WAR  of  the  MICROWORLDS  

How do I kill Thee?   Let me count the Ways!   (# 18)  click here for full list

Triacutus subcuticularis: the fungus attacks rotifers using three-pronged spores with sharply pointed tips.  These prongs impale the victim and the fungus grows into the host.  Uniquely, and remarkably, the fungus is subcuticular but does not grow into living organs inside the body.  It occupies the 'space' between the outer cuticle and the hypodermis.   Normally the hypodermis is pressed tightly against the outer cuticle to which it is anchored by occasional connectives.  The hyphae develop within this 'space', enlarging it, and eventually packing it with hyphal segments.   Segments of the fungal hyphae finally restrict  normal movements and activities of the rotifer and it succumbs.  Hundreds of   'tridentate' spores now develop around the periphery of the corpse (diagram).   Interestingly, it seems that each segment gives rise to a one or a few spores whose production involves emptying the segment of its protoplasmic content.   DEUTEROMYCOTA.  (For further details on this species see Barron, G.L. and S.S. Tzean. 1981. A subcuticular endoparasite attacking rotifers with three-pronged spores. Can. J. Bot. 59: 1207-1212).

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Three pronged conidia (arrow) of  Triacutus

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Bdelloid rotifer under attack by the fungus Triacutus subcuticularis. 

The conidial prongs have penetrated the cuticle and invasive hyphae are now growing between the outer cuticle and the hypodermis causing the living parts of the nematode (red arrows) to shrink away from the cuticular casing.   Fungal growth between the cuticle and the hypodermis of the animal eventually packs the space with hyphal segments.  This interferes with bodily functions and   prevents normal movement and activities and the rotifer dies and is then completely colonized.  

In this unique method of parasitism,  the fungus must encourage or control leakage products from the living body to move into the space between the cuticle and the hypodermis for  growth of the assimilative hyphae.   Hyphae commonly break up into short segments as they grow (arrows).