Hydroides Gunnerus, 1768 (Annelida, Serpulidae) is feminine: a nomenclatural checklist of updated names

Abstract As a service to taxonomists and ecologists using names in the well-known and species-rich ship-fouling serpulid genus Hydroides we present an update of all 107 non-synonymised scientific names, with additional information on Hydroides nomenclature, original names, etymologies, and type localities derived from original literature, and in accord with the World Register of Marine Species (WoRMS) database. An update is needed because the gender of genus Hydroides has from 1 January 2000 reverted to the original feminine, due to a change in the wording of International Code of Zoological Nomenclature which was overlooked at that time, and is contrary to the usage in practice of Hydroides as masculine which had started about 1992, although Code-required from the 1960s. We match 31 further original names of current WoRMS subjective junior synonyms to each non-synonymised name, and also report on the world distribution of the genus as illustrated by type localities of the valid names. We include notes on seven species inquirenda. The correct rendering is given of six names that have been altered for gender agreement for the first time herein. Hydroides gottfriedi nom. n. replaces junior homonym Hydroides rostrata Pillai, 1971. Currently there are 41 non-synonymised species-group names in Hydroides which should be gender invariant, and 23 names which would only change if moved to a neuter genus; the remaining 43 names are fully gender variable. Place-names (23), and personal names (16) make up more than a third (36%) of the species names, with most of the remainder (68) being descriptive of species character states, usually of operculum morphology (54). All species, except Hydroides norvegica (63°N), have type localities in shallow-water coastal locations in temperate to tropical waters below latitude 44°, with the highest number of new species (54) from the adjoining Western Pacific and Indian Ocean areas. The other concentration of new species (31) are those first found on the Pacific and Atlantic coasts of North America and in the Caribbean.


