Ceriantharian structures are not ho- 
mologous with those of the Actiniaria. Carl- 
gren suggested the term "mucocraspedoneme” 
for the structures found in the Ceriantharia, 
but in later papers adopted the term "acontioid” 
introduced by Pax (1914:394). 
With this background, no purpose was 
served by Torelli’s statement ( 1960:376-379) 
that acontia are not present in Ceriantharia, 
especially since her opinion was based on an 
investigation of two species for which previous 
authors had not even claimed the presence of 
acontioids, i.e., Cerianthus membranaceus and 
Pachycerianthus dohrni (the Cerianthus viridis 
of her paper). 
We may now consider the description of 
Pachycerianthus , Roule (1904^: 792-793; 
1904^:708-710) described Pachycerianthus 
benedeni and designated it the type of the genus. 
The description is poor but includes the follow- 
ing characters of possible generic significance: 
1. Mesenteries are short; only the ventral 
mesenteries (83 in the terminology proposed 
by van Beneden) reach the aboral extremity 
and border a narrow band which continues 
the sulcus and contains the vestiges of the D 
and Si mesenteries. 
2. The mesenteries on either side of the S3 
diminish in length toward the dorsal region 
but do not show a distinct quatro-septal dispo- 
