Chitonomyces aculeifer Speg. MB#150989 Fig. 20A–B Anales del Museo Nacional de Historia Natural de Buenos Aires 27: 44 (Spegazzini 1915b; as aculeiferus). – Type: “ Sobre las patas del Laccophilus virescens, pescado en el lago de Tarzo, Veneto, Ag. 1914”; LPS. [Italy] Chitonomyces bruchii Speg. (Spegazzini 1917: 479) [MB#166509] Chitonomyces ceratomycetalis Thaxt. (Thaxter 1926: 517) [MB#260283] Diagnostic features Dimorphic. In the typical form the perithecium bears a conspicuous straight to strongly arcuate or sigmoidal darkened horn-like outgrowth arising from the preapical wall cell in the posterior margin (Fig. 20A, arrow). [Detailed descriptions: Scheloske 1969; Majewski 1994b; Santamaria 2003; De Kesel & Haelewaters 2012] Distribution and hosts On Haliplus, Peltodytes Régimbart, 1878 (Col. Haliplidae), Laccophilus? (type of Ch. aculeiferus) and Graptodytes (Col. Dytiscidae) from Europe: Czech Republic, Germany, Italy, Poland, Spain, Bulgaria (Rossi et al. 2019a), Belgium (De Kesel & Haelewaters 2012), as well as in South America (Argentina, type of Ch. bruchi) and Asia (China, type of Ch. ceratomycetalis). Collections examined from Denmark On Graptodytes bilineatus (Sturm, 1835) (Col. Dytiscidae) DENMARK – Nordøstsjaelland (NEZ) • Amager Faelled; 55°38.631′ N, 12°34.729′ E; UB47; 22 Apr. 2018; JP 1037; JP det.; ZMUC C-F-123553. On Haliplus ruficollis (Degeer, 1774) (Col. Haliplidae) DENMARK – Lolland, Falster, Møn (LFM) • Busemarke Mose; 54°57.688′ N, 12°26.619′ E; UA39; 19 Aug. 2019; JP 1495; JP det.; ZMUC C-F-124082, C-F-124083. Remarks First record from Denmark. It is broadly accepted that this species exists in two “growth forms” or “morphotypes” related to the sex of the host and growth position on the body. The typical horned form grows under the margins of the pronotum or neighbouring areas in females, and the not horned form grows between the anterior or medium claws in males.

Published as part of Santamaria, Sergi & Pedersen, Jan, 2021, Laboulbeniomycetes (Fungi, Ascomycota) of Denmark, pp. 1-425 in European Journal of Taxonomy 781 on pages 99-100, DOI: 10.5852/ejt.2021.781.1583, http://zenodo.org/record/5828924