Introduction
An unusual situation has arisen concerning the correct formulation and spelling of historic species-group names in Hydroides Gunnerus, 1768 (Serpulidae) with respect to the established requirement of the International Code of Zoological Nomenclature (hereafter the Code) that the suffix spelling of a Latin or Latinized adjectival speciesgroup name must agree in gender with its genus (ICZN 1999: Article 31.2). The stability of Hydroides names is important for tracking name usages as it is the largest serpulid genus, currently with 107 non-synonymised names, and also a further 31 original names currently placed as subjective synonyms. Hydroides includes H. elegans (Haswell, 1883), a model organism for settlement and genetic study (e.g., Hadfield 1998), and some other economically important species such as H. ezoensis Okuda, 1934, H. dianthus (Verrill, 1873, H. dirampha Mörch, 1863, and H. sanctaecrucis Krøyer [in] Mörch, 1863, which are foulers of ship hulls, harbour structures, and aquaculture equipment . Hydroides species are easily recognisable by the morphology of the plug which closes the mouth of their calcareous tubes. It is a two-tier operculum with a basal funnel and a distal spinous structure called the verticil. The distinctive and varied structure of the verticil spines has enabled many Hydroides species to be detected. Identification from tubes alone is problematic, thus past diversity is difficult to determine from the fossil record in the absence of the opercula. Hydroides has no current subgenera, but Eupomatus Philippi 1844, the most prominent junior synonym of Hydroides, and the little-used Eucarphus Mörch, 1863, were both at times used as subgenera defined by verticil morphology. The taxonomic history is reviewed in Bastida-Zavala and ten Hove (2002).
We recently realised that the gender agreement serpulid taxonomists had been applying to adjectival Hydroides species-group names for the last 16 years was the opposite of that required by the fourth edition of the Code (ICZN 1999, effective 1 January 2000, in that authors since that date had continued using or creating masculine instead of feminine Latin forms. Additionally, taxonomists had not consistently observed the different Code rule applicable prior to 1999, with one author producing new Hydroides names seemingly of both genders in the same publication (Straughan 1967a). Therefore we have compiled a checklist of Hydroides name spellings we believe are currently correct, including also identifying the names not subject to gender agreement.
The derivation of Hydroides as an Annelida genus name is known. Stearn (1983: 266) explains that substantives derived from -oides were commonly used for new genera before and during Linnaeus' era to indicate resemblance to a genus already known, sometimes just as temporary names. The -oides suffix is originally adjectival, transliterated from Greek οειδης. Gunnerus had at first used the cnidarian genus of Hydra (named for the creature of Greek myth) as the genus name for his new tube-dwelling worm in 1766 correspondence with Linnaeus, but shortly thereafter changed it to Hydroides for his new species H. norvegica as published in 1768, "until Mr. v. Linné makes its genus known" (Gunnerus 1768, Moen 2006). The link to hydrozoans was spurious, but the genus name persisted. Usage of the same spelling applied to true hydrozoans persists in Romance language works, where "hydroïdes" (hydroids) can substitute for the formal higher group name, Hydrozoa. The pair of usages are not homonyms in the strict Code sense, but there is some false positive reporting of the Hydroides annelid genus in bioinformatics search results (e.g., from some of the Hydrozoa works of Billard, such as Billard 1907).
Hydroides was feminine because Gunnerus clearly treated it as feminine when he used the feminine 'norvegica' as epithet for the worm instead of the masculine 'norvegicus' (likewise the calcareous tube was separately named Serpula norvegica by Gunnerus). However, in recent years Gunnerus's original feminine gender assignment for Hydroides became not obvious to most. This is exemplified by Moen (2006), who in the summary of her historical paper on Gunnerus reports without qualification that "in 1768 J. E. Gunnerus first described the species Hydroides norvegicus". Although Moen was well aware Gunnerus did not use that spelling she perhaps believed the 'correct' masculine ending (although incorrect since 2000) was always to be used, regardless of what was originally written.
The Code in its first edition indicated that genus names ending in -oides were to be treated as masculine (ICZN 1961: 33, Article 30(a)(ii) Examples), whereas in botany they were treated as feminine (Stearn 1983: 265). By the time of the Code third edition (ICZN 1985: 30, Article 30(b) Examples) the article text was the same, with the examples text explaining that these masculine genus names were substantivated adjectives, thus for Hydroides the adjectival descriptive of 'hydra-like' was functioning as a noun. Mandatory gender agreement, although much debated, was retained in the Code fourth edition, but changes were made in order "to simplify the identification of gender in genus-group names" (ICZN 1999: XXVI).
Unexpectedly one of the qualifying clauses now included in the Code fourth edition (ICZN 1999) had a major effect on Hydroides Gunnerus by reverting it to feminine status after almost 40 years as the opposite gender. The wording of Article 30.1.4.4 in full is "A compound genus-group name ending in the suffix -ites, -oides, -ides, -odes, or -istes is to be treated as masculine unless its author, when establishing the name, stated that it had another gender or treated it as such by combining it with an adjectival species-group name in another gender form." Why the Code editorial group thought the refinement was necessary is unknown, but presumably it was regarded as better matching contemporary practice with the original 18-19 th century usages.
Hydroides began as feminine in 1768, and feminine adjectival endings matching this were usual for over 220 years but not universal (e.g., H. bifurcatus Pixell, 1913). Hartman (1965: 79) had maintained original feminine endings in her supplementary world catalogue, although not long later she had used the masculine for H. pacificus Hartman (Hartman 1969). Masculine endings, which the Code had required from the early 1960s onwards, otherwise only became common around 1992 (Moen 2006: 121), although H. bifidus Imajima, 1982 andH. bisectus Imajima &ten Hove, 1989 were newly described somewhat earlier. Ben-Eliahu and ten Hove (1992: 37) correctly pointed out that the Code third edition (ICZN 1985) had Hydroides as masculine (actually in place since the first edition). Serpulid taxonomists then adopted the use of masculine endings and continued with this right up to August 2015, unaware of the change back to feminine required from 1 January 2000 when the new Code came into effect. The fourth edition Code was incorrectly cited as continuing masculine endings in ten Hove and Ben-Eliahu (2005: 128). In summary, for nearly 40 years species names in Hydroides were required to have masculine endings according to the ICZN Code, although largely ignored for about 30 years, and now for the last 16 years they were required to have the feminine ending as begun by Gunnerus, also ignored. The conflict was first reported in WoRMS by one of us (GBR) in July 2015, after a misinterpretation of the Code requirement for Hydroides names was published in Tovar-Hernández et al. (2016, as first online July 2015. Gender-corrected names were subsequently used in Sun et al. (2015), Kupriyanova et al. (2015), and Sun et al. (2016).
Code Article 31 (ICZN 1999) explains some of the requirements and exceptions regarding species-group Latin name formation. In general, most species-group names ending in the suffixes -us, -a, -um are declinable and likely to be adjectives. There are some exceptions applicable here such as -spina, which is a noun in apposition and should not change with gender, and most other name endings will not change. The only possible endings of changeable adjectives are -a, -us (these two make up over 60% of all names), -is, -um, -e, -er, -ior, whereas nouns can have all endings (Welter-Schultes 2013). Personal names as species-group names are usually (exceptions) formed as genitive-case nouns (ICZN 1999, Article 31.1). Nouns with Latin adjectival suffixes can become adjectives, notably non-Latin place-names with the suffixes -ensis (masculine/feminine) or -ense (neuter), indicating of that place, or suffix '-anus -a', indicating belonging to. However, nouns compounded with dictionary Latin adjectives are treated as noun phrases in apposition (ICZN 1999, glossary).
Here we present an update of all non-synonymised names, and additional information on Hydroides nomenclature, as derived in conjunction with the World Register of Marine Species (WoRMS) Polychaeta database (Read and Fauchald 2016), where further details are available. Certain species inquirenda (seven names which are otherwise valid but require taxonomic clarification due to inadequate original descriptions) are included and examined in the checklist for analytic purposes, while noting (as explained by ICZN 1999, Article 23.9.6) that the inclusion of these names should not later be considered as new usages.
We have taken this opportunity to investigate type localities of all the species, and to geolocate them to modern standards if possible. Prior to satellite-based navigation only vessel-based collections were likely to provide type-locality geolocations, and the descriptions used to pinpoint coastal sites could be vague or problematic. For instance Treadwell (1939: 164) gave an update that the "precise position" of his Mayagüez Bay station 6062 of 1902 could be relocated based on using a red buoy at the harbour entrance as a reference point, but we are doubtful of the 100 year longevity of this buoy. We have been able to suggest placements for at least three species for which only a vague location was previously available. Type localities are mapped to show the world distribution.

