Hydroids ( Cnidaria : Hydrozoa : Leptothecata and Limnomedusae ) on 2011 Japanese tsunami marine debris landing in North America and Hawai ‘ i , with revisory notes on Hydrodendron Hincks , 1874 and a diagnosis of Plumaleciidae , new family

Twenty-eight species of hydroids are now known from Japanese tsunami marine debris (JTMD) sent to sea in March 2011 from the Island of Honshu and landing between 2012 and 2016 in North America and Hawai‘i. To 12 JTMD hydroid species previously reported, we add an additional 16 species. Fourteen species (50%) were detected only once; given the small fraction of debris sampled, this suggests that the diversity of the total arriving hydroid fauna was likely larger. Our ongoing studies provide the first documentation of these species being rafted from one continental margin to another. Plumalecium plumularioides (Clark, 1877) is newly reported for the Japanese hydroid fauna. Fourteen species (52%), held to be either naturally amphi-Pacific or possibly introduced by ships at some earlier date, were already known from the Pacific coast of North America. We suggest that Obelia griffini Calkins, 1899, as represented in the JTMD fauna, may be a North Pacific oceanic neustonic species. We propose that Hydrodendron mirabile (Hincks, 1866) and its congeners be included in the family Phylactothecidae Stechow, 1921, here emended. We establish a new family, Plumaleciidae Choong and Calder, 2018, to accommodate the genus Plumalecium Antsulevich, 1982.


Introduction
The Great East Japan Earthquake and Tsunami of March 11, 2011 sent into the North Pacific Ocean a vast field of floating debris derived from the Tōhoku coastline of northeast Honshu.Rafted objects with living Japanese species began arriving on the shores of North America in the spring and summer of 2012 and in the Hawaiian Islands in the fall of 2012 (Carlton et al. 2017).One of the most common groups of organisms in the biofouling communities on this debris was hydroids.Choong and Calder (2013) reported on the presence of the Japanese hydroid Sertularella mutsuensis Stechow, 1931 on a large dock lost during the tsunami from the Port of Misawa (Aomori Prefecture) that landed 14 months later, in June 2012, on the Oregon coast.Calder et al. (2014) reported upon collections of 11 additional coastal thecate species (and one likely pelagic hydroid, Obelia griffini Calkins, 1899) from biofouling on tsunami debris intercepted in 2012 and 2013 landing in Oregon and Washington.
We report here on additional collections of hydroids recovered from Japanese tsunami marine debris collected in Washington, Oregon, California, andHawai'i between 2012 and2016, and analyze the total hydroid fauna found to date.

Morphological analyses
Samples were obtained from JTMD objects (identified as such through multiple lines of evidence; see Carlton et al. 2017) landing in North America and the Hawaiian Islands (Supplementary material Table S1).Each object was assigned a unique identification number preceded by JTMD-BF-(Japanese Tsunami Marine Debris-BioFouling-). Specimens retrieved from the field were either preserved directly in 95% ethanol, or frozen and transferred into ethanol at a later date.All specimens studied here are deposited in the collections of the Invertebrate Zoology Section, Department of Natural History, Royal Ontario Museum (ROMIZ) and the Royal British Columbia Museum (RBCM/BCPM).The classification and implied relationships of hydroids adopted here generally follows Leclère et al. (2009), Maronna et al. (2016), and Cunha et al. (2017).Species descriptions are provided where warranted.Several taxa in this study were described and illustrated in our previous work (Calder et al. 2014).

Genetic analyses
Three approximately 20 × 20 cm scrapings were taken from the sides of a floating dock (JTMD-BF-1) originating from the Port of Misawa, Aomori Prefecture, which landed on the central Oregon coast in early June 2012 (Table S1).The samples were preserved in 70% ethanol and sent to the Geller Laboratory at Moss Landing Marine Laboratories, Moss Landing, California USA.The ethanol was later decanted and samples were rinsed with distilled water, drained, and homogenized in an IKA (Wilmington, NC, USA) A11 analytical mill.10 g of homogenate were used in a MoBio PowerSoil DNA extraction kit (Qiagen, Germantown, Maryland, USA).Genomic DNA was quantified using Nanodrop ND-1000 (ThermoFisher, Waltham, Massachusetts USA). 5 ng of each total DNA extraction were amplified in PCR cocktails comprising a final concentration of 1 × Green Go Taq Master Mix, 0.2 mg mL -1 BSA, 1.5 mM MgCl 2 , and 0.2 µM of each primer in a 50 µL reaction.We used primers jgHCO2198 and jgLCO1490 from Geller et al. (2013).Reaction conditions consisted of an initial 3 minute melt at 94 °C, followed by 32 cycles of a 1 minute at 95 °C, 45 seconds at 47 °C, and 90 seconds at 72 °C.PCR amplicons were viewed on a 2% agarose gel stained with ethidium bromide.Samples were purified with 1.4 × the sample volume of Agencourt Ampure (Brea, California USA) beads, according to the manufacturer's protocol.
Samples were quantified using Picogreen High sensitivity DNA assay according to the manufacturer's protocol (Qiagen).100 ng of sample were fragmented with the IonXpress Ion Shear enzyme kit (Thermo-Fisher).Samples were purified with 1.4 × the sample volume of Agencourt Ampure beads.Samples were then ligated with IonXpress barcodes and sequencing adapters, size selected for ca.400 bp using an e-gel cassette, purified once more with 1.4 × Ampure beads.Samples were quantified using the Agilent (Santa Clara, California, USA) Bioanalyzer high sensitivity chip assay and combined into an equimolar pool.Samples were run using the Ion Torrent 400 bp sequencing kit and v314 chip according to the manufacturer's protocol, yielding 500,000 reads passing filter.Reads were trimmed of primers and clustered into groups using a 95% similarity threshold using the software package Geneious v9 (Biomatters, Auckland, New Zealand).
