Roa rumsfeldi, a new butterflyfish (Teleostei, Chaetodontidae) from mesophotic coral ecosystems of the Philippines

Abstract A new species of the butterflyfish genus Roa is herein described from the Verde Island Passage in the Philippines, West Pacific Ocean. Roa rumsfeldi sp. n. was found on mesophotic coral ecosystems at Puerto Galera and Batangas, and sampled through technical mixed-gas rebreather diving at 100–130 m depth. This represents the fifth known species of Roa. The main differences between Roa rumsfeldi sp. n. and its congeners are the lower number of pored scales in the lateral line, longer snout, longer caudal peduncle, shorter caudal fin, pelvic fin color (dark first spine vs. white in all other Roa), and genetics (8.4% divergence from its closest relative Roa modesta in the mitochondrial COI gene). Roa spp. are usually seen in pairs, but the two specimens we collected were solitary individuals. We have kept one of the specimens alive in the California Academy of Sciences’ Twilight Zone exhibit for more than one year, where it thrives and is feeding on a variety of dried and fresh food.


Introduction
While collecting live specimens in Anilao, Philippines to display at the California Academy of Sciences' Twilight Zone: Deep Reefs Revealed exhibit in 2016, LAR collected a butterflyfish identified at the time as Roa cf. modesta. After the specimen arrived in San Francisco and entered quarantine, MW noticed that the recent arrival differed from our previously collected specimens by having a black spine in the ventral fin (white in others). We went through our previous years' collections and found a second specimen of this species collected by spear in 2015 in Puerto Galera, Philippines.
These specimens represent an undescribed species of the genus Roa Jordan, 1923, which currently contains four species, all from mesophotic coral ecosystems (MCEs; 30-150m depth) in the Indo-Pacific. Although some taxonomists consider this genus as a "modestus species complex" within Chaetodon (Kuiter 2004, Eschmeyer et al. 2017, Roa species are remarkably different from all other butterflyfishes (Tea 2015). They display high dorsal spines (usually increasing in height from spines one to three or four, and decreasing to the last), a very conspicuous color pattern (bands of brown and white), and typically occur at MCEs (Kuiter 2004).
The currently recognized species of Roa have largely allopatric distributions: Roa modesta (Temminck & Schlegel, 1844) was described from Japan and is distributed along the northwestern Pacific, recorded in the Philippines, Hong Kong, Taiwan, Ryukyu and Ogasawara Islands, and Nagasaki, in Japan (Eschmeyer et al. 2017, Froese andPauly 2017). Roa jayakari (Norman, 1939) occurs in the northwestern Indian Ocean, from India to the Red Sea, while Roa excelsa (Jordan, 1921) is only known from the Pacific oceanic islands of Hawaii, Johnston Atoll, Pohnpei, and Guam (Eschmeyer et al. 2017). The most recently described species, Roa australis Kuiter, 2004, is only known from northwestern Australia, usually between 100 and 300 m depth (Kuiter 2004). Here we describe a fifth species of Roa, so far only found on MCEs of the Verde Island Passage in the Philippines.

Methods
The specimens were collected using hand nets or a Hawaiian sling while diving on mixed-gas, closed-circuit rebreather (Hollis Prism 2). Counts were performed using a microscope, and morphological characters were measured to the nearest 0.1 mm following . The last two soft rays articulating on the last complex pterygiophore in the dorsal and anal fins were counted as one ray. Morphometric and meristic data for the holotype and other Roa species are presented in Table 1. The specimen was deposited in the fish collection of the Philippines National Museum of Natural History (PNM), and comparative material was obtained from the California Academy of Sciences (CAS) fish collection. Mitochondrial Cytochrome c oxidase subunit I (COI) DNA was sequenced and analyzed for the new species. DNA extraction and PCR amplification of the COI were performed following Weigt et al. (2012) protocols. DNA sequences were then compared to all other Roa species available in GenBank (Roa jayakari: KF268176, KF268177, KF268178, KF268184, KF268185, KF268186; R. modesta: KP267584, KU944197, KU944203, KU944230). GenBank accession number for the new species is MF995631.

