Nanozoanthus undetermined

Fujii, Takuma & Reimer, James Davis, 2013, A new family of diminutive zooxanthellate zoanthids (Hexacorallia: Zoantharia), Zoological Journal of the Linnean Society 169 (3), pp. 509-522 : 512-515

NANOZOANTHUS HARENACEUS SP. NOV.

( FIGS 3A, B AND 4 )

Holotype

Specimen number NSMT-Co-1555. Cape Maeda, Onna, Okinawa, Japan (26°26′36″ N, 127°46′22″ E), 9 m depth, collected by Takuma Fujii ( T.F.), 15 February 2012, half of colony fixed in 5–10% formalin, other half of colony fixed in 99% EtOH, deposited in National Museum of Nature and Science, Tokyo, Japan ( NSMT). GenBank accession numbers: mt COI, KF499609 ; 16S rDNA, KF499601 .

Description of holotype

Substrate of colony fragment of dead coral: dimensions 30 × 30 × 20 mm for formalin-fixed specimen; dimensions 30 × 20 × 15 mm for EtOH-fixed specimen. Polyps cylindrical, connected by narrow stolon. Height of polyps (n = 37) 1.2–4.5 mm, diameter 0.4– 1.8 mm. Mineral particles encrusted in column from aboral end to edge of oral disc.

Paratypes (all from Japan)

Paratype 1: Specimen number USNM-1221444. Cape Maeda, Okinawa, Japan (26°26′36″ N, 127°46′22″ E), 22 m depth, collected by T . F., 21 December 2011, half of colony fixed in 5–10% formalin, other half of colony fixed in 99% EtOH, deposited in National Museum of Natural History , Smithsonian Institution, Washington, D.C., USA ( USNM) .

Paratype 2: Specimen number RUMF-2G-04372. Oura Bay, Okinawa, Japan (26°32′16″ N, 128°4′48″ E), 20 m depth, collected by T . F., 13 March 2012, fixed by 99% EtOH, deposited in Ryukyu University Museum Fujukan , Okinawa, Japan ( RUMF) .

Paratype 3: Specimen number RMNH Coel. 41502. Zatsun, Okinawa, Japan (26°49′42″ N, 128°14′33″ E), 23 m depth. Collected by T.F., 24 October 2010, fixed

by 99% EtOH, deposited in Naturalis Biodiversity Center, Leiden, the Netherlands (RMNH).

Other materials

Specimen number MISE-TF-101. Sunabe Beach, Okinawa, Japan, 15 m depth. Collected by T.F., 16 June 2011, half of colony fixed in 5–10% formalin, other half of colony fixed in 99% EtOH. Specimen number MISE-TF-143. Oura Bay, Okinawa, Japan. 10 m depth. Collected by T.F., 20 April 2012, fixed by 99% EtOH .

Common name

Kakure-sunaginchaku (new Japanese name), Okinawan nanozoanthid.

Diagnosis

Morphology: Colonies with up to 20 well-developed polyps connected by narrow stolons. Polyps cylindrical. Polyp diameter up to 1.8 mm, average 1.1 mm (n = 30 polyps from five colonies, standard variation = 0.38 mm), height up to 4.5 mm, average 2.35 mm (n = 30 polyps from five colonies, standard variation = 0.96 mm). Between 16 and 20 tentacles (n = 9 polyps), 1.0–2.5 times as long as diameter of oral disc. Oral disc forming concave depression. Distal tip of contracted polyps rounded. Mineral particles encrusted in column from aboral end to edge of oral disc. Irregularly sized particles encrusted into ectoderm and few particles in mesoglea. Tentacles transparent, with tiny brown dots visible upon magnification (= individual zooxanthellae). Zigzagged, white colour pattern following outside edge of oral disc. Oral disc brown, occasionally white.

Internal morphology: Macrocnemic. Mesentery number same as tentacle number. Ten perfect mesenteries, eight macrocnemes. Marginal mesogleal sphincter muscle. No lacunae or ring sinus.

Symbiosis: Zooxanthellate. Symbiodinium subclade C 3 in three polyps from three different sites around Okinawa Island, Japan ( Fig. 5 ).

