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Marine Biodiversity
ISSN 1867-1616
Volume 49
Number 6
Mar Biodiv (2019) 49:2571-2586
DOI 10.1007/s12526-019-00987-3
Xylocythere sarrazinae, a new cytherurid
ostracod (Crustacea) from a hydrothermal
vent field on the Juan de Fuca Ridge,
northeast Pacific Ocean, and its
phylogenetic position within Cytheroidea
Hayato Tanaka, Yann Lelièvre & Moriaki
Yasuhara
1 23
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ORIGINAL PAPER
Xylocythere sarrazinae, a new cytherurid ostracod (Crustacea)
from a hydrothermal vent field on the Juan de Fuca Ridge, northeast
Pacific Ocean, and its phylogenetic position within Cytheroidea
Hayato Tanaka
1
&Yann Lelièvre
2,3
&Moriaki Yasuhara
4
Received: 2 May 2019 / Revised: 23 June 2019 /Accepted: 10 July 2019
#Senckenberg Gesellschaft für Naturforschung 2019
Abstract
This paper described Xylocythere sarrazinae sp. nov. (Ostracoda: Cytheroidea: Cytheruridae: Eucytherurinae), collected at
2196 m depth from the Grotto hydrothermal edifice (Main Endeavor Field, Juan de Fuca Ridge) in the northeastern Pacific
Ocean. This new species was found living in association with Ridgeia piscesae tubeworm assemblages. It is the second
representative of Xylocythere described from such vents. Xylocythere sarrazinae sp. nov. is easily distinguished from the seven
described species of Xylocythere by the surface ornamentations of its carapace, with the most similar species to it being
Xylocythere pointillissima Maddocks & Steineck, 1987. However, Xylocythere sarrazinae sp. nov can be distinguished from
X. pointillissima based on the following characters: having a subsquare basal capsule outline, a spatulate upper ramus, a flattened
distal lobe of the male copulatory organ, and having 15 maxillula branchial plate setae. We found that one specimen of this new
species had multiple spherical objects associatedwith the internal openings of its pore clusters. These objects were quite similar in
shape to that of chemoautotrophic bacteria, which were previously reported from the outer surfaces of pore clusters in other
Xylocythere species. Finally, we provided a preliminary phylogenetic analysis of this new species based on 18S rRNA gene
sequences to determine the phylogenetic position of the subfamily Eucytherurinae within the superfamily Cytheroidea. This
analysis revealed that Xylocythere (Eucytherurinae) may be the most ancestral lineage among the Cytheruridae and identified
paraphyletic relationships among the three subfamilies within Cytheruridae. This result supported certain previous studies’
conclusions based on morphology and fossil records.
Keywords Chemosynthetic habitat .Crustacea .Eucytherurinae .Meiofauna .Pore clusters
Introduction
Ostracods are tiny crustaceans covered by a calcified car-
apace with two valves. They are important representatives
of the meiofaunal compartment. They occur in a wide
variety of aquatic environments including deep-sea che-
mosynthetic habitats. According to a recent review on
living and fossil ostracods from chemosynthetic ecosys-
tems (Karanovic and Brandão 2015), most deep-sea spe-
cies have been described from the eastern Pacific Ocean
(Kornicker 1991; Kornicker and Harrison-Nelson 2005;
Maddocks 2005). Additionally, several species left in
open nomenclature have been reported from the equatorial
Pacific and northern Atlantic oceans (van Harten 1992,
1993; Zeppilli and Danovaro 2009; Degen et al. 2012).
Recently, the first ostracod species from hydrothermal
vents in the western Pacific Ocean was described by
Tanaka and Yasuhara (2016). Regardless of their recent
This article is registered in ZooBank under http://zoobank.org/
247A9AE9-F577-45E8-9901-FD5E4FDFDF14
Communicated by S. Gollner
*Hayato Tanaka
Cladocopina@gmail.com
1
Tokyo Sea Life Park, 6-2-3 Rinkai-cho, Edogawa-ku,
Tokyo 134-8587, Japan
2
Ifremer Centre de Bretagne, REM/EEP, Laboratoire Environnement
Profond, 29280 Plouzane, France
3
Département de Sciences Biologiques, Université de Montréal, C.P.
6128, Succursale Centre-ville, Montreal, Québec H3C 3J7, Canada
4
School of Biological Sciences and Swire Institute of Marine Science,
The University of Hong Kong, Pokfulam Road, Hong Kong, SAR,
China
https://doi.org/10.1007/s12526-019-00987-3
Marine Biodiversity (2019) 49:2571–2586
/Published online: 14 August 2019
Author's personal copy
distribution, fossil records of vent ostracods trace back to
the middle Devonian (Olempska and Belka 2010).