Methods
The checklist is based on a review of original literature for all Hydroides species-group names, and a review of about 250 Hydroides-related name records at WoRMS (Read and ten Hove 2016). Under Code Article 34.2 (ICZN 1999), prior usages in literature are not required-here we simply formulate and present correct spellings. Gender agreement is mandatory, which means that non-agreeing scientific names strictly do not exist as valid spellings, and can be updated without explanation (to the bewilderment of many in the past, so we strongly advise annotation of new gender-spelling variants to avoid uncertainty). It is also worth noting that, while gender-agreement variants obviously are minor spelling changes, the Code is worded so that these different spellings are not treated as separate usages under prevailing usage rules.
All original literature for Hydroides names was examined. Names as given are our derivations of correct endings for gender agreement, and are followed as necessary with the original binominal combination and comments on current status. The etymology (author's and/or interpreted dictionary entries) is given, followed by our evaluation of the type of name (adjective, invariant noun in apposition, etc.) from available information. The derivation of names is unambiguous when authors give full etymologies, but this is rare for old names, and often sketchy for modern ones. Derivations are frequently only evident by matching likely character states mentioned, and occasionally there seems no obvious basis for the name chosen. The sources we have used to study derivations include online dictionaries and meta Greek/Latin language resources (Harper's Etymonline; Logeion; Lexilogos), the Lewis and Short (1891) Latin dictionary (print, also online), as well as analytical dictionaries on the classical languages in science (Brown 1956;Stearn 1983). We have included the current subjective synonyms at WoRMS (if any) of each name (and their type localities), but have not included the other superseded recombinations, nor any misspellings of the valid name (these are fully listed at WoRMS and links to the current and original name records at WoRMS are in the Suppl. material 1 which also summarises the name analysis).
The type locality names have been investigated and their geolocations are included, usually derived by retrospective georeferencing. They are mapped to place the original discoveries in a geographic context and to locate where topotype material could be sought. Current place-names were geolocated using several web-based gazetteers (e.g., GeoNames, GEOLocate, Marineregions (WoRMS), Wikipedia). Disused historic names were sought via general web searches and Wikipedia. Holotype georeference information in online collections databases and in subsequent publications was evaluated if available (these data can be based on retrospective approximations, rather than information supplied by authors on labels). Occasionally modern authors have published geolocations that are obviously imprecise or displaced, and we have pointed these out. The point-geolocations of the older taxa are our informed coastal assignments (indicated as map estimates) if derived from place-names which are towns, islands, or occasionally only known as strips of coast or other imprecise geographic extents. Sometimes positioning was assisted by further information from or about authors. A few times we were unable to narrow the collection site to any point and we indicate when we have given a general geolocation instead. We are unable to calculate the uncertainties (in extent) of our derived coordinates, and caution that each is a precise point location of the possible site, the nearest logical coastal geolocation at this time, as adjusted with satellite image overlay of terrain using the Wikipedia GeoLocator mapping tool. A list of geolocations is in the Suppl. material 1.  Straughan, 1967awith H. operculata Treadwell, 1929 was re-confirmed by Sun et al. (2015: 63), but is being re-examined, and we provisionally include the H. basispinosus original name analysis separately. Etymology: Not stated, but the compound name for H. basispinosus means 'spinypedestal' as derived from Latin (originally Greek) feminine noun basis 'pedestal' and adjective spinosus -a -um 'spiny'. Basal internal spinules on opercular spines are mentioned (not figured).

Checklist of
Evaluation: Gender-variable adjective (in practice). Elsewhere in the article Straughan used feminine adjectival new species names, and in relation to the basal spinules Straughan probably intended another adjectival compound name. Her error in gender ending can be corrected to '-spinosa'. However, she used the feminine Latin noun 'basis' (pedestal), not the adjectival 'basalis' (basal) which would have become 'basalispinosa'. If a noun phrase with a feminine noun then 'basispinosus' was incorrect Latin (it should also have been 'basispinosa'), and the original spelling must be maintained (ICZN 1999, Article 31.2.1). While this can be noted, Straughan is not the only author to adopt 'basis' as if adjectival, and it seems best not to apply the strictest interpretation here. Usage as 'basispinosa' already exists (e.g., Sun et al. 2015: 63 Day (1951: 64), was silently corrected to 'bifurcata' in Day (1967: 808 Bush (1910). Geolocation: Imprecisely known (possible place of origin, Castle Harbour, 32.3472°, -64.6872°, Bermuda). WoRMS: 421083 Synonyms: No subjective synonyms.

