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Key to Godzillius 1. Mx1 segment 4 without digitiform endite........................................... Godzilliognomus Yager, 1989 ��� Mx1 segment 4 with digitiform endite..............................................................................................2 2. Mx1 endite segment 4 with ten conical denticulae.................................. Godzillius louriei sp. nov. ��� Mx1 endite segment 4 with six to eight conical denticulae..............................................................3 3. Left md lacinia mobilis with five denticulae............................................................................................................................................................ Godzillius fuchsi Gonzalez, Singpiel & Schlagner, 2013 ��� Left md lacinia mobilis with six denticulae... Godzillius robustus Schram, Yager & Emerson, 1986, Published as part of Ballou, Lauren, Iliffe, Thomas M., Kakuk, Brian, Gonzalez, Brett C., Osborn, Karen J., Worsaae, Katrine, Meland, Kenneth, Broad, Kenneth, Bracken-Grissom, Heather & Olesen, J��rgen, 2021, Monsters in the dark: systematics and biogeography of the stygobitic genus Godzillius (Crustacea: Remipedia) from the Lucayan Archipelago, pp. 115-139 in European Journal of Taxonomy 751 (1) on page 129, DOI: 10.5852/ejt.2021.751.1383, http://zenodo.org/record/4905975, {"references":["Gonzalez B. C., Singpiel A. & Schlagner P. 2013. Godzillius fuchsi, a new species of Remipedia (Godzilliidae) from Abaco Island, Bahamas. Journal of Crustacean Biology 33: 275 - 285. https: // doi. org / 10.1163 / 1937240 X- 00002132","Schram F. R., Yager J. & Emerson M. J. 1986. Remipedia Part 1. Systematics. San Diego Society of Natural History, Memoir 15: 1 - 60."]}

Detailed description of the XXI muscle groups, measures, and supplementary Figures 1-5

DNA barcoding and population genetic studies have revealed an unforeseen hidden diversity of cryptic species among microscopic marine benthos, otherwise exhibiting highly similar and simple morphologies. This has led to a paradigm shift, rejecting cosmopolitism of marine meiofauna until genetically proven and challenging the “Everything is Everywhere, but the environment selects” hypothesis that claims ubiquitous distribution of microscopic organisms. With phylogenetic and species delimitation analyses of worldwide genetic samples of the meiofaunal family Dinophilidae (Annelida) we here resolve three genera within the family and showcase an exceptionally broad, boreal, North Atlantic distribution of a single microscopic marine species with no obvious means of dispersal besides vicariance. With its endobenthic lifestyle, small size, limited migratory powers and lack of pelagic larvae, the broad distribution of Dinophilus vorticoides seems to constitute a “meiofaunal paradox”. This species feasts in the biofilm among sand grains, but also on macroalgae and ice within which it can likely survive long-distance rafting dispersal due to its varying lifecycle stages; eggs encapsulated in cocoons and dormant encystment stages. Though often neglected and possibly underestimated among marine microscopic species, dormancy may be a highly significant factor for explaining wide distribution patterns and a key to solving this meiofaunal paradox.