In this paper, we describe a new ostracod species belonging
to the genus Xylocythere Maddocks & Steineck, 1987 that was
recently discovered on the Juan de Fuca Ridge, northeastern
Pacific. The type species of this genus, Xylocythere turnerae
Maddocks & Steineck, 1987, was collected from deep-sea
experimental wood falls at approximately 3500 m depth de-
ployed on the southeast of Woods Hole, MA (USA).
Simultaneously, three other Xylocythere species were also de-
scribed from the Tongue of the Ocean (Bahamas), off Sainte
Croix (Virgin Islands), and from the Panama basin (Maddocks
and Steineck 1987)(seeFig.1and Table 1). Five years later,
van Harten (1992)discoveredaXylocythere species from a
vent field of the East Pacific Rise and discussed the relation-
ships between deep-sea wood-island habitats and vent fauna
with regard to their distribution and trophic ecology.
Subsequently, this species was formally described as
Xylocythere vanharteni Maddocks, 2005 based on newly col-
lected specimens (Maddocks 2005). Thus, five living
Xylocythere species are known and all of them are endemic
to chemosynthetic habitats. Additionally, two fossil species
are known, namely Xylocythere producta (Colalongo &
Pasini, 1980), from the Middle Miocene to the Early
Pleistocene (Colalongo and Pasini 1980;Dall’Antonia
2003), and Xylocythere carpathica Szczechura, 1995 from
the Middle Miocene (Szczechura 1995,2000). Several un-
named fossil species of Xylocythere were also reported from
the Late Eocene to the Holocene (Steineck et al. 1990;
Corrège 1993; Kiel and Goedert 2006; Bergue and Coimbra
2008; Yasuhara et al. 2009; Machian-Castillo et al. 2014).
Notably, the oldest Xylocythere fossil (Late Eocene) was re-
corded as a member of wood-fall assemblages (Kiel and
Goedert 2006). Their wide geographical distribution and
bathymetric range (Fig. 1; Table 1) imply ancient origins.
This study describes a new Xylocythere species based on the
Fig. 1 Global distribution and fossil occurrences of Xylocythere species.
Species list and references are shown in Table 1. Numbers correspond
with localities: 1, 190 miles southeast of Woods Hole, depth 3506 m; 2,
Tongue of the Ocean, Bahama Islands, depth 2066 m; 3, off north coast of
St. Croix, Virgin Islands, depth 4000 m; 4, Panama Basin, depth 3900 m;
5, this study, Juan de Fuca Ridge, depth 2196 m, details are shown in Fig.
2; 6, Tica and Riftia hydrothermal vent fields at 9° 50′NontheEast
Pacific Rise, depth 2500 m; 7, Tremiti Islands, fossil; 8, Calabria, fossil;
9, Hyblean Plateau, fossil; 10, Jamnica borehole, southern Poland, fossil;
11, Goban Spur, Northeast Atlantic Ocean, Deep Sea Drilling Site S49A,
fossil; 12, Queensland Plateau, southwest Pacific, Deep Sea Drilling Site
209, fossil; 13, northwest Gulf of Mexico, depth 1500 m, fossil; 14,
Central equatorial Pacific, Deep Sea Drilling Site 575A, fossil; 15,
western Coral Sea, depth 2023 m, fossil; 16, western Coral Sea, depth
2230 m, fossil; 17, Mason County, western Washington State, USA,
fossil; 18, Santos Basin, Brazil, fossil; 19, Carolina Slope, western
North Atlantic, Ocean Drilling Program Site 1055, depth 1795 m,
fossil; 20, southern Gulf of Mexico, depth 2929 m, fossil
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Table 1 Species list of living and fossil Xylocythere. Numbers correspond with locality are indicated in Fig. 1. Abbreviations: E, Eocene; H, Holocene; HV, hydrothermal vent; M, Miocene; Og,
Oligocene; Ps, Pleistocene; WF, wood fall
Late E Late Og Early M Middle M Lare M Eearly Ps Late Ps H Recent HV Recent WF References
Xylocythere turnerae Maddocks & Steineck, 1987 1, 2, 3 Maddocks and Steineck
(1987)
X. pointillissima Maddocks & Steineck, 1987 1, 2, 3 Maddocks and Steineck
(1987)
X.rimosa Maddocks & Steineck, 1987 4 Maddocks and Steineck
(1987)
X. tridentis Maddocks & Steineck, 1987 1 Maddocks and Steineck
(1987)
X.sarrazinae sp. nov. 5 This study
X.vanharteni Maddocks, 2005 6VanHarten(1992,1993);
Maddocks (2005)
X.producta Colalongo & Pasini, 1980 7, 9 8 Colalongo and Pasini
(1980); Dall’Antonia
(2003)
X. carpathica Szczechura, 1995 10 Szczechura (1995,2000)
X.sp.1fromSteinecketal.(1990)11 Steineck et al. (1990)
