The slime moulds are characterized by the presence of:

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Hint: Slime mould or slime moulds are an informal name given to many types of eukaryotic non-related species that can live freely as single cells but can form multicellular reproductive structures together. Formerly known as fungi, slime moulds are no longer considered part of that kingdom.

Complete answer:
-Elaters: An elater is a hygroscopic cell that will change its shape in response to environmental moisture changes. Elaters come in a number of types, but they are often related to plant spores. Elaters are present in bryophytes and assist in spore dispersal. Hence option A is incorrect.
-Pseudoelaters: Pseudo-elaters are small, filamentous structures which in many liverwort species superficially resemble the spiral elaters that are a feature of the capsules. In the genus Anthoceros, these pseudo-elaters do not spiral and assist in the release of spores. Hence option B is incorrect.
-Capillitium: The fruiting body of slime moulds contains Capillitium. They are sterile filaments and they are active in spore dispersal. Hence option C is correct.
-Capitulum: The primary inflorescence contained in the Compositae, sometimes referred to by the layman as a flower while seeing a traditional radiate capitulum, and often in many texts ahead, is composed of an involucre of defensive bracts covering the florets around the receptacle (the phyllaries). Hence option D is incorrect.

Hence option C: capillitium is the correct answer.

Note: The existence of capillitium characterises slime moulds. It is a branched sterile fibre system that is found within the fruit body. In some bryophytes, elaters and pseudoelaters occur, whereas capitulum is a form of the inflorescence.