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Research Article
Three new species and the molecular phylogeny of Antipathozoanthus from the Indo-Pacific Ocean (Anthozoa, Hexacorallia, Zoantharia)
expand article infoHiroki Kise§, Takuma Fujii§|, Giovanni Diego Masucci§, Piera Biondi§, James Davis Reimer§§
‡ Palau International Coral Reef Center, Koror, Palau
§ University of the Ryukyus, Nishihara, Japan
| Kagoshima University, Amami, Japan
Open Access

Abstract

In this study, three new species of macrocnemic zoantharians (Hexacorallia, Zoantharia) are described from localities in the Indo-Pacific Ocean including the Red Sea, the Maldives, Palau, and southern Japan: Antipathozoanthus obscurus sp. n., A. remengesaui sp. n., and A. cavernus sp. n. Although the genus Antipathozoanthus is currently restricted to species living on antipatharians, A. obscurus sp. n. is not associated with any living substrate and instead is found on coral reef carbonate substrate within narrow caves or cracks. The two new species that have association with antipatharians, A. remengesaui sp. n. and A. cavernus sp. n., can be distinguished by their relative coenenchyme development and the antipatharian species that each uses as substrate. Additionally, all new species described in this study have unique nuclear internal transcribed spacer region of ribosomal DNA (ITS-rDNA) sequences. Our results indicate that more phylogenetic studies focusing on increasing the numbers of species examined within each of the genera of Parazoanthidae are required in order to better understand the evolutionary history of substrate specificity within the family Parazoanthidae.

Keywords

antipatharian, cave-dwelling, diversity, evolution, new species, substrate specificity

Introduction

Zoantharia Rafinesque, 1815 is the third most speciose order within the subclass Hexacorallia Haeckel, 1896. Zoantharians can be found in a wide variety of marine environments from intertidal zones to deep-sea cold seeps (e.g., Reimer et al. 2007b), and are characterized by having two rows of tentacles and the unique bilateral arrangements of the mesenteries, with most species forming clonal colonies without hard structures such as skeletons of the order Scleractinia. Zoantharia is currently divided into two suborders; Brachycnemina Haddon & Shackleton, 1891, and Macrocnemina Haddon & Shackleton, 1891, based on differences in the fifth pair of mesenteries from the dorsal directive. Zoantharians within suborder Macrocnemina are distributed worldwide, and are usually found in associations with other invertebrates. Within Macrocnemina, the largest family is Parazoanthidae Delage & Hérouard, 1901, which currently contains 13 genera (Low et al. 2016). Most species of these genera live in association with other marine invertebrates, including antipatharians (Ocaña and Brito 2003; Sinniger et al. 2010), octocorals (Reimer et al. 2008; Bo et al. 2012; Sinniger et al. 2013), and sponges (Haddon and Shackleton 1891; Swain and Wulff 2007; Montenegro et al. 2015, 2016). Historically, establishing the taxonomic framework of Parazoanthidae was challenging due to relatively few diagnostic morphological characteristics (Sinniger et al. 2005; Montenegro et al. 2015), and the family was shown to be paraphyletic in initial molecular studies (Sinniger et al. 2005). Recently, however, studies based on molecular phylogeny combined with ecological data have greatly revised the taxonomy within the family Parazoanthidae (Sinniger et al. 2005, 2013; Sinniger and Häussermann 2009; Montenegro et al. 2015, 2016). As a consequence of these studies, nine genera within Parazoanthidae have been described since 2008 and another genus, Bergia Duchassaing & Michelotti, 1860, has been resurrected. Key to this new taxonomic framework is the idea initially proposed by Sinniger et al. (2005, 2010) that different parazoanthid genera share long evolutionary histories with the associated marine invertebrates they use as substrates.

One of these recently erected genera is Antipathozoanthus Sinniger, Reimer & Pawlowski, 2010. As the generic name indicates, species in this genus utilize antipatharians (Hexacorallia, Antipatharia) as their obligate substrate. The genus currently includes two valid species; A. macaronesicus (Ocaña & Brito, 2003) from the eastern Atlantic and A. hickmani Reimer & Fujii, 2010 from the Galapagos Islands. Additionally, several potentially undescribed species have been reported from the Red Sea (Reimer et al. 2014b), the South China Sea (Reimer et al. 2017), and Japan (Sinniger et al. 2010; Reimer et al. 2013, 2014a). However, the species diversity of Antipathozoanthus spp. in the Indo-Pacific Ocean remains generally unknown. In this study, three new Antipathozoanthus species are formally described based on specimens collected from a number of regions in the Indo-Pacific Ocean, and the genus is redescribed based on these findings.

Materials and methods

Specimen collection. Antipathozoanthus specimens were collected between 2009 to 2016 from three localities in the Red Sea, three localities in the Maldives, five localities in Japan, and two localities in Palau (Fig. 1), with one comparative specimen of A. macaronesicus collected from Pico Island, Azores, Portugal. All specimens were collected by SCUBA. Specimen images were taken in situ for gross external morphological analyses. Collected specimens were preserved in 99.5% ethanol (Table 1).

Figure 1. 

Sampling location in the Indian Ocean and Pacific Ocean of specimens used in this study. Location of specimens collected in this study represented by closed symbols. Species abbreviations after locations: (Ao) Antipathozoanthus obscurus sp. n.; (Ar) A. remengesaui sp. n.; (Ac) A. cavernus sp. n.

List of examined specimens, and GenBank Accession Numbers.

