258 



SUBANTARCTIC ISLANDS OF NEW ZEALAND. 



[Oligochaeta. 



Fam. TUBIFICIDAE. 

 Rhizodrilus, F. Smith, 1900. 

 Rhizodrilus aucklandicus, sp. nov. (Plate X, figs. 2-7.) 



Of this littoral worm I obtained several. 



Colour, as in Tubificids generally, red, owing to the blood in the integument 

 and elsewhere showing through the transparent skin. 



Dimensions. — Long, narrow, with feebly expressed segments, due perhaps to 

 the condition of preservation. Length, 29 mm. by 0-5 mm., 

 with 80 segments, which are triannulate — anteriorly, at 

 least. 



Prostomium rather long, greater than the length of 

 segments 1 and 2 together. 



Chaetae. — Two bundles of forked sigmoids on each side 

 of each segment ; the two prongs are of equal length and 

 of comparatively large size. Dorsals, 3 or 4, in tlie anterior 

 part of the body ; 1 or 2 posteriorly. Ventrals, anteriorly 

 3 or 4, occasionally 5 ; but posteriorly 2, or rarely 1. The 

 chaetae are absent in 11 and 12. In some of the segments 

 long fine hairs have become entangled with the chaetae, 

 which at first examination were mistaken for capillariform 

 chaetae. 



Dorsal pores commence at the anterior end of the 4th 

 segment ; they are not really intersegmental, as they lie 

 behind the first annulus, while the septum is inserted in 

 front of this annulus. 



CliteUuin on dorsal and lateral surface of 10, and sur- 

 rounding the body of 11, 12. 



Genital Pores. — The male pores are paired on 11, at 

 the junction of annuli a, h, at the position of the absent 

 ventral chaetae. Spermathecal pores also paired at 9/10, 

 in line with ventral chaetae. Oviducal pores at 11/12, in 

 the same line. 



RmZODItlLCS AUCKLANDICUS. 



Ventral view of the genital 

 region, showing the anmilation 

 of the clitellar segments, the 

 actual number of chaetae, and 

 the genital pores, a, sjx^rma- 

 thecal pore ; b, male pore ; 

 c, oviducal pore. 



Internal Anatomy. 



There is an elaborate integumental blood-plexus, but I did not work out the 

 details, nor am I able to state whether the characteristic moniliform structure of 

 these vessels, as described by Goodrich and others, is or is not present. I did not 

 detect any " hearts." 



The pharynx is very feebly developed. The roof is recessed, but has only an 

 extremely slight musculature, either intrinsic or extrinsic. This recess is lined 

 by tall ciliated cells, which take the stain but feebly. The nuclei are basal in posi- 

 tion. On the floor is a well-defined pad of high ciliated cells of quite a different 

 character, more triangular in form, with distal or central nuclei and deeply staining 

 cytoplasm ; amongst them are a few large gland-cells. This pharynx lies in the 

 3rd segment. The ciliated pad and the ciliated cells of the recess are very sharply 



