New Species of Osedax (Siboglinidae: Annelida) from New Zealand and the Gulf of Mexico Author Berman, Gabriella H. Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093 - 0202, USA Author Hiley, Avery S. Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093 - 0202, USA Author Read, Geoffrey B. National Institute of Water & Atmospheric Research (NIWA), 301 Evans Bay Parade, Hataitai, Wellington New Zealand Author Rouse, Greg W. Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093 - 0202, USA text Zootaxa 2024 2024-04-23 5443 3 337 352 http://dx.doi.org/10.11646/zootaxa.5443.3.2 journal article 10.11646/zootaxa.5443.3.2 1175-5326 11045291 AB6A5DE3-D85B-4103-A92F-917936F19EF3 Osedax craigmcclaini n. sp. Fig. 3B, C , 5A, B , 6B Osedax sp. McClain et al. , 2019 , p. 7 of 14 Material examined . Holotype : SIO-BIC A13910 (GenBank COI sequence ON211944), collected from experimentally deployed alligator ( Alligator mississippiensis ) bones deployed at 2,034 m depth in the Gulf of Mexico , offshore of New Orleans , Louisiana , ( 27.312° N ; 88.927° W ), ROV Global Explorer dive number 16, April 12, 2019 . Fixed and preserved in 95% ethanol. Diagnosis and description. Holotype palps are pinnulated, white in preserved state; less than 1 mm long ~ 0.33 mm wide ( Fig. 5B ). No other body parts observed. No dwarf males observed. The rDNC diagnosis for Osedax craigmcclaini n. sp. was recovered as: ‘C’ at site 318, ‘T’ at site 333, and ‘C’ at site 462 of mitochondrial COI. Distribution. Osedax craigmcclaini n. sp. was recovered from an alligator skeleton at 2,034 m off the Mississippi River Delta region, Louisiana , in the Gulf of Mexico ( Fig. 1 ). Etymology. Osedax craigmcclaini n. sp. is named for Dr. Craig McClain, an esteemed deep-sea biologist and colleague who led the experimental alligator fall project ( McClain et al. , 2019 ) and provided the Osedax specimens for this study. Remarks. Osedax craigmcclaini belongs to Clade V, a pinnulate clade ( Fig. 2 ). Evidence for this species was originally published in McClain et al. (2019) with COI only (GenBank Accession number MN258704), from SIO-BIC A10731. In addition, 16S ( ON217799), 18S ( ON220153), 28S ( ON226742), and H3 ( ON254807) were sequenced from the remaining the SIO-BIC A10731 DNA extraction for this study. Specimen SIO-BIC A13910 has been designated here as the holotype based on its COI sequence (ON211944) closely matching MN258704 from McClain et al. (2019) (1.2% uncorrected distance). Both sequences showed the three rDNC diagnostic bases. Based on the phylogeny shown in Figure 2 , a proximate species is Osedax fenrisi Eilertsen et al. , 2020 , a pinnulate species collected from 2,341 m on the Arctic Mid-Ocean Ridge ( Eilertsen et al. 2020 ). The minimum interspecific distance between the two species was 14.6% ( Table 3 ). There are species of Osedax with smaller uncorrected COI distances, such as Osedax crouchi Amon et al. , 2014 from Antarctica , which belongs to the nude palp Clade II ( Fig. 2 ), and McClain et al. (2019) reported the new species as falling within this clade. However, this proposed placement was based on COI data only, which can be misleading ( Vrijenhoek et al. 2009 ), and the five gene phylogeny and photographs of the holotype confirm O. craigmcclaini n. sp. as actually a member of the pinnulate Clade V. Osedax craigmcclaini n. sp. showed two unique haplotypes with seven nucleotide substitutions between them ( Fig. 5B ). Specimens were not observed alive, however in situ images of the alligator corpse from which O. craigmcclaini was collected show red Osedax coating the jawbone and spine ( Fig. 3B, C ), suggesting that living O. craigmcclaini n. sp. may have red palps.