Specimen ID Genus Species Locality Coordinates Collecter Sampling date Depth (m) Accession number (COI) Accession number (16S–rDNA) Accession number (ITS–rDNA)
Latitude / Longitude
AZCN Antipathozoanthus macaronesicus Pico Island, Azores, Portugal N38°28"3.8", W28°24′0″ P Wirtz 13-May-16 43 MG384664 MG384684 MG384696
BISE1 Antipathozoanthus obscurus Bise, Motobu, Okinawa, Japan N26°42'34.4", E127°52'49.2" JD Reimer, I Kawamura 14-Aug-14 5 MG384644 MG384685 MG384691
BISE3 Antipathozoanthus obscurus Bise, Motobu, Okinawa, Japan N26°42'34.4", E127°52'49.2" JD Reimer, I Kawamura 14-Aug-14 5 MG384693
MAL46 Antipathozoanthus remengesaui Coral Garden, Maldives N3°05'24.3", E72°58'04.5" JD Reimer 06-May-14 24 MG384658 MG384679
MAL82 Antipathozoanthus remengesaui Wall Street, Maldives N3°07'14.2", E72°58'46.5" JD Reimer 07-May-14 9 MG384657
MAL83 Antipathozoanthus remengesaui Wall Street, Maldives N3°07'14.2", E72°58'46.5" JD Reimer 07-May-14 9 MG384656
MAL84 Antipathozoanthus remengesaui Wall Street, Maldives N3°07'14.2", E72°58'46.5" JD Reimer 07-May-14 9 MG384655 MG384702
MAL85 Antipathozoanthus remengesaui Wall Street, Maldives N3°07'14.2", E72°58'46.5" JD Reimer 07-May-14 9 MG384654 MG384678 MG384701
MAL145 Antipathozoanthus remengesaui Wall Street, Maldives N3°07'14.2", E72°58'46.5" JD Reimer 10-May-14 12 MG384653 MG384677
MAL147 Antipathozoanthus remengesaui Wall Street, Maldives N3°07'14.2", E72°58'46.5" JD Reimer 10-May-14 10 MG384652
MAL2592601 Antipathozoanthus cavernus Capital Reef, Maldives N3°02'55.8", E72°53'21.2" M Oliverio 16-May-14 19 MG384651 MG384676 MG384697
MAL2592602 Antipathozoanthus remengesaui Capital Reef, Maldives N3°02'55.8", E72°53'21.2" M Oliverio 16-May-14 19 MG384675
MAL261 Antipathozoanthus remengesaui Wall Street, Maldives N3°07'14.2", E72°58'46.5" JD Reimer 17-May-14 9 MG384650 MG384674
KINKO1 Antipathozoanthus cavernus Sakurajima, Kagoshima, Japan N31°35'23.5", E130°35.27.8" JD Reimer 20-Sep-15 21 MG384660 MG384681 MG384699
KINKO2 Antipathozoanthus remengesaui Sakurajima, Kagoshima, Japan N31°35'23.5", E130°35'27.8" JD Reimer 20-Sep-15 21 MG384659 MG384680
PALAU2 Antipathozoanthus remengesaui Blue Hole, Palau N7°8'29.4", E134°13'23.3" JD Reimer 15-Sep-14 23 MG384649 MG384673 MG384703
PALAU3 Antipathozoanthus remengesaui Siaes Tunnel. Palau N7°18'54.8", E134°13'13.3" JD Reimer 15-Sep-14 37 MG384648
PALAU4 Antipathozoanthus remengesaui Blue Hole, Palau N7°8'29.4", E134°13'23.3" JD Reimer 12-Sep-14 28 MG384647 MG384672
PALAU5 Antipathozoanthus cavernus Siaes Tunnel. Palau N7°18'54.8", E134°13'13.3" JD Reimer 15-Sep-14 39 MG384698
HK70 Antipathozoanthus remengesaui Siaes Tunnel. Palau N7°18'54.8", E134°13'13.3" H Kise 12-Sep-14 NA MG384663 MG384683
HK90 Antipathozoanthus remengesaui Blue Hole, Palau N7°8'29.4", E134°13'23.3" H Kise 15-Sep-14 22 MG384662
TF54 Antipathozoanthus obscurus Cape Zanpa, Yomitan, Okinawa, Japan N26°26'26.5", E127°42'43.7" T Fujii 06-Apr-09 3 MG384641 MG384689
TF78 Antipathozoanthus obscurus Cape Manza, Onna, Okinawa, Japan N26°30'18.3", E127°51'02.3" T Fujii 02-Oct-09 5 MG384640 MG384668 MG384687
TF102 Antipathozoanthus remengesaui Sakurajima, Kagoshima, Japan N31°35'23.5", E130°35'27.8" T Fujii 26-Jul-11 20 MG384646 MG384704
TF103 Antipathozoanthus remengesaui Sakurajima, Kagoshima, Japan N31°35'23.5", E130°35'27.8" T Fujii 26-Jul-11 40 MG384645 MG384705
TF148 Antipathozoanthus obscurus Cape Manza, Yomitan, Okinawa, Japan N26°30'18.3", E127°51'02.3" T Fujii 22-Oct-12 10 MG384642 MG384669 MG384688
TF173 Antipathozoanthus remengesaui Onna, Okinawa, Japan N26°26'20.9", E127°47'7.2" T Fujii 27-Jun-14 15
JDR190 Antipathozoanthus obscurus Al Wajh Shaybarah, Saudi Arabia N25°21', E36°54' JD Reimer 03-Oct-13 3 MG384667 MG384692
JDR191 Antipathozoanthus obscurus Al Wajh Shaybarah, Saudi Arabia N25°21', E36°54' JD Reimer 03-Oct-13 3 MG384666 MG384694
JDR192 Antipathozoanthus obscurus Al Wajh Shaybarah, Saudi Arabia N25°21', E36°54' JD Reimer 03-Oct-13 3 MG384643 MG384665 MG384695
JDR209 Antipathozoanthus remengesaui Yanbu , Saudi Arabia N24°26', E37°14' JD Reimer 04-Oct-13 11 MG384700
JDR211 Antipathozoanthus remengesaui Yanbu , Saudi Arabia N24°26', E37°14' JD Reimer 04-Oct-13 12 MG384682
JDR214 Antipathozoanthus remengesaui Yanbu , Saudi Arabia N24°26', E37°14' JD Reimer 04-Oct-13 12 MG384661
JDR279 Antipathozoanthus obscurus Shib Nazar, Saudi Arabia N22°19', E38°51' JD Reimer 10-Oct-13 4 MG384671 MG384690
KU1 Antipathozoanthus obscurus Ara, Kumejima Island, Okinawa, Japan N26°19'15.0", E126°45'21.3" T Fujii 20-Nov-09 15 MG384639 MG384670 MG384686

Molecular analyses. Antipathozoanthus DNA was extracted using the guanidine protocol following Sinniger et al. (2010). PCR was performed for three genetic markers: mitochondrial cytochrome oxidase subunit I (COI), mitochondrial 16S ribosomal DNA (16S-rDNA), and the nuclear internal transcribed spacer region of ribosomal DNA (ITS-rDNA) using a HotStarTaq Master Mix Kit (Qiagen, Tokyo, Japan). COI was amplified with the following primers: COIZoanF (5’-TGA TAA GGT TAG AAC TTT CTG CCC CGG AAC-3’) (Reimer et al. 2007b) and COIantr (5’-GCC CAC ACA ATA AAG CCC AA TAY YCC AAT-3’) (Sinniger et al. 2010). 16S-rDNA was amplified with the following primers: 16SarmL (5’-GGC CTC GAC TGT TTA CCA AA-3’) (Fujii and Reimer 2011) and 16SbmoH (5’-CGA ACA GCC AAC CCT TGG-3’) (Sinniger et al. 2005). The ITS-rDNA was amplified with the following primer pairs: either ITSf (5’-CTA GTA AGC GCG AGT CAT CAG C-3’) and ITSr (5’-GGT AGC CTT GCC TGA TCT GA-3’) (both Swain 2009) or Zoan-f (5’-CTT GAT CAT TTA GAG GGA GT-3’) and Zoan-r (5’-CGG AGA TTT CAA ATT TGA GCT-3’) (both Reimer et al. 2007a). The markers were amplified following the thermal cycle conditions: 5 min at 95 °C followed by 35 cycles of: 30 s at 94 °C, 1 min at 40 °C, and 1 min 30 s at 72 °C, and followed by a 7 min extension at 72 °C for COI; 5 min at 95 °C and then 35 cycles of: 1 min at 95 °C, 1 min at 52 °C, and 2 min at 72 °C, followed by a 7 min extension at 72 °C for 16S-rDNA; and 5 min at 95 °C then 35 cycles of: 1 min at 94 °C, 1 min at 50 °C, and 2 min at 72 °C, followed by a 10 min extension at 72 °C for ITS-rDNA. Amplified PCR products were checked by 1.5 % agarose gel and positive PCR products were sequenced in both directions by Fasmac (Kanagawa, Japan) after clean up using shrimp alkaline phosphatase (SAP) and Exonuclease I (Takara Bio Inc., Shiga, Japan).

Molecular phylogenetic analyses. Newly obtained sequences were inspected by eye and manually edited using Geneious v8.1 (Kearse et al. 2012, http://www.geneious.com) and deposited in GenBank (accession numbers MG384639MG384705; Table 1). Nucleotide sequences of COI, 16S-rDNA and ITS-rDNA from specimens were aligned with previous study sequences from various parazoanthid genera (Antipathozoanthus, Bergia, Bullagummizoanthus, Corallizoanthus, Hurlizoanthus, Kauluzoanthus, Kulamanamana, Mesozoanthus, Parazoanthus, Umimayanthus, Zibrowius) using the Muscle algorithm (Geneious plug-in; Edgar 2004) (Suppl. material 1). Sequences of the genus Epizoanthus were selected as the outgroup for all three markers’ alignments. The A. hickmani sequence from Reimer and Fujii (2010; EU333790) was not included in the COI phylogenetic tree in this study due to its short length (280 bp). The 16S-rDNA and ITS-rDNA indels were aligned following previous studies (Sinniger et al. 2010; Montenegro et al. 2016). Three alignment datasets were generated; 430 sites of 48 sequences for COI; 589 sites of 57 sequences for 16S-rDNA and 938 sites of 48 sequences for ITS-rDNA. The alignment data are available as electronic supplementary material (Suppl. material 14).

The generated alignments of each marker were used to construct a concatenated alignment. All missing data, including gaps, were replaced with “N". All specimens of Antipathozoanthus included in the concatenated alignment included at least ITS-rDNA sequences. The concatenated alignment consisted of 1957 positions and 54 sequences. Phylogenetic analyses of the concatenated alignment were performed using maximum likelihood (ML) and Bayesian inference (BI), with gene partitions set for ML in RAxML v8 (Stamatakis 2014), and gene partitions for BI as indicated by jModelTest version 0.0.1 (Posada 2008) per each marker in MrBayes v3.2.2 (Huelsenbeck and Ronquist 2001) as shown below. Phylogeny reconstructions were performed for each marker using neighbor joining (NJ), ML and BI.

The NJ phylogeny reconstruction was performed using Geneious v8.1 (Kearse et al. 2012, http://www.geneious.com) with the Hasegawa-Kishino-Yano genetic distance model (HKY) (Hasegawa et al. 1985) and 1000 replicates of bootstrapping. The best-fitting models for ML phylogeny reconstruction were performed by jModelTest under Akaike Information Criterion (AIC). The following models were suggested by jModelTest: TrN+I for the COI dataset; K80+G for the 16S-rDNA dataset; HKY+I+G for ITS-rDNA dataset. ML phylogenetic trees were constructed with PhyML (Guindon and Gascuel 2003) for each marker independently. PhyML was performed using an input tree generated by BIONJ with the models suggested by jModelTest, with 8 gamma-categories of substitution rates. Bootstrap replicates (1000) were conducted using the same parameters. The best fitting models for BI phylogeny reconstruction was performed by jModelTest under Bayesian Information Criterion (BIC). The following models were suggested by jModelTest: K80+G for the COI dataset; K80+G for the 16S-rDNA dataset; and HKY+I+G for the ITS-rDNA dataset. BI phylogenetic trees were constructed with the program MrBayes as a plug-in in Geneious with the models suggested by jModelTest. One cold and three heated Markov chain Monte Carlo (MCMC) chains with default temperature were run for 20,000,000 generations, subsampling frequency of 1000 and a burn in length of 3,000,000 (15%) for all alignments. Average Standard Deviation of Split Frequency (ASDOSF) values were <0.01 for all three Bayesian datasets.

Morphological analyses. Numbers of tentacles, polyp coloration, oral disk coloration, relative tentacle lengths, and polyp dimensions (oral disk diameter/polyp height) were examined using in situ images. Additionally, the relative development of the coenenchyme was examined using a dissecting microscope. Coenenchyme development was classified as 1) “highly developed coenenchyme" when polyps covered the antipatharian substrate completely, or 2) “poorly developed coenenchyme" when polyps did not completely cover the antipatharian substrate and the antipatharians were clearly visible. For internal morphological analyses, we observed mesentery arrangement and numbers, and location and shape of marginal muscle. Histological sections of 8 µm thickness were made and stained with hematoxylin and eosin after decalcification with Bouin’s fluid for 24h.

Cnidae analyses. Cnidae analyses were conducted using undischarged cnidocysts from tentacles, column, actinopharynx, and mesenteries filaments of holotype polyps (n = 6) for all new species under a Nikon Eclipse80i stereomicroscope (Nikon, Tokyo). Cnidae sizes were measured using ImageJ v1.45s (Rasband 2012). Although cnidae classification basically followed England (1991) and Ryland and Lancaster (2004), basitrichs and microbasic mastigophores were considered as the same type of nematocyst based on studies by Schmidt (1974), Hidaka et al. (1987), and Hidaka (1992), and therefore these two types were pooled together in this study.

Abbreviations used

NSMT National Science Museum, Tsukuba, Ibaraki, Japan

RMNH Naturalis Biodiversity Center, Leiden, Netherlands

RUMF Ryukyu University Museum, Fujukan, University of the Ryukyus, Nishihara, Okinawa, Japan

MISE Molecular Invertebrate Systematics and Ecology Laboratory, University of the Ryukyus, Nishihara, Okinawa, Japan

Results

Systematics

Phylum Cnidaria Hatschek, 1888

Class Anthozoa Ehrenberg, 1831

Subclass Hexacorallia Haeckel, 1896
Order Zoantharia Rafinesque, 1815
Suborder Macrocnemina Haddon & Shackleton, 1891
Family Parazoanthidae Delage & Hérouard, 1901

Antipathozoanthus Sinniger, Reimer & Pawlowski, 2010

Type species

Antipathozoanthus macaronesicus (Ocaña & Brito, 2003)

Diagnosis

Macrocinemic zoantharians with cteniform endodermal muscle or endo-meso transitional sphincter muscle (Swain et al. 2015). Substrate consists of either antipatharians or coral carbonate (reef). Genetic distance of mitochondrial COI sequences and insertion/deletion patterns in 16S-rDNA sequences are significantly different from those in other parazoanthid genera (Sinniger et al. 2005, 2010).

Remarks

Four of five formally described species grow mainly on antipatharians, but this character is not exclusive to all species in the genus as A. obscurus sp. n. is not associated with any host organism. Results of the current study showed that A. obscurus sp. n. is clearly placed within this genus according to COI and 16S-rDNA sequence analyses. Thus, these non-associated species/specimens are within the genus based on their phylogenetic position but do not fit the original definition of the genus by Sinniger et al. (2010).

Antipathozoanthus obscurus sp. n.

Fig. 2a, b

Antipathozoanthus sp. 3 sensu Reimer and Fujii 2017, 394, fig. 14.4e.

Material examined

Holotype: NSMT-Co1602 (MISE-BISE1), collected from the wall of a shallow cave in a coral reef. Preserved polyps are approximately 3.0–4.5 mm in diameter, and approximately 3.0–8.0 mm in height from the coenenchyme. Approximately 15–20 polyps connected by a stolon form a mesh network, with additional solitary polyps close by (n = 6). Polyps and coenenchyme are heavily encrusted by various fine sand particles. External color light orange when alive, light beige when fixed. Collected from Cape Bise, Motobu, Okinawa-jima Island, Japan (26°42'34.4"N, 127°52'49.2"E) at a depth of 5 m by James Davis Reimer (JDR), 14 August 2014.

Paratypes: RUMF-ZG-4390 (MISE-JDR190), collected from Al Wajh Shaybarah, Saudi Arabia, (25°21'N, 36°54'E) at a depth of 3 m by JDR, 3 October 2013; RUMF-ZG-4391 (MISE-JDR191), collected from Al Wajh Shaybarah, Saudi Arabia, (25°21'N, 36°54'E) at a depth of 3 m by JDR, 3 October 2013; RUMF-ZG-4392 (MISE-JDR192), collected from Al Wajh Shaybarah, Saudi Arabia, (25°21'N, 36°54'E) at a depth of 3 m by JDR, 3 October 2013; RUMF-ZG-4393 (MISE-JDR279), collected from Shib Nazar, Saudi Arabia, (22°19'N, 38°51'E) at a depth of 3 m by JDR, 3 October 2013; RUMF-ZG-4394 (MISE-KU1), collected from Kume-jima Island, Okinawa, Japan (26°19'15.0"N, 126°45'21.3"E) at a depth of 15 m by Takuma Fujii (TF), 20 November 2009; RUMF-ZG-4395 (MISE-TF54), collected from Cape Zanpa, Yomitan, Okinawa-jima Island, Japan (26°26'26.5"N, 127°42'43.7"E) at a depth of 3 m by TF, 6 April 2009, divided into two pieces, one portion fixed in 99.5% ethanol, and other in 5–10% saltwater formalin; RUMF-ZG-4396 (MISE-TF78), collected from Cape Manza, Onna, Okinawa-jima Island, Japan (26°30'18.3"N, 127°51'02.3"E) at a depth of 5 m by TF, 2 October 2009, divided into two pieces, one portion fixed in 99.5% ethanol, and other in 5–10% saltwater formalin; RMNH.Coel.42320 (MISE-TF148), collected from Cape Manza, Onna, Okinawa-jima Island, Japan (26°30'18.3"N, 127°51'02.3"E) at a depth of 10 m by TF, 22 October 2012.

Other materials examined: MISE-BISE3, collected from Cape Bise, Motobu, Okinawa-jima Island, Japan (26°42'34.4"N, 127°52'49.2"E) at a depth of 5 m by JDR, 14 August 2014.

Diagnosis

External morphology: Open oral disks are approximately 5–10 mm in diameter, and polyps approximately 5–10 mm in height when open (Fig. 2). Polyps of a single colony are usually connected by a stolon forming a mesh-like network. Antipathozoanthus obscurus sp. n. has approximately 26–32 bright brown and/or orange tentacles that are as long as or longer than oral disk diameter. Polyps and coenenchyme have a heavily encrusted ectoderm including numerous various sand particles (usually 1 to 8 mm in size). Capitular ridges (= number of complete mesenteries) are slightly visible on tops (= capitulum) of closed polyps.

Figure 2. 

Polyp images of Antipathozoanthus obscurus sp. n., A. remengesaui sp. n. and A. cavernus sp. n. in situ. a A. obscurus sp. n. . NSMT-Co1602 (MISE-BISE1), Collected from Cape Bise, Motobu, Okinawa-jima Island, Japan (26°42'34.4"N, 127°52'49.2"E) at a depth of 5 m by JDR, 14 August 2014. b A. obscurus sp. n., closed polyp with heavy encrustion by various fine sand particles. MISE-TF54, collected from Cape Zanpa, Yomitan, Okinawa-jima Island, Japan (26°26'26.5"N, 127°42'43.7"E) at a depth of 3 m by TF, 6 April 2009. c A. remengesaui sp. n., colony connected by poorly developed coenenchyme with white polyps on Antipathes sp. NSMT-Co1603 (MISE-PALAU2) collected from Blue Hole, Palau (7°8'29.4"N, 134°13'23.3"E) at a depth of 23 m by JDR, 15 September 2014 d A. cavernus sp. n., polyp connected by highly developed coenenchyme with orange ring around oral disk. RMNH.Coel.42322 (MISE-PALAU5) collected from Siaes Tunnel, Palau (7°18'54.8"N, 134°13'13.3"E) at a depth of 39 m by JDR, 1 September 2014.

Internal morphology: Azooxanthellate. Fine sand particles and silica heavily encrusted into ectoderm and mesoglea. We could not obtain cross-sections or images to observe internal morphology such as mesenterial arrangement, marginal muscle or siphonoglyph due to heavy sand and silica encrustation.

Cnidae: Holotrichs (large), basitrichs and microbasic p-mastigophores (usually difficult to distinguish), spirocysts (Fig. 3; Table 2).

Figure 3. 

Cnidae in the tentacles, column, pharynx, and filament of Antipathozoanthus obscurus sp. n., A. remengesaui sp. n. and A. cavernus sp. n., respectively. Abbreviations: (HL) holotrich large, (HM) holotrich medium, (O) bastrichs or mastigophores, (S) spriocysts.

Cnidae types and sizes observed in three new Antipathozoanthus species. Frequency: relative abundance of cnidae type in decreasing order; numerous, common, occasional, rare (n = number of cnidae).

Antipathozoanthus obscurus sp. n. A. remengesaui sp. n. A. cavernus sp. n.
Length (min-max, average) Width (min-max, average) n Frequency Length (min-max, average) Width (min-max, average) n Frequency Length (min-max, average) Width (min-max, average) n Frequency
Tentacles Spirocysts 11–20, 16.3 2–5, 3.1 48 Occasional 11–25, 18.0 2–7, 3.4 98 Numerous 14–25, 18.0 2–5, 2.9 137 Numerous
Holotrichs (L) 21–33, 28.1 10–15, 11.9 39 Occasional 20–29, 21.8 7–14, 10.1 27 Occasional 20–31, 22.7 9–17, 11.4 28 Occasional
Holotrichs (M) 10–19, 17.0 5–17, 9.9 105 Numerous 14–19, 17.9 7–14, 10.0 95 Numerous
Bastrichs and Mastigophores 10–23, 16.3 2–6, 4.2 31 Occasional 15–19, 16.7 4–6, 4.7 7 Rare
Column Spirocysts 12–22, 18.2 2–5, 3.1 57 Numerous 17–25, 19.7 2–4, 3.1 20 Occasional 11–28, 17.5 2–16, 5.6 44 Numerous
Holotrichs (L) 22–34, 28.2 9–15, 11.8 78 Numerous 20–29, 25.1 9–17, 12.5 40 Occasional 20–32, 25.6 9–16, 11.2 24 Occasional
Holotrichs (M) 11–19, 17.0 8–12, 9.9 21 Occasional 12–19, 16.5 5–13, 8.8 40 Occasional
Bastrichs and Mastigophores 12–25, 18.2 2–5, 3.6 29 Occasional 14–18, 15.9 4–8, 5.9 16 Common 2 5 1 Rare
Pharynx Spirocysts 13–25. 16.5 2–5, 3.0 69 Numerous 11–24, 17.7 2–6, 3.4 65 Numerous 13–23, 18.2 2–5, 3.2 101 Numerous
Holotrichs (L) 20–34, 28.5 8–15, 11.5 76 Numerous 20–31, 23.4 7–18, 11.7 35 Occasional 20–31, 22.7 9–15, 12.0 33 Occasional
Holotrichs (M) 10–19, 16.8 6–13, 9.5 76 Numerous 13–19, 17.6 6–13, 10.0 85 Numerous
Bastrichs and Mastigophores 13–18, 16.1 3–6, 3.4 18 Common 13–21, 16.5 2–8, 4.5 52 Numerous 12–21, 16.9 2–5, 3.4 37 Occasional
Mesenteries Spirocysts 13–21, 17.4 2–6, 3.4 64 Numerous 13–25, 17.9 2–6, 3.3 60 Numerous 3–26, 18.0 2–5, 3.1 61 Numerous
Holotrichs (L) 23–38, 28.2 7–14, 11.5 27 Occasional 20–34, 24.3 8–15, 10.8 31 Occasional 20–36, 27.6 10–15, 11.8 52 Numerous
Holotrichs (M) 10–19, 16.5 4–15, 9.4 86 Numerous 12–19, 16.2 6–13, 8.3 61 Numerous
Bastrichs and Mastigophores 13–18, 16.0 3–5, 3.8 16 Common 13–22, 16.9 3–9, 4.6 71 Numerous 10–18, 14.6 2–5, 2.7 21 Occasional

Habitat and distribution

Antipathozoanthus obscurus sp. n. is found in low-light environments such as within crevasses of reef slopes and reef floors, and coral reef caves. Specimens were found from 3 to 15 m. This species has been found from the Red Sea and Okinawa.

Differential diagnosis

Antipathozoanthus obscurus sp. n. is easily distinguished from all other Antipathozoanthus species, including the two other new species in this study, which all have associations with antipatharians. A. obscurus sp. n. is not associated with antipatharians and instead is found on coral reef carbonate substrate within caves or cracks. Additionally, the cnidome of A. obscurus sp. n. is different from all other known Antipathozoanthus species, including the other new species in this study, as there are no medium holotrichs in any tissue of A. obscurus sp. n., and instead only large holotrichs are found in all tissues.

Although A. obscurus sp. n. is not associated with antipatharians, phylogenetic data indicate that A. obscurus sp. n. is very closely related to other Antipathozoanthus species associated with antipatharians, with identical COI and 16S-rDNA sequences to those of A. macaronesicus (EU591618).

Remarks

The samples of Antipathozoanthus obscurus sp. n. in the present study contain two morphotypes; one with bright brown tentacles that are longer than the oral disk (MISE-TF54); and the other morphotype with orange tentacles that are only as long as the oral disk (MISE-BISE1, MISE-BISE3, MISE-JDR190, MISE-JDR191, MISE-JDR192, MISE-JDR279, MISE-KU1, MISE-TF78, MISE-TF148). However, the sequences of all specimens formed a monophyletic clade and therefore we have described A. obscurus sp. n. in this study as containing two morphotypes. Genetic variation in all three genetic markers in the samples of A. obscurus sp. n. was observed, and the possibility remains that A. obscurus sp. n. may contain cryptic species. Thus, we have excluded specimen MISE-BISE3 from the type series, although it was tentatively identified as A. obscurus sp. n. Further specimens and fine-scale genetic analyses are required to better understand if there is any cryptic diversity within this species.

Etymology

Antipathozoanthus obscurus sp. n. is named from the Latin “obscura" meaning “dark", as this species can be found in dark environments.

Common name

Tsuno-nashi-sunaginchaku (new Japanese name).

Antipathozoanthus remengesaui sp. n.

Fig. 2c

Antipathozoanthus sp. sensu Reimer et al. 2014a, 2, fig. 1d

Antipathozoanthus sp. 1 sensu Reimer and Fujii 2017, 304, fig. 14.4c.

Material examined

Holotype: NSMT-Co1603 (MISE-PALAU2), colony of approximately 70 polyps connected by poorly developed white coenenchyme on genus Antipathes antipatharian (Hexacorallia: Antipatharia: Antipathidae). Preserved polyps approximately 1.5–3.0 mm in diameter, and approximately 1.5–2.0 mm in height from coenenchyme. Collected from Blue Hole, Palau (7°8'29.4"N, 134°13'23.3"E) at a depth of 23 m by JDR, 15 September 2014.

Paratypes: RMNH.Coel.42321 (MISE-MAL84), collected from Wall Street, Maldives (3°07'14.2"N, 72°58'46.5"E) at a depth of 9 m by JDR, 7 May 2014; RUMF-ZG-4397 (MISE-MAL85), collected from Wall Street, Maldives (3°07'14.2"N, 72°58'46.5"E) at a depth of 9 m by JDR, 7 May 2014; RUMF-ZG-4398 (MISE-JDR209), collected from Yanbu, Saudi Arabia, (24°26'N, 37°14'E) at a depth of 11 m by JDR, 4 October 2013; RUMF-ZG-4399 (MISE-TF102), collected from Okoga-shima Island, Kagoshima, Japan (31°33'58.75"N, 130°35'32.01"E) at a depth of 20 m by TF, 26 July 2011; RUMF-ZG-4400 (MISE-TF103), collected from Okoga-shima Island, Kagoshima, Japan (31°33'58.75"N, 130°35'32.01"E) at a depth of 40 m by TF, 26 July 2011.

Other materials examined: MISE-PALAU3, collected from Siaes Tunnel, Palau (7°18'54.8"N, 134°13'13.3"E) at a depth of 37 m by JDR, 15 September 2014; MISE-PALAU4, collected from Blue Hole, Palau (7°8'29.4"N, 134°13'23.3"E) at a depth of 28 m by JDR, 12 September 2014; MISE-KINKO2, collected from Hakamagoshi, Sakurajima, Kagoshima, Japan (31°35'23.5"N, 130.35.27.8"E) at a depth of 21 m by JDR, 20 September 2015; MISE-TF173, collected from Onna, Okinawa, Japan (26°26'20.9"N, 127°47'7.22"N) at depth of 15 m by TF, 27 June 2014; MISE-MAL46, collected from Coral Garden, Maldives (3°05'24.3"N, 72°58'04.5"E) at a depth of 24 m by JDR, 6 May 2014; MISE-MAL82, collected from Wall Street, Maldives (3°07'14.2"N, 72°58'46.5"E) at a depth of 9 m by JDR, 7 May 2014; MISE-MAL83, collected from Wall Street, Maldives (3°07'14.2"N, 72°58'46.5"E) at a depth of 9 m by JDR, 7 May 2014; MISE-MAL2502602, collected from Capital Reef, Maldives (3°02'55.8"N, 72°53'21.2"E) at a depth of 19 m by Marco Oliverio, 16 May 2014; MISE-MAL145, collected from Wall Street, Maldives (3°07'14.2"N, 72°58'46.5"E) at a depth of 12 m by JDR, 10 May 2014; MISE-MAL147, collected from Wall Street, Maldives (3°07'14.2"N, 72°58'46.5"E) at a depth of 10 m by JDR, 10 May 2014; MISE-MAL261, collected from Wall Street, Maldives (3°07'14.2"N, 72°58'46.5"E) at a depth of 9 m by JDR, 17 May 2014; MISE-HK70, collected from Siaes Tunnel, Palau (7°18'54.8"N, 134°13'13.3"E) by Hiroki Kise (HK), 12 September 2014, depth not available; MISE-HK90, collected from Blue Hole, Palau (7°8'29.4"N, 134°13'23.3"E) at a depth of 22 m by HK, 15 September 2014; MISE-JDR211, collected from Yanbu, Saudi Arabia, (24°26'N, 37°14'E) at a depth of 12 m by JDR, 4 October 2013; MISE-JDR214, collected from Yanbu, Saudi Arabia, (24°26'N, 37°14'E) at a depth of 12 m by JDR, 4 October 2013.

Diagnosis

External morphology: Polyps in situ are approximately 4–8 mm in diameter, and approximately 3–8 mm in height in situ when oral disks expanded (Fig. 2). Colonial zoantharian, white or off-white polyps that may be solitary or connected by a white and poorly developed coenenchyme on Antipathes substrate. Antipathozoanthus remengesaui sp. n. has approximately 40–42 tentacles that are pinkish or/and translucent. Tentacles are usually as long as open oral disk diameter. Oral disk is pink or bright brown in color, and the capitulum is also pinkish or bright brown in color when polyps are closed. Polyps encrusted with visible sand particles (1–3 mm) in their coenenchyme and ectodermal tissue. Colonies attached on axis from proximal extremity to base of Antipathes.

Internal morphology: Cteniform endodermal marginal muscle sensu Swain et al. 2015 (Fig. 4). Azooxanthellate. The large scattered lacunae in ectoderm and mesogleal are present due to their encrustations.

Figure 4. 

Images of histological section of Antipathozoanthus species. a longitudinal section of A. remengesaui sp. n. b longitudinal section of A. cavernus sp. n.. Abbreviations: (CEMM) cteniform endodermal marginal muscle, (OD) oral disk, (A) actinopharynx. Scale bars: a 200 µm, b 50 µm.

Cnidae: Holotrichs (large and medium), basitrichs and microbasic p-mastigophores (usually difficult to distinguish), spirocysts (Fig. 3; Table 2).

Habitat and distribution

Antipathozoanthus remengesaui sp. n. has been found on the sides and/or floors of cave entrance, and always on Antipathes. Specimens were collected from depths of 9 to 40 m. This species is known from Palau, Kagoshima in Japan, the Maldives, and the Red Sea.

Differential diagnosis

In the Pacific, Antipathozoanthus remengesaui sp. n. can be distinguished from A. hickmani by the development of the coenenchyme and in part by polyp size; the larger polyps (4–12 mm in diameter and 4–15 mm in height) of A. hickmani are connected by a well-developed coenenchyme on Antipathes galapagensis, while the slightly smaller polyps (4–8 mm in diameter and 3–8 mm in height in situ) of A. remengesaui sp. n. are either connected by a poorly developed coenenchyme or may even be solitary on Antipathes. Additionally, the cnidomes of these species are different; A. hickmani does not have spirocysts in the column, while A. remengesaui sp. n. has spirocysts in the column.

Remarks

The Antipathozoanthus remengesaui sp. n. specimens found in Kagoshima, Japan have different morphological features compared to the specimens found in all other regions. Specimens collected from Kagoshima have relatively large polyps (6–8 mm in diameter, and approximately 5–8 mm in height in situ) compared to specimens from other regions. The coloration of oral disks is also different between Kagoshima and other regions; A. remengesaui sp. n. from Kagoshima has a bright brown oral disk, while those from other regions have pink oral disks. However, sequences of these specimens collected from all regions formed a monophyletic clade for all genetic markers including ITS-rDNA. In terms of substrate organisms, A. remengesaui sp. n. collected from all regions in this study was associated with black corals of the genus Antipathes. Here, we have described this group as a single species, A. remengesaui sp. n., based on phylogeny and substrate specificity, although we have excluded some specimens for which we could not amplify ITS-rDNA successfully from the type series.

Etymology

Antipathozoanthus remengesaui sp. n. is named after Tommy Esang Remengesau, Jr., the current president of the Republic of Palau, who has greatly contributed to marine research and conservation in Palau.

Common name. Momoiro-mame-tsuno-sunaginchaku (new Japanese name).

Antipathozoanthus cavernus sp. n.

Fig. 2d

Material examined

Holotype: NSMT-Co1604 (MISE-KINKO1), colony of approximately 125 polyps connected by a highly developed coenenchyme on genus Myripathes (Antipatharia: Myriopathidae). Preserved polyps approximately 2.0–5.0 mm in diameter, and approximately 2.0–5.0 mm in height from coenenchyme. Collected from Sakurajima, Kagoshima, Japan (31°35'23.5"N, 130.35.27.8"E) at a depth of 21 m by JDR, 20 September 2015.