Consensus sequences were compared to Genbank for any matches to COI sequences annotated as derived from Hydrozoa.Candidate novel sequences were aligned with hydroid sequences downloaded from Genbank, aligned with MAFFT (Katoh and Standley 2013).Maximum likelihood trees were constructed with FastTree (Price et al. 2010) from within Geneious.
Samples of individual hydroids collected from a wide variety of JTMD objects (below) were also submitted for genetic analysis (by analytical techniques as described in McCuller et al. 2018), but failed to yield useful sequences.

Results
To the 12 hydroid species previously identified on JTMD and believed to originate from the Japanese coast (based upon evidence reviewed in Calder et al. 2014, and further detailed in the Discussion below), we now add an additional 16 species (Table S2).Two of the 12 taxa reported earlier only to genus, Phialella quadrata (Forbes, 1848) and Plumularia caliculata Bale, 1888, are now resolved to species level based upon the availability of additional material.Campanulariid hydroids (sensu lato, here treated in the families Campanulariidae, Clytiidae, and Obeliidae) are the most diverse group in the JTMD hydroid fauna.
In addition to these species, Calder et al. (2014) found two anthoathecate species (?Bougainvillia muscus (Allman, 1863) and Stylactaria sp.); additional athecate hydroids are in hand, and these will be treated separately in a subsequent report.
Fourteen of the 28 species collected from JTMD objects (50%) were detected only once (three species reported earlier by Choong and Calder (2013) and Calder et al. (2014), and 11 additional species newly reported herein) (See Table S2).Forty-three percent (six) of these unique species arrived in 2015, in concert with a peak of detected overall JTMD diversity (Carlton et al. 2017).
Twenty-four species (89% of the JTMD hydroid fauna) were already reported from Japan (Table S2); two species, Hydrodendron gracile and Plumalecium plumularioides represent new records for the country (one reported earlier by Calder et al. 2014), and two, not taken to species level, Clytia sp. and Antennella sp. are of uncertain geographic distribution.In turn, 14 species (52%) already known from the North East Pacific Ocean (Table S2), are held to be either naturally amphi-Pacific in distribution or possible ship-borne introductions.Twelve taxa are unknown from the Pacific coast of North America.However, they are not treated here as new records for the Eastern Pacific because they are present only on intercepted debris and are not yet known to have established populations.Six hydroid species (Orthopyxis caliculata (Hincks, 1853), Obelia dichotoma (Linnaeus, 1758), Amphisbetia furcata, Plumularia setacea, and Plumalecium plumularioides) were found on debris arriving in the Hawaiian Islands; two of these (O.dichotoma and P. setacea) were previously known from Hawai'i, recognized there as introduced and cryptogenic, respectively (Carlton and Eldredge 2009).
Notably, species of Clytia Lamouroux, 1812 were absent on JTMD arriving in 2012 and 2013, but began to appear in 2014.Clytia sp., whose affinities are discussed below, was found once (BF-363) on an object landing in Washington during early 2015.Clytia linearis (Thornely, 1900) was discovered on a derelict vessel (BF-538) arriving in Oregon in spring 2016.Clytia hemisphaerica (Linnaeus, 1767) appeared on six items in Oregon and Washington between 2014 and 2015.Clytia linearis is a distinctive warmwater species, although Galea (2007) reported it from colder waters of the Subantarctic in the fjords region of southern Chile.Its later appearance on JTMD may be due to a longer, more circuitous route through lower latitudes before the rafted vessel became caught up in ocean currents moving north and east.Clytia sp., although currently unidentified, was accompanied by a warm-water, southern species of neustonic bryozoan, Jellyella eburnea (Hincks, 1891), also indicating a longer route through lower latitudes (McCuller and Carlton 2018).The six objects on which C. hemisphaerica arrived, however, bore no distinctive indication of their route after departure from the Tōhoku coast in March 2011.Finally, the most common hydroid in our samples was Obelia griffini.We suggest below that it may be an element of the open ocean neustonic fauna.
Details are provided below on identification, taxonomy, and geographic distribution of 24 species of neritic hydroids on JTMD, and of the putatively pelagic hydroid Obelia griffini.Four additional JTMD leptothecate species (Halecium tenellum, Hydrodendron gracile, Sertularella mutsuensis, and Sertularella sp.), not represented in the newer samples analyzed here, are recorded in Calder et al. (2014).Remarks.-Inour previous study (Calder et al. 2014) we reported (as Phialella sp.) the occurrence of a species, closely resembling P. quadrata, on a floating dock (JTMD-BF-1) from Misawa, Japan.It was compared as well with Opercularella rugosa (Nutting, 1901) and O. lacerata (Johnston, 1847).Specimens in one of our present samples (JTMD-BF-382), growing on young species of Lepas Linnaeus, 1758, had both stolonal and erect stems.Stolonal colonies of P. quadrata have been reported in other zoobenthic communities (Voronkov et al. 2010 S1) (G.Ruiz and J. Geller) based upon morphological and genetic analyses.Family Campanulariidae Johnston, 1837 Campanularia volubilis (Linnaeus, 1758) (Figure 1)  (1915).Gonothecae in C. volubilis have no neck when young (Cornelius 1995b).The shape of the hydrotheca in Hirohito's specimen appears to be morphologically closer to C. volubilis than C. groenlandica as shown by Naumov (1960), and by Schuchert (2001).The pedicel in our specimen and those of Hirohito are not as annulated as in most descriptions of C. volubilis but Cornelius (1995b) reported straight to spirally grooved pedicels in this species.