Results
Roa rumsfeldi sp. n. http://zoobank.org/DA519076-63AA-4866-B4D3-300C1B2F3CC8 Figure 1-2, Description. Dorsal fin rays XI, 20, last soft ray branched to the base and counted as one; dorsal-fin base length: spines 40.0% in SL, and soft rays 31.1% in SL; spines increase in height from the first to the fourth: length of first spine 9.1% in SL, length of second spine 18.3% in SL, length of third spine 24.5% in SL, length of fourth spine 29.1% in SL. Soft dorsal fin follows sharp descent of rear portion of body. First soft ray 12.0% in SL. Anal-fin rays III, 17, last soft ray branched to the base and counted as one; anal-fin base 34.2% in SL; second spine very long, 25.3% in SL. Pectoral fin 13; length 29.1% in SL (Table 1). Pored lateral-line scales 27, plus 13 scales (without pores) to the peduncle. Body deep, 69.8% in SL, and compressed, 15.5% in SL; large head, length 41.1% in SL; snout long, length 35.9% in HL; eye diameter 32.2% in HL; interorbital 27.5% in HL; caudal peduncle depth 10.7% in SL, and length 8.5% in SL (Table 1).
Origin of dorsal fin above the origin of pectoral fin, posterior end of head; fin base long and mostly horizontal; soft part of dorsal fin curves downward from the third ray to caudal peduncle; soft rays posterior margin vertical; origin of anal fin below 9th spine of dorsal fin; pelvic fin with strong spine and filamentous first soft ray. Body and head with ctenoid scales, becoming smaller towards nape and snout. Scales extending to about one third of the median fins. Tubed scales of lateral line rising at a steep angle from origin with 22 scales in an almost straight line, bending abruptly downward, ending behind posterior third of soft dorsal fin.
Color in life. Roa rumsfeldi sp. n. (Figure 1, 2) is white with three vertical dark brown bands. The first band is the narrower and runs from the origin of the dorsal fin through eye and over cheek; the second partially covers 2nd to 7th dorsal spines, going down towards the abdomen; and 3rd from the last 3-4 dorsal spines towards caudal peduncle, narrowing and covering the end of anal fin rays. Two black spots with white borders, one on the 2nd dorsal fin spine and the other on the soft dorsal fin between 2nd and 7-8th rays; all anal fin spines are white; pelvic fin, including spine, dark brown; caudal fin brown basally with translucent rays. Color in alcohol. As described above in color in life, but with lighter brown bands. Etymology. We name Roa rumsfeldi to honor Donald Rumsfeld who immortalized the quote: "there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns -the ones we don't know we don't know." He said that when referring to the uncertainties of war, but we think it applies perfectly to the taxonomy of MCE species: We only realized this species was new after we took a good look at it here at the aquarium in San Francisco, so we think it's a perfect example of an unknown unknown.
Distribution and habitat. Roa rumsfeldi sp. n. is only known to occur in the Verde Island Passage, central Philippines. It was found on MCEs of Puerto Galera, Oriental Mindoro, and Bauan, Batangas, between 100 and 130 m depth. However, the species likely has a wider distribution and remains undetected because of its preferred depth range. The ecosystems where it was found vary from sheltered rocky outcroppings heavily covered by fine sediment to areas exposed to strong currents. The ambient seawater temperature varied between 19 and 21°C during our dives, which were conducted in April-May over several years. Azooxanthellate gorgonians, black corals, and solitary stony corals are the most abundant benthic invertebrates in this habitat.
Comparative remarks. In addition to the singular characteristics presented in the diagnosis section, Roa rumsfeldi sp. n. differs from its congeners by a lower number of dorsal soft rays (20) than R. jayakari (22-24); longer head (41.0% in SL) than R. excelsa (34.9-37.1); fewer dorsal-fin rays (20) and shorter dorsal-fin rays base (31.1% in SL) than R. modesta (22 rays and 35.3-40.8% in SL); and shorter 3rd anal-fin spine (12.8% in SL) and longest anal-fin ray (13.8% in SL) than R. australis (17.6-23.9, 18.9-23.0 and 17.5-23.2% in SL, respectively). Moreover, the COI gene sequence of Roa rumsfeldi does not match any other Roa species available at Genbank. The uncorrected genetic divergence at the COI gene between R. rumsfeldi and the two other available Roa (R. jayakari and R. modesta) is 10.5% and 8.4%, respectively.

Discussion
Despite a few records of Roa modesta and R. excelsa in shallow waters of Japan and Hawaii, Roa species are normally found at depths exceeding 100 m, with trawling being the most common sampling method for these species (Kuiter 2004). As trawling is limited to bottoms lacking structural complexity, information about these reef fishes is scarce. Technical SCUBA and rebreather diving using mixed gases to explore lower MCEs (60 to 150 m) is enabling new records of reef fishes around the globe (Kane et al. 2014, Pinheiro et al. 2015, Simon et al. 2016, as well as the discovery of several new species (Anderson et al. 2016. The expansion of scientific deep diving is slowly filling our knowledge gap of the diversity and distribution of most MCE taxa, including Roa species. Here we consider Roa as a valid genus due to its morphological and niche uniqueness, however, a more detailed phylogenetic study is necessary to understand the evolutionary history of this group and its relationship with the Chaetodon lineage.