Trilobodrilus ellenscrippsae sp. nov. urn:lsid:zoobank.org:act:47A17B17-80FA-4F67-A07F-15996730BE79 Fig. 3, Tables 1, 3���7 Diagnosis Short Trilobodrilus with two pairs of prostomial compound cilia encircled by four pairs of intermediate ciliary tufts anterior to first ciliary band. Additional ciliary tufts between first and second ciliary band. Dorsally continuous third ciliary band. Incomplete fourth ciliary band, posterior of third ciliary band with broad dorsal gap. Etymology This species is named (as a noun in the genitive case) to honour Ellen Browning Scripps (1836���1932), a founding benefactor of the Scripps Institution of Oceanography (McClain 2017) in La Jolla, California. No species have been named for her to date, yet Ellen Browning Scripps��� impact on science has been very important (see McClain 2017). Material examined Holotype UNITED STATES OF AMERICA: complete adult, 485 ��m long (platinum-palladinium-coated and mounted on stub for SEM), La Jolla Cove, La Jolla, California, 32��51���03��� N 117��16���20��� W, 9 m depth, 19 Apr. 2009, K. Worsaae and G. Rouse leg. (SIO-BIC A8209). Additional specimens mounted on slides were unfortunately lost after conducting the measurements. Description Measurements given first in the text from holotype, ranges in in parenthesis include measurements taken from the lost specimens. Compact body, light brown tint (fixed specimens, Fig. 3A). Body length 485 ��m (306���774 ��m, n = 4, Tables 1, 7), width 122 ��m (91���229 ��m, n = 4, Tables 1, 7), body segments indistinct (Fig. 3A���C). Prostomial shape conical (Fig. 3, Table 7). No eyes. Middle of the mouth located 69���88 ��m (n = 4) posterior of terminal prostomium (mo, Fig. 3A, C, F, Table 1). Four compound cilia terminally on prostomium (pcc, Fig. 3, Tables 1, 7), each consisting of approximately 30 cilia (n = 3); dorsal compound cilia spaced 19 ��m apart (16���29 ��m, n = 3), length similar to the cilia in the prostomial ciliary bands (10���18 ��m long, n = 3). Prostomial compound cilia surrounded by four pairs of semicircular arranged apical ciliary tufts (act, Fig. 3B, D���E, Table 7). Two prostomial ciliary bands on prostomium and one ciliary band posterior to the nuchal organs, as well as one additional incomplete fourth ciliary band posterior to these bands (cb1���4, Fig. 3B, E, Table 7). First dorsally continuous ciliary band (13 ��m wide, n = 1) encircles prostomium (Fig. 3A, D���E, Table 7). Several intermediate ciliary tufts located laterally between first and second ciliary band (ict, Fig. 3B, D���E, Table 7). Second ciliary band (cb2, Fig. 3A���B, D���F; 24 ��m wide, n = 1) dorsally incomplete with 48 ��m wide gap (n = 1) and one mid-dorsal ciliary tuft in center of gap (mdt, Fig. 3B, E, Table 7, 40���60 cilia, n = 1). One lateral pair of nuchal organs located between second and third ciliary band (no, Fig. 3F). Third ciliary band (10 ��m wide, n = 1) dorsally continuous (cb3, Fig. 3B���E, Table 7) posterior to nuchal organs. Fourth ciliary band extends laterally approx. 24 ��m (n = 1) from the ventral ciliary tract (cb4, Fig. 3B, E, Table 7). Ciliary tufts arranged laterally along the body (lct, Fig. 3B, Table 7). Ventral ciliary tract extends from posterior prostomium to posterior pygidium (vct, Fig. 3B���C, E; width of tract relative to total body width approximately 0.44 (n = 1)). Anus opening dorso-anteriorly on pygidium. No eggs present in the investigated specimens. Epidermal inclusions and spindle glands in the epidermis could not be described and measured due to insufficient preservation in the investigated specimens. Molecular information The following sequences were determined by Sanger sequencing from a single, non-type specimen collected on 19 April 2009, for which no morphological voucher remains: 18S rDNA, MG588090 (1857 nucleotides (nt), Table 4); 28S rDNA, MG588092 (1126 nt, Table 5); COI, MG588094 (644 nt, Table 6); CytB, MG588096 (426 nt). In the following, the sequences of T. ellenscrippsae sp. nov. are first compared to the most similar sequences found in