Oligochaeta.'] 



SUBANTARCTIC ISLANDS OF NEW ZEALAND. 



281 



DiPOROCHAETA, Beddard, 1890. 

 Diporochaeta heterochaeta, sp. nov. (Plate XI, figs. 27-29.) 



Colour. — Rich red-brown, paler posteriorly and ventrally ; the chaetae are 

 surrounded by white areas, so that in the hinder region of the body, as the pigment 

 gets less, each segment appears to be marked by a white line ; hence the worm as a 

 whole has a striped appearance. The clitellum is pale brown. 



The average size is somewhere about 125 mm. in length, with a diameter of 3 mm. ; 

 but there is a good range even among mature forms — thus, one extreme is 50 mm., 

 the other is 170 mm. ; in both cases the specimens are soft, so that the true length 

 is not represented by these figures. Whereas in a group of well-preserved specimens 

 the numbers run from 65 mm. to 135 mm. for mature ones, several immature indi- 

 viduals are longer than the smallest mature ones. The number of segments ranges 

 from 85 to 140. In this instance there is a direct relation between the length of body 

 and the number of segments. 



The prostomium is half epilobic. 



The clitellum covers the three segments 14, 15, and 16 ; it is very well marked, 

 and surrounds the body. 



The chaetae are 32 per segment in the post-clitellar region, though in the anterior 

 segments the number is less. The dorsal gap equals the ventral, which is about 

 twice the ordinary interchaetal space. The chaetae on the lower surface are rather 

 longer and stouter than those on the upper, there being a gradual transition from 

 below upwards. The most noticeable external feature of the species is the large 

 size of the two ventral chaetae. In segments 5, 6, 7, 8, and 

 9 these are very greatly enlarged, so as to be relatively of 

 enormous size as seen in section (Plate XI, figs. 27, 28). 

 Those of segments 3, 4, 10, 11, 12, 13, and 14 are also 

 enlarged, though not to such a noticeable degree as the 

 former. It is the remarkably stout chaetae in the preclitellar 

 segments to which the specific name refers. The number of 

 chaetae seems to increase with age, or at least with size, for 

 an individual of about 70 mm., with 100 segments, has in 

 the hinder segments 28 chaetae ; in the 3rd, 20 ; in the 7th, 

 24 ; in the 9th, the full number, 28. On the other hand, a 

 specimen measuring about 120 mm., with 130 segments, 

 bears 32 on the hinder segments ; the 3rd has 26 ; the 7th, 

 28 ; the 21st, 30 ; while the 23rd has 32. This number is 

 not invariable, as some segments bear as many as 34. 



Genital and other Pores. — The nude pore is carried on a 

 papilla in the 18th, in line with the chaeta d or e. The 

 papilla is not very evident, as it is only on the mesial side 

 that it rises above the level of the body ; on this aspect 

 there is a slight groove, in which lies the actual pore, which 

 is microscopic. 



In only two specimens are tvhercula puhertatis present, as a pair of interseg- 

 mental structures, close to the median line at 18/19 in one case, or 19/20 in the 

 other. 



DiPOBOCHAKTA HETEKOCHAETA. 



Ventral view of the genital 

 segments. (X 4.) 



