Hydrophilomyces hydraenae W. Rossi & M. Leonardi, sp. nov.
Index Fungorum number: IF 557383; MycoBank number: MB 557383; Facesoffungi number: FoF 07847; Fig. 1
Etymology – Named after the host insect.
Holotype – FI WR2462
Thallus hyaline or nearly so. Receptacle consisting of 11–12 superposed cells, of which the basal is irregularly rhomboid, the following 2–3 cells, small, each producing laterally an elongate and variably curved buffer cell, the others gradually increasing in length from almost flattened to slightly longer than broad. Appendage usually curving outwards and downwards, consisting of 8–10 subequal cells, each separating a small corner cell on the anterior side; these corner cells give rise to short branchlets bearing distally 2–4 elongate antheridia soon displaced by long and slender sterile branchlets, which are repeatedly divided in the distal portion of the appendage. Perithecial venter ovoid, relatively short, tapering without abrupt transition to the broad neck; the latter almost isodiametric, up to three times longer than the venter, with an elongate and undistinguished tip ending in rounded apex. Total length from foot to perithecial apex 300–345 µm; length of perithecium 205–250 µm; perithecial venter 35×60 µm.
Material examined – USA, CA, Santa Barbara Co., W Camino Cielo (rd.) at Hwy. 154, 590 msl, 34°30.273′ N 119°48.806′ W, edge of a stream in hardwood forest, 19 July 2000, A. Newton and M. Thayer, at the base of the legs of Hydraena vandykei Orchymont (Coleoptera, Hydraenidae) (FI WR2462, holotype; FI WR2477, paratype).
Notes – The species of Hydrophilomyces described so far are 16, of which 8 are reported on Hydraenidae (genera Ochtebius and Limnebius), the other 8 on Hydrophilidae. These species can be distinguished from Hydrophilomyces hydraenae (Fig. 1) by the following characteristics: H. gracilis, H. lumbricoides, H. major, H. reflexus and H. rhynchophorus (all parasitic on Hyrophilidae) lack any buffer cells and have a very elongate receptacle consisting of 20 or more cells; H. coneglianensis has the perithecial neck about as long as the venter; H. arcuatus, H. pusillus, H. rhytidopus have the perithecial neck much shorter than the venter; H. aduncus, H. deflexus, H. hamatus, H. limnebii have a distinctly curved perithecial neck; H. atroseptatus has a stout and tapering appendage, consisting of flattened cells bearing corner cells separated by constricted dark septa from antheridia or sterile branchlets; H. riberae has a shorter receptacle and a broader perithecial neck; H. digitatus has the receptacle consisting of more or less isodiametric cells, a more elongate perithecial venter, a slenderer and shorter perithecial neck distinctly broadened at the junction with the tapering and truncate tip (Spegazzini 1917; Thaxter 1908; Huldén 1983; Majewski 1994; Santamaria 2003, 2006; Santamaria et al. 2020).
Figure 1 – Hydrophilomyces hydraenae (FI WR2462, holotype). a Thallus from the type slide stained with acid fuchsin. b Thallus from the paratype slide stained with acid fuchsin. Scale bars: a, b=100 µm