Hydroides brachyacantha Rioja, 1941a (original binomen)
Etymology: Not stated, and the description of H. brachyacantha does not indicate why the name derives from Greek βραχυ (brachy) 'short', ακανθα (akantha) 'spine', feminine noun, thus short-spine. In New Latin acantha has frequently been used as part of feminine compound names in both genera and species-group names. An identical spelling might be expected to be a noun form in both, but species-group names ending as -acantha -acanthus have regularly been treated as Latinized Greek adjectives, and that may have been the intention of the author. Evaluation: Gender-variable adjective with correct feminine ending. Usages as 'brachyacanthus' exist (e.g., Bastida-Zavala and ten Hove 2003: 73

Hydroides dianthus (Verrill, 1873) (originally as Serpula dianthus)
Etymology: Verrill (1873: 28) states for S. dianthus that the name alludes to the resemblance to Dianthus flowers as the colours of its branchiae "recalls the varied hues and forms of different kinds of pinks, (Dianthus.)". The botanical generic name Dianthus (flower of Zeus) is New Latin (Linnaeus and earlier) from Greek Δηοσ (Dios), genitive of Zeus, and ανθος (anthos) 'flower'. As Serpula is feminine and dianthus is masculine it seems Verrill intended the name as a noun (Actinia dianthus Ellis, 1768 is an earlier similar pairing). Evaluation: Invariant noun in apposition.

Hydroides diplochone (Grube, 1878a) (originally as Serpula (Hydroides) diplochone)
Status: Name now disused and representing a species inquirenda. A single subsequent valid usage of the name was later identified as an occurrence of Hydroides ezoensis (a junior name), but it is uncertain that Grube's original serpulid (type missing) was the same (fide Zibrowius 1978: 144;Sun et al. 2015: 37). Etymology: Not stated, but the name for Serpula diplochone derives from Greek Latinized as diplos 'two-fold' and feminine Greek noun χοάνη (choani) 'funnel', thus double funnel, evidently in reference to the two-tier operculum that Grube describes (a generic character). There are no other names based on chone in Serpulidae, but it is part of several generic names in Sabellidae. Evaluation: Invariant noun in apposition. Type locality: Askold Island, outer Peter the Great Gulf, North Japan Sea. We infer this to be the type locality. Grube does not present location information beyond that the material was from "nordjapanischen Meeres", but it is also mentioned that the collector was the Siberian-based Polish naturalist Dybowski, whose travels in the region are documented. In 1874 Benedykt Dybowski collected fauna at Askold Island, near Vladivostok, Primorsky Krai (fide Zoological Museum, University of Lliv [no date]). Geolocation: 42.7333°, 132.3333° (map estimate, Askold Island). WoRMS: 333639 Synonyms: As species inquirenda has no synonyms, although H. ezoensis has been suggested.

Hydroides exaltata vesiculosa Fauvel, 1919 (originally as H. exaltatus var. vesiculosus)
Status: Name now disused and representing a species inquirenda. Similarities of the original description to Hydroides albiceps have been noted, but the name is yet to be synonymised. Etymology: Not stated, but H. exaltata vesiculosa was evidently named for its vesicular dorsal verticil spine. Evaluation: Gender-variable adjective with incorrect original ending, corrected to feminine (e.g., Monro 1937: 316

Hydroides ezoensis Okuda, 1934 (original binomen)
Etymology: Not stated, but H. ezoensis is evidently named after its area of collection, as Ezo (also as Yezo) is a former name for the island of Hokkaido, Japan. The speciesgroup name 'ezoensis' has often been used for Japanese taxa, along with 'yezoensis'.
Evaluation: Masculine/feminine invariant '-ensis' adjective created from non-Latin geographic name. Type locality: Not fixed by author. Original records are from "Akkeshi, Muroran, and Oshoro", which are widely separated places around the coast of Hokkaido Island, with the first two having marine stations. Geolocation: Imprecisely known (possibly as 43.0209°, 144.8368° for Akkeshi Marine Station). WoRMS: 131003 Synonyms: See comments for H. diplochone.

Hydroides floridana (Bush, 1910) (originally Eupomatus floridanus, new name for Eupomatus uncinatus non Philippi sensu Ehlers, 1887)
Etymology: Not stated, but E. floridanus is evidently named after its purported region of collection. 'Florida' is Spanish for flowery land and is here combined with the Latin adjectival suffix -anus -a -um, indicating from Florida. Evaluation: Gender-variable adjective based on a non-Latin geographic name, corrected to feminine herein. Usages in Hydroides as 'floridanus' exist (e.g., Bastida-Zavala and ten Hove 2002: 118) but not previously as 'floridana'. Type locality: Unknown, not certain to be off namesake Florida. When Ehlers (1887: 286) described the Polychaeta collected from voyages of Coast Survey Steamer "Blake" he wrote in his native German but recorded the two locations for the Eupomatus specimens literally in English as "inside fishing ground Cape Rear" and also "off W. down Cape Dear Rio" (both at 7 fathoms). However, these place-names seem to be misreadings as they could not be found in the Caribbean or Florida, nor do the "Blake" voyage reports include the names. The similarity of names suggests the location is possibly off Cape Fear, North Carolina, with its associated Cape Fear (Rio) River, disregarding that Ehlers' monograph title appears to exclude Atlantic coast voyages the "Blake" also made. As the types are believed lost the original label cannot be checked. No specimens are currently listed in the Yale Peabody Museum online catalogue although Bush (1910: 498)  Hydroides furcifera (Grube, 1878b) (originally as Serpula furcifera) Etymology: Not stated but Grube described for S. furcifera forked spines in the opercular funnel as well as the verticil, thus Latin furca 'fork', combined with adjectival suffix -fer -a -um 'bear'. Lewis and Short (1891: 795) include furcifera as a feminine noun meaning phallus, but it is unlikely this was Grube's intention. A more common adjectival form would be furcillata 'forked'. Evaluation: Gender-variable adjective with correct original feminine ending. Names ending in -fer may be nouns or masculine adjectives (ICZN 1999, Article 31.2.2 example). The usage of Grube was adjectival as he used feminine -fera. A listing-only usage in Hydroides as 'furcifer' exists (ten Hove and Kupriyanova 2009: 53

