Introduction

Collembolan mouth-parts are described as entognathous, and it is generally recognised that there are two distinct types. In what is considered to be the more primitive or generalized type (Salmon 1964; Massoud, 1967) the mouth is a wide opening at the distal border of the head. The mandible is robust and carries an apical toothed area or "pars incisiva" and a broader molar plate provided with a number of rows of teeth, the "pars molaris" of Massoud (1967). It is assumed that forms with this type of mandible chew their food, although some doubt has been cast upon this interpretation by Goto (1972). In the second group the mouth region is tapered to form a cone shaped structure known as the buccal cone. The mandible lacks a molar or grinding plate and is described by Massoud (1967) in the Neanuridae, as reduced to a long, slender, flattened plate carrying an apical toothed area the "pars incisiva". This plate is said to have a cutting action although this does not seem to be in agreement with the theory accepted throughout entomological literature, that forms provided with a buccal cone suck their food. It seems possible however, that a suction method of feeding has been attributed to these forms because of the apparently sharply pointed nature of the cone, rather than on a knowledge of the fine structure of the mouth-parts.

Recent writers including Goto (1972) and Massoud and Ellis (1974) describe the fine structure of several chewing type Collembola, but the structure and function of the mouth-parts of forms lacking a molar plate is little understood.

Wolter (1963) while accepting the view that forms with a buccal cone suck their food, drew attention to differences in the structure of the maxillary heads. He considered that those with a well developed toothed maxillary head probably rasped their food while those with a stylet-like head probably pierced it, before sucking the fluid material through the cone.

The diet of forms lacking a molar plate is unknown. It was noted however, in feeding studies by Macnamara (1924) and Poole (1959), that in subsequent preparations of the gut of these particular species, there were rarely any visible gut contents. This seemed to suggest that page 2they are fluid feeders. Singh (1969) also observed mainly fluid gut contents in Friesea mirabilis (Tullberg) agreeing with the results of Poole (1959) on the same species. Particles identified in the gut included fungal spores and hyphae, yeast, bacteria and collembolan eggs.

Adams and Salmon (1972) in a study of Brachystomella parvula (Schaeffer), a collembolan lacking a molar plate, observed that a sucking tube is not formed during feeding and the mouth-parts could not be described as adapted for sucking. It was noted that the gut contents were mainly of a fluid nature containing structures resembling bacteria, encysted protoza and fine unidentifiable particles.

Recently attention has been drawn to the enigma in detritivore communities of a high degree of species diversity, accompanied by an apparently low degree of feeding specificity (Anderson, 1975; Joosse, 1975) and Collembola would seem to be no exception to this (Anderson and Healey, 1972; McMillan, 1975). It is suggested therefore that a greater knowledge of the fine structure and function of collembolan mouth-parts could provide more specific information on their feeding habits.

In this study the fine structure of the mouth-parts of Ceratrimeria leleupi, a species lacking a mandibular molar plate and formerly regarded as a piercing and sucking type, is examined using the scanning electron microscope.

Specimens are also examined under the light microscope for evidence of food in the gut.