Umimayanthus, Montenegro, Sinniger & Reimer, 2015

Montenegro, Javier, Fromont, Jane, Richards, Zoe, Kise, Hiroki, Gomez, Oliver, Hoeksema, Bert W. & Reimer, James Davis, 2024, Museum collections as untapped sources of undescribed diversity of sponge-zoantharian associations with the description of six new species of Umimayanthus (Zoantharia: Parazoanthidae) from Western Australia and eastern Indonesia, Contributions to Zoology 93 (5), pp. 466-522 : 514-515

Umimayanthus

The specificity of host-zoantharian associations in Umimayanthus has not been thoroughly studied, primarily because of the taxonomic uncertainty of the groups involved in the symbioses. This study provided a rare situation where taxonomists with specialties in both taxa worked in collaboration to provide a more complete picture of associations (see also Swain & Wulff, 2007).

Earlier work on host-zoantharian associations concluded that it is relatively common for a single zoantharian species to associate with multiple host species, but it is more unusual to find one host associated with more than one zoantharian species ( Swain & Wulff, 2007). It is worth noting that multiple exceptions are known for host sponges in the genera Agelas Duchassaing & Michelotti, 1864 ,

Cribrochalina Schmidt, 1870 , Xestospongia de Laubenfels, 1932 , Svenzea Alvarez, van Soest & Rützler, 2002 and Hymeniacidon Bowerbank, 1858 ( Swain & Wulff, 2007; Montenegro et al., 2020). However, in general terms, this pattern first observed by Swain & Wulff (2007) appears to be valid for host- Umimayanthus associations ( table 2). For instance, U. wunanggu sp. nov. was found in association with two different sponge species in the genus Endectyon ; U. mirnangga sp. nov. was in association with two species in two genera, as was U. discolor sp. nov.; and U. raksasa sp. nov. is likely associated with more than one species in the genus Phakellia . Remarkably, Caribbean U. parasiticus has been reported in association with 23 species of sponges across 10 different genera of host sponges ( Swain & Wulff, 2007; Montenegro et al., 2020). Other species such as U. chanpuru , U. miyabi and U. nakama are likely associated with multiple genera of encrusting and calcareous sponges, but no detailed taxonomic data are yet available on the identity of their host sponges ( Montenegro, pers. observ.).

The only confirmed exceptions to this generalized pattern are U. cf. aruensis , which appears to have a specialized association with Trikentrion flabelliforme , and U. kanabou consistently found in association with a gorgonian in the genus Ellisella , although the identity of the species remains unknown ( Fujii et al., 2021). Other species such as U. jebarra sp. nov. and U. lynherensis sp. nov. are only known from a single record, and thus is not possible to draw conclusions on the specificity of the associations for these species.

On the other hand, the host sponges in this study appear to be quite restricted to

CONTRIBUTIONS TO ZOOLOGY 93 (2024) 466–522

the specific Umimayanthus species, with most of them associated with a single zoantharian species. Two exceptions were found: Trikentrion flabelliforme , which had associations with two phylogenetically distinct species, U. cf. aruensis and U. discolor sp. nov.; and Endectyon (Endectyon) fruticosum , which was associated with U. wunanggu sp. nov. and U. mirnangga . sp. nov. Given that the latter two sibling species are closely phylogenetically related, we speculate that some level of overlap in host preference is to be expected ( Brändle et al., 2000; Blomberg & Garland, 2002).

Based on the results of our phylogenetic analyses, it is clear that these species represent a large radiation of sponge-associated Umimayanthus , with species and clades having generally different niches, based on host species and depth. For instance, Clade I was found inhabiting depths of 12–39 m, Clade II between 41–59 m, and Clade III overlapping all other depth ranges with records from depths of 4– 100 m. However, a closer look revealed strati- fication by depth within Clade III, with U. raksasa sp. nov. and U. lytherensis sp. nov. restricted to deeper waters while U.discolor sp. nov. inhabits shallow waters.

Many studies have shown the Central Indo-Pacific (the Coral Triangle) to be the center of marine biodiversity for a vari- ety of marine taxa such as algae, larger benthic forams, crustaceans, fishes, mol- luscs, and scleractinian corals ( Hoeksema, 2007; Förderer et al., 2018); but whether the region also harbors high diversi- ties of many less studied taxa, including zoantharians, still needs to be examined ( Reimer et al., 2014). The current study, focused on species associated with only four families of sponges, indicates that zoantharians may also follow the Coral Triangle centre of biodiversity, and further studies are needed to better confirm this.