Hydroides fusicola Mörch, 1863 (as H. (Eupomatus) fusicola)
Etymology: Not stated, but H. fusicola is evidently named after the gastropod genus Fusus (now Fusinus) combined with -cola 'dweller', as it was found attached to a 'Fuso' sp. Evaluation: Invariant compound noun in apposition with -cola as a substantival suffix. The Code has a stipulation (ICZN 1999, Article 30.1.4.2) that genera with -cola endings be treated as masculine compound nouns (or mostly so treated, similar to the -oides situation). It has no advice for species-group names with -cola suffixes, but they are recommended to be treated similarly (David and Gosselin 2002: 34), not declined to agree with the first noun or the genus. Type locality: Japan (not further specified). Mörch only knew the specimen was from the collection of Wessel in Hamburg. Geolocation: Unknown (gazetteer Japan central point as 37°, 138°  Rioja (1941a: 174) writes of "una robusta protuberancia . . .en forma de glande" for H. glandifera, it is likely to be a functional name for the bulbous dorsal verticil spine from Latin glans 'acorn' combined with adjectival suffix -fer -a -um 'bear'. It is unclear why Rioja (incorrectly) used the neuter form 'glandiferum' at first, but he later (Rioja 1941b: 733) Straughan, 1967awith H. operculata Treadwell, 1929 was followed by Sun et al. (2015: 63), but is being re-examined, and we provisionally include the H. gradata record separately. Etymology: Not stated, but for H. gradata the Latin gradata 'gradual' is evidently describing the gradual size change of the ring of opercular spines. Evaluation: Gender-variable adjective with correct original feminine ending. Type locality: Pretty Beach, 40 km north of Cairns, Queensland, Australia Geolocation: -16.6111°, 145.5318° (map estimate). WoRMS: 384604 Synonyms: See H. operculata comments.

Hydroides heterocera (Grube, 1868) (originally as Serpula (Eupomatus) heterocerus)
Etymology: Not stated but the name for S. heterocerus is likely describing the dimorphism in verticil spines, from Greek hετεροσ (heteros) 'different' and κερασ (keras) 'horn'. The Latinized heterocerus is an adjectival form to be declined. Evaluation: Gender-variable adjective corrected to feminine in Zibrowius (1971: 715). Grube (1868: 639) originally incorrectly created a masculine 'heterocerus' in agreeing with the masculine subgenus Eupomatus rather than the feminine genus Serpula. Usages exist in Hydroides as 'heterocerus' (e.g., Ben Eliahu and ten Hove 2011: 26), and as the misspelling 'heteroceros' (e.g., Day 1967: 807). Type locality: Unspecified Red Sea. Grube's report title refers to Red Sea worms collected by Georg Ritter von Frauenfeld. Grube states in his opening sentence that the worms were handed to him without any other information, and it seems he did not investigate this further. In the narrative of his visit von Frauenfeld (1855) mentions Suez, the Sinai Peninsula, and seeing countless annelids on the Red Sea shore, but he does not match observation to locality. Geolocation: Imprecisely known, but perhaps northern Red Sea (a gazetteer Red Sea mid-point is 20.3°, 38.6°). WoRMS: 851900 Synonyms: No subjective synonyms. However, the misidentification Serpula (Hydroides) uncinata non Philippi, sensu Gravier, 1906, has been assigned to H. heterocera (e.g., Pixell 1913: 75).

