Bioacoustics of Santjordia pagesi

Molecular Phylogeny The analysis of sequences of the mitochondrial 16S gene using maximum likelihood (ML) and Bayesian methods gave congruent tree topologies ( Fig. 6 ). Robust support was evident for the semaeostome clades Drymonematidae and Cyaneidae , and for another clade including the ulmarid subfamilies Poraliinae and a member of the Ulmarinae, but also including the recently erected family Phacellophoridae . In fact, higher support was evident for Diplulmaris (Ulmarinae) and Phacellophora ( Phacellophoridae ) being more closely related to each other than for a close relationship between some of the ulmarid genera investigated. Somewhat surprisingly, there was reasonable support for Santjordia pagesi gen. et sp. nov. belonging to a sister group to a clade including the ulmarid subfamilies lacking marginal tentacles—Stygiomedusinae + Tiburoniinae + Deepstariinae . A BLAST search for the COXI sequence returned a maximum percentage identity of 82.62% with a query cover of 95% matched with Aurelia coerulea , with the next closest match being Rhopilema aff. esculentum at 82.21% and 97%, respectively. These low values are indicative of the COXI marker not being suitable for resolving higher phylogenies and further analysis was not attempted. Sequences determined in the present study have been registered on GenBank under accession numbers ON391151-ON391163 for 16S and ON496462 for the single COXI sequence, belonging to Santjordia pagesi gen. et sp. nov. All sequences used in the molecular analysis are listed in Tables 1 and 2 . Images of sequenced specimens, where available, are available online on Zenodo ( Lindsay 2022a –k). Remarks The medusa was swimming upwards at a pulse rate of 0.4 Hz at a depth of 812 m and an altitude of 101 m above the bottom. Only two individuals were observed over 91 minutes of observation time during descent below the caldera rim at 400 m depth inside the Sumisu Caldera, and no individuals were observed during a second dive during descent to a maximum depth of 893 m above the outer wall slope of the caldera on the previous day ( 31°29.1′N , 140°09.3′E ; total observation time below 400 m : 115 min). Compared to environmental parameters outside the caldera in the open ocean, temperature at 812 m depth was elevated within the caldera (10.2˚C vs 5.5 ˚C), as was the dissolved oxygen concentration (2.8 ml/L vs 1.7 ml/L). The oceanographic environment within the Sumisu Caldera is described and discussed in more detail by Hidaka et al. (2021) . The caldera wall around this depth is comprised of monomictic lava breccia, coherent facies or talus blocks, while most of the caldera floor is covered with pumiceous sand and pebbles with some lobes of coarser debris ( Tani et al . 2008 ). Other organisms observed in the same depth layer as Santjordia pagesi gen. et sp. nov. included the calycophoran siphonophore Clausophyes sp. (see Hidaka et al. 2021 ), pyrosomes ( Pyrosomatidae spp.) (see Hidaka et al. 2021 ), euphausiids, sergestid shrimps, the hyperiid amphipod Platyscelus ovoides , a presently undescribed species of lobate ctenophore with vestigial auricles (Undescribed Lobata “No auricles” of Hidaka et al. 2021 ), and cydippid larvae of at least one species of lobate ctenophore (“Cydippid larvae” of Hidaka et al. 2021 ).