Distribution.-Japan(Fraser 1946;Yamada 1950).Fraser (1946) characterized C. volubilis as a naturally circumpolar species, widespread through the North Atlantic and North Pacific Oceans, from the Bering Sea to the Galapagos Islands in the Eastern Pacific (Fraser 1937(Fraser , 1946)), although the conspecificity of warmtemperate and tropical populations is improbable.
Following our earlier work, we retain O. caliculata as a separate species from O. integra based upon observed trophosomal characters, particularly the presence of bilaterally symmetrical hydrothecae in the former, rather than being radially symmetrical as in the latter.The validity of O. caliculata as a species has been corroborated through a re-evaluation of morphological diagnostic characters, including differential hydrothecal perisarc thickness resulting in bilateral symmetry, together with molecular analyses (Cunha et al. 2015).Our specimens correspond with Japanese material considered by Hirohito (1995) as O. caliculata (although referred by him to the genus Campanularia Lamarck, 1816).
Remarks.-We are unable to assign the limited material in hand to a known Japanese species.In many respects, our specimen corresponds to Clytia universitatis Torrey, 1904(see Fraser 1937), particularly in details of the trophosome and fascicled stem.We compared the present material to Fraser's specimen of C. universitatis from Isla Partida, Gulf of California, Mexico, in the holdings of the Royal BC Museum (BCPM 976-395-1).Some hydrothecae in our specimen are broader than those in Fraser's material and that illustrated by Torrey (1904), which are uniformly deeply campanulate, and increase in diameter very slightly from base to margin.Clytia universitatis, however, is known largely from southern California and Mexico (with reports as far north as San Francisco Bay; Fraser 1946), and the JTMD trajectories do not bring objects past these lower latitudes along the North American coast toward Washington.The absence of any other unique Eastern Pacific species on BF-363 further argues against recruitment in the eastern Pacific Ocean.

Clytia hemisphaerica (Linnaeus, 1767)
(Figure 3) Remarks.-Theoccurrence of C. hemisphaerica in JTMD samples is notable because of the presence of morphologically variable colonies.In the material examined, the colonies possess extremely long pedicels and repeated branching, but also possess distinctly annulated gonothecae, suggesting the possibility that populations settling in coastal fouling communities may change morphology as they drift for long periods of time at sea.West and Renshaw (1970) found that branching in Clytia sp. can vary in response to food and temperature conditions.Clytia hemisphaerica, along with Obelia dichotoma and O. geniculata (Linnaeus, 1758), which also occur in the JTMD samples, have been found on a wide variety of vertebrate, invertebrate and algal substrates, which phoretic habitat may facilitate dispersal through long-distance transoceanic transport (Cornelius 1982).Our samples are found on various anthropogenic substrates, overgrowing young Lepas sp., with Scruparia ambigua epizoic.Distribution.-Clytiahemisphaerica was reported from the Tōhoku region by Nishihira (1968) and from Matsuyama by Yamada (1958).This species is reported to be nearly cosmopolitan in coastal waters (Schuchert 2001), and may thus involve a species complex.
Clytia linearis (Thornely, 1900) (Figure 4)  Remarks.-Ourmaterial corresponds to the descriptions of Fraser (1938) and Lindner and Migotto (2002), with the exception of the general shape of the hydrothecal cusps, which resemble those of Clytia ?obliquaClarke, 1907 in being triangular instead of long and narrow.Material with similar cusps is described by Migotto (1996).Cornelius (1982) did not consider the angle of slope of the hydrothecal cusps to be significant, and assigned Clarke's species to C. linearis.The fold of the perisarc projecting inward into the internode lumen in the apophyseal region was also observed by Lindner and Migotto (2002).Clytia linearis is widely reported in both benthic habitats and in the open ocean on plankton, where, if the same species, it facultatively rafts and disperses as an epizooite on pteropods (Cornelius 1982(Cornelius , 1987)).