Hydroides hexagona (Bosc, 1802) (originally Serpula hexagona)
Status: A name disused by taxonomists and representing a species inquirenda. The original description and figure are rudimentary and the species Bosc saw will remain indeterminable unless original specimens are found (unlikely). However, the name cannot be a nomen oblitum as it was revived as H. hexagonus [sic] in three widely used manuals on invertebrates of the United States eastern coast (Pratt 1916, Grave 1937, Costello et al. 1957). These instances should be considered misidentifications, and might be referable either to the junior name H. dianthus (fide Zibrowius 1971: 697, Bastida-Zavala and ten Hove 2002: 108), or to other similar species. Nevertheless, there are multiple modern citations of the research on Hydroides sperm (e.g., Colwin and Colwin 1961) in which the name appeared. Etymology: Bosc described the tube of Serpula hexagona as "montrant la moitié d'un prisme hexagone …", and the name is a New Latin adjectival form for six-sided, modified from Greek. Bosc's figure shows two ridges so the tube cross-section would be trapezoidal, not literally hexagonal as named, but half (la moitié) of that. Evaluation: Gender-variable adjective with correct feminine ending herein. Usages in Hydroides as 'hexagonus' and 'hexagonis' exist (e.g., Pratt 1916: 302, Grave andOliphant 1930: 234) but not previously as 'hexagona'. Type locality: Charleston Harbour, Charleston, South Carolina, Atlantic coast USA. Geolocation: 32.8186°, -79.9279° (gazetteer). WoRMS: 384606 Synonyms: As species inquirenda has no synonyms.

Hydroides huanghaiensis Sun & Yang, 2000 (original binomen)
Etymology: Not stated, but H. huanghaiensis is evidently named after the sea in which the worm was collected as "Huanghai" means Yellow Sea in Chinese. Evaluation: Masculine/feminine invariant '-ensis' adjective created from a non-Latin geographic name, Huanghai.

Hydroides inornata Pillai, 1960 (original binomen)
Status: The current synonymy of H. inornata with H. operculata is being re-evaluated, and meantime it is included separately here. Etymology: Not stated, but for H. inornata it is likely that the Latin inornatus 'unadorned' is referring to the verticil spines without side spinules. Evaluation: Gender-variable adjective with correct original feminine ending. Usages as 'inornatus' exist (e.g., Amoureux et al.: 57). Type locality: Maha Alamba (not found, perhaps disused), "about a mile" from the Negombo Lagoon entrance (an aquatic research institute is nearby), north of Colombo, west coast of Sri Lanka. Geolocation: 7.1945°, 79.8392° (map estimate). WoRMS: 338018 Synonyms: No subjective synonyms, and has been regarded as junior to H. operculata (e.g., Sun et al. 2015: 62).

Hydroides microtis Mörch, 1863 (originally as H. (Eucarphus) microtis)
Etymology: Not stated, but for H. microtis the 'micro' derives from Greek μικρος (micros) 'small', and perhaps is combined with Greek neuter noun genitive οτοσ (otos) 'ear'. The Latinizations 'microtis' and 'microtus' are in use as both genus and species-group names for small-eared biota. Whether the same derivation applies for H. microtis is unclear, as the verticil spines are knob-tipped and not notably small or ear-like. Evaluation: Invariant whether a noun in apposition or (masculine/feminine) intended as adjectival. Type locality: North America (unspecified) as "ad Americam borealem" on Argopecten irradians (was as Pecten), collected by A. B. Mayer, presumably on the Atlantic coast as A. irradians is the bay scallop of that region. Geolocation: Unknown (unspecified Atlantic coast of North America, with 44°, -68° the mid point of the coastal extent). WoRMS: 333641 Synonyms: No subjective synonyms.

Hydroides novaepommeraniae Augener, 1925 (originally as Hydroides (Eupomatus) novae-pommeraniae)
Etymology: Not stated, but the name for H. novaepommeraniae is evidently a Latinized form of the former name of the island of collection, New Britain, Bismarck Archipelago, now part of Papua New Guinea, once a German colony named Neupommern, after the Baltic (Ostsee) coastal lands besides Pommersche Bucht. Evaluation: Invariant noun in the genitive case created from a non-Latin geographic name Latinized as 'novaepommeran'. Type locality: "Hanam-Hafen" (Hannan or Garua Harbour), north coast of New Britain, Papua New Guinea. Geolocation: -5.2833°, 150.0333° (map estimate). WoRMS: 131010 Synonyms: Hydroides grubei Pillai, 1965 (Binakayan, Cavite, Manila Bay, Philippines) Hydroides ochotereana Rioja, 1941a Etymology: Rioja (1941a: 167) stated the name for H. ochotereana was "dedicar esta especie al Maestro D. Isaac Ochoterena", but he used the spelling 'ochotereana' for the species-group name. Evaluation: Incorrect Latinization to be treated as a noun in apposition. The use of H. ochotereana has been regarded as an accidental incorrect original spelling by Bastida-Zavala and ten Hove (2003), who cited Article 32.5 (ICZN 1999) as justification for using 'ochoterena', although that would be an unchanged noun in apposition, rather than a genitive. Instead, we cannot reject the likelihood that Rioja had intentionally used the altered '-eana' ending (after all he used it consistently five times but correctly spelled the name of dedicatee Ochotorena) aiming to create an adjectival form of Ochotorena. His adaptation could be intended as a rendering using the suffix '-anus' -ana' (belonging to), frequently used for adjectival Latinization of nouns based on personal and geographic names. As it was the author who was responsible for an incorrect Latinization (ICZN 1999, Article 32.5.1) his original spelling is not corrected (also see Welter-Schultes, 2013: 77). This also avoids the name looking like an authorship (ICZN 1999, recommendation 31A). Type locality: La Aguada and La Quebrada beaches, Acapulco, Mexico. Geolocation: 16.8461°, -99.9156° (La Quebrada, map estimate). WoRMS: 328462 Synonyms: No subjective synonyms.

