THE STRUCTURE of the OPISTHAPTOR of ASPIDOGASTER CONCHICOLA BAER, 1826 (ASPIDOGASTRIDAE, TREMATODA) by K. E. BAKKER and P. C. DI
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THE STRUCTURE OF THE OPISTHAPTOR OF ASPIDOGASTER CONCHICOLA BAER, 1826 (ASPIDOGASTRIDAE, TREMATODA) by K. E. BAKKER and P. C. DIEGENBACH (ZoologicalLaboratory, Universityof Amsterdam, The Netherlands) SUMMARY We have attempted as well from the observed movements of A. conchi- cola's suckers, as from a reconstruction of the musculature of the haptor, to explain the working of the haptor. We also studied the ultrastructure of the marginal organs, composed of muscle-fibres of which the ar- rangement and working have been discussed. The ultrastructure of all cells situated within the haptor have been discussed. A theory about the function of the gland cells is proposed. The presence of sense cells in the tegument of the haptor is mentioned. INTRODUCTION The haptor of the Aspidogastridae is a very complex entity, with a complicated muscular arrangement (there are about 110 separately functioning suckers in this haptor) and with two rows of about 25 marginal organs which form a part of the secretory system found there. Two perpendicular muscular layers separate the haptor from the rest of the body. The first extensive description of the haptor of Aspidogaster conchicola is STAFFORD'S ( 1896) . The function of the margin- al organs remained obscure. VoEr.TZxow (1888) grouped them with the sensory organs. OSBORN (1903) described a similar organ in Coty- laspis insignis and, on the basis of its anatomy, believed it to have a glandular function. ROHDE (1971) described the marginal organs of Multicotyle purist and concluded that the organ forms part of a se- cretory system. The secretion is formed by those cells in the haptor which lie above the outer two rows of alveoli. HALTON & LYNESS (1971) described the skin with sensory cells. Also BAILEY & TOMP- KINS (1971) studied the ultra structure of the integument. In this study we have attempted to give a complete description of the structure of the haptor, in which the marginal organs take up an important place, in order to throw some light on the role of these organs in the animal. 163 MATERIALS AND METHODS Aspidogaster conchicola was obtained from the pericardial and renal cavities of Lamellibranchiata. The origin of the material and the methods used are described else- where (BAKKER & DIEGENBACH, 1973). The 1 sections were stained with paragon. The scanning electron microscopy was done on frozen dried, gold coated specimens in collaboration with the scanning- microscope group of the University of Amsterdam (Pl. IV). RESULTS 1. Functional morphology of the haptor In an adult worm (2.5-3.5 mm) the haptor is about 0.6 mm wide and about 2.5 mm long. It is 150-200 ym thick and consists of 26 rows of four alveoli (suckers, Fig. 1), two rows of two alveoli (one row on either side of the rows of four), and one alveolus at the anterior and one at the posterior end of the haptor. The suckers can contract and relax separately. This is clearly seen under a dissection microscope when the worm 'hangs' with the haptor (ventral side) onto the water surface. The transformations of the haptor indicate the function of the various muscle groups. However, it is impossible to fix the haptor in a predeterminated position (contracted or relaxed, Pl. V figs. 8, 9). Few movements are seen in a worm which is attached to a substra- tum. However, the suckers contract and relax about every 15 seconds when it is 'hanging' onto the water surface. This can perhaps be ex- plained as an attempt to acquire a better grip. The suckers relax simultaneously while the contraction begins at the anterior end and spreads to the posterior end within about two seconds. 2. Muscle fibres in the haptor Reconstruction of the muscular arrangement (fig. 1) from 1 [im Epon sections (Pl. I figs. 1, 2), together with the form changes of the haptor of a living worm, led us to the conclusions that 9 groups of muscles play a role in the functioning of the suckers. The position of these muscles is indicated in Fig. 1. To understand the function of the various groups of muscles, the state of contraction of the alveoli in the two positions (alveoli attached to or loose from a surface) can be correlated with the state of contraction of the various groups of muscles. It then appears that in an attached position muscle groups 4 and 5 are relaxed (the alveolus is large), muscle groups 2 and 3 are contracted (the ridges between the alveoli are small) and muscle group 1 is also .