THE AMPHINEURA 61 
SUB-ORDER 2. CHAETODERMOMORPHA. 
Aplacophora without distinct longitudinal ventral (or pedal) 
groove, with unpaired unisexual gonad, with differentiated liver, 
and with posterior cloacal chamber provided with two bipectinate 
gills. 
Anatomy.—The mantle covers the whole surface of the body, 
which is therefore cylindrical and vermiform in appearance. The 
hinder half of the body is a little stouter than the anterior; the 
posterior extremity swollen and bell-shaped, forming the widely 
cloacal chamber. The whole body has a uniform covering of short, 
compressed, calcareous spicules implanted in the cuticula. 
The mouth is anterior, terminal, and crescentic, owing to the 
presence of a rounded ventral shield.  Chaetoderma radulifera alone 
is provided with mandibles. The buccal cavity, whose anterior part 
is partially protrusible, bears on its floor a very peculiar radula, 
which may consist of (a) a single large tooth (Fig. 43, C), upon which 
two small teeth are placed (C. nitidulum and C. productwm); (b) a 
single large tooth, upon which 
is a row of teeth (C. guttu- 
rosum; (c) no large tooth, 
several rows of three teeth one 
behind the other (C. raduli- 
tera) ; (d) several distichous Chaetoderma nitidulum, Loven. The cephalic 
rows of two teeth each (C. enlargement is to the left, the cloacal or pallial 
: 2 - chamber (containing the concealed pair of ctenidia) 
challengert). 'Two pairs of sali- to the right. (From Lankester, after Graff.) 
vary glands, similar to those 
in the Neomeniomorpha, open into the buccal cavity. The diges- 
tive tract is quite straight, and narrows towards the middle of 
its course to form the intestine. Just before it narrows it receives 
the duct of a more or less extensive hepatic caecum, which extends 
backwards on the ventral side of the intestine. The hepatic caecum, 
large in most species, is feebly developed in C. challengeri. The 
anus opens in the median line in the cloacal chamber (Fig. 43, B). 
The heart is posterior and dorsal, ana lies nearly free in the 
pericardial cavity. It is traversed by the retractor muscles of the 
gills. In its main features the circulatory system resembles that 
of the Neomeniomorpha. The posterior extremity of the body is 
hollowed to form a bell-shaped cloacal cavity, which has a con- 
tractile aperture and contains a pair of large branchiae placed 
symmetrically right and left of the anus. Each branchia bears a 
double row of branchial plates, as is the case in the Polyplacophora 
(Fig 43, B). 
The two renal ducts are more evidently true excretory organs 
than in the Neomeniomorpha. ‘They originate from the posterior 
Fic. 42. 