X. sp. 2 from Steineck et al. (1990)12 Steineck et al. (1990)
X. sp. 3 from Steineck et al. (1990)13 Steineck et al. (1990)
X. sp. 4 from Steineck et al. (1990)13 Steineck et al. (1990)
X. sp. 5 from Steineck et al. (1990)11 Steineck et al. (1990)
X. sp. 6 from Steineck et al. (1990)13 Steineck et al. (1990)
X. sp. 7 from Steineck et al. (1990)14 Steineck et al. (1990)
X. sp. from Corrège (1993)15, 16 Corrège (1993)
X. sp. from Kiel and Goedert (2006)17 Kiel and Goedert (2006)
X. sp. from Bergue and Coimbra (2008)18 Bergue and Coimbra (2008)
X. sp. from Yasuhara et al. (2009)19 Yasuhara et al. (2009)
X. sp. from Machian-Castillo et al. (2014)20 Machian-Castillo et al.
(2014)
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morphology of the carapace and soft parts. This is the second
representative of Xylocythere coming from a hydrothermal
vent field. The objective of this study is to provide the detailed
morphological description of this new species of Xylocythere,
which was found at 2196 m depth on the Grotto hydrothermal
edifice located on the Juan de Fuca ridge northeast Pacific.
The new species was found living in association with Ridgeia
piscesae tubeworm assemblages, in areas of low fluid emis-
sions. We also provide a preliminary phylogenetic analysis of
this new species based on nearly complete 18S rDNA se-
quence in order to detect the phylogenetic position of subfam-
ily Eucytherurinae within superfamily Cytheroidea.
Materials and methods
Study site
The 90-km Endeavor segment, located on the northern part of
the Juan de Fuca Ridge (JdFR), is a hydrothermally active
region harboring five major hydrothermal vent fields (Kelley
et al. 2012). Among these, the Main Endeavor Field (MEF)
(Fig. 2) includes Grotto (47.949292 N, 129.098433 W), a 10-
m high active hydrothermal sulfide vent cluster located at a
depth of 2196 m. This large complex covers a surface area of
450 m
2
and forms a cove with an opening to the north (Xu
et al. 2014). Located in the Endeavor Hydrothermal Vent
Marine Protected Area (MPA), this site was selected as a target
for sensor deployment as part of the cabled deep-sea
observatory of Ocean Networks Canada (ONC) to study and
monitor the temporal dynamics of deep-sea vent ecosystems.
Like many other sulfide structures within the MEF, Grotto is
colonized by a mosaic of faunal assemblages (Sarrazin et al.
1997; Sarrazin and Juniper 1999), including the low-flow as-
semblages of the tubeworm Ridgeia piscesae Jones, 1985 and
their associated fauna.
Sampling
The Ocean Networks Canada Expedition 2015: Wiring the
Abyss cruise was conducted from aboard the R/V Thomas G.
Thompson vessel with the Remotely Operated Vehicle (ROV)
Jason from August 25 to September 14, 2015. The specimens
of ostracods examined were collected on September 7, 2015,
within two samples of R. piscesae tubeworms taken from the
Grotto edifice. The locations of the two samples were as fol-
lows: dive J0831-S1 (47.949292 N, 129.098433 W, 2196 m
depth) and dive J0831-S3 (47.949302 N, 129.098491 W,
2196 m depth). Details of the sampling methods used can be
found in Lelièvre et al. (2018). After bringing the faunal sam-
ples aboard, the siboglinid tubeworm assemblages were
washed over stacked sieves (with 250 μm, 63 μm, and
20 μm mesh sizes). Ostracod specimens were picked out from
the remnants in the 250-μm sieves and preserved in 96%
ethanol. A total of 35 individuals of Xylocythere were random-
ly extracted from the two samples (dive J0831-S1 and J0831-
S3) and examined for the present taxonomic study. The
Fig. 2 Sampling locality. alocation of the Juan de Fuca Ridge, northeast
Pacific and the seven segments. A rectangular indicating the Main
Endeavor Field; bBathymetric map and the positions of hydrothermal
vent edifices of the Main Endeavor Field (Endeavor, Juan de Fuca Ridge).
A star indicates the Grotto hydrothermal edifice, the type locality of
Xylocythere sarrazinae sp. nov.
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remaining ostracod specimens were used in isotopic analyses
and biodiversity studies (Lelièvre et al. 2018).
Morphology
The collected ostracod specimens were fixed in 96% etha-
nol and preserved at room temperature for description and
DNA extraction. The soft parts were separated from the
valves and dissected using fine needles under a stereo-
binocular microscope (SZH 10, OLYMPUS). The valves
were preserved on a cardboard cell slide and the soft parts
mountedinagum-chloralmedium, Neo-Shigaral (Shiga
Konchu Fukyusha, Japan), on glass slides. The specimens
were then observed and sketched using a transmitted light
binocular microscope (BX 50, OLYMPUS) with a differ-
ential interference contrast system and a camera Lucida.
