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Research Article
A new Antipathozoanthus species (Cnidaria, Hexacorallia, Zoantharia) from the northwest Pacific Ocean
expand article infoHiroki Kise‡§, Masami Obuchi|, James Davis Reimer‡
‡ University of the Ryukyus, Nishihara, Japan
§ Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, Higashi, Japan
| Endo Shell Museum of Manazuru, Manazuru, Japan

Corresponding author: Hiroki Kise ( hkm11sea@yahoo.co.jp )

Academic editor: Bert W. Hoeksema
© 2021 Hiroki Kise, Masami Obuchi, James Davis Reimer.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation: Kise H, Obuchi M, Reimer JD (2021) A new Antipathozoanthus species (Cnidaria, Hexacorallia, Zoantharia) from the northwest Pacific Ocean. ZooKeys 1040: 49-64. https://doi.org/10.3897/zookeys.1040.62309
ZooBank: urn:lsid:zoobank.org:pub:4244D08F-F6D8-47FC-BB71-0F8187DC13ED
Open Access

Abstract

A new species of zoantharian within the genus Antipathozoanthus is described based on specimens collected from the coast of mainland Japan, northwest Pacific Ocean. Antipathozoanthus tubus sp. nov. is characterized by its substrate (epibiotic on polychaete tube) and habitat (exposed rock). As well, the results of molecular phylogenetic analyses using concatenated multiple genetic markers also support the distinction between A. tubus sp. nov. and its congenerics. Antipathozoanthus tubus sp. nov. is the first species of Antipathozoanthus species reported to be epibiotic on polychaete tubes, and is the second species in the genus that is not associated with antipatharians.

Keywords

molecular phylogeny, polychaete, Sagami Bay, symbiosis, zoantharians

Introduction

The order Zoantharia Rafinesque, 1815 (Cnidaria: Anthozoa) consists of primarily colonial hexacorallians that are commonly found in most marine environments, including extreme environments such as intertidal zones and methane cold seeps in the deep sea (Reimer et al. 2007; Sinniger et al. 2010). The number of studies in Japanese waters on these species have increased in recent decades and have played key roles in the systematic re-appraisal and revision of zoantharians around the globe (Reimer and Fujii 2017). Moreover, the number of overall diversity records of zoantharian species from Japan has increased since 2006 by the addition of more than 20 formally described species (see Reimer and Fujii 2017). In particular, zoantharians within the suborder Macrocnemina Haddon & Shackleton, 1891 have been well studied in Japan as most newly described species belong to this suborder, and the total number of macrocnemic zoantharian species continues to rise by reports of many possibly undescribed species in Japanese waters (e.g., Sinniger et al. 2010; Reimer et al. 2010, 2019).

Antipathozoanthus Sinniger, Reimer & Pawlowski, 2010 within the family Parazoanthidae Delage & Hérouard, 1901 is a genus that has been the subject of recent research in Japanese waters (Sinniger et al. 2010; Kise et al. 2017). This genus currently contains five species (Reimer and Sinniger 2021), with records from Madagascar (Sinniger et al. 2010), the Red Sea, Palau, Maldives, Japan (Reimer et al. 2014; Kise et al. 2017; Reimer et al. 2019) in the Indo-West Pacific, and Ecuador (Reimer and Fujii 2010; Bo et al. 2012; Jaramillo et al. 2018) in the eastern Pacific Ocean, as well as from St. Helena (Santos et al. 2019), Cape Verde, Principe Islands (Ocaña and Brito 2003; Ocaña et al. 2007; Sinniger et al. 2010), and Curaçao (Montenegro et al. 2020) in the Atlantic Ocean and the Caribbean. As the generic name indicates, Antipathozoanthus species generally utilize antipatharians (Hexacorallia: Antipatharia) as their obligate substrate (Sinniger et al. 2010). However, A. obscurus Kise et al., 2017 described from Okinawa, Japan, and the Red Sea, is not associated with any antipatharians and instead is found in cracks and caves on coral-reef substrates (Kise et al. 2017). Thus, substrate specificity to antipatharians within the genus Antipathozoanthus is not all-inclusive, unlike as originally theorized (Sinniger et al. 2010).