Clytia linearis is one of two species represented in the JTMD hydroid fauna apparently acquired by tsunami objects south of the Boso Peninsula.While many of the other species considered here are regarded as wide ranging from lower-latitude warm climates to sub-boreal if not boreal waters, C. linearis is considered a species of warmer waters (Kirkendale and Calder 2003;Calder 2013).JTMD-BF-538, a Japanese vessel washing ashore in spring 2016 in southern Oregon, also had aboard warmer-water western Pacific bivalves, in addition to a typical colder-water fauna representative of the tsunami strike zone of the Tōhoku coast.Many JTMD objects were transported by coastal currents to southern Japan and the South China Sea and acquired species typical of warmer, southern waters, before being reengaged by ocean currents and being swept north and east to North America (Carlton et al. 2017).Similarly, Boero et al. (2005) recorded the possible colonization and invasion of colder European waters by C. linearis as an alien species.Distribution.-Japan(Yamada 1959;Hirohito 1995).Originally described from Papua New Guinea, it is widely reported from subtropical and tropical waters of the Atlantic, Pacific, and Indian Oceans (Kirkendale and Calder 2003;Calder 2013), and may thus also represent a species complex.Bouillon et al. (2004) suggested that C. linearis is a Lessepsian migrant into the Mediterranean through the Suez Canal.Material.-Oregon,on float, several pedicels with hydrothecae, without gonothecae (JTMD-BF-18), ROMIZ B4200; Oregon, on pallet, stem fragments, with gonothecae (JTMD-BF-24), ROMIZ B4190; Hawai'i, on I-beam, stems arising from stolon, no hydrothecae or gonothecae (JTMD-BF-72), ROMIZ B4197; Washington, on post-and-beam wood, colony, Remarks.-Obeliadichotoma remains a problematic taxon due to a high degree of morphological variation in the characters used to delimit the species (Cornelius 1982(Cornelius , 1995b;;Calder 2013).Nevertheless, although the non-monophyly of O. dichotoma remains problematic (Cunha et al. 2017), some widespread populations appear to be identical based upon nematocyst types and isoenzyme patterns (Ӧstman 1982) and hydranth characters (Cornelius 1987).Despite intraspecific variability, branching pattern and shape of the hydrothecal rim remain useful in delimiting hydroids attributed to the O. dichotoma species complex from its congeners such as O. geniculata, O. longissima and O. griffini (Kubota 1981(Kubota , 1999;;Calder et al. 2014) from Japanese waters.Specifically, we assigned our specimens to O. dichotoma based on the presence of hydrothecae with polyhedral margins, and with walls that are polygonal in cross-section, rather than round as in O. griffini (Cornelius 1995b;Calder et al. 2014).Obelia dichotoma is also less profusely branched than O. griffini (Fraser, 1914).Specimens referable to O. dichotoma also occurred on a test panel recovered from the Tōhoku Coast in August 2016 (RBCM 017-00023-001).
Distribution.-Japan,where it is the most widely distributed species of Obelia (Kubota 1999).A likely cosmopolitan species complex.
Obelia geniculata (Linnaeus, 1758) (Figure 6)  (Yamada 1958;Hirohito 1995;Kubota 1999) and elsewhere in having thickened perisarc of the stem, only one annulation between the internodes of the stem, and the lack of branching.Our samples contain remnants of coenosarc, but the gonothecae were empty, and the hydrothecal margins showed some damage from weathering the elements.

Obelia griffini Calkins, 1899
Obelia griffini Calkins 1899: 357, pl. 4, figs.Obelia griffini was found on three of four stranded objects sampled in our previous study (Calder et al. 2014).It is also the most common Obelia species found in the present study, and the most abundant hydroid in the JTMD material.Distribution.-NorthPacific Ocean (see discussion, below).
Occasionally thickening of perisarc below diaphragm, especially on adcauline side, forming pseudodiaphragm.Gonothecae not present.Remarks.-Althoughgonothecae are absent, the trophosomes in our material correspond most closely with accounts of Halecium delicatulum from Japan (Hirohito 1995) and elsewhere in having erect monosiphonic stems, irregular branching, oblique nodes twisted in opposite directions on successive internodes, and hydrothecal margins everted.Additionally, in our material, the primary hydrophore is short or almost sessile, with the hydrothecal rim very close to touching the internode supported by the apophysis of the hydrophore-bearing internode.Although variable, the length of the primary hydrophores and the strongly everted hydrothecal rim primarily characterize H. delicatulum (Vervoort and Watson 2003).A pseudodiaphragm was observed in several hydrothecae (Leloup 1938, as Halecium flexile var.japonica; Ralph 1958;Hirohito 1995).Hirohito (1995) reported both monosiphonic and polysiphonic colonies from Japan.
The vessel on which H. delicatulum was found also bore a southern species of open ocean, neustonic bryozoan, Jellyella eburnea, indicating that this raft passed through lower latitude waters in the North Pacific before arriving in Washington (McCuller and Carlton 2018).Distribution.-Japan(Hirohito 1995); considered circumglobal in tropical, subtropical and boreal waters (Vervoort and Watson 2003).Described originally from Dunedin harbor, New Zealand, it may be introduced to the southwest Pacific (Hewitt et al. 2004), or may represent a global species complex (Schuchert 2005;Galea et al. 2014).(Nutting 1901(Nutting , 1904)), but kept the two species separate based on trophosomal differences (A.inconstans being less robust), and the gonosome (greater variation in A. inconstans, although he did not examine the gonothecae).Antsulevich (1987) provided a diagnosis for the gonothecae of A. costata and its congeners: gonothecae oval, short neck, small pedicel; aperture circular, without cusps or internal projections; gonothecal wall wavy, 4-6 longitudinal ribs; gonothecae may be irregular due to deformation, without the neck, and underdeveloped or curved ribs.According to Antsulevich, the variability in the gonosome of A. inconstans is due to deformation when the gonothecae are densely packed.
Remarks.-The occurrence of Amphisbetia furcata originating in Japan was discussed in our previous study (Calder et al. 2014).We follow Antsulevich (1987) in regarding A. furcata originally described from San Francisco Bay, California, and A. pacifica Stechow, 1931, type locality Mutsu Bay, Japan, as conspecific.Yamada (1959) distinguished A. pacifica from A. furcata by the presence of two distinct spiral constrictions at the base of the stem, and in having gonothecae which are not globular but elongatedoval with indistinct shoulders.However, illustrations of A. furcata from California by Torrey (1902) and of A. pacifica from Japan by Hirohito (1995) show that the gonothecae of both putative species to be very similar, and correspond to those present in our material.The spiral twists at the base of the stem described by Yamada are clearly visible in Fraser's specimen of A. furcata (BCPM 976-652-1) (Fraser 1937 as Sertularia furcata) examined by one of us (HHCC) as well as in our material.Distribution.-KurileIslands to the Sea of Japan, Japan, and Yellow Sea (Antsulevich 2011); in northeast Pacific from British Columbia to Ecuador (Fraser 1937(Fraser , 1946)).