Hydroides operculata (Treadwell, 1929) (originally as Eupomatus operculata [sic])
Etymology: Not stated, but the name for E. operculata derives from the Latin verb operculo -avi -atum 'to cover', and in New Latin operculata is used as an adjectival form. It is unclear why Treadwell chose the name as all Hydroides have opercula. His specimen was endowed with two, but he didn't name it 'bioperculata'.

Hydroides pectinata (Philippi, 1844) (originally as Eupomatus pectinatus)
Status: Name now disused and representing a species inquirenda. It is not eligible as a candidate nomen oblitum (used in taxonomy by Iroso 1921: 49, Naples), but is indeterminable unless original specimens are found. The operculum figured by Philippi is similar to that of H. elegans (Haswell, 1883) (fide Zibrowius 1971. Etymology: Philippi's brief Latin description of E. pectinatus describes the operculum spines as 'utrinque pectinatis' (pectinate both sides) with three sharp teeth. The Latin adjective pectinatus indicates comb-like divisions. Evaluation: Gender-variable adjective recombined in Hydroides with correct feminine ending (e.g., Mörch, 1863: 377). Type locality: Unspecified Mediterranean, but can be narrowed to the Tyrrhenian Sea coast of Italy as Philippi's activities were in western Italy, and plausibly to Naples as he was based there prior to 1844. Geolocation: Unknown (Tyrrhenian Sea, with Naples shore (40.8327°, 14.2358° map estimate) a possible point location). WoRMS: 393822 Synonyms: As species inquirenda has no synonyms although H. elegans has been suggested.

Hydroides pseudouncinata Zibrowius, 1968 (original binomen)
Status: Currently valid but it is possibly the same as the disused H. euplaeana (see above). Etymology: Not stated, but evidently H. pseudouncinata was named because it represents one of the taxa previously confounded under H. uncinata (see below), a name regarded as of indeterminable identity from its original description (fide Zibrowius 1971: 709). Evaluation: Gender-variable adjective with correct original feminine ending. Usages as 'pseudouncinatus' species (or nominal subspecies) exist (e.g., ten Hove and Kupriyanova 2009: 54). Type locality: East off Île Gaby (also Degaby), Marseille, France, Mediterranean Sea (not in Zibrowius 1968, fide Zibrowius 1971

Hydroides recta Straughan, 1967a (original binomen)
Etymology: Not stated, but the name for H. recta is perhaps a reference to the 8 th enlarged dorsal verticil spine with its "pointed process perpendicular to it" from Latin rectus 'perpendicular'. Evaluation: Gender-variable adjective with correct original feminine ending. Usages as masculine 'rectus' exist (e.g., Pillai 2009: 132

Hydroides rhombobula Chen & Wu, 1980 (originally as H. rhombobulus)
Etymology: Not stated, but the name for H. rombobulus may be referring to the shape of the verticil spines, derived from a combination of Greek ρομβος (rombos) 'rhombus', which is a parallelogram with only opposite angles equal, and Latin -ulus, which is a diminutive in masculine-form. Evaluation: Clearly intended as an adjectival name, so it is corrected herein to feminine rhombobula. Type locality: Dongshan, Fujian Province, China Geolocation: 23.6689°, 117.3969° (map estimate). WoRMS: 882579 Synonyms: No subjective synonyms. Pillai, 1971 (original name, junior homonym, replacement name Hydroides gottfriedi nomen novum) Status: Previously unreplaced junior homonym preoccupied by the invalid Hydroides rostrata Iroso, 1921, which was a n. nom. for the specimen of Eupomatus uncinatus non Philippi, sensu Ehlers, 1887, but a junior objective synonym of Hydroides floridana (Bush, 1910) as Bush had already re-named it. Replaced by Hydroides gottfriedi nom. n. here. Etymology: Not stated, but H. rostrata is likely named after the large rostrum-like verticil spine figured by the author. The adjective rostratus -a -um, means having a beak. The genitive replacement name H. gottfriedi is in memory of Telesphore Gottfried Pillai (1930Pillai ( -2013, the original-name author. Evaluation: Gender-variable adjective with correct original feminine ending. Usages as 'rostratus' exist (e.g., ten Hove and Kupriyanova 2009: 54). Hydroides similis (Treadwell, 1929) (originally as Eupomatus similis) Etymology: Not stated, but an instance of the Latin adjective similis 'similar to'. Later in the same work Treadwell (1929: 12) considered his H. californicus (now H. crucigera) as similar to his E. similis, which isn't compared to any taxon, so the more logical application of the names would have been in reverse. Evaluation: Masculine/feminine invariant adjective (similis -e) (Stearn 1983: 94

Hydroides trivesiculosa Straughan, 1967b (originally H. trivesiculosus)
Etymology: Not stated, but the name for H. trivesiculosus is evidently referring to the three lobes of the enlarged dorsal spine of the verticil, thus tri with Latin adjective vesiculosus -a um 'full of blisters'. Evaluation: Gender-variable adjective with ending feminine as in Sun et al. (2015: 85) and Kupriyanova et al. (2015;293), both mistakenly reporting the original name as 'trivesiculosa'). Usages as 'trivesiculosus' (besides original) exist (e.g., ten Hove and Ben Eliahu 2005: 134). Type locality: Heron Island, Queensland coast, Australia, collected close to the marine station by Dew (map in Straughan 1967b

Hydroides uncinata (Philippi, 1844) (originally as Eupomatus uncinatus)
Status: Name now disused and representing a species inquirenda which is the type species of Eupomatus. It is not a candidate nomen oblitum (used in taxonomy as valid by Zibrowius 1968: 109, Hartman 1969: 757, Gibbs 1971: 202, Pillai 1972: 15, Day 1973: 132, and others), but the taxon it represents may be indeterminable unless original specimens are found. Zibrowius (1968) named H. pseudouncinata to establish a separation from H. uncinata, and Pillai (1972) did likewise with H. okudai. The name does not obviously threaten the validity of subsequent names, but it is notable that several H. uncinata usages have been assigned elsewhere, e.g., Serpula (Hydroides) uncinata non Philippi, sensu Gravier, 1906 to H. heterocera. Etymology: Not stated, but Philippi described the verticil spines as with "cornubus octo, apice incurvo uncinatis" (eight horns, curved tip hooked), thus the name refers to the hooked spines, from the Latin adjective uncinatus 'hooked'. Evaluation: Gender-variable adjective with correct feminine ending. Usages in Hydroides as 'uncinatus' exist (e.g., Ehlers 1913: 582). Type locality: Unspecified Mediterranean, but can be narrowed to the Tyrrhenian Sea coast of Italy as Philippi's activities were in western Italy, and plausibly to Naples as he was based there prior to 1844. Geolocation: Unknown (Tyrrhenian Sea, with Naples shore (40.8327°, 14.2358° map estimate) a possible point location). WoRMS: 156135 Synonyms: As species inquirenda has no synonyms.

Name characteristics and potential variation
Place-names (23), and personal names (16) make up more than a third (36%) of the 107 non-synonymised species-group names in Hydroides, with most of the remainder (68) being descriptive of species character states, with a remarkable number relating to operculum morphology (54). The (perhaps) 'small-eared' H. microtis was the only species where the reason for the author's choice was not obvious. Otherwise three species were named for their attractive appearance (H. dianthus, H. elegans, H. elegantula), three were named for the animals they were found on (H. fusicola, H. protulicola, H. spongicola), four names are comparative (H. affinis, H. pseudouncinata, H. similis, H. similoides), two species names probably relate to body size (H. humilis, H. parva), and one species name relates to the tube form (H. hexagona).
Currently the 107 names include 41 which should be gender invariant (including 17 nouns in apposition, including two acronyms), and 23 with adjectival masculine/ feminine endings in -is, which would only change (to -e) if moved to a neuter genus (13 of these are place-names). The remaining 43 names are fully gender variable. There are 68 adjectival names in total (including 19 adjectival place-names), with only two adjectival names completely invariant.

Type locality distribution
Type localities of the Hydroides serpulids listed are, with one exception, in shallow-water coastal locations in temperate to tropical waters between 43.3°N and 35.3°S (Figs 1-2). Hydroides norvegica is the exception from deeper water (but still inshore), and occurred at the highest latitude at 63.4°N. It is the most cold tolerant based on type locality, with a 20° latitudinal gap to all other species type localities, although its distribution extends south into the Mediterranean (Zibrowius 1971). The western Pacific Ocean (Australia to northern Japan) has the biggest group of new species at 39, with another 15 species in the northern Indian Ocean and Red Sea (Fig. 1), a total of 54 for the greater Indo-Pacific. The Americas north of the equator have 13 new species on the East Pacific coast, and 18 on the Western Atlantic coast and the Caribbean/Gulf of Mexico area (Fig. 2), a total of 31 for North American and Caribbean coasts combined. Europe (including Azores) has only 10 new species, mostly in the Mediterranean Sea (Fig. 1). This leaves only 12 other species described from elsewhere. Notably, few new species (9) have been reported from the major continental coasts of the South American coast south of the equator, and the African coast (outside of the Red Sea and Mediterranean, and including Madagascar), but this may be partly a reflection of lesser sampling effort, and also the consequence of other areas being examined first, given that Hydroides species are readily translocated on the floating objects and vessel hulls they colonise. and Stephen Keable (Australian Museum) for help with some locality data; Sameer Kumar Pati (Zoological Survey of India) for providing a little-known Lakshmana Rao article; lastly Rolando Bastida-Zavala (Universidad del Mar, Mexico) for improvements suggested during review. The contributions to the study by EKK and YS were supported by Australian Biological Resource Study grant RF213-19 to EKK.