Recently, we collected two specimens in Japanese waters of an undescribed species belonging to the genus Antipathozoanthus, which were unexpectedly found as epibionts on an empty polychaete tube. Here, we formally describe this new species, Antipathozoanthus tubus sp. nov., utilizing morphological and phylogenetic data. With this addition, the entire Japanese zoantharian fauna now comprises 37 recorded species, representing 16 of the 28 currently-recognized genera across nine families (see also Reimer and Fujii 2017; Kise et al. 2017, 2018, 2019; Reimer et al. 2019).

Materials and methods

Specimen collection

The examined specimens were collected in shallow waters of Sagami Bay, Kanagawa, Japan on 2019 and 2020, by SCUBA (Table 1). Specimen images were taken in situ for gross external morphological observation.

Table 1.
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Information of specimens examined in this study.

Familiy Species Voucher number Locality Coordinates Date Depth Collecter GenBank accession numbers
18S–rDNA ITS–rDNA 28S–rDNA COI 12S–rDNA 16S–rDNA
Parazoanthidae Antipathozoanthus tubus sp. nov. NSMT–Co 1742 Iwa Beach, Sagami Bay, Kanagawa, Japan 35°09'36"N, 139°08'36"E 26 Jul 2019 13.6 M. Obuchi MW652773 MW652765 MW652768 MW649812 MW652761 MW652770
NSMT–Co 1743 Kotogahama, Sagami Bay, Kanagawa, Japan 35°08'48"N, 139°09'05"E 6 Jul 2020 14 M. Obuchi – – – – – –
A. hickmani CMNH–ZG 05883 Roca Onan, Pizon Island, Galapagos, Ecuador 0°35'27.2"S, 90°41'09.6"W 14 Mar 2007 27 A. Chiriboga MW652771 MW652764 – – MW652759 MW652769
A. cavernus NSMT–Co 1604 Sakurajima, Kagoshima, Japan 31°35'23.5"N, 130°35.27.8"E 20 Sep 2015 21 JD. Reimer – MG384699 MW652766 MG384660 MW652763 MG384681
A. remengesaui NSMT–Co 1603 Blue Hole, Palau 7°8'29.4"N, 134°13'23.3"E 15 Sep 2014 23 JD. Reimer MW652772 MG384703 MW652767 MG384649 MW652762 MG384673
A. obscurus NSMT–Co 1602 Cape Bise, Motobu, Okinawa–jima Island, Japan 26°42'34.4"N, 127°52'49.2"E 14 Aug 2014 5 JD. Reimer MW652774 MG384691 – MG384644 MW652760 MG384685

DNA extraction, PCR amplification, and sequencing

We extracted genomic DNA from tissue of the holotype specimen preserved in 99.5% EtOH using a spin-column DNeasy Blood and Tissue Extraction Kit (Qiagen, Hilden, Germany) following the manufacturer’s protocol. PCR amplification using Hot Star Taq Plus Master Mix Kit (Qiagen, Hilden, Germany) was performed for each of COI (mitochondrial cytochrome oxidase subunit I), mt 12S-rDNA (mitochondrial 12S ribosomal DNA), mt 16S-rDNA (mitochondrial 16S ribosomal DNA), 18S-rDNA (nuclear 18S ribosomal DNA), ITS-rDNA (nuclear internal transcribed spacer region of ribosomal DNA), and 28S-rDNA (nuclear 28S ribosomal DNA) using published primers (Medlin et al. 1988; Folmer et al. 1994; Apakupakul 1999; Chen et al. 2002; Sinniger et al. 2005; Swain 2009, 2010; Fujii and Reimer 2011). All PCR products were purified with 1 U of shrimp alkaline phosphatase (SAP) and 5 U of Exonuclease I (Takara Bio Inc., Shiga, Japan) at 37 °C for 40 min followed by 80 °C for 20 min. Cleaned PCR products were sequenced in both directions on an ABI 3730Xl Genetic Analyzer (Applied Biosystems, Thermofisher) at the Fasmac Co., Ltd., Kanagawa, Japan. Obtained sequences in this study were deposited in GenBank under accession numbers MW652759–MW652774.

Molecular phylogenetic analyses

Forward and reverse sequences were assembled and edited in Geneious v10.2.3 (Kearse et al. 2012). Multiple alignments for each marker were performed with previously published Parazoanthidae sequences obtained from GenBank (Suppl. material 1: Table S1) using MAFFT ver. 7.110 (Katoh and Standley 2013) with the auto algorithm under default parameters for all genetic markers. In this study, sequences of two selected taxa within the zoantharian genus Epizoanthus were used as outgroups. We obtained a dataset of 549 bp for 34 sequences of COI, 757 bp for 22 sequences of mt 12S-rDNA, 772 bp for 40 sequences of mt 16S-rDNA, 1756 bp for 23 sequences of 18S-rDNA, and 902 bp for 33 sequences of ITS-rDNA, 936 bp for 16 sequences of 28S-rDNA. These alignments were subsequently concatenated to obtain a final dataset of 5672 bp for 40 OTUs. All aligned datasets are available from the first author and at treebase.org (ID: S27965).

Phylogenetic analyses were performed on the concatenated dataset using Maximum likelihood (ML) and Bayesian inference (BI). ModelTest-NG v0.1.6 (Darriba et al. 2019) under the Akaike information criterion was used to select the best fitting model for each molecular marker, independently for ML and BI. The best selected models for ML and BI analyses were HKY+G for COI, GTR+I+G for mt 12S-rDNA, SYM+I+G for mt 16S-rDNA, HKY+I+G for 18S-rDNA, TPM3uf+I+G (BI: HKY+I+G) for ITS-rDNA, and GTR+I+G for 28S-rDNA. Independent phylogenetic analyses were performed using model partition per each region in RAxML-NG v0.9.0 (Kozlov et al. 2019) for ML, and MrBayes v3.2.6 (Ronquist and Huelsenbeck 2003) for BI. RAxML-NG was configured to use 12345 initial seeds, search for the best tree among 100 preliminary parsimony trees, branch length was scaled and automatically optimized per partition, and model parameters were also optimized. MrBayes was configured following the models and parameters as indicated by ModelTest-NG, 4 MCMC heated chains were run for 5,000,000 generations with a temperature for the heated chain of 0.2. Chains were sampled every 200 generations. Burn-in was set to 1,250,000 generations at which point the average standard deviation of split frequency (ASDOSF) was steadily below 0.01.

Morphological observations

Morphological data were collected from whole, dissected, and serial sections of the preserved specimens. Histological sections of 10–15 mm thickness were made using a RM-2125 RTS microtome (Leica, Germany) and were stained with hematoxylin and eosin after decalcification with a Morse solution for 48 h (1:1 vol; 20% citric acid: 50% formic acid). Classification of marginal muscle shapes followed Swain et al. (2015). Cnidae analyses were conducted using undischarged nematocysts from tentacles, column, actinopharynx, and mesenterial filaments of two polyps of holotype specimen under a Nikon Eclipse80i stereomicroscope (Nikon, Tokyo). Cnidae sizes were measured using ImageJ ver. 1.45 (Rasband, 2012). Cnidae classification generally followed England (1991) and Ryland and Lancaster (2004).

Abbreviations

NSMT National Science Museum, Tsukuba, Ibaraki, Japan;

CMNH Coastal Branch of Natural History Museum and Institute, Chiba, Japan.

Results

Taxonomic description

Order Zoantharia Rafinesque, 1815

Suborder Macrocnemina Haddon & Shackleton, 1891

Family Parazoanthidae Delage & Hérouard, 1901

Antipathozoanthus Sinniger, Reimer & Pawlowski, 2010

Diagnosis

(revised from Sinniger et al. 2010; Swain and Swain 2014, 2015; Kise et al. 2017; additions in bold). Macrocnemic zoantharians with cteniform endodermal muscle or endo-meso transitional sphincter muscle. Encrustations of the column to the outer mesoglea. No mesogleal canals or encircling sinus. Tentacles at least 26 in number. Substrate consists of antipatharians, external surfaces of parchment-like tubes of polychaetes, or calcium carbonate (coral reef).

Type species

Gerardia macaronesicus Ocaña & Brito, 2003, by original designation.