The valves were washed with distilled water and gold-
coated by an ion sputtering device (JFC-1100, JEOL).
The valves were then observed by scanning electron mi-
croscopy (SEM; JSM-5600LV, JEOL). The type series was
deposited in the collection of the University Museum, the
University of Tokyo (UMUT) with the prefix “UMUT
RA.”Terminology on appendage and carapace morphol-
ogies is adapted from Maddocks (2005).
DNA extraction, amplification, and sequencing
Total DNA extraction from holotype (UMUT RA32930) was
performed using the DNeasy Blood and Tissue Kit (Qiagen,
USA) following the manufacturer’s protocol. Morphological
voucher was prepared following by Tanaka and Ohtsuka
(2016) and deposited in the UMUT.
Nearly complete sequence of the nuclear 18S rRNA
gene was PCR amplified using the eukaryotic primers
(Moon-van der Staay et al. 2000). The 25 μl reaction
contained 0.125 μl of TaKaRa Ex Taq HS (TAKARA
BIO Inc., Japan), 2.5 μl of 10× Ex Taq buffer, 2 μlof
dNTP mix, 1 μl of each primer (5 pmol each), 5 μlof
template DNA, and 13.375 μl sterilized distilled water.
The PCR protocol consisted of an initial denaturation step
at 95 °C for 2 min, followed by 40 cycles of denaturation at
98 °C for 10 s, annealing at 52 °C for 30 s, extension at
72 °C for 2 min, and a final extension at 72 °C for 10 min.
Quantity and length of the PCR products were checked by
1% agarose S (Nippon Gene, Japan) gel electrophoresis and
stained with ethidium bromide. The products were purified
for sequencing using a FastGene Gel/PCR Extraction Kit
(NIPPON Genetics Co, Ltd., Japan), according to the man-
ufacturer’s protocol. Sequencing was performed by the
Macrogen Japan Corp. (Tokyo, Japan) with the same
primers as those used for PCR amplification.
Sequence analysis and phylogenetic reconstruction
A homology search of 18S rDNA sequence was performed by
BLAST (Altschul et al. 1990,1997) with the megablast pro-
gram from the National Center for Biotechnology Information
(NCBI, http://blast.ncbi.nlm.nih.gov/Blast.cgi). All of already
existing 44 sequences of 18S rRNA gene of superfamily
Cytheroidea Baird, 1850 and two outgroup sequences
(Neonesidea oligodentata (Kajiyama, 1913), Bairdioidea Sars,
1866, AB076615 and Heterocypris incongruens (Ramdohr,
1808), Cypridoidea Baird, 1845, EU370424) were
downloaded from GenBank at May 2019. The sequences
were aligned with MAFFT v. 7.310 (Katoh et al. 2002,2005;
Katoh and Standley 2013) using the L-INS-i algorithm. The
ambiguous regions of the aligned sequences were detected
and deleted using GBLOCKS 0.91b (Castresana 2000).
Phylogenetic analyses were performed with the maximum like-
lihood (ML) and Bayesian inference (BI) methods using in
PhyML v. 3.0 (Guindon and Gascuel 2003; Guindon et al.
2010) and MrBayes v. 3.2.2 (Ronquist and Huelsenbeck
2003), respectively. The jModelTest v. 2.1 (Darriba et al.
2012) for ML and MrModeltest v. 2.3 (Nylander 2004)forBI
were used to find the best-fit evolutionary model for the present
data set under the Akaike information criterion (AIC, Akaike
1974). For ML, the bootstrap values (Felsenstein 1985)were
calculated with 1000 replications. For the BI method, four
Markov chains were run for 1,000,000 generations and were
sampled every 100 generations. The convergence was assessed
by using Tracer v1.6 (Rambaut et al. 2014). The first 2500
samples from each run were discarded as burn-ins.
Results
Taxonomy
Subclass Podocopa Sars, 1866
Order Podocopida Sars, 1866
Superfamily Cytheroidea Baird, 1850
Family Cytheruridae Müller, 1894
Subfamily Eucytherurinae Puri, 1974 (emend. Maddocks
and Steineck 1987)
Genus Xylocythere Maddocks & Steineck, 1987
Xylocythere sarrazinae sp. nov.
http://zoobank.org/66E0D33D-CAB8-4C4F-8758-
D7E95A7CAC69.
Material examined. Holotype: adult male (UMUT
RA32930), right valve length without anterior spines
548 μm, height 247 μm, left valve length 556 μm, height
254 μm, soft parts mounted on a glass slide and valves pre-
served in a micropaleontological slide. Paratypes: 6 adult
males (UMUT RA32931–32936) and 4 adult females
(UMUT RA32937–32940).