Free part approximately 88 µm, gutter-shaped, not tubular, foramen to hydrotheca visible.Corbula three times longer than height, with one basal hydrotheca, 9-15 pairs of unfused ribs, with narrow openings in between.
Remarks.-Identification of Aglaophenia aff.pluma is difficult due to the lack of specific diagnostic characters (Cornelius 1995a), and 16S rRNA analyses of north-east Atlantic and west Mediterranean specimens strongly suggests that A. pluma is likely a species complex including A. pluma, A. tubiformis Marktanner-Turneretscher, 1890, and A. octodonta Heller, 1868 (Leclère et al. 2009;Moura et al. 2012).These three species show extremely low levels of 16S sequence divergence, and probably reflect intraspecific variation, with the name A. pluma having priority (Moura et al. 2008).Aglaophenia tubiformis was recorded in the eastern Atlantic and the Mediterranean Sea and A. octodonta from the Mediterranean and adjacent Atlantic (Svoboda and Cornelius 1991).Assessment of the true distribution is difficult (Cornelius 1995b).Our material closely corresponds with Fraser's specimen from England (BCPM 976-797-1) and the descriptions of A. pluma by Cornelius (1995b), Fraser (1937), and Svoboda and Cornelius (1991).The number of leaves reported in the corbulae of A. pluma is quite varied, ranging from nine in Fraser (1937) to 5-10 (or more) by Svoboda and Cornelius (1991).Corbulae in our samples varied in length within a colony, from 9-15 leaves (Figure 10).Distribution.-Aglaopheniapluma was reported from Japan as A. pluma var.dichotoma M. Sars, 1857 (Rees and Thurfield 1965); the variety was included in A. pluma by Svoboda and Cornelius (1991).Fraser (1946) noted records from Vancouver Island and Mexico, both of which would require confirmation.
The true distribution of this European boreal species remains unclear, as reliable records from elsewhere have yet to be confirmed (Svoboda and Cornelius 1991).
(Figure 9B) Material.-Oregon,on vessel, colony arising from hydrorhiza, without gonothecae (JTMD-BF-210), RBCM 017-00007-001; Washington, on buoy, colony arising from hydrorhiza, without gonothecae (JTMD-BF-341), ROMIZ B4105.Description.-Unbranched,erect, monosiphonic stem arising directly from anastomosing hydrorhiza, individual hydrocauli < 10 mm long.Segmentation heteromerous; alternating transverse and oblique nodes.Basal part of stem divided into segments (two or more) divided by transverse nodes, distal-most segment with oblique node.Hydrothecate and ahydrothecate internodes present.Hydrothecae confined to middle part of internodes, cup-shaped, abcauline wall straight in side view, rim even, hydrothecal opening approximately 50° with main axis, adcauline side adnate for approximately 1/3 its length.Hydrotheca surrounded by three nematothecae: one median inferior, conical with rim of upper chamber lowered adaxially, outer side often reaching or exceeding hydrothecal base; and two laterals, placed on short apophyses, one on each side of hydrothecal aperture, not fused to hydrotheca, not reaching hydrothecal margin, two-chambered, conical with inner side lowered.No axillar nematothecae.Ahydrothecate internodes with one median nematotheca.Gonothecae not present.Remarks.-Inhaving no axillar nematothecae behind the free adcauline wall of the hydrothecae, our species differs from other Japanese species such as A. quadriaurita Ritchie, 1909(= A. variabilis Fraser, 1936 from Japan, which also has two pairs of lateral nematothecae); A. varians (Billard, 1911), with two pairs of lateral nematothecae and regular absence of median inferior nematothecae; or A. secundaria (Gmelin, 1791), with median nematothecae on the upper part of the oblique node.Antennella avalonia Torrey, 1902 reported from the west coast of North America by Fraser (1946) is likely conspecific with A. secundaria (Calder 1997;Schuchert 1997), although it is currently accepted as valid in WoRMS.Our samples were mostly devoid of coenosarc and appeared weathered.

Halopteris aff. campanula (Busk, 1852)
(Figure 11) Material.-Washington, on vessel, sections of branched hydrocauli with hydrocladia, and fragments of hydrocauli, with gonothecae (JTMD-BF-449), RBCM 017-00008-001.Hirohito (1995) and Schuchert (1997) in the number and position of the nematothecae, shape and position of the gonothecae and associated pedicel, hydrothecal shape and thickening of the abaxial wall of the hydrotheca.However, it differs in the following respects: the outer wall of the lateral nematothecae lacks the distinct emargination over half its height (spanner-type) as described in Schuchert (1997), i.e., the apical chamber is conical, not globular; the gonothecae are slightly smaller in our material than in Schuchert (1997) at 900 µm.We are unable to determine if the branched colony is polysiphonic from the available material.
Distribution.-Japan:Sagami Bay south to Kagoshima Prefecture (Hirohito 1995); widespread through the Indo-West Pacific to the Red Sea, as well as Australia and New Zealand (Schuchert 1997).As JTMD-BF-449 did not have otherwise a clear signature of warmer-water, southern species, this vessel may have proceeded along slightly south of the Boso Peninsula in order to acquire this hydroid, which has not yet been reported from the Tōhoku coast.Material.-Washington,on vessel, colony fragment, remnants of coenosarc in hydrothecae and nematothecae, no gonothecae (JTMD-BF-40), ROMIZ B4234; Oregon, on vessel, several broken plumes attached to hydrorhiza, without gonangia (JTMD-BF-533), RBCM 017-00021-002.
