Oceanitis scuticella-like organisms

Nagano, Yuriko, Abdel-Wahab, Mohamed A., Nakajima, Ryota & Yabuki, Akinori, 2024, Oceanitis abyssalis sp. nov., a new deep-sea fungus from sunken wood collected at the depth of 5707 m in the Northwest Pacific Ocean, Phytotaxa 663 (4), pp. 171-183 : 175-180

Oceanitis scuticella-like organisms and phylogenetic analyses

Dupont et al. (2009) recorded twelve collections of Oceanitis scuticella -like fungus from trawled samples from the bottom of the South Pacific Ocean off Vanuatu from depths between 551 m and 1273 m. The authors identified their fungal collections as O. scuticella , although it has a significantly different morphological characteristics from the original collection of O. scuticella that Kohlmeyer described from the Gulf of Angola, Atlantic Ocean, by having stromatic ascomata vs. aggregated ascomata and a thinner walled peridium than the Angola’s material ( Dupont et al. 2009; Kohlmeyer 1977). Dupont & Schwabe (2016) also reported a collection of Oceanitis scuticella -like fungus from the sunken wood collected by trawling at abyssal depth from the Kuril-Kamchatka Trench in the Northwest Pacific Ocean. The authors identified their collection as O. scuticella although it has unicellular ascospores with much smaller polar appendages and smaller drop-shaped ascomata than the Angola’s materials. We believe that both collections made by Dupont et al. (2009) and Dupont & Schwabe (2016) represent undescribed species different from O. scuticella , as the shape of ascomata and the spore septation are important characteristics for classifying fungal species. Detailed comparison of the morphology of Oceanitis species is summarized in Table 1.

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In order to clarify the phylogenetic position of O. abyssalis and Oceanitis scuticella -like organisms, the LSU rDNA region of O. abyssalis was aligned with other Oceanitis sequences and other appropriate sequences retrieved from GenBank ( Fig. 4 ). The new species, O. abyssalis is well placed in the genus Oceanitis clade with 100% support in the ML phylogenetic analysis. Oceanitis abyssalis was placed with the Kuril-Kamchatka Trench material (M0229768) but located separately from other Oceanitis taxa. The LSU and ITS rDNA sequences of O. abyssalis showed 100% match with the Kuril-Kamchatka Trench material (M0229768). Both Oceanitis abyssalis and the Kuril-Kamchatka Trench material (M0229768) have drop-shaped ascomata and unicellular ascospores. They were collected from a similar environment, the abyssal plain of the North Pacific Ocean. From a morphological perspective, as well as considering the 100% similarity in ITS rDNA sequences and ecological aspects of the collected material, we inclined to consider that M0229768 reported as O. scuticella in Dupont & Schwabe (2016) is a representative of O. abyssalis . Although there are slight morphological differences between M0229768 and O. abyssalis ( Table 1), specifically, they differ in the dimensions of the ascospores (58–77 × 4–5 µm for O. abyssalis vs. 52 × 2.3 µm for M0229768), and ascomata of Oceanitis abyssalis are larger in size with a thicker, three-layer peridial wall ( Dupont & Schwabe 2016). Also, ascospores of Oceanitis abyssalis have two types of appendages, while the collection of the Kuril-Kamchatka Trench has one polar uncoiling appendage. Some of these differences may result from a lack of detailed comprehensive observation and further findings of the specimens and detailed analyses will be needed to determine their precise identification. Therefore, we concluded in the present study that the Kuril-Kamchatka Trench material (M0229768) should be treated as Oceanitis cf. abyssalis ( Table 1 and Fig. 4 ).

The South China Sea material (CP4157) was closely related to O. abyssalis and Kuril-Kamchatka Trench material (M0229768) but placed independently within the Oceanitis scuticella -like clade and showed 3 nucleotide differences in the LSU rDNA sequence and one nucleotide difference in the SSU rDNA sequence from O. abyssalis (ITS rDNA sequence data is not available). As the detailed morphological information of the South China Sea material (CP4157) is not available, it cannot be discussed further. The Vanuatu materials (CP2457b, CP2429, CP2421) formed a clade being separate from CP4157 and O. abyssalis . There are 3 to 4 nucleotide differences in the LSU rDNA sequence and 11 to 14 bases (2.5–3.0%) differences in ITS rDNA sequence between the Vanuatu materials and O. abyssalis . Morphological and phylogenetic analyses suggested that the Vanuatu materials (CP2457b, CP2429, CP2421) are likely another undescribed Oceanitis species different from the original O. scuticella and O. abyssalis . Therefore, we concluded in the present study that the Vanuatu materials (CP2457b, CP2429, CP2421) should be treated as unidentified Oceanitis spp. ( Table 1 and Fig. 4 ). The South China Sea material (CP4157), of which details are unknown, might be an another unidentified Oceanitis sp. because of its independent phylogenetic position. To clarify the taxonomy of these collections and to understand the diversity within the genus Oceanitis more accurately, additional collections, including O. scuticella sensu stricto from the type locality, are needed. Furthermore, comprehensive morphological and phylogenetic studies are essential to formally describe these species.

Figures

FIGURE 4. Phylogenetic relationships of Oceanitis abyssalis and other Oceanitis species analyzed by the maximum likelihood tree (ML), based on the nucleotide sequences of the LSU rDNA. Numbers at nodes are bootstrap indices of support (ML/MP), and only branches with bootstrap values above 50% from an analysis of 1,000 bootstrap replicates are indicated. New species are highlighted in bold and underlined. The collections previously identified as O. scuticella and newly proposed as Oceanitis cf. abyssalis, or unidentified Oceanitis species in this study, are marked with an asterisk.