Paratypes: RUMF-ZG-4401 (MISE-MAL2592601), collected from Capital Reef, Maldives (3°02'55.8"N, 72°53'21.2"E) at a depth of 19 m by Marco Oliverio, 16 May 2014; RMNH.Coel.42322 (MISE-PALAU5), collected from Siaes Tunnel, Palau (7°18'54.8"N, 134°13'13.3"E) at a depth of 39 m by JDR, 15 September 2014.

Diagnosis

External morphology: Polyps in situ are approximately 4–15 mm in diameter when oral disk is expanded, and approximately 3–10 mm in height (Fig. 2). Colonial zoantharian with polyps connected by highly developed coenenchyme on Myripathes. Antipathozoanthus cavernus sp. n. has approximately 32–40 translucent tentacles of approximately 1 to 5 mm in length. Tentacle lengths are either as long as or slightly shorter than expanded oral disk diameter. Polyps have orange oral disk with orange or light orange ring around oral disk. When polyps are closed, capitular ridges are present and observed clearly, numbering approximately 16–20. The capitulum is orange or light orange in color. Polyps encrusted with visible sand particles (1–8 mm) in their coenenchyme and ectodermal tissue. Polyps usually much more encrusted than coenenchyme. Colonies attached on axis from proximal extremity to base of Myripathes.

Internal morphology: Cteniform endodermal arrangement marginal muscle sensu Swain et al. (2015) in longitudinal section (Fig. 4). Azooxanthellate. Large scattered lacunae in ectoderm and mesogleal are present due to their encrustations.

Cnidae: Holotrichs (large and medium), basitrichs and microbasic p-mastigophores (usually difficult to distinguish from each other), spirocysts (Fig. 3; Table 2).

Habitat and distribution

Antipathozoanthus cavernus sp. n. is found on the sides and/or floor of cave entrances, and on steep slopes, and always on Myripathes. Specimens were collected from depths of 19 to 39 m.

Differential diagnosis

Antipathozoanthus cavernus sp. n. occurs in similar environments as A. remengesaui sp. n., but these species can be distinguished by their coenenchyme development and by the generic identity of the antipatharian host. A. remengesaui sp. n. is associated with genus Antipathes (family Antipathidae) covered by a poorly developed coenenchyme, while A. cavernus sp. n. is associated with genus Myripathes (family Myripathidae) covered by a highly developed coenenchyme. A. cavernus sp. n. can be distinguished from A. hickmani by a different coloration and by its antipatharian association; A. cavernus sp. n. does not have red or cream colored polyps as seen in A. hickmani. Additionally, A. hickmani is associated with Antipathes galapagensis, while A. cavernus sp. n. is associated with genus Myripathes. A. macaronesicus is easily distinguishable from A. cavernus sp. n. by their polyp coloration (orange and light orange versus pinkish and yellowish, and their antipatharian host (genus Antipathes versus genus Myripathes). Finally, all species above have unique ITS-rDNA sequences.

Etymology

Antipathozoanthus cavernus sp. n. is named from the Latin “caverna" meaning “cave", as this species is found in caves.

Common name

Hana-tsuno-sunaginchaku (new Japanese name).

Phylogenetic analyses

Concatenated alignment. All Antipathozoanthus species together formed a large monophyletic clade within the Parazoanthidae with complete support (ML = 100%, BI = 1) in the concatenated (COI+16S-rDNA+ITS-rDNA) alignment phylogeny (Fig. 5). Within the Antipathozoanthus clade, the various Antipathozoanthus species were divided into two subclades, an ‘associated’ subclade consisting of species associated with antipatharians, and a ‘non-associated’ subclade consisting only of A. obscurus sp. n. found directly on non-biotic substrates. The associated subclade consisted of A. macaronesicus, A. hickmani, A. remengesaui sp. n. and A. cavernus sp. n. and had very strong support (ML = 95%, BI = 0.99), while the non-associated subclade of A. obscurus sp. n. had complete support (ML = 100%, BI = 1). Within the associated clade, A. hickmani and A. cavernus sp. n. were sister to each other (ML = 59%, BI = 0.96). A. remengesaui sp. n. was basal to a poorly nodal supported clade (ML ≤ 50%, BI ≤0.95) containing other associated Antipathozoanthus spp. (A. macaronesicus, A. hickmani and A. cavernus sp. n.). A. macaronesicus formed a subclade with very strong support (ML = 97%, BI = 1).

Figure 5. 

Maximum likelihood (ML) tree based on concatenated alignments of 16S-rDNA, COI and ITS-rDNA. Numbers on nodes represent ML bootstrap values (> 50% are shown). Bold branches indicate high supports of Bayesian posterior probabilities (> 0.95).

COI. All Antipathozoanthus species formed a large monophyletic clade within the Paraozoanthidae with a very strong support (NJ = 99%, ML = 99%, BI = 1) in the COI phylogeny (Suppl. material 2). Within the clade, Antipathozoanthus species were divided into two subclades (associated subclade + non-associated subclade). The topology within the large monophyletic associated subclade was very similar to that as seen in the 16Sr-DNA phylogeny. Both the associated subclade (NJ =77%, ML = 66%) and the non-associated subclade had moderate support (NJ = 86%, ML = 85%, BI = 0.99). Sequences of Antipathozoanthus species within each of the subclades showed no differences in sequences. The difference in sequences between the associated subclade and the non-associated subclade was 3 bp (0.69%).

16S-rDNA. All Antipathozoanthus species formed a large monophyletic clade within the Parazoanthidae with generally high support (NJ = 99%; ML = 85%; BI = 1) in the 16Sr-DNA phylogeny (Suppl. material 3). Within this large clade, Antipathozoanthus species were divided into two subclades; an associated subclade (A. macaronesicus, A. hickmani, A. remengesaui sp. n., and A. cavernus sp. n.); and the other subclade not associated with antipatharians (A. obscurus. sp. n.; ‘non-associated subclade’). The associated subclade formed only in NJ phylogenetic tree with moderate support in the 16S-rDNA tree (NJ = 78%), while the non-associated subclade had strong support in each phylogeny (NJ = 97%; ML = 95%; BI = 0.96). Sequences of Antipathozoanthus species within the associated subclade were identical with the exception of A. hickmani (EU333757), which differed by one base substitution, while within the non-associated subclade there were a few small sequence differences (maximum difference 3 bp). Differences of sequences between the associated and the non-associated subclades were 4–6 bp (0.67 to 1.01%).

ITS-rDNA. All Antipathozoanthus species formed a large monophyletic clade within the Parazoanthidae with complete support (NJ = 100%, ML = 100%, BI = 1) in the ITS-rDNA phylogeny (Suppl. material 4). Within the Antipathozoanthus clade there were again two subclades, corresponding to the associated subclade and the non-associated subclade, as seen in both the mitochondrial COI and 16S-rDNA phylogenies. The associated subclade had moderate support (NJ = 100%, ML = 69%, BI = 0.96), while the non-associated subclade had very strong support (NJ = 96%, ML = 100%, BI = 1). Within the associated subclade, all four species had different sequences; A. macaronesicus formed a monophyletic grouping with very strong support (NJ = 99%, ML = 90%, BI = 0.99), while A. remengesaui sp. n., A. cavernus sp. n., and A. hickmani each formed monophyletic groupings with moderate support (NJ = 95%, ML = 69%, BI = 0.62; NJ = 86%, ML = 62%, BI = 0.96; NJ = 79%; ML = 84%, BI = 0.96, respectively). A. obscurus sp. n. formed a monophyletic clade with very strong support (NJ = 96%; ML = 100%; BI = 1).

