 |
| Hadaka nudidomus Lau & Reimer, 2019
DOI: 10.3390/d11100176
|
Abstract
Shallow water coral reefs are the most diverse marine ecosystems, but there is an immense gap in knowledge when it comes to understanding the diversity of the vast majority of marine biota in these ecosystems. This is especially true when it comes to understudied small and cryptic coral reef taxa in understudied ecosystems, such as mesophotic coral reef ecosystems (MCEs). MCEs were reported in Japan almost fifty years ago, although only in recent years has there been an increase in research concerning the diversity of these reefs. In this study we describe the first stoloniferous octocoral from MCEs, Hadaka nudidomus gen. nov. et sp. nov., from Iriomote and Okinawa Islands in the southern Ryukyus Islands. The species is zooxanthellate; both specimens host Cladocopium LaJeunesse & H.J.Jeong, 2018 (formerly Symbiodinium ‘Clade C’) and were collected from depths of ~33 to 40 m. Additionally, H. nudidomus gen. nov. et sp. nov. is both sclerite-free and lacks free pinnules, and both of these characteristics are typically diagnostic for octocorals. The discovery and morphology of H. nudidomus gen. nov. et sp. nov. indicate that we still know very little about stoloniferous octocoral diversity in MCEs, their genetic relationships with shallower reef species, and octocoral–symbiont associations. Continued research on these subjects will improve our understanding of octocoral diversity in both shallow and deeper reefs.
Keywords: Cladocopium; cryptofauna; marine biodiversity; mesophotic coral reef environments (MCEs); Octocorallia; stoloniferous octocorals; Symbiodiniaceae; taxonomy
 |
| Figure 2. Photographs of Hadaka nudidomus gen. nov. et sp. nov.: (a) in situ holotype NSMT-Co 1681, scale bar approximately 1 mm; (b) in situ paratype NSMT-Co 1682, scale bar approximately 1 mm; (c) holotype in ethanol, scale bar 1 mm; (d) holotype in methylene blue staining, scale bar 0.1 mm. |
Class Anthozoa
Subclass Octocorallia Ehrenberg, 1831
Order Alcyonacea Lamouroux, 1812
Family Clavulariidae Hickson, 1894
Genus Hadaka gen. nov.
Type species: Hadaka nudidomus sp. nov. by original designation and monotype.
Diagnosis: Colony with polyps connected through flattened ribbon-like stolons, which are loosely attached to a hard substrate. Polyps retract fully into the calyx, which is cylindrical to conical in shape, narrowing at the base and does not retract fully into the stolon. Tentacles have a wide rachis with a protruding ridge and pseudopinnules of different lengths arranged on either side, giving the polyps feather shaped tentacles. No sclerites. Zooxanthellate.
Remarks: Hadaka gen. nov. et sp. nov. shows gross resemblance to Hanabira Lau, Stokvis, Imahara & Reimer, 2019 in having a similar polyp shape with feather or petal shaped tentacles and fused pinnules, which can still be distinguished by shallow furrows. Hadaka gen. nov. et sp. nov. differs from Hanabira in having no sclerites in any part of the colony and having a protruding ridge on the upper side of the tentacle. Genetically, Hadaka gen. nov. is well-supported and positioned in a different phylogenetic clade from Hanabira. The closest sister taxa of Hadaka gen. nov. is Acrossota Bourne, 1914, which is also sclerite-free, but morphologically very different; Acrossota lacks pinnules completely.
Etymology: From the Japanese word hadaka (裸), meaning naked, bare, nude; denoting the absence of two characteristic features of octocorals, sclerites, and free pinnules. Gender: feminine.
Hadaka nudidomus sp. nov.
Distribution: Southwestern Japan, southern Ryukyus Islands, around northern Okinawa Island, and inside the bay of western Iriomote Island in the East China Sea. Specimens were collected from depths of ~33–40 m.
Remarks: The polyps of paratype NSMT-Co 1682 were all used for DNA extraction and sclerite examination, as they were initially thought to be a Hanabira yukibana specimen; three fragments of rock with stolon remain. The holotype colony (NSMT-Co 1681) was attached to sponge tissue, but this epibiont is not obligate, as the paratype was attached to rock.
Habitat: The holotype (NSMT-Co 1681) was found attached to sponge on a large piece of coral rubble (>15 cm) lying on a mixed small rubble/soft sediment bottom. The paratype (NSMT-Co 1682) was found on consolidated hard carbonate bottom. Both colonies were on the upward-facing side of the bottom.
Etymology: From Latin nudus, meaning naked or bare, and domus, meaning home or house; denoting the ‘naked’ host habitat in which the zooxanthellae reside, as the species is sclerite-free.
 |
| Figure 1. Map of the Ryukyus Islands (RYS), with the six island group divisions (grey dotted lines) and the two dive locations where Hadaka nudidomus gen. nov. et sp. nov. specimens were found (red dots) at Iriomote (NSMT-Co 1681, holotype) and Okinawa (NSMT-Co 1682, paratype) Islands. |
Yee Wah Lau and James Davis Reimer. 2019. Zooxanthellate, Sclerite-Free, and Pseudopinnuled Octocoral Hadaka nudidomus gen. nov. et sp. nov. (Anthozoa, Octocorallia) from Mesophotic Reefs of the Southern Ryukyus Islands. Diversity. 11(10), 176. DOI: 10.3390/d11100176