Remarks.-This material corresponds in morphology to the specimen examined previously (Calder et al. 2014: 434, figures 5e-f) through its hydrothecae with a convex abaxial wall, which distinguishes it from P. setacea (Linnaeus, 1758).In P. setacea the abcauline wall is straight or occasionally curved inward in the middle, never curved outwards (Schuchert 2013).Although the previous specimen could not be differentiated with certainty from Plumularia lagenifera Allman, 1885 due to its condition and the lack of gonothecae, the substrate and collection date of that sample (the floating dock from Misawa, Honshu, Japan, JTMD-BF-1, 05 June 2012) pointed to P. caliculata of Japanese origin.The present material also supports the identification of this species as P. caliculata; in the cauline internodes in our samples we observed two nematothecae associated with the apophysis bearing the hydrocladium.While apophyses with two nematothecae were observed occasionally in northeastern Pacific and Atlantic P. setacea, this character seems to be invariable in P. lagenifera in the northeastern Pacific (one nematotheca only) (Schuchert 2013).As our specimens possess hydrothecae with inwardly curved abaxial wall and two apophyseal nematothecae were observed, we assign them to P. caliculata.Distribution.-Australia,its type locality; Japan, and likely Korea (Calder et al. 2014).
Remarks.-In our previous study (Calder et al. 2014) we reported Plumularia setacea from JTMD.The present material also corresponds morphologically to other accounts of P. setacea in having a straight outer wall of the hydrotheca, one nematotheca associated with the apophysis bearing the hydrocladium, and a nematotheca on the ahydrothecate internode of the hydrocladia, as well as nematothecae on the internodes of the hydrocaulus (Calder 1997;Schuchert 2013).Gonothecae were observed arising from apophyses via short pedicels, fusiform in shape.Both male and female gonothecae are present.Our material was in good condition, with a significant amount of coenosarc present, partially overgrown by the bryozoan Scruparia ambigua.
Distribution.-Japan(Hirohito 1995); Pacific coast of North America from Alaska to southern California (Fraser 1937), and reported from all oceans; almost certainly a species complex (Mills et al. 2007;Schuchert 2014).
Family Phylactothecidae Stechow, 1921 Diagnosis (emended) and Systematic Discussion.-Colonies stolonal or erect, arising from creeping hydrorhiza; hydrocauli monosiphonic or polysiphonic; hydrothecae shallow to bell-shaped, sessile or pedicellate, basal region with delicate diaphragm, with or without desmocytes; hydranths usually much larger than hydrothecae, with or without an intertentacular web.Nematophores present, with variably reduced nematothecae.Gonophores fixed sporosacs; gonothecae solitary or aggregated to form a glomulus.Watson (1969) noted the need for revision of nominal genera of nematophore-bearing hydroids in Haleciidae, which was reiterated by Cornelius (1975a) who recognized the arbitrary nature of the limits of these genera.The inclusion of the genus Hydrodendron Hincks, 1874 within the family Haleciidae is indeed problematic, as shown by phylogenetic analysis using 16S as well as combined 16S, 18S, and 28S rRNA data; Hydrodendron shows a marked divergence from the Halecium species studied (Moura et al. 2008;Leclère et al. 2009;Maronna et al. 2016).Rees and Vervoort (1987) had previously noted the usefulness of gonosomal characters in separating Hydrodendron from Halecium.Hydrodendron mirabile shares the presence of nematophores and nematothecae with Plumularioidea.Maronna et al. (2016) proposed the taxon Plumupheniida (which includes the families within Plumularioidea) to accommodate H. mirabile.There is some support for the inclusion of Hydrodendron within Plumularioidea, suggesting that the presence of nematothecae in Plumularioidea and Hydrodendron is not due to convergence, and that defensive polyps (dactylozoids) were acquired only once within Macrocolonia in the ancestor of Plumularioidea (Leclère et al. 2009).Nematophorebearing haleciid species were included under Hydrodendron, Ophiodissa Stechow, 1919 andPhylactotheca Stechow, 1913 (the latter two currently included as synonyms of Hydrodendron) to accommodate forms having shallow to deeply campanulate hydrophores (Watson 1969).We propose that Phylactothecinae Stechow, 1921 be elevated to full family rank, and that Hydrodendron mirabile and its congeners are included in the family Phylactothecidae Stechow, 1921 within the superfamily Plumularioidea.
While the family name Hydrodendriidae (see Nutting 1905) exists, it is based on the genus Hydrodendrium Nutting, 1905.Phylactotheca is the type genus of the subfamily Phylactothecinae.The name is currently included as a synonym of Haleciidae, but from the evidence in Maronna et al. (2016), outlined above, this synonymy is incorrect.Although its type genus (Phylactotheca) is a junior subjective synonym of Hydrodendron, the name is not thereby invalidated under the code (ICZN Art.40.1).Under the Principle of Coordination in nomenclature, Stechow (1921) is credited as author of the family name as well as the subfamily name.Further analysis which includes the other species of Hydrodendron, and especially its type species H. gorgonoide (G.O.Sars, 1874), is required to clarify the taxonomic position of H. mirabile and its congeners, but clearly Hydrodendron is shown to be remote from Haleciidae and merits assignment to its own family.
Internodes smooth or with one basal wrinkle.Hydrotheca borne on long internode process, shallow, widening moderately towards hydrothecal opening.
