THE AMPHINEURA 



55 



General Description. The mantle covers the whole body, 

 and is clothed by a rather thick cuticle, in which are implanted 

 spicula (Fig. 35) developed from the tegumentary epithelium. The 

 foot is nearly aborted or wanting. The nervous system consists of 

 four great longitudinal trunks, with pedal and pedo-pallial anasto- 

 moses. The digestive tract is straight, the Aplacophora being carni- 

 vorous. The blood is red. The gonads are in open continuity with 

 the fore part of the pericardium. The coelomo-clucts, corresponding 

 to the renal sacs of the Polyplacophora, are gonaducts, and open 

 externally into a posterior cloacal chamber, which serves as a 

 rudimentary branchial cavity. There are two groups of Aplaco- 

 phora : the Neomeniomorpha and the Chaetodermomorpha. 



Fio. 35. 



Spicules of various Aplacophora. A, Neomenia (Wiren); B, Dondcrsia (Hubrecht) ; C, 

 Paramenia (Pruvot} ; D, Proneomenia ; E, Stylomenia (Pruvot) ; F, .Myzomcnia (Pruvot) ; G, 

 Chaetoderma (Wiren). i.c, internal cavity. 



SUB-ORDER 1. NEOMENIOMORPHA. 



Aplacophora with a distinct longitudinal ventral groove ; bi- 

 sexual, with paired genital glands and without differentiated liver. 



I. EXTERNAL CHARACTERS. 



The mantle extends over the sides of the body so as to cover 

 the greater part ot tne ventral surface, leaving only a narrow 

 median longitudinal furrow uncovered. The pallial cuticle, which 

 is very thick in some species, contains a number of long, hollow, 

 calcified, acicular, or flattened spicules (Fig. 35) borne on epithelial 

 papillae. In some cases, when it is very thick, the cuticle also 

 includes sensory papillae. A small longitudinal projection in the 

 ventral furrow is the vestige of the foot. The antero-ventral region 

 of the body is occupied by a large mucous gland, whose secretion is 

 poured into a ciliated pit in the anterior part of the ventral furrow, 

 the whole structure corresponding to the embryonic pedal gland of 

 some Chitones. Smaller mucous glands are also found along the 

 pedal projection. Posteriorly there is a terminal cloacal or branchial 

 cavity, into which opens a thick mucous gland, situated between 

 the foot and anus. 