T. windansea sp. nov., and the range of similarities with the addition of the respective species are subsequently listed. Trilobodrilus ellenscrippsae sp. nov. 18S rDNA is 99.9% similar to the 18S rDNA of T. windansea sp. nov., and 99.5% (T. axi) ��� 99.9% (T. nipponicus) similar to the other sequenced species (Table 4). Its 28S rDNA is 99.9% similar to the 28S rDNA of T. windansea sp. nov. and 98.5% (T. axi) ��� 99.4% (T. nipponicus) similar to the other species (Table 5). COI is 84.9% similar to T. windansea sp. nov., and 76% similar to the T. itoi and T. nipponicus (Table 6). Cytochrome B resembles the sequence of T. windansea sp. nov. to 85.6%. Habitat Subtidal in coarse to silty shell gravel at the surface layer at 9 m depth (subtidal). Distribution Trilobodrilus ellenscrippsae sp. nov. is known from La Jolla Cove, La Jolla, San Diego, California only. Remarks Trilobodrilus ellenscrippsae sp. nov. shows closest morphological resemblance to T. nipponicus (but nests with T. windansea sp. nov. in the molecular tree), but is much shorter, has a higher number of apical ciliary tufts on the prostomium, and its ciliary tufts along the body are not arranged in an as distinctive a pattern as in T. nipponicus (Fig. 3, Table 7). Trilobodrilus ellenscrippsae sp. nov. resembles T. windansea sp. nov. by having apical and intermediate ciliary tufts on the prostomium, and a dorsally incomplete second ciliary band with a mid-dorsal tuft (Fig. 3B, D���E, Table 7). However, T. ellenscrippsae sp. nov. differs from T. windansea sp. nov. in the shape of the prostomium, the additional ciliary row posterior to the second ciliary band, and by having a dorsally continuous third ciliary band as well as an incomplete fourth ciliary band (Fig. 3, Tables 1, 7). Trilobodrilus ellenscrippsae sp. nov. further differs in its genetic sequences from all other species, see Molecular information above or Tables 4���6., Published as part of Kerbl, Alexandra, Vereide, Emilie Hernes, Gonzalez, Brett C., Rouse, Greg W. & Worsaae, Katrine, 2018, Two new meiofaunal species of Trilobodrilus (Dinophilidae, Annelida) from California, USA, pp. 1-18 in European Journal of Taxonomy 421 on pages 12-15, DOI: 10.5852/ejt.2018.421, http://zenodo.org/record/1228304, {"references":["McClain M. 2017. Ellen Browning Scripps: New Money and American Philanthropy. University of Nebraska Press, Lincoln."]}

Trilobodrilus windansea sp. nov. urn:lsid:zoobank.org:act:A9DB66C3-C548-45C1-98F6-6 EFBA 019CF40 Fig. 1, Tables 1, 3���7 Diagnosis Trilobodrilus with two pairs of long prostomial compound cilia (1.5���2 times longer than locomotory cilia), encircled by five pairs of intermediate ciliary tufts anterior to the prostomial ciliary bands. First ciliary band with small dorsal gap. Dorsally incomplete second ciliary band with mid-dorsal ciliary tuft and additional posterior ciliary row. Dorsally incomplete third ciliary band posterior to nuchal organs, elongated epidermal inclusions, no spindle glands. Etymology This species is named after the beach where it was collected, Windansea Beach. Material examined Holotype UNITED STATES OF AMERICA: complete adult, 805 ��m long (platinum-palladinium-coated and mounted on stub for SEM), Windansea Beach, La Jolla, San Diego, California, 32��49���46��� N, 117��16���51��� W, coarse sand in holes at 0.5 m and 1 m at the mid ‐ and high ‐water mark, respectively, 14 Apr. 2009, K Worsaae and G Rouse leg. (SIO-BIC A8206). Paratypes UNITED STATES OF AMERICA: 4 specimens (2 mounted on same stub as holotype for SEM, 2 in 70% EtOH), same locality and sampling site as the holotype, 14 and 17 April 2009 (SIO-BIC A8207, SIO-BIC A8208, NHMD- 210468). Additional specimens mounted on slides were unfortunately lost after conducting the measurements. Description Measurements given from holotype, ranges given in parenthesis include paratypes and lost specimens. Transparent body, light brown to dark brown tint (live and fixed specimens) (Fig. 1A). Body length 715 ��m (499���1040 ��m, n = 12), width 86 ��m (84���189 ��m, n = 12), body