Remarks

We herein modify the diagnosis of Antipathozoanthus, as A. tubus sp. nov. is clearly located within the clade of Antipathozoanthus with very high support in our molecular phylogenetic analyses. Skeletal secretion as has been reported in A. macaronesicus (Ocaña & Brito, 2003) was not found in any other Antipathozoanthus species, including A. tubus sp. nov.

Antipathozoanthus tubus sp. nov.

http://zoobank.org/70CBDCBE-87C2-4A84-AF9D-D4841A082CEC
Figures 1, 2, 3

Material examined

Holotype. NSMT-Co 1742, collected from Iwa Beach, Sagami Bay, Kanagawa, Japan (35°09'36"N, 139°08'36"E) at a depth of 14 m by M. Obuchi, 26 July 2019, divided in two pieces, one portion fixed in 99.5% EtOH and the other in 5–10% saltwater formalin. Paratype. NSMT-Co 1743, collected from Kotogahama, Sagami Bay, Kanagawa, Japan (35°08'48"N, 139°09'05"E) at a depth of 14 m by M. Obuchi, 6 June 2020, divided in two pieces, one portion fixed in 99.5% EtOH and the other in 70% EtOH.

Figure 1. 

Images of external morphology of Antipathozoanthus tubus sp. nov. (holotype: NSMT-Co 1742) a colony on branched polychaete tubes in situ b close-up image of polyps in situ c colony on branched polychaete tubes in preserved condition d close-up image of closed polyp. Abbreviations: MT: marginal teeth, T: tube of polychaete. Scale bars: 10 mm (a, c), 5.0 mm (b), 0.5 mm (d).

Material examined for comparison

Antipathozoanthus obscurus NSMT-Co1602 (holotype), collected from Cape Bise, Motobu, Okinawa-jima Island, Japan, by J.D. Reimer, 14 August 2014. Antipathozoanthus remengesaui NSMT-Co1603 (holotype), collected from Blue Hole, Palau, by J.D. Reimer, 15 September 2014. Antipathozoanthus cavernus NSMT-Co1604 (holotype), collected from Sakurajima, Kagoshima, Japan, by J.D. Reimer, 20 September 2015. Antipathozoanthus hickmani CMNH-ZG-05883 (paratype), collected from Roca Onan, Pinzon Island, Galapagos, Ecuador, by A. Chiriboga, 14 March 2007.

Type locality

Iwa Beach, Sagami Bay, Kanagawa, Japan

Description

External morphology. Colonial zoantharian, with cylindrical polyps connected by well-developed dark red colored coenenchyme (Fig. 1a). External branched tube of dead polychaete mostly covered by coenenchyme. Scapus of column dark red in situ, dark brown in preserved specimens. Capitulum of column orange in situ, dark violet in preserved specimens. Column and coenenchyme heavily encrusted with visible sand and silica particles in ectodermal tissue to outer mesoglea (Fig. 1c, d). Preserved, contracted polyps 2.0–6.0 mm in height, 1.0–3.0 mm in diameter. In situ, opened polyps approximately < 8.0 mm in height, < 10 mm in diameter. Oral disk 5.0–8.0 mm in diameter, orange to light orange in coloration. Number of oral furrows the same as the number of tentacles, and cream white circular protrusion in central oral disk bears slit-like mouth aligned with directives. Tentacles arranged in two rows (15–17 inner endocoelic tentacles and 15–17 outer exocoelic tentacles), as long as the expanded oral disk diameter. Number of tentacles 30–34, transparent in coloration. 15–17 marginal teeth present under inner endocoelic tentacles (Fig. 1b). Tips of tentacles usually cream in coloration. Capitular ridges indiscernible.

Internal morphology. Azooxanthellete. Mesentery number 30–34, complete 15–17, incomplete 15–17. Mesenteries in macrocnemic arrangement (Fig. 2c). Mesoglea thickness 0.01–0.10 mm, and thicker than ectoderm. Developed siphonoglyph distinct and U-shaped. Mesenterial filaments present (Fig. 2a). Endodermal marginal muscle, short comb-like mesogleal pleats supporting the entire length of the marginal muscle (cteniform endodermal marginal muscle: Fig. 2b). Basal canals of mesenteries absent (Fig. 2d). Additionally, possible gametes observed in several longitudinal sections.

Figure 2. 