The adcauline peridermal thickening or pseudodiaphragm, sometimes present near the base of the hydrophore in H. caciniformis (Hincks, 1866) (now reduced to a synonym of the present species; see Cornelius 1975a) observed by Millard (1975) and Vervoort (1959), was not mentioned by Hirohito (1995) in H. mirabile from Japan, nor was it observed in our samples.Cornelius (1975aCornelius ( , 1995b) ) considered larger colonies (in growth length) of H. caciniformis (= O. caciniformis) to be due to intra-specific population variation.Size comparisons of some characters of H. mirabile given in various accounts are summarized in Table 2. Our material corresponds to that of Hirohito (1995) in general dimensions, and in the occasional presence of secondary hydrophores.
No gonothecae were seen in our material.
Plumalecium Antsulevich, 1982 (type species: Halecium plumularioides Clark, 1877) appears referable to superfamily Plumularioidea based on trophosomal characters, notwithstanding the lack of nematothecae.We propose that the diagnosis of Plumularioidea be amended to accommodate this species lacking nematothecae.In that character it differs from all known families of plumularioids, as defined in works such as those of Cornelius (1995b), Calder (1997), Bouillon et al. (2006), Leclère et al. (2007), and Maronna et al. (2016).A new family, Plumaleciidae, is thus proposed herein to accommodate the genus.Plumalecium is currently monotypic, with P. plumularioides as its only known species.Halecium linkoi Antsulevich, 1980 resembles P. plumularioides, but it seems to differ (Antsulevich 2015: 366) in having hydrocladia that are repeatedly and consistently branched rather than being branched or unbranched, with hydrothecae in the latter case being arranged in a straight series.
Remarks.-No additional specimens of Gonionemus were recovered from the Misawa fisheries dock (JTMD-BF-1) that landed in June 2012 in central Oregon.However "Misawa 1" supported vast biofouling communities (exceeding 75 square meters), only a small portion of which was sampled, and it is thus not surprising that the small polyps of this species were not recovered.Our material aligns with the toxic clade of Gonionemus vertens from the Northwest Pacific Ocean, which is distinct from the non-toxic clade of G. vertens known from the Northeast Pacific Ocean (Govindarajan et al. 2017).
The toxic Western Pacific clade was recently introduced to New England (Govindarajan et al. 2017).

Biogeographic sources of JTMD hydroid fauna
We suggest that all of the species reported here, with the exception of Obelia griffini (discussed in detail below), originate from the coast of Japan (or, in the case of Clytia linearis discussed earlier, slightly farther south).In concert with the findings of Elvin et al. (2018) and Cordell (2018), reporting on JTMD sponges and copepods, respectively, we also found that diversity per object declined over time.As suggested by Elvin et al. (2018) and Cordell (2018), if species were being regularly acquired by JTMD after entering the coastal zone of North America or Hawai'i, there would be no reason for diversity to decline over time.Rather, this decline suggests a steady attrition of species richness per object raft originating from Japan, as would be expected from the challenges of long-term survival by coastal species rafting for years in an oceanic environment.It is possible that survival in many species may have been prolonged through resting stages (menonts).However, we also observed (in the present study and in Calder et al. 2014) large, weathered colonies with empty gonothecae in some species such as Obelia longissima, suggesting persistence of these colonies on the debris for extended periods.In addition, a number of JTMD species arriving in North America, including Orthopyxis caliculata, O. dichotoma, Amphisbetia furcata, Aglaophenia aff.pluma, and Plumalecium plumularioides, were found on debris arriving in Hawai'i.As none of these species are known from Hawai'i, their only source is the Western Pacific Ocean.Finally, as noted by Calder et al. (2014), Carlton et al. (2017), andElvin et al. (2018), if JTMD objects were being typically colonized after arrival in the Eastern Pacific, it would be highly unlikely that the only species to do so would also be those occurring in Japanese or other Western Pacific waters.We documented no hydroid species believed to be unique to North America or the Hawaiian Islands on JTMD.

Obelia griffini as a potential member of the North Pacific Oceanic Fauna
We propose that the abundant hydroid Obelia griffini may be a member of the poorly known North Pacific open ocean neustonic fauna.Obelia griffini was described from either Bremerton or Port Townsend, Washington, without habitat data, by Calkins (1899).Two species described in the same paper are now held to be synonyms of O. griffini: Obelia gracilis, "on grasses" from Scow Bay, Port Townsend Harbor, and Obelia surcularis, on "water grasses" from the same location.O. griffini was first synonymized with Obelia dichotoma by Cornelius (1975b), but we regard it as a distinct species, as noted earlier, based upon morphological criteria (Calder et al. 2014).
As reviewed by Calder et al. (2014), O. griffini has also been reported (as O. gracilis) from benthic habitats in China and the South Kurile Islands.In contrast, we find O. griffini to be not only the most common hydroid on tsunami debris, but also to be the only species (or in sole company with the native oceanic gooseneck barnacle Lepas spp.) often on marine debris (JTMD as well as non-Japanese tsunami debris).Of interest in this regard is Cornwall's (1927) report that hydroids on the whale barnacle Coronula diadema (Linnaeus, 1767) (taken from a humpback whale off Vancouver Island) were identified by Charles H. O'Donoghue as O. griffini.The populations of O. griffini on JTMD are typically too expansive to have been acquired in the nearshore Eastern Pacific by debris in the brief time most of this debris field is believed to have rafted along the coast prior to landing, especially considering (as discussed above) that no uniquely Eastern Pacific hydroid species were found on any of these objects.Further, O. griffini is found on JTMD arriving in the Hawaiian Islands, where no members of this speciesgroup are known to occur, thus making it unlikely that the populations were acquired there.