segments indistinct (Fig. 1A��� C, Tables 1, 7). Prostomial shape square (Fig. 1A���F, Table 7). Eyes lacking. Middle of mouth located 110 ��m (77��� 133 ��m, n = 9) posterior of the apical tip (mo, Fig. 1A, C���D, Table 1). Four compound cilia terminally on prostomium (pcc, Fig. 1B, E���F), each consisting of approximately 50���60 cilia (n = 3), spaced 32 ��m apart (18���32 ��m, n = 10). Compound cilia substantially (up to two times) longer than locomotory cilia in ciliary bands (19���43 ��m relative to 8���20 ��m in ciliary bands, n = 10, Fig. 1A, D, Table 1). Prostomial compound cilia surrounded by five pairs of semicircularly arranged apical ciliary tufts (act, Fig. 1B, E���F, Tables 1, 7). Two ciliary bands on prostomium and one ciliary band posterior to the nuchal organs (cb1���3, Fig. 1A���F, Table 7). First ciliary band (12���19 ��m wide, n = 3) encircles prostomium with 7���8 ��m wide dorsal gap (cb1, Fig. 1A���B, E���F, Table 7). One pair of intermediate ciliary tufts located laterally between first and second ciliary band (ict, Fig. 1B, E). Second ciliary band (13���19 ��m wide) dorsally incomplete with 43���46 ��m wide gap and one mid-dorsal ciliary tuft in center of gap (mdt, Fig. 1B, E���F, Table 7; consisting of 50���70 cilia, n = 3). One additional thin row of cilia (5���7 ��m wide, n = 2) lines the second ciliary band postero-laterally, not extending dorsally for the entire length of the second ciliary band (acr, Fig. 1E���F, Table 7). One lateral pair of nuchal organs located between the second and third ciliary band (no, Fig. 1B, E���F). Third ciliary band dorsally incomplete with wide gap (cb3, Fig. 1B, E���F, Table 7); width of third ciliary band 10���17 ��m, width of gap 39���50 ��m (n = 3). Individual cilia scattered across the body (Fig. 1B, E). The ventral ciliary tract extends from posterior prostomium to posterior pygidium (vct, Fig. 1B���C, E; width of tract relative to total body width approximately 0.6 (n = 3)). Anus opening dorso-anteriorly on pygidium. Eggs 126���143 ��m long, located 534���464 ��m posterior to the prostomial tip and 209���194 ��m (n = 2) anterior to pygidial tip (Fig. 1G). Epidermal inclusions in the epidermis (Fig. 1H, Table 7); average measurement of envelope 4 �� 9 ��m, 4���8 spherules per envelope (n = 12); no spindle glands. Molecular information The following sequences were determined by standard sequencing from a single, non-type specimen collected on 14 Apr 2009, for which no morphological voucher remains: 18S rDNA, MG588089 (1857 nucleotides (nt), Table 4); 28S rDNA, MG588091 (1126 nt, Table 5); COI, MG588093 (644 nt, Table 6); CytB, MG588095 (421 nt). In the following, the sequences of T. windansea sp. nov. are first compared to the most similar sequences found in T. ellenscrippsae sp. nov., and subsequently the range of similarities to the respective species is listed. Trilobodrilus windansea sp. nov. 18S rDNA fragment is 99.9% similar to the 18S rDNA of T. ellenscrippsae sp. nov., and 99.1% (T. nipponicus) ��� 99.5% (T. axi) similar to the 18S rDNA fragments of the other sequenced species (Table 4). Its 28S rDNA fragment is 99.9% similar to the 28S rDNA of T. ellenscrippsae sp. nov., and 98.6% (T. axi) ��� 99.4% (T. nipponicus) similar to the 28S rDNA fragments of the other sequenced species (Table 5). COI is 84.9% similar to the COI of T. ellenscrippsae sp. nov., and 76.9% (T. itoi) ��� 78.6% (T. nipponicus) similar to the sequences of the other species (Table 6). Cytochrome B is 85.6% similar to T. ellenscrippsae sp. nov. In both the maximum-likelihood as well as the Bayesian analyses, T. windansea sp. nov. was found to be the sister species of T. ellenscrippsae sp. nov. with full support, the two of them forming the sister group to the T. itoi ��� T. nipponicus clade (Fig. 2). These Pacific species were shown to be the sister clade to the group formed by the Atlantic species T. axi and T. heideri (Fig. 2). All Trilobodrilus -species form a sister-clade to Dinophilus sp., a representative of the second dinophilid genus (Fig. 2). Habitat