Discussion

Distribution of Antipathozoanthus species in the Indo-Pacific Ocean. Antipathozoanthus hickmani is found in only the Galapagos with A. cf. hickmani reported from the coast of Ecuador (Bo et al. 2012), suggesting an East Pacific distribution. On the other hand, A. remengesaui sp. n. was found in the Red Sea, the Maldives, Palau, and mainland Japan and Okinawa, Japan, while A. cavernus sp. n. was found in the Maldives, Palau, and mainland Japan, and A. obscurus sp. n. was found in the Red Sea and Okinawa, Japan. Additionally, unidentified Antipathozoanthus species have been previously reported from the central Indo-Pacific Ocean (Reimer et al. 2014a), the South China Sea (Reimer et al. 2017), and mainland Japan (Reimer et al. 2013). These results indicate that the three new Antipathozoanthus species described herein are likely widely distributed across the Indo-Pacific Ocean, and also that Antipathozoanthus species diversity is higher than has been previously known.

Evolution of macrocnemic zoantharians in caves. Antipathozoanthus obscurus sp. n. without host was found in similar environments as the ‘associated’ Antipathozoanthus species, but this species does not associate with antipatharians and is instead directly attached to coral reef carbonate. Ocaña and Brito (2003) explained the relationship between Antipathozoanthus and antipatharians as a case of facultative parasitism, although this association still requires further research. It has been revealed that some macrocnemic species gain an advantage in plankton feeding by utilizing substrate organisms that filter feed in environments where plankton organisms are scarce (e.g., Hydrozoanthus species on oligotrophic coral reefs; Di Camillo et al. 2010), and this could be one reason that most Antipathozoanthus spp. utilize antipatharians as substrate. However, moderate currents conducive to plankton feeding may occur in coral reef caves by inflow of tidal currents or terrestrial runoff (Iliffe and Kornicker 2009), and it may be unnecessary to have an association with antipatharians for obtaining sufficient plankton in such environments. Additionally, in marine caves, there are fewer predators of zoantharians, such as fishes (e.g., Bussotti et al. 2002), and perhaps fewer competitors for substrate space. Such environments may promote the speciation of ‘non-associated’ zoantharian species as seen here with A. obscurus sp. n.

All new species in the present study are azooxanthellate, and this trait is common within macrocnemic zoantharians to the exception of some species such as Bergia cutressi (West, 1979) and Nanozoanthus harenaceus Fujii & Reimer, 2013. Irei et al. (2015) suggested that cave-dwelling Palythoa species within Brachycnemina lost their zooxanthellae to adapt to environments in caves and cracks. On the other hand, macrocnemic cave-dwelling species may originally have lacked zooxanthellae rather than undergone a loss of zooxanthellae. However, more investigations are needed to evaluate the species diversity of zoantharians in caves to more comprehensively understand the evolution of these zoantharian species.

Substrate specificity within Antipathozoanthus. Within the family Parazoanthidae, different generic lineages likely have long evolutionary histories associated with their substrate organisms, based on the fact that many parazoanthid genera form monophyletic clades in accord to their substrates (Sinniger et al. 2005, 2010, 2013; Montenegro et al. 2015). In this study, we found two different subclades within Antipathozoanthus (Fig. 5, Suppl. Materials 2–4) that corresponded to substrate differences. The genetic distances between the associated subclade (A. hickmani, A. macaronesicus, A. remengesaui sp. n., A. cavernus sp. n.) and the non-associated subclade of A. obscurus sp. n. were 0.60% (COI) to 1.01% (16S-rDNA). Additionally, we observed characteristic insertions and deletions in the 16S-rDNA between the associated and non-associated subclades. Although the two clades formed in accordance to their substrate (antipatharians, coral reef carbonate), we consider the genetic distances between the two clades as intra-generic based on previous comparisons of genetic distances (Sinniger et al. 2010). While many taxonomic and molecular studies focusing on the family Parazoanthidae have been conducted using various genetic markers (e.g., Sinniger et al. 2005, 2010; Reimer et al. 2008; Montenegro et al. 2015), little research has been conducted focusing on the phylogenetic relations within different parazoanthid genera, except for studies examining Bergia, Parazoanthus, and Umimayanthus, which are all associated with sponges (Sinniger et al. 2005; Montenegro et al. 2015, 2016; Carreiro-Silva et al. 2017). There is a need for more phylogenetic studies focusing on increasing the numbers of species examined within each of the genera of Parazoanthidae in order to better understand the evolutionary history of substrate specificity and other traits within the family Parazoanthidae (Swain et al. 2015, 2016).

Acknowledgements

We thank the following people and institutions for supporting fieldwork and logistics; in Okinawa, all members of the Molecular Invertebrate Systematics and Ecology Laboratory (MISE) at the University of Ryukyus (UR), the KUMEJIMA 2009 expedition organized by the Transdisciplinary Research Organization for Subtropical and Island Studies of the University of the Ryukyus, the Center for Marine Bioscience & Biotechnology of the National Taiwan Ocean University, National University of Singapore, and the Biodiversity Research Center of the Academia Sinica; in Kagoshima, S. Dewa (Diving Service Umiannai), M. Matsuoka, R. Terada (both Kagoshima University) and D. Probizanski; in Palau, G. Mereb and A. Merep at the Palau International Coral Reef Center (PICRC) supported by the SATREPS P-CoRIE Project “Sustainable management of coral reef and island ecosystem: responding to the threat of climate change", funded by the Japan Science and Technology Agency (JST) and the Japan International Cooperation Agency (JICA) in cooperation with PICRC and Palau Community College. H. Takaoka (Okinawa Churaumi Aquarium, Okinawa) is acknowledged for identification of antipatharians. We also thank the University of Milano-Bicocca Marine Research and High Education Centre in Magoodhoo, the Ministry of Fisheries and Agriculture, Republic of Maldives and the community of Maghoodhoo, Faafu Atoll, for field work in the Maldives, and M.L. Berumen at the King Abdullah University of Science and Technology (KAUST), Saudi Arabia for Red Sea field work. The second author was partially supported by the “Establishment of Research and Education Network on Biodiversity and Its Conservation in the Satsunan Islands" project of Kagoshima University adopted by the Ministry of Education, Culture, Sports, Science and Technology, Japan and JSPS KAKENHI Grant numbers 17K15198 and 17H01913. Comments by Dr. S. Stampar and the editor improved the manuscript.

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