Image of internal morphology of Antipathozoanthus tubus sp. nov. (holotype: NSMT-Co 1742) a longitudinal section of polyp b closed-up image of cteniform endodermal marginal muscle c, d cross-section of polyp. Abbreviations: A: actinopharynx, MF: mesenterial filament, CEMM: cteniform endodermal marginal muscle, DD: dorsal directives, VD: ventral directives, S: siphonoglyph, 5th: 5th mesentery from dorsal directives, M: mesoglea, CM: complete mesentery, IM: incomplete mesentery. Scale bars: 0.5 mm (a, c), 0.1 mm (b, d).

Cnidae. Basitrichs and microbasic b-mastigophores, microbasic p-mastigophores, holotrichs, and spirocysts (Fig. 3, Table 2).

Table 2.
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Cnidae types and sizes observed in Antipathozoanthus tubus sp. nov. Frequency: relative abundance of cnidae type in decreasing order; numerous, common, occasional, rare (n = number of cnidae).

Tissue Type of cnidae Antipathozoanthus tubus sp. nov.
Length Width Mean±SD Frequency n
(min-max) (min-max) (Length × Width)
Tentacles Spirocysts 8.0–19.0 1.0–4.0 15.6±2.0 × 2.1±0.5 Numerous 325
Bastrichs 7.0–16.0 1.0–4.0 10.4±1.5 × 2.0±0.7 Numerous 37
Holotrichs medium 12.0–19.0 7.0–8.0 17.8±2.6 × 7.6±0.5 Occasional 6
Holotrichs large 20.0–22.0 8.0–11.0 20.7±0.6 × 9.4±0.8 Occasional 10
Column Special microbasic b-mastigophores 12.0 6.0 – Rare 1
Actinopharynx Spirocysts 10.0–16.0 1.0–3.0 12.7±1.6 × 2.4±0.7 Occasional 9
Bastrichs 11.0–15.0 2.0–3.0 12.5±1.0 × 2.3±0.4 Numerous 37
Microbasic b-mastigophores 8.0–15.0 2.0–3.0 10.0±1.9 × 2.6±0.5 Rare 5
Microbasic p-mastigophores 9.0–11.0 3.0 10.0±0.8 × 3±0 Rare 3
Holotrichs medium 16.0–19.0 5.0–8.0 18.3±0.1 × 6.8±0.1 Rare 4
Holotrichs large 20.0–22.0 8.0–10.0 20.7±0.9 × 9.0±0.7 Occasional 15
Mesenterial filaments Microbasic b-mastigophores 10.0–14.0 2.0–3.0 12.2±1.8 × 2.5±0.5 Rare 4
Microbasic p-mastigophores 8.0–16.0 2.0–4.0 10.1±0.2 × 3.2±0.6 Numerous 60
Holotrichs medium 12.0–19.0 5.0–10.0 17.8±1.9 × 9.3±1.2 Common 23
Holotrichs large 20.0–25.0 10.0–12.0 21.1±1.2 × 10.7±0.5 Numerous 36
Figure 3. 

Cnidae in the tentacles, column, actinopharynx, and mesenterial filaments of holotype of Antipathozoanthus tubus sp. nov. Abbreviations: HL: holotrich large, HM: holotrich medium, B: basitrichs, BM: microbasic b-mastigophores, SBM: special microbasic b-mastigophores, PM: microbasic p-mastigophores, S: spriocysts.

Habitat and distribution

Northwestern Pacific Ocean: Sagami Bay, Kanagawa, Japan at depths < 14 m.

Associated host

We could not identify host polychaete species as there were no polychaetes in the tubes. However, the tubes that Antipathozoanthus tubus sp. nov. was attached to may belong to species within the genus Eunice, as polychaete species that build parchment-like branched tubes have been reported from this genus (e.g., Díaz-Díaz et al. 2020).