Intertidal zone of a clean, coarse, well-sorted sandy beach, 0.5���1 m below the mid- and high water mark. Distribution Trilobodrilus windansea sp. nov. is only known from Windansea Beach, La Jolla, San Diego, California. Remarks Trilobodrilus windansea sp. nov. most closely resembles T. itoi in morphology (but T. ellenscrippsae sp. nov. in its molecular profile), but still differs by having more apical ciliary tufts, by having an additional row of cilia posterior to the second ciliary band, and by lacking a fourth ciliary band as well as segmentally arranged ciliary tufts along the body (Fig. 1, Table 7). Furthermore, the epidermal inclusions are more elongated and include fewer spherules than in T. itoi (Table 7). Trilobodrilus windansea sp. nov. resembles the other Californian species, T. ellenscrippsae sp. nov., in having a dorsally incomplete second ciliary band with mid ‐dorsal tuft, but differs in having longer prostomial compound cilia, one more pair of apical ciliary tufts, a small dorsal gap in the first ciliary band, an additional row of cilia posterior to the second ciliary band, a dorsally incomplete third ciliary band, and by lacking a fourth ciliary band (Fig. 1, Table 7). Trilobodrilus windansea sp. nov. further differs from T. ellenscrippsae sp. nov., T. itoi, T. axi and T. heideri in comparison of gene fragments, see Molecular information above or Tables 4���6., Published as part of Kerbl, Alexandra, Vereide, Emilie Hernes, Gonzalez, Brett C., Rouse, Greg W. & Worsaae, Katrine, 2018, Two new meiofaunal species of Trilobodrilus (Dinophilidae, Annelida) from California, USA, pp. 1-18 in European Journal of Taxonomy 421 on pages 6-12, DOI: 10.5852/ejt.2018.421, http://zenodo.org/record/1228304, {"references":["Kajihara H., Ikoma M., Yamasaki H. & Hiruta S. F. 2015. Trilobodrilus itoi sp. nov., with a re-description of T. nipponicus (Annelida: Dinophilidae) and a molecular phylogeny of the genus. Zoological Science 32: 405 - 417. https: // doi. org / 10.2108 / zs 140251"]}

Land-locked anchialine blue holes are karstic sinkholes and caves with tidally influenced, vertically stratified water bodies that harbor endemic fauna exhibiting variable troglomorphic features. These habitats represent island-like systems, which can serve to elucidate evolutionary and biogeographic processes at local scales. We investigated whether the ‘continuous spelean corridor’ hypothesis may elucidate the biogeographical distributions of the stygobitic annelid Pelagomacellicephala iliffei (Polynoidae) collected from the Great Bahama and Caicos Banks of the Bahamas Archipelago. Phylogenetic reconstructions were performed using Bayesian Inference on individual and combined datasets of three molecular markers (16S rDNA, COI, 18S rDNA) and species delimitation employed three widely accepted methods in DNA taxonomy, namely GMYC, bPTP, and ABGD. Mantel tests were used to test the effect of geography on genetic structure. Using these analyses, we recovered five independently evolving entities of the focal species across four islands of the Great Bahama Bank including Cat, Eleuthera, Exumas, and Long. Genetic data yielded strong correlations between islands and phylogenetic entities, signifying independent evolutionary histories within anchialine caves across the platform. The island of Eleuthera showed intra-island gene flow and dispersal capabilities between blue holes separated by 115 km, providing evidence of a crevicular spelean corridor within the island. However, no evidence of inter-island dispersal is present in the analyzed system. Consistent with previous biogeographic studies of cave crustaceans, the major barriers shaping the cave biota of the Bahamas Archipelago appears to be the deep trenches and channels separating the Bahamian banks.

Petersen, H. Cecilie B., Gonzalez, Brett C., Martínez, Alejandro, Worsaae, Katrine (2016): New species of Pisionidens (Sigalionidae, Annelida) from Akumal, México. Zootaxa 4136 (1): 165-173, DOI: http://doi.org/10.11646/zootaxa.4136.1.8

Pisionidens ixazaluohae n. