Helicocephalidaceae (Boedijn, 1958) was originally included in the Mucorales, and it was retained in the order by Hesseltine and Ellis (1973) whereas Zycha et al. (1969) maintained Rhopalomyces and several unrelated genera in Choanephoraceae; Helicocephalum was not mentioned. Helicocephalum has been treated by some mycologists as a hyphomycete (Kendrick and Carmichael, 1973; Carmichael et al., 1980).
Mil’ko (1974) indicated that Rhopalomyces and Helicocephalum were members of Zoopagales. Benjamin (1979) accepted this idea placing Helicocephalidaceae in the order along with Cochlonemataceae, Piptocephalidaceae, and Zoopagaceae. O’Donnell (1979) also adopted Benjamin’s classification.
Helicocephalidaceae contains three genera, Brachymyces, Helicocephalum, and Rhopalomyces. Present information indicates that members of Helicocephalidaceae are haustorial parasites of nematodes and nematode eggs, rotifers, and possibly other small animals. Many of these fungi can be isolated on soil plates especially if seeded with the proper host (Barron, 1980b) or if the substrate contains a host or its eggs (humus; rotting vegetation, dung, etc.).
An unidentifed species of Helicocephalum was not induced to germinate and sporulate in pure culture, without a host, using the procedure recommended by Ellis (1963) for Rhopalomyces elegans Corda. There have been several reports of spore germination in Helicocephalum spp. occuring on natural substrates (Drechsler, 1934, 1943; Barron, 1975), but usually a good culture has not been reestablished.
Helicocephalidaceae Boedijn, 1958  (Sydowia 12: 355).
Vegetative hyphae very thin, delicate, highly branched, aseptate. Sporophores aseptate, provided with a rhizoid-like, basal holdfast, tip remains straight or coils, becomes moniliform and septa form at the constrictions producing spores, or the apex becomes vesiculate and spores form blastically. Merosporangia unispored, relatively large, pigmented. Presumably heterothallic. Zygospores unknown. Haustorial parasites of nematodes and nematode eggs, and other small animals.
Type genus: Helicocephalum Thaxt.
Key to the genera of HelicocephalidaceaeA. Sporangiophore apex straight or coiled, becoming septate and disarticulating into spores —— Helicocephalum
AA. Sporangiophore apex vesiculate, spores formed simultaneously and blastically —— BB. Fertile vesicle comprising most of the length of the sporophore which is constricted basally; 1-4 spores formed; parasitic on bdelloid rotifers —— Brachymyces
BB. Fertile vesicle occuring only at the sporophore apex; many spores formed; parasitic on nematodes and their eggs —— Rhopalomyces
Synopsis of Genera
BRACHYMYCES Barron, 1980 (Canad. J. Bot. 58: 2450).
HELICOCEPHALUM Thaxter, 1891 [Bot. Gaz. (Crawfordsville) 16: 201].
RHOPALOMYCES Corda, 1839 (Practflora, p. 3).
Updated Feb 10, 2005