The Hooked or Combed Areas of the Larva

A diagram of these combed pads or areas has been given in the previous paper (Gatenby, 1959). The subject has been reviewed because Tasmanian and N.S.W. larvae became available, and it was hoped that specific differences between the three types of larvae might be discovered. In all larvae, the large mainly ventral combed area between the ultimate and penultimate segments is present, but it differs within members of the N.Z. species in its pigmentation and emphasis. Elucidation of the arrangement of the areas in front of segment seven is difficult because the segmentation of the larvae is usually not easy to make out, and the hooked areas may appear irregularly spaced owing to contraction, and are often difficult to see at all. The best specimens possessed by the writer were kindly examined by Dr. F. B. O'Connor, of this Department, but he could not establish that the arrangement of the bands was quite the same in each N.Z. larva. The combed areas stretch up from the ventral surface towards the lateral regions, leaving the dorsal surface of the larva without combs.

In Pl. 40, fig. 7, is a plan of the segmentation of a N.Z. larva Beginning at segment eight (LO) there is the large hooked area (I) which is single, and which lies within and at the anterior edge of the eight segment. Passing forward one finds four paired areas (II-V), then two single areas (VI–VII). In front of this there are cross ridges in appropriate places, but hooks appear absent. There can be no doubt at all that the large area at (I) varies very considerably in different specimens of the N.Z. larva. This variation appears to be due not so much to large differences in the number of rows of hooks but to their size and pigmentation. In Pl. 40, fig. 10A, are two rows of hooks from two N.Z. larvae of the same stage of development. In the upper row the hooks are barely twice the size, and they are darker. The last double area is apparently in the fourth and abdominal segment and the two areas in front are single bands in nearly every case examined. There are usually from ten to twelve rows of hooks on each combed ridge. As shown in Pl. 42, Fig. 17, the hooks end forwards, and obviously are used to hold the weight of the animal when it reaches down to examine parts of the snare below the runway. In addition the hooks would assist the larva when it lies ventral surface down and is retreating backwards. By anchoring itself at the eighth segment it could rapidly pull its body into a contracted condition. Presumably, however, the hooks would impede the larva if it were retreating forwards ventral side down.

On Pl. 40, fig. 9 is a plan from a Faure preparation (unstained) of the hooked areas in nearly full grown N.Z. larva. In this larva there were altogether six hooked regions. The roman numerals on the right correspond to the positions given in Pl. 40, fig. 7, save that in Fig. 7 there were seven hooked areas. In fig. 9, there were about thirteen rows of hooks on I, nine and eleven respectively on the two areas in II, the same but reversed in III and IV, and only eight in the sixth area (VI). The double areas in IV and V closely resembled their neighbours, but are not put in this figure. The groups of hooks varied from about 8–27 when not joined, and were sometimes staggered.

The numbers (arabic) refer to the number of groups in the middle of each area; at the sides reaching up laterally the rows become reduced, so that each pad is spindle-shaped. It is interesting to note that in this specimen the group in the eight segment (I) is smaller than usual, and less pigmented.

One Tasmanian larva mounted in Faure's medium has been examined for hooked areas. These are present, but smaller than in any N.Z. or N.S.W. larva.