Molecular phylogeny

Both ML and BI phylogenetic analyses showed similar topologies as indicated in Fig. 4. The genus Antipathozoanthus appeared as a monophyletic clade located within the family Parazoanthidae with strong nodal support (ML=100%, BI=1) and was close to a Parazoanthidae clade containing species associated with stalked hexactinellid sponges. Within Antipathozoanthus, two subclades were formed; one subclade consisted of the antipatharian-associated species A. macaronesicus, A. hickmani, A. remengesaui, and A. cavernus (ML = 100%, BI = 0.97), and the other subclade consisted of A. tubus sp. nov. and A. obscurus (ML = 82%, BI = 0.92). Genetic distances in COI, 16S-rDNA, and ITS-rDNA sequences between A. tubus sp. nov. and other Antipathozoanthus species were 0.000 to 0.009, 0.002 to 0.010, and 0.010 to 0.128, respectively. As well, A. tubus sp. nov. and other Antipathozoanthus species shared unique insertion/deletion patterns in 16S-rDNA sequences.

Figure 4. 

Maximum likelihood tree based on combined dataset of COI, mt 12S-rDNA, mt 16S-rDNA, 18S-rDNA, ITS-rDNA, and 28S-rDNA sequences. Number at nodes represent ML bootstrap values (> 50% are shown). White circles on nodes indicate high support of Bayesian posterior probabilities (>0.95).

Remarks

Antipathozoanthus tubus sp. nov. can be easily distinguished from A. remengesaui Kise et al., 2017, A. macaronesicus (Ocaña & Brito, 2003), and A. hickmani Reimer & Fujii, 2010 by the number of tentacles as well as different coloration; Antipathozoanthus remengesaui, A. macaronesicus, and A. hickmani have up to 42 tentacles (Ocaña and Brito 2003; Reimer and Fujii 2010; Kise et al. 2017), while A. tubus sp. nov. has fewer tentacles (30–34). The dark red colored polyps and coenenchyme of A. tubus sp. nov. are not found in these other three Antipathozoanthus species. In addition, A. tubus sp. nov. differs from A. cavernus Kise et al., 2017 with regards to polyp coloration (A. cavernus has orange or light orange polyps: Kise et al. 2017). Although A. tubus sp. nov. and A. obscurus Kise et al., 2017 are phylogenetically close, their COI, 16S-rDNA, and ITS-rDNA sequences are all unique (genetic distances in COI, 16S-rDNA and ITS-rDNA sequences between A. tubus sp. nov. and A. obscurus were 0.009, 0.03, and 0.12, respectively). As well, these two species can be separated by coloniality; polyps of A. obscurus are connected by a stolon forming a mesh network (Kise et al. 2017), while polyps of A. tubus sp. nov. are connected by a well-developed coenenchyme. Furthermore, A. macaronesicus, A. remengesaui, A. cavernus, A. hickmani, and A. obscurus have holotrichs in their column (Ocaña and Brito 2003; Reimer and Fujii 2010; Kise et al. 2017), while holotrichs were not observed in the column of A. tubus sp. nov.

Antipathozoanthus is a circumglobally distributed genus, as species have reported from the Indian, Pacific, and Atlantic Oceans (Ocaña and Brito 2003; Sinniger et al. 2010; Reimer and Fujii 2010; Bo et al. 2012; Reimer et al. 2014; Kise et al. 2017), with members living from shallow waters (A. obscurus at 3 m depth; Kise et al. 2017) to mesophotic depths (153–169 m for Antipathozoanthus sp. sensu Reimer et al. 2019). The most distinctive attributes of A. tubus sp. nov. are its substrate and habitat. Antipathozoanthus macaronesicus, A. hickmani, A. remengesaui, and A. cavernus are found on antipatharians within the families Antipathidae and Myriopathidae (Ocaña and Brito 2003; Reimer and Fujii 2010; Sinniger et al. 2010; Bo et al. 2012; Kise et al. 2017), while A. obscurus is directly attached to coral reef carbonate (Kise et al. 2017). On the other hand, A. tubus sp. nov. is the only species of the genus found to date on tubes of polychaetes. Four Antipathozoanthus species are known from low light environments; A. macaronesicus, A. remengesaui, and A. cavernus have been found in cave entrances, and A. obscurus is found in crevasses and/or coral reef caves (Ocaña and Brito 2003; Kise et al. 2017). On the other hand, the habitat of A. tubus sp. nov. is not a low-light environment, but the specimens were instead found on a polychaete tube attached to exposed rock.

Within Parazoanthidae, until now, Isozoanthus altisulcatus Carlgren, 1939 is the only species described as living on the tubes of polychaetes. However, several morphological differences exist between A. tubus sp. nov. and I. altisulcatus. Capitular ridges are developed and conspicuous in I. altisulcatus, whereas they are indiscernible in A. tubus sp. nov. The marginal teeth on the capitulum found in A. tubus sp. nov. were not observed in I. altisulcatus. Although Carlgren (1939) did not describe the numbers of tentacles of I. altisulcatus, the numbers of mesenteries are 34–42 (Carlgren 1939). As numbers of tentacles are known to be equal to the number of mesenteries (Bourne 1900), the number of tentacles of I. altisulcatus is likely to be 34–42, which is greater than the number of tentacles of A. tubus sp. nov. (30–34).

Genetic distances of COI sequence between A. tubus sp. nov. and other Antipathozoanthus species can be considered as intra-generic differences based on previous comparisons of genetic distances (Sinniger et al. 2010). As well, A. tubus sp. nov. shared unique insertion/deletion patterns in 16S-rDNA sequences with other Antipathozoanthus species. Thus, we consider that A. tubus sp. nov. should belong to the genus Antipathozoanthus and does not warrant the erection of a new parazoanthid genus.

Etymology

Antipathozoanthus tubus sp. nov. is named from the Latin tuba, as this species is found on polychaete tubes. The Japanese name is ‘Iwa-tsuno-sunaginchaku’.

Discussion

Japanese waters are composed of a wide variety of physical, geographical, and topographical environments due to the latitudinal extension of Japan spanning from the near-tropics of Okinawa to the near-subarctic Hokkaido, and also to the dynamic geology of the region, and thus, Japanese waters have high marine species diversity levels (Fujikura et al. 2010). At the same time, it is estimated that more than 70% of the marine taxa in this region remain undescribed (Fujikura et al. 2010). The order Zoantharia is one such taxon for which much work remains to be done. Although many zoantharian studies have been conducted in Japan, taxonomic studies are still biased by region; southern Japan including Kochi and the Ryukyu Archipelago have been focused on in comparison to other regions (Reimer and Fujii 2017). As a result, 16 species have been described based on type specimens collected from southern Japan (mainly from the Ryukyu Archipelago) (e.g., Irei et al. 2015). In other regions, historical taxonomic works have been conducted in Sagami Bay by Lwowsky (1913), Tischbierek (1929), and Carlgren (1934), with the description of three macrocnemic species; Hydrozoanthus gracilis Lwowsky, 1913, Epizoanthus cnidosus Tischbierek, 1929 (junior synonym of Hydrozoanthus gracilis), and Epizoanthus ramosus, Carlgren 1934. As well, Hertwig (1882) reported the carcinoecium-forming Epizoanthus parasiticus (Verill, 1864) based on the specimens collected from the Sea of Enshu during the Challenger expedition. However, few taxonomic studies have been conducted in these regions since these past historical works, and for many other regions, almost no literature exists (e.g. the Sea of Japan). Thus, in order to understand species richness and the distribution patterns of zoantharians in Japan, further diversity studies with sampling efforts focused on understudied regions are required.

Acknowledgements

We would like to thank Tetsuaki Tabata, Yodai Tano, Marie Chiba, and Masaru Furuya (Iwa Diving Center). We are also grateful to Dr. Kensuke Yanagi (Coastal Branch of Natural History Museum and Institute) for permission to subsample specimens, and assistance in visiting the CMNH. Prof. Akihiro Takemura (University of the Ryukyus) is thanked for giving us technical support. The first author was supported by JSPS KAKENHI grant number 19J12174. We thank two reviewers and the editor, who all provided helpful comments on earlier versions of this manuscript.

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Supplementary material

Supplementary material 1 

Table S1

Hiroki Kise, Masami Obuchi, James Davis Reimer

Data type: GenBank accession numbers

Explanation note: GenBank accession numbers used for phylogenetic analyses in this study. Newly obtained sequences indicated in bold.

This dataset is made available under the Open Database License (http://opendatacommons.org/licenses/odbl/1.0/). The Open Database License (ODbL) is a license agreement intended to allow users to freely share, modify, and use this Dataset while maintaining this same freedom for others, provided that the original source and author(s) are credited.
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