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Internal Anatomy (Plate 107, fig. 2)
There are no thickened septa.
Alimentary Canal. The pharynx is globular and muscular and occupies the first four segments. To its dorsal surface is attached a covering of salivary glands. The gizzard, which is elongate and thick walled, is confined to v, but appears superficially to occupy v, vi and vii and the anterior portion of viii. The oesophagus extends from vi to xvi, and has a single pair of calciferous glands in xiii. The intestine commences in xvii, is very narrow and has a marked typhlosole.
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Vascular System. The dorsal blood vessel is single throughout. There are three pairs of hearts in x, xi and xii.
Reproductive System. There are two pairs of testes, a pair in x and a pair in xi, and the vas deferens of each side opens close to the prostatic duct in xvii. A single pair of ovaries is present in xiii and very prominent oviducts lead posteriorly from the funnels in xiii and open to the exterior in xiv. There are two pairs of spermathecae, a pair in viii and a pair in ix. Each spermatheca consists of a large ovoidal sac, with a rounded diverticulum extending into the adjacent anterior segment and opening into the spermathecal duct (Plate 107, fig. 3). A pair of elongate convoluted tubular prostates is present. Each prostate arises from a narrow coiled duct in xvii and extends posteriorly through xvii and xviii to xix, where it terminates. An elongate sac containing several penial chaetae lies close to each prostatic duct. Each penial chaeta has a slender gently curved shaft, which is sharply recurved distally (Plate 107, fig. 4). There are two pairs of vesiculae seminales surrounding the oesophagus, a pair in xi and a pair in xii. Each vesicula is made up of small nodules of vesicular tissue held together by a sheet of connective tissue.
Small coiled nephridia are present in each of the segments except the first.
Remarks. This species is similar in its general form to R. kermadecensis Benham (1904) and to R. parvus Benham (1905), but differs from these species in having two pairs of spermathecae (R. kermadecensis has three pairs and R. parvus one pair) and also in other points of internal anatomy.
Ecological Notes. R. sutherlandi was collected from the subsoil horizon of the Tutamoe clay loam, under poor pasture dominantly browntop (Agrostis tenuis Sibth.) with stunted bracken (Pteridium aquilinum var. esculentum Hook. f.), used seasonally for extensive cattle grazing.
In an adjacent area of rain-forest, composed mainly of Weinmannia sylvicola Soland., Knightia excelsa R. Br., Phyllocladus glaucus Carr. and tree-ferns, R. sutherlandi was distributed throughout the topsoil and the subsoil. This suggests that the destruction of the native forest to provide rough grazing, when unaccompanied by liming and top-dressing, causes sufficient alteration in the soil environment to initiate a series of changes in the endemic earthworm fauna, in the first stage of which the endemic species retreat into the subsoil. A second endemic species, Megascolex sp., which was present under the forest conditions, had completely disappeared from under the rough pasture. The only earthworm inhabiting the topsoil of this pasture was Octolasium cyaneum. Pasture areas which have been top-dressed show the following progressive stages:
| (a) |
In lightly top-dressed pastures no endemic species are found and the only earthworms present are Lumbricus rubellus, Octolasium cyaneum and Allolobophora caliginosa, in varying numerical proportions. |
| (b) |
In heavily top-dressed areas Lumbricus rubellus is rare, and the only species commonly found is Allolobophora caliginosa, which is often present in fairly large numbers. |
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It would seem that endemic species cannot adapt themselves readily to marked changes in soil conditions. The introduced species, especially Allolobophora caliginosa, have a wider range of tolerance.
Rhododrilus papaensis n.sp. (Plate 108, figs. 1–4)
A single specimen was collected from soil derived from mudstone under a small forest remnant near the top of the Gentle Annie Hill, three miles east of Wairenga-o-Kuri beside the Gisborne-Wairoa road.
The specimen is 126 mm. in length, with 194 segments, and is 4 mm. in diameter. It is pale yellowish-brown in colour with a sienna brown clitellum developed over the entire surface of xiii to xvii except for the area of xvii lying between the prostatic papillae. The prostomium is proepilobous. There are eight chaetae on each segment, arranged in four pairs. On xxiv:
ab = 0·75; cd = 1·5 mm.; bc = 2 mm.; aa = 2 mm.; dd = 4 mm.
Spermathecal pores are not visible externally. A small female pore is situated slightly anterior and medial to chaeta a on each side of xiv. The prostatic pores are situated on the apices of a pair of small rounded papillae on xvii. The papilla of each side lies in line with the chaetal interval ab of that side. A longitudinal groove is visible on each papilla, from the prostatic pore to the anterior margin of xviii, terminating at the male pore on each side of xviii.
Nephridiopores commence on ii and lie in a single series on each side of the body, close to the anterior margins of the segments and anterior to chaeta c on each side of the segments.
Paired tubercula pubertatis are situated on xviii, in the form of a small rounded pad posterior to chaeta b on each side.