Palythoa umbrosa, Irei, Yuka, Sinniger, Frederic & Reimer, James Davis, 2015

Irei, Yuka, Sinniger, Frederic & Reimer, James Davis, 2015, Descriptions of two azooxanthellate Palythoa species (Subclass Hexacorallia, Order Zoantharia) from the Ryukyu Archipelago, southern Japan, ZooKeys 478, pp. 1-26 : 7-10

Taxon classification Animalia Zoantharia Sphenopidae

Palythoa umbrosa sp. n. Figures 1, 2, 4, 6, 7, 8, 9, Suppl. material 1-2: Table 1-2

" Palythoa sp. tokashiki" - Reimer et al. 2011b (specimen from Lyudao (=Green Island), Taiwan), Reimer et al. 2013 (specimen from Lyudao). Synonymy.

Type material.

Type-specimens. Holotype. Specimen number NSMT-Co1561 (original number IRI_TF3). Split into two pieces and fixed in 99.5% ethanol and 4-10% formalin, respectively. Deposited in National Museum of Nature and Science, Tokyo, Japan. Original label: "HOLOTYPE Palythoa umbrosa , Japan, Yaeyama Islands, Sotobanari Island, 8 m depth, 9 November 2012, J. Reimer leg." Paratypes. Paratype 1. Specimen number RMNH Coel. 41730 (original number IRI_TF1), Japan, Okinawa Prefecture, Yaeyama Islands, Taketomi, Sotobanari Island, 24°22'46"N, 123°43'53"E, at 9 m depth, 9 November 2012, T. Fujii leg. Split into two pieces and fixed in 99.5% ethanol and 4-10% formalin, respectively. Deposited in Naturalis Biodiversity Center, Leiden, The Netherlands. Paratype 2. Specimen number USNM 1231376 (original number IRI_TF2), Japan, Okinawa Prefecture, Yaeyama Islands, Taketomi, Sotobanari Island, 24°22'46"N, 123°43'53"E, at 10 m depth, 9 November 2012, T. Fujii leg. Split into two pieces and fixed in 99.5% ethanol and 4-10% formalin, respectively. Deposited in Smithsonian Institution National Museum of Natural History, Washington, D.C., USA. Paratype 3. Specimen number RUMF-ZG-04376 (original number IRI_31), Japan, Okinawa Prefecture, Yaeyama Islands, Taketomi, Iriomote-suido, 24°21'51"N, 123°57'25"E, at 6 m depth, 7 May 2008, Y. Irei leg. Fixed in 99.5% ethanol, deposited in University Museum, University of the Ryukyus (Fujukan).

Type-locality.

Japan, Okinawa Prefecture, Yaeyama Islands, Taketomi, Sotobanari Island, 24°22'46"N, 123°43'53"E, on wall of reef cave at 8 m depth, 9 November 2012, J. Reimer leg.

Description of holotype.

Size of colony approximately 2 cm × 2 cm, consisting of three polyps, 6.1 mm in height and 2.7-3.0 mm in diameter. Columns yellowish white with irregular black blotches. Dark brown polyp heads. Horizontal wrinkles (3-5 in number) of approximately half the length of column periphery, on mostly inner side of bent polyps. Tentacles approximately 32 in number, white in color. Columns heavily incrusted with irregularly-sized sand grains.

Habitat and behavioral features.

This species inhabits low-light environments such as floors or sides of caves, crevasses or under reef overhangs on coral reef flats and reef slopes. In general, polyps are open at night with extended tentacles, and are closed during the daytime. Polyps tend to bend parallel to the surrounding substrate when closed (Figures 2f, 6b) and become erect in a diagonal direction at an acute angle when open, with oral disks generally facing the opening of the cave or crevasse.

Distribution.

Southern Ryukyu Archipelago (Yaeyama Islands) and Taiwan (Lyudao) (Figure 1)

Diagnosis.

General. Azooxanthellate brachycnemic zoantharian with heavily sand-incrusted ectoderm and mesoglea. Colonies usually composed of several to 20 polyps with each polyp loosely connected to neighbor(s) by a thin stolon (= “liberae”, Pax 1910). Solitary polyps are also commonly seen. Polyps are cylindrical and upper portion of polyps around pharynx is often but not always constricted when closed (Figure 6b, d). Columns occasionally have several horizontal wrinkles (1 to 10 in number) of one quarter to half the length of column periphery, on mostly inner side of bent polyps (Figure 6d).

Polyp size. 0.5-0.9 cm in length and 0.3-0.5 cm in width after fixation in 4-10% seawater formalin or 70-99.5% ethanol.

Coloration of polyp column and oral disk. Since sampling of Palythoa umbrosa was performed only during the daytime, images of expanded polyps in situ were not available and observations were performed under a stereomicroscope. The color of external polyp columns was ivory to tan, occasionally with irregular black/brown blotches (Figures 2f, 6a,b). The color of oral disks was also ivory to tan.

Tentacles. 32-38 in number and white to ivory in color (Figure 6a). Occasionally, very small (<0.01 mm) black dots are present (Figure 6c). No stripes on tentacles, unlike Palythoa mizigama .

Cnidom. There were four major cnidae types observed (Figure 4). The dominant types of cnidae were spirocysts (length 21.9 ± 3.1 μm, width 3.5 ± 0.7 μm, n=80) in the tentacles, basitrichs (length 29.5 ± 3.3 μm, width 3.7 ± 0.4 μm, n=80) in the pharynx, and p-mastigophores (length 20.5 ± 3.9 μm, width 5.5 ± 0.9 μm, n=80) and holotrichs (length 13.3 ± 1.5 μm, width 5.0 ± 1.1 μm, n=55) in the mesenterial filaments (Suppl. material 2: Table 2). For all cnidae types except holotrichs, the average lengths were significantly longer in Palythoa umbrosa than in Palythoa mizigama (t-test p<0.05). However, there were relatively large overlaps in the range of lengths between these two species (Suppl. material 2: Table 2).

Etymology.

Named for habitat environment of this species. The specific epithet “umbrosa” means “shadowy” in latin. Japanese name: Shirote-yami-iwasunaginchaku. “Shirote” means "white hands" in Japanese.

Remarks.

The azooxanthellate species Palythoa macmurrichi has previously been described from the Torres Strait, northern Australia. It was described based on a single polyp collected from a channel at 20 fathoms (approximately 36.5 m), and the holotype was lost when it was used for histological examination in Haddon and Shackleton (1891). While the few figures of Palythoa macmurrichi in the original description could be either of the two new species in this study, they could also be any of many other Palythoa species with “liberae” morphology ( Pax 1910). Unfortunately, we are unable to examine Palythoa macmurrichi specimens, as this species has not been mentioned in the literature since Verrill (1900) (asides in nomenclators such as Walsh 1967). The current two new species differ from Palythoa macmurrichi in their smaller polyp sizes and external markings. Additionally, the two Palythoa species in this study were found only in shallow areas (<12 m depth), different from Palythoa macmurrichi , which was collected from ~37 m depth. Our SCUBA surveys in Okinawa and New Caledonia investigated channels of similar depths as the type locality of Palythoa macmurrichi but we never came across any similar specimens. Thus, for now, we consider Palythoa macmurrichi to be a different species from the two new azooxanthellate species described in this study.