Laboulbeniomycetes (Fungi, Ascomycota) of Denmark Author Santamaria, Sergi Unitat de Botànica, Departament de Biologia Animal, de Biologia Vegetal i d’Ecologia, Facultat de Biociències, Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès (Barcelona), Spain. sergi.santamaria@uab.cat Author Pedersen, Jan Natural History Museum of Denmark (Zoological Museum), University of Copenhagen, Universitetsparken 15, 2100 København Ø, Denmark. japedersen@snm.ku.dk text European Journal of Taxonomy 2021 2021-11-26 781 1 425 http://dx.doi.org/10.5852/ejt.2021.781.1583 journal article 10.5852/ejt.2021.781.1583 2118-9773 5828924 Genus Chitonomyces Peyr. MB#1002 Sitzungsberichte der Kaiserlichen Akademie der Wissenschaften. Wien . Mathematischnaturwissenschaftliche Classe. Abteilung 1 68: 250 ( Peyritsch 1873 ). – Type species: C. melanurus Peyr. Heimatomyces Peyr., Sitzungsberichte der Kaiserlichen Akademie der Wissenschaften. Wien . Mathematisch-naturwissenschaftliche Classe. Abteilung 1 68: 251 ( Peyritsch 1873 ) [MB#2252] Brief description Monoecious. Receptacle six-celled. The primary appendage, which is subtended by cell IIIa, is two-celled and consists of a dome-shaped basal cell and a filiform distal cell. Only one antheridium for each thallus, usually also dome-shaped and mostly similar to the basal cell of the primary appendage (this corresponds to the genus Chitonomyces in the strict sense, see below), embedded between cell IIIa and the perithecium. Remarks The genus consists of 89 species, of which 13 in Europe, seven in Denmark . The most recently described species is C. tylopus ( Santamaria 2001b ) . This is an isolated and well-characterized genus associated with aquatic beetles, mostly Dytiscidae , but also Haliplidae and Gyrinidae . Some species show a high degree of specialization by growing on very restricted areas of host bodies ( Goldmann & Weir 2012 ). Thalli show a bizarre morphology requiring a particular terminology. Thaxter (1924) divided the genus in two subgenera, Euchitonomyces and Chitonomyces s. str. for species with six or eight receptacular cells, respectively. The only further difference between the two types seems to be related to the distinctiveness of the antheridium which is, weakly distinguished in Euchitonomyces (e.g., C. bidessarius ). Otherwise we see no reason to separate the two groups. The six receptacular cells are named I, Ia, II, IIa, III, and IIIa ( Santamaria 2003 ; Goldmann & Weir 2012 ) ( Fig. 20B ). Because of the absence of a thorough study of thallus development in this genus, the exact identity of some cells has not been clearly interpreted, particularly the cells lying under the perithecium, as m, n, n′ and VII. Key to the Danish species (partially following Santamaria 2003 ) 1. Species with some kind of horn-like outgrowth perithecial cell, including basal and stalk cells .... 2 – Species without this kind of outgrowths on or near the perithecium ............................................... 4 2. A perithecial outgrowth on the top, arising from an uppermost wall cell. Thalli growing under the posterior margin of left elytron. On Laccophilus Leach, 1815 (Col. Dytiscidae ) ............................... ............................................................................................................... C. paradoxus (Peyr.) Thaxt. – Perithecial outgrowth lateral. Thalli on other locations of host body............................................... 3 3. A perithecial outgrowth arising from a preapical wall cell. Thalli growing under the margins of the pronotum. On Graptodytes Seidlitz, 1887 (Col. Dytiscidae ) and Haliplus Latreille, 1802 (Col. Haliplidae ) ............................................................................................................. C. aculeifer Speg. – A perithecial outgrowth arising from the lower third of the anterior side of the perithecium, sometimes also including a bulging cell VI which resembles a second protuberance. Thalli growing on the last tarsus of left hind leg. On Laccophilus (Col. Dytiscidae ) ........................................ C. ensifer Speg. 4. Cell IIIa proliferating into a lateral outgrowth. On Laccophilus (Col. Dytiscidae ) ............................ .................................................................................................................................. C. italicus Speg. – Cell IIIa not proliferating into an outgrowth .................................................................................... 5 5. Cell IIIa and basal cell of primary appendage blackened and with a hook-shaped tip. On Laccophilus (Col. Dytiscidae ).................................................................................................. C. melanurus Peyr. – Cell IIIa and basal cell of primary appendage hyaline to pale yellowish-brown, concolorous with the remaining thallus .............................................................................................................................. 6 6. Cell I very elongate, 5–10 or even more longer as broad. Thalli concealed under the last abdominal sternite of Laccophilus (Col. Dytiscidae ) ............................................................. C. elongatus Speg. – Cell I shorter, at most twice longer as broad. On Hygrotus Stephens, 1828 (Col. Dytiscidae )........... ............................................................................................................ C. bidessarius (Thaxt.) Thaxt.