Acanthopharynx Marine Nematodes (Nematoda, Chromadoria, Desmodoridae) Dwelling in Tropical Demosponges: Integrative Taxonomy with Description of a New Species

In the exploration of the meiofauna associated with sponges and corals in the shallows of Cuba, we investigated nine species of sponges (Demospongia), wherein 26 nematode species were revealed. Most nematode specimens (50-95% of all individuals) in all sponge samples belonged to the family Desmodoridae (order Desmodorida), followed by the family Chromadoridae (order Chromadorida). A major part of Desmodoridae is constituted by the genus Acanthopharynx. A statistical morphometric analysis (principal component analysis and multidimensional scaling with testing via analysis of similarities) revealed two close cohorts that differed in size and pharynx shape. Molecular genetic analyses (COI, 18S, and 28S) also distinguished two groups of specimens that corresponded to morphometric cohorts. Based on the morphometry and molecular genetics, the larger-sized group was defined as Acanthopharynx micans (Eberth, 1873), while the smaller-sized group was considered A. parva sp. n. In light of the taxonomic review of the Acanthopharynx, emended generic diagnosis, and the annotated list of ten valid species, A. parva sp. n. differed from other Acanthopharynx species by its peculiar shape of the pharynx (gradually widened to cardia), smaller body size, and pattern of precloacal organs.

Automated summary

This study explored meiofauna associated with sponges and corals in the shallow waters of Cuba, uncovering 26 nematode species in nine sponge species. The majority of nematodes belonged to the Desmodoridae family, with a significant presence of the genus Acanthopharynx. Morphometric and molecular genetic analyses revealed two distinct cohorts within Acanthopharynx, differing in size and pharynx shape. A new species, A. parva sp. n., was identified based on its unique pharynx shape, smaller body size, and precloacal organ pattern.