Palythoa mizigama, 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 : 5-7

Taxon classification Animalia Zoantharia Sphenopidae

Palythoa mizigama sp. n. Figures 1, 2, 3, 4, 5, 7, 8, 9, Suppl. material 1-2: Table 1-2

" Palythoa sp. tokashiki" - Reimer 2010, Reimer et al. 2011b (specimen from Kenting, Taiwan), Reimer et al. 2013 (specimen from Kenting). Synonymy.

Type material.

Type-specimens. Holotype. Specimen number NSMT-Co1560 (original number MIZ_33). Fixed in 99.5% ethanol, deposited in National Museum of Nature and Science, Tokyo, Japan. Original label: "HOLOTYPE Palythoa mizigama , Japan, Okinawa Island, Kadena, Mizugama, 5 m depth, 13 May 2008, Y. Irei leg. Paratypes: Paratype 1. Specimen number RMNH Coel. 41729 (original number TOK_2), Japan, Okinawa Prefecture, Kerama Islands, Tokashiki Island, Mutizuni, 26°09'07"N, 127°21'11"E, in a hollow of reef slope at 5 m depth, 5 January 2008, Y. Irei and F. Sinniger leg. Fixed in 99.5% ethanol, deposited in Naturalis Biodiversity Center, Leiden, The Netherlands. Paratype 2. Specimen number USNM 1231375 (original number ODO_25), Japan, Okinawa Prefecture, Okinawa Island, Itoman, Odo, 26°05'06"N, 127°42'32"E, on the wall of reef cave at 11 m depth, 13 January 2008, Y. Irei and F. Sinniger leg. Fixed in 99.5% ethanol, deposited in Smithsonian Institution National Museum of Natural History, Washington, D.C., USA. Paratype 3. Specimen number RUMF-ZG-04375 (original number IRI_JR2829), Japan, Okinawa Prefecture, Yaeyama Islands, Taketomi, Iriomotesuido, 24°21'51"N, 123°57'25"E, at 4.4-5.3 m depth, 1 September 2012, J. Reimer leg. Fixed in 99.5% ethanol, deposited in University Museum, University of the Ryukyus (Fujukan).

Type-locality.

Japan, Okinawa Prefecture, Okinawa Island, Kadena, Mizugama, 26°21'35"N, 127°44'18"E, on wall of reef cave at 5 m depth, 13 May 2008, Y. Irei leg.

Description of holotype.

Size of colony approximately 2 cm × 3 cm, consisting of six polyps, 3.8-11.2 mm in height and 2.0-3.8 mm in diameter. External color brownish gray to yellowish white with small black blotches on polyp heads and columns. Horizontal wrinkles (1-7 in number) of approximately half the length of column periphery, mostly on inner side of bent polyps. Tentacles approximately 32 in number, color same as column with 7-10 narrow black horizontal lines on tentacles. Columns heavily incrusted with irregularly-sized sand grains.

Habitat and ecological 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 in daytime. Polyps tend to bend parallel to the surrounding substrate when closed although polyps become somewhat erect in a diagonal direction at an acute angle (e.g. not perpendicular to substrate) when open, with oral disks generally facing the opening of the cave or crevasse (Figure 2 a–d).

Distribution.

Southern Ryukyu Archipelago (Okinawa Island, Tokashiki Island, Yaeyama Islands), Taiwan (Kenting), and New Caledonia (Tibarama, Poindimié) (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 others by a thin stolon (= “liberae”, Pax 1910). Solitary polyps are also commonly seen. Polyp is cylindrical and upper part of the polyp around pharynx is occasionally constricted when closed (Figure 3a). Expanded polyps are flared, with column becoming wider towards the oral disk and a large oral disk (Figure 2a, c). Columns occasionally have several horizontal wrinkles (1 to up to 10 in number) of one quarter to half the length of column periphery, mostly on inner side of bent polyps (Figure 3a).

Polyp size. Approximately 0.5-1.0 cm in length and 0.2-0.4 cm in width after fixation in 4-10% seawater formalin or 70-99.5% ethanol.

Coloration of polyp column and oral disk. The color of external polyp columns varies from ivory to tan in life, occasionally with irregular black blotches. The color of oral disk is also ivory to tan, often with black radial lines extending outwards from the mouth (Figure 2 a and b, Figure 3 b).

Tentacles. 32-40 in number. Extended tentacles are of the same length or longer than the diameter of oral disks (Figure 2a, c). Tentacle color is white to ivory with 4-10 horizontal black stripes (Figure 3b). The number and density of stripes on the tentacles are variable between different polyps (Figure 3c, d).

Cnidom. Four major cnidae types observed; spirocysts, basitrichs, p-mastigophores, and holotrichs. The dominant types of cnidae were spirocysts (length 20.5 ± 3.5 μm, width 3.4 ± 0.7 μm, n=140) in the tentacles, basitrichs (length 23.7 ± 2.3 μm, width 3.6 ± 0.4 μm, n=139) in the pharynx, and p-mastigophores (length 15.7 ± 3.6 μm, width 4.7 ± 0.7 μm, n=140) and holotrichs (length 13.5 ± 1.9 μm, width 4.9 ± 0.7 μm, n=140) in the mesenterial filaments (Figure 4, Suppl. material 2: Table 2). In addition to the four major cnidae types, three large holotrichs were found. Three individual polyps contained one large holotrich each, with two from tentacles (length 28.4 μm, width 13.0 μm; length 25.7 μm, width 11.7 μm) and one from the mesenterial filaments (length 33.4 μm, width 16.9 μm).

Etymology.

The specific epithet “mizigama” was named after the type locality of Mizugama. Additionally, “mizi” and “gama” mean “water” and “cave”, respectively, in the Okinawan language. Japanese name: Shimate-yami-iwasunaginchaku. “Shimate”, “yami”, and “iwasunaginchaku” mean "striped hands", “dark”, and " Palythoa ", respectively, in Japanese.

Remarks on reproduction.

Simultaneous hermaphrodite. Reproductive polyps containing ovaries and spermaries were found from specimens collected in August - September 2010 at Mizugama, Okinawa Island, Japan (Figure 5).