Cnidae: Holotrichs in column; basitrichs and microbasic p-mastigophores in filaments; basitrichs, microbasic p-mastigophores, and holotrichs in tentacles ( Table 2).

Habitat: Nanozoanthus harenaceus sp. nov. occurs on rocky substrates on the slopes of coral reefs. Almost all observed colonies almost completely buried in sand ‘pools’ that formed in small pockets or depressions in the hard coral substrate of reef slopes, with only tentacles and oral disc protuding above the surface of sand when polyps open ( Fig. 3A ). Found from the east and west coasts of Okinawa Island, Japan. Depth 9–27 m.

DNA sequences: GenBank accession numbers: COI, KF499609 ; 16S rDNA, KF499601 , with Symbiodinium ITS rDNA sequences KF499598 .

Remarks

Only one species has been described in Nanazoanthidae fam. nov., and the diagnostic characters are as for family above. Internal morphology is unavailable for the holotype because the encrusted sand inhibited making useable sections of the polyps.

The distribution of family Nanozoanthidae fam. nov. is currently known from only a few sites in Okinawa and from one site in western Australia. The lack of reports or other information undoubtedly results from the difficulty in finding colonies because of their tiny size and the cryptic appearance of the polyps. This species is one of the smallest zoanthids described, along with Caribbean Parazoanthus parasiticus (Duchassaing and Michelotii, 1860) and some unidentified sponge-associated Parazoanthidae spp. from the Pacific, with all of these species having polyp diameters of <2 mm. Additionally, the transparent and sandy body colour make N. harenaceus sp. nov. very cryptic, in contrast to the bright body colours of many sponge-associated zoanthids. Therefore, this small and cryptic zoanthid is likely to have a wider distribution in the Indo-Pacific than is described here.

The two specimens from Ningaloo Reef, Western Australia, are considered to be an undescribed species of genus Nanozoanthus gen. nov. by the results of molecular analyses. Additional specimens from regions other than Okinawa of colonies with enough polyps to properly observe both molecular and morphological characters are needed to more fully explore the species diversity of Nanozoanthus gen. nov.

Etymology

Named from the latin ‘harenaceus’ meaning ‘sandy’, as living polyps are buried in sand and resemble particles or clumps of sand because of their small size, and for the coloration of the oral disc and tentacles.

ZooBank: urn:lsid:zoobank.org:act:8AF484C9-B2EC-41D5-BA3F-A6764CE34DB8 .

Figures

Figure 3. Nanozoanthus harenaceus sp. nov. from Okinawa Island. A, colony with open polyps in situ, specimen RUMF-2G-04372 (paratype2), Oura Bay, Okinawa, Japan, 20 m depth, 13 May 2012. B, contracted polyps in situ, specimen RUMF-2G-04372 (paratype2), Cape Maeda, Okinawa, Japan, 22 m depth, 21 December 2011. C, part of a colony of preserved specimen fixed by 5–10% formalin seawater, specimen NSMT-Co1555 (holotype), Cape Maeda, Okinawa, Japan, 9 m depth, 15 February 2012. Scale bars: approx. 1 mm.

Figure 4. Histological section of specimen USNM-1221444 (paratype1). A, longitudinal section with mesogleal sphincter muscles at capitulum. B, cross section with macrocnemic mesenterial arrangement. Asymmetric arrangement caused by bias of cutting angle (perfect mesenteries appear similar to imperfect mesenteries). Abbreviations: 5th, 5th mesentery; Ac, actinopharynx; Dd, dorsal directive; Ec, ectoderm; En, endoderm; Me, mesoglea; Sm, sphincter muscles; Sp, existence of incrusted sand particles.

Figure 5. Maximum-likelihood (ML) tree of internal transcribed spacer of ribosomal DNA (ITS rDNA) regions from Symbiodinium. Values at branches represent ML and neighbour-joining (NJ) bootstrap probabilities, respectively (> 50%). Specimens collected in this study are set in bold. Sample names with GenBank accession numbers are from a previous study.