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Type locality. The holotype specimen and the paratypes
were collected from the Grotto edifice of the Juan de Fuca
Ridge, northeast Pacific (dive J0831-S1; 47.949292, −
129.098433; depth 2196 m).
Diagnosis
Carapace, elongate-ovoid. Surface nearly smooth and covered
with numerous pore clusters. Two wedge-shaped denticles
present at mid-height on the anterior margin of each valve.
Male copulatory organ; copulatory process very short, bend-
ing dorsally; distal process, lamelliform bending ventrally
with flattened distal end and one thin small process; upper
ramus spatulate shaped; lower ramiform appendage with one
short seta located distally.
Description
Adult male
Carapace (Figs. 4,5a–d, g,6). Size difference in length and
height between left and right valves inconspicuous (Table 2).
Both left and right valves of male slightly smaller than valves
of female (Table 2;Fig.3). Elongate-ovoid outline, no
conspicuous caudal process. Surface nearly smooth and cov-
ered with numerous pore clusters (Fig. 5a, b). Simple sensil-
lum pores with rims locating on anterior and posterior region
and without rims locating within muri. A prominent, posteri-
orly directed postero-ventral spine present on the lateral sur-
face of each valve (Figs. 4and 5a, b). Two wedge-shaped
denticles present at mid-height on the anterior margin of each
valve (Fig. 5a). In dorsal view, carapace elongated-ovate with
greatest thickness located slightly behind mid-length.
Marginal infold broad (Fig. 5c, d). In interior view, numerous
pore clusters visible (Fig. 5c, d). Adductor muscle scars four
in vertical row (Figs. 4and 6h). Hingement modified
merodont-entomodont (Fig. 6a, b); left valve with deep
sockets as anterior and posterior elements (Fig. 6c, e); right
valve with kidney-shaped prominent terminal teeth as anterior
and posterior elements (Fig. 6d, f); several crenulations devel-
oping at both ends of the median elements (Fig. 6c–f); middle
part of median elements smooth bar.
Antennula (Fig. 7a). Six articulated podomeres, slen-
der. First podomere bare. Second podomere with one
seta on middle of posterior margin and setulae on ante-
rior margin. Third podomere with one setulous seta on
antero-distal end and setulae on anterior margin. Fourth
podomere with two setae on antero-distal end and one
Fig. 4 External view of valves of Xylocythere sarrazinae sp. nov., male, holotype (UMUT RA32930). ainternal lateral view of left valve; binternal
lateral view of right valve. Scale bar 100 μm
Fig. 3 Scatter plots of valves of Xylocythere sarrazinae sp. nov. from the type locality. Triangle and circle indicate male and female, respectively
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seta on postero-distal end. Fifth podomere with three
setae on antero-distal end and one seta on postero-
distal end. Sixth podomere with two setae and one blunt
tipped seta (aestetasc) on distal end.
Antenna (Fig. 7b). Five articulated podomeres. First
podomere (basis) with one long four-segmented exopodite
(spinneret seta). Second (first endopodite) podomere with
two setae on postero-distal end. Third (second endopodite)
podomere with two setae on posterior end. Fourth podomere
(third endopodite) with one slender spatulate seta on lateral
surface of proximal part, one seta in middle of anterior margin,
and one short stout seta on postero-distal part. Fifth (fourth
Fig. 5 Scanning electron microscope images of valves of Xylocythere
sarrazinae sp. nov. a,bmale paratype (UMUT RA32931); c,dmale
paratype (UMUT RA32932); e,ffemale paratype (UMUT RA32937);
gmale paratype (UMUT RA32933); hfemale paratype (UMUT
RA32938): aexternal lateral view of right valve; bexternal lateral view
of left valve; cinternal lateral view of right valve; dinternal lateral view of
left valve; eexternal lateral view of right valve; fexternal lateral view of
left valve; gdorsal view of carapace, a posteriorly directed postero-ventral
spine of both valves are broken; hdorsal view of carapace. Scale bar
100 μm
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Fig. 6 Scanning electron microscope images of valves of Xylocythere
sarrazinae sp. nov., internal lateral view, male paratype (UMUT
RA32932). aHingement of left valve; bhingement of right valve; c
posterior element of left valve; dposterior element of right valve; e
anterior element of left valve; fanterior element of right valve; g
internal view of pore clusters; hadductor muscle scars. Scale bars
100 μm(a,b), 50 μm(c–h)
Table 2 Dimension of valves of
Xylocythere sarrazinae sp. nov.