Finally, neither O. griffini, O. gracilis, nor O. surcularis have been reported from the Japanese hydroid fauna.While it may be that since 1976 populations matching the morphology of these species have been assigned by Japanese workers to O. dichotoma following Cornelius (1975b, but not issued until November 1975), O. griffini and O. gracilis were in regular use prior to that date, O. gracilis in particular having been identified in other Asian hydroid studies, and with other workers in the Western Pacific continuing to recognize O. griffini after 1975 as well (for example, Antsulevich 1992).While we report here and in Calder et al. (2014) other less common hydroid species that we interpret as new records for Japan, the abundance and ubiquity of O. griffini on JTMD make it difficult to imagine that it has been overlooked in the Japanese coastal fauna.Rather, we suggest that JTMD acquired O. griffini during the North Pacific transit, and that this is a native high-seas species.
This said, the presence of oceanic, neustonic speciessuch as Obelia griffini, as well as the gooseneck barnacle Lepas, the crabs Planes spp.and Plagusia spp., the nudibranch Fiona pinnata (Eschscholtz, 1831) and the polychaete worm Amphinome rostrata (Pallas, 1766), all of which have been found on JTMD (Carlton et al. 2017)-in benthic habitats in China, Russia, or the Pacific Northwest would be highly anomalous.While all of these oceanic species may be found on occasion washed ashore, they are not regular members of coastal benthic communities.Thus, Obelia griffini may represent a cryptic species complex, with apparently morphologically identical benthic and pelagic clades.Molecular genetic studies are called for to clarify the status of purported oceanic and shore populations.If the pelagic taxon were to be found to represent a distinct taxon, it would likely require a new name.
A number of species of hydroids are regarded as naturally occurring in both benthic and pelagic habitats (such as Clytia hemisphaerica and Clytia linearis, both treated herein; see also Calder 1995, for species from the Sargasso Sea, many of which are also reported from nearshore benthic communities).While all or most of these species likely represent species complexes as well, in the case of O. griffini, we underscore the observation that this abundant species is not known from the Tōhoku source region of JTMD, thus making its high seas acquisition en route through the Pacific Ocean more probable.While hydroids have been previously reported on debris drifting in the North Pacific Ocean (Calder et al. 2014;Goldstein et al. 2014), they have not been regarded as part of the naturally occurring neustonic fauna.
There is some evidence in our material for direct settlement of Obelia griffini larvae on Lepas or other substrates in the open ocean (that is, sexually produced colonies as opposed to clonally produced colonies or stolonal extension of colonies growing originally on Japanese substrates).For example, runner-like hyperplastic stolons exhibiting directional growth were observed on an O. griffini colony on the pelagic crab Plagusia sp.(ROMIZ B4174), which colony is small and relatively sparse, indicating that larval recruitment is probable.Production of hyperplastic stolons exhibiting directional growth have been observed in sexually produced colonies of Hydractinia symbiolongicarpus Buss andYund, 1989 (Van Winkle andBlackstone 2002).The presence of these colonies, in addition to tightly packed "sheets" indicating later development of stolonal mats (also present in our material) supports the argument for open larval recruitment and persistence of these colonies.It is possible that the availability of planulae of O. griffini, as well as those species such as Amphisbetia furcata, which is probably not part of the oceanic neustonic fauna sensu stricto, may be mediated by the release of mature medusae which do not need to feed or by release of larval stages from fixed gonophores.This life cycle plasticity has been observed in Clytia linearis, Obelia sp., and A. operculata (Lindner and Migotto 2002;Genzano et al. 2008).

Conclusions: JTMD hydroid diversity and transoceanic dispersal
Campanularioid hydroids in the genera Campanularia, Orthopyxis, Clytia, Laomedea, and Obelia, are frequent and well-known members of ship fouling (Hutchins 1952;Zvyagintsev 2003Zvyagintsev , 2005)), harbor fouling (Karlson and Osman 2012), and, often, rafting (Thiel and Gutow 2005;Farrapeira 2011) communities.Not surprisingly, 10 species in these genera comprise the most diverse group of JTMD hydroids.Thiel and Gutow (2005) summarized records of hydroids reported in the literature as rafting species.Other than taxa associated with the drifting brown alga Sargassum in the North Atlantic's Sargasso Sea (Calder 1995), they noted five species whose association with rafting was based only upon circumstantial evidence or distributional inference, rather than direct observation, and an additional four species reported from local or regional coastal debris.Goldstein et al. (2014) reported three species, Clytia gregaria (Agassiz, 1862), Obelia sp., and Plumularia setacea from marine debris collected floating in the North Pacific.The present report represents the first documentation of the 28 species reported here and earlier (Choong and Calder 2013;Calder et al. 2014) as rafting from one continental margin to another.
That half of the species found in our collections occurred only once speaks to the strong probability that JTMD hydroid diversity is far greater than reported here.Only a small fraction of Japanese tsunami marine debris was sampled (Carlton et al. 2017), suggesting that the many thousands of objects not intercepted and studied may have transported many more hydroid species to the Central and Eastern Pacific.
Following our previous study, we retain O. griffini as distinct from generally considered conspecific species such as O. dichotoma.Obelia surcularis Calkins, 1899 and O. gracilis Calkins, 1899 are simultaneous synonyms, with nomenclatural priority having been assigned to the binomen O. griffini (see Calder et al. 2014 for discussion and description).