from the type locality
Length (μm) Height (μm)
Mean Observed range Number Mean Observed range Number
Male RV 542 528–549 7 257 247–263 7
LV 542 530–556 6 262 254–267 6
Female RV 557 541–576 12 272 266–280 12
LV 555 538–578 10 277 270–284 10
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Fig. 7 Xylocythere sarrazinae sp. nov. a,bmale holotype (UMUT
RA32930); c–fmale paratype (UMUT RA32932); g–jmale paratype
(UMUT RA32934). aAntennula; bantenna; cmandibula; d
mandibula, first podomere of endopodite; emandibula, coxal endites; f
maxillula, branchial plate, and refluxed setae; gmaxillula, palp, and
endites (without setae); hmaxillula, dorsal endite; imaxillula, middle
endite; jmaxillula, ventral endite. Abbreviations and numbers at tips of
setae indicate the segments of insertion: 1en to 4en, first to fourth
endopodite; 4 to 6, fourth to sixth podomere. Scale bar 50 μm
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Fig. 8 Xylocythere sarrazinae sp. nov. a–cmale paratype (UMUT RA32932); d,emale paratype (UMUT RA32935). afifth limb; bsixth limb; c
seventh limb; dbrush-shaped organ; ehead capsule in left lateral view. Scale bar 50 μm
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endopodite) podomere with one short simple postero-distal
seta and one stout distal claw.
Mandibula (Fig. 7c–e). Coxa with one long setulous dorsal
seta. Coxal endite consisting of eight teeth (Fig. 7e). Palp
consisting of four podomeres. First podomere (basis) with
one long seta (exopodite) near proximal end and one long seta
on ventro-distal end (Fig. 7d). Second podomere (first
endopodite) with three setae ventro-distal end. Third
podomere (second endopodite) with two setae on ventro-
distal end and four setae on dorsal middle margin. Fourth
podomere (third endopodite) with two setae on distal end.
Maxillula (Fig. 7f–j). Branchial plate (exopodite) with 15
plumose setae and two reflexed setae (Fig. 7f). Basal
podomere with one palp (endopodite) and three endites (Fig.
7g). Palp consisting of two articulated podomeres: first
podomere (first endopodite) with five distal setae; second
podomere (second endopodite) very small, with two distal
setae (Fig. 7g). Endites: dorsal one with five setae (Fig. 7h);
middle one withfour setae (Fig. 7i); ventral one with five setae
(Fig. 7j).
Fifthlimb(Fig.8a). Four articulated podomeres. First
podomere with one setulous and one stout postero-lateral se-
tae, one long antero-lateral seta and two antero-distal setae.
Second podomere with one short antero-distal seta. Third
podomere bare. Fourth podomere with one distal claw.
Sixth limb (Fig. 8b). Four articulated podomeres. First
podomere with two setulous setae on anterior middle margin,
one stout postero-lateral seta, and one antero-distal seta.
Second podomere with one antero-distal seta. Third podomere
bare. Fourth podomere with one distal claw.
Seventh limb (Fig. 8c). Four articulated podomeres. First
podomere with one setulous antero-distal seta. Second
podomere with one setulous antero-distal seta. Third
podomere bare. Fourth podomere with one long distal claw
with small spines on distal area.
Brush-shaped organ (Fig. 8d). Consisting of two branches
each with 8 setae on distal margin.
Head capsule (Fig. 8e). Subcircular in lateral view. One
paired rake-shaped structure in atrium space.
Male copulatory organ and posterior body (Fig. 9a). Basal
capsule in lateral view subsquare tapering distally. Copulatory
process very short, bending dorsally (cp). Distal process (dp),
lamelliform bending ventrally with flattened distal end and one
thin small process. Upper ramus (ur) spatulate shaped. Lower
ramiform appendage (lra) with one short seta originating distal-
ly. Furca with two setulous setae.
Fig. 9 Xylocythere sarrazinae sp. nov. amale copulatory organ and posterior body, holotype (UMUT RA32930); bfemale copulatory organ and
posterior body, paratype (UMUT RA32937). cp copulatory process, dp distal process, lra lower ramiform appendage, ur upper ramus. Scale bar 50 μm
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Adult female
Carapace (Fig. 5e–h). Both left and right valves of
female slightly larger than valves of male (Table 2;
Fig. 3).
Female copulatory organ and posterior body (Fig.
9b). Sclerotized framework of paired genital openings
circular (right genital opening shown in figure).
Posterior body with one stout long and two medium
setulous setae on ventral margin, and post-abdominal
bristle with rows of setulae.
Distribution
Only recorded from the type locality.
Fig. 10 aMaximum likelihood (ML) tree based on 18S rDNA sequences
using the GTR + I + G model of nucleotide substitution. The number of
branches indicates bootstrap value (ML) and posterior probabilities
(Bayesian inference). Scale bar indicates substitutions per site. The clade
including Xylocythere sarrazinae sp. nov. indicated by gray box; bThe
cladogram of clade including X. sarrazinae sp. nov. extracted from Fig.
9a. Scanning electron microscope image shows left valves in external
view: the upper row, X. sarrazinae sp. nov., Cytheropteron sp.,
Semicytherura sagittiformis Yamada & Tanaka, 2011; the lower row,
Paracytherois chukchiensis Joy & Clark, 1977, Obesostoma obesum
(Schornikov, 1974)
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18S rDNA sequence From holotype (UMUT RA32930),
1792 bp of the 18S rRNA gene sequence of Xylocythere
sarrazinae sp. nov. was obtained and is available in the
DNA Data Bank of Japan/European Molecular Biology
Laboratory/NCBI databases under the accession number
LC380020.
Etymology The new species is named in honor of Dr. Jozée
Sarrazin (Ifremer: Institut Français de Recherche pour
l’Exploitation de la Mer) for her longtime contribution to
deep-sea research and particularly to vent ecology.
Molecular phylogenetic analysis The alignment dataset of 45
sequences of Cytheroidea and two out-groups contained
1452 bp, including 488 variable sites. jModelTest identified
GTR + I + G (proportion of invariable sites= 0.45, gamma
shape = 0.50) as the best-fit model under AIC (Akaike 1974).
The molecular phylogenetic analysis performed in this study
basedon18SrDNAsequences indicates that the family
Cytheruridae and subfamily Cytherurinae may be
paraphyletic. Species of Cytherurinae join the same clade as
Paradoxostomatidae, moderately supported by bootstrap val-
ue (79) and Bayesian posterior probability (1.00) (Fig. 10).
Although, we newly include Cytheroisinae sp. as representa-
tives of subfamily Cytheroisinae (family
Paradoxostomatidae), general topology was already demon-
strated by previous molecular phylogenetic analyses
(Yamaguchi 2003). Our analyses showed that Xylocythere
sarrazinae sp. nov. (Eucytherurinae) is the most basal of all
included cytherurids with strong nodal support (bootstrap val-
ue = 100, Bayesian posterior probability = 1.00).
Discussion
Xylocythere sarrazinae sp. nov. is easily distinguished from
all described species of Xylocythere except for
X. pointillissima Maddocks & Steineck, 1987. The surface
ornamentation of Xylocythere sarrazinae sp. nov. is weak
and smooth, in contrast with that of X.turnerae Maddocks
& Steineck, 1987, X.rimosa Maddocks & Steineck, 1987,
X. tridentis Maddocks & Steineck, 1987, X.vanharteni
Maddocks, 2005, X.producta Colalongo & Pasini, 1980,
and X.carpathica Szczechura, 1995, which all show distinctly
reticulated surface ornamentation on their carapaces. Other
small differences also exist between Xylocythere sarrazinae
sp. nov. and the seven other species cited above, as described
in the following sentences. (1) The morphology of the male
copulatory organ differs between X. turnerae and
X. sarrazinae sp. nov. in that the outline of the basal capsule
is subcircular in the former species, while it is subsquare in the
latter; the upper ramus is conical in the former species and
spatulate in the latter; and the tip of the distal lobe is tapered
distally in the former species, while it is flattened in the latter.
(2) Xylocythere rimosa differs from X. sarrazinae sp. nov.
because it has a fairly large carapace that is more coarsely
reticulated on its exterior surface. (3) Xylocythere tridentis
has three large, wedge-shaped denticules located on the ante-
rior margin of the carapace, while X. sarrazinae sp. nov. has
only two denticules there that are much smaller. (4)
Xylocythere vanharteni has a large, broad, sinuously curved
upper ramus on the male copulatory organ, while the shape of
upper ramus is spatulate in X. sarrazinae sp. nov. (5, 6) The
two fossil species, Xylocythere producta and X.carpathica,
have much more elongated, wedge-shaped carapaces in lateral
view compared to that of X. sarrazinae sp. nov. (7) Finally,
Xylocythere sarrazinae sp.nov.hasasimilarmorphologyto
that of X. pointillissima Maddocks & Steineck, 1987, which
was described from an experimental wood-fall located off
Sainte Croix (Virgin Islands, USA). However, Xylocythere
sarrazinae sp. nov. and X. pointillissima can be distinguished
based on the following characters: the outline of the basal cap-
sule is subsquare in the former species versus subcircular in the
latter; the upper ramus is spatulate in X.sarrazinae sp. nov.
versus conical in X. pointillissima; the tip of the distal lobe of
the male copulatory organ is flattened in the former species
versus rounded in the latter; and the number of setae on the
maxillula branchial plate is higher in former species than that
in the latter (15 versus 12, respectively). In addition, the overall
size of X.sarrazinae sp. nov. exceeds that recorded for
X. pointillissima at all three locations (Maddocks and
Steineck 1987). Their spatial distributions also differ, as the
former species was found in the northeast Pacific at 2196 m
depth, while the latter was found in the western Atlantic at
4000 m depth.
In addition to Xylocythere sarrazinae sp. nov., we found
another species of ostracods in the samples, which was
Euphilomedes climax Kornicker, 1991 (Myodocopa:
Philomedidae). The type locality of E. climax is the
Upper Magic Mountain Vent located at 49° 46′N, 130°
116′W on the Explorer Ridge, northeast Pacific at a depth
of 1700 m. Euphilomedes climax was also previously
found on the Juan de Fuca Ridge, at the Long Time
Observatory Vent, Endeavor segment (2250 m) and at the
Hammond’s Hell Vent, Axial Seamount (1570 m)
(Kornicker 1991),butitwasreportedfromtheGrottoed-
ifice for the first time in the present study.
The subfamily Eucytherurinae that includes the genus
Xylocythere is characterized by the presence of pore clusters
on the carapace (Maddocks and Steineck 1987). These pore
clusters were initially defined by Maddocks and Steineck
(1987). The occurrence of bacterial flocks around the exterior
surface of pore clusters of Xylocythere was first described by
van Harten (1993), Fig. 2A, C-D, G-I). These authors consid-
ered that it could represent an “exosymbiosis.”They also pro-
posed that the pore clusters may contribute to the absorption
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of oxygen. In our new species X.sarrazinae sp. nov., multiple
spherical structures were observed into the internal openings
of the pore clusters, but only in one specimen (Fig. 6g). The
shape and size (approximately 1.5 μm in diameter) of these
structures were similar to those of the chemosynthetic bacteria
observed to be symbionts in other invertebrates (Cavanaugh
et al. 1981;Cavanaugh1983; Van Dover 2002). Additional
samples would be required to verify the potential links be-
tween X.sarrazinae sp. nov. and such bacteria.
Finally, our phylogenetic analysis based on 18S rDNA
sequences showed that Xylocythere sarrazinae sp. nov.
(Eucytherurinae) is the most basal species of cytherurids,
with strong nodal support for this conclusion (bootstrap
value = 100; Bayesian posterior probability = 1.00). This
result supports the taxonomic arrangement of there being
three subfamilies within the family Cytheruridae
(Cytherurinae, Cytheropterinae, and Eucytherurinae), as
proposed by Maddocks and Steineck (1987) and Mazzini
and Gliozzi (2000), rather than two (Cytherurinae and
Cytheropterinae), as proposed by Whatley and Boomer
(2000). The fossil record of Cytheruridae extends back to
the early Mesozoic or possibly the latest Permian. Species of
the extant genera Eucytherura (Eucytherurinae) and
Cytheropteron (Cytheropterinae) are known from the
Triassic and Jurassic, respectively (Whatley and Boomer
2000). The basal position of Xylocythere sarrazinae sp. nov.
in the molecular phylogenetic analysis performed in this study
supports the hypothesized ancient origin of Eucytherurinae.
Although our phylogenetic analysis is preliminary in nature
because it was based on a single gene (18S) and limited taxon
sampling, we used all of the available data that could possibly
reconstruct the subfamily level phylogeny within Cytheroidea
at the present time. The accumulation of more genetic data
than just 18S sequences and increased taxon sampling will
allow the phylogenetic relationships within this family to be
revealed more rigidly.
Acknowledgments The authors thank the captain and crew of the R/V
Thomas G. Thompson and the staff of Ocean Networks Canada and
ROV’sJason pilots during the “Ocean Networks Canada Expedition
2015: Wiring the Abyss”cruise. We thank also Kim Juniper and the
government of Canada in obtaining of works permit to study in
Canadian waters (XR281, 2015). We are also grateful to Thomas Day
for his assistance in sample sorting and Akira Tsukagoshi for providing
the research facilities for taxonomy and molecular work. This research
was part of Yann Lelièvre PhD thesis supervised by Legendre, P.
(Université de Montréal) as well as Mariolaine Matabos and Jozée
Sarrazin (Université de Bretagne Occidentale/Ifremer).
Funding This study was funded by the grants from the Japan Society for
the Promotion of Science for Young Scientists (No. 263700) (to HT), the
Research Grants Council of the Hong Kong Special Administrative
Region, China (project codes: HKU 17306014, HKU 17311316) (to
MY), Ifremer internal funds and a fellowship from the “Laboratoire
d’Excellence”LabexMER (ANR-10-LABX-19) (to YL) and NSERC
research grant to Pierre Legendre.
Compliance with ethical standards
Conflict of interest The authors declare that they have no conflict of
interest.
Ethical approval All applicable international, national, and/or institu-
tional guidelines for the care and use of animals were followed by the
authors.
Sampling and field studies All necessary permits for sampling and
observational field studies have been obtained by the authors from the
competent authorities and are mentioned in the acknowledgements.
Data availability statement Sequence data of Xylocythere sarrazinae
sp. nov. that support the findings of this study have been deposited in
GenBank with the accession codes LC380020 (https://www.ncbi.nlm.
nih.gov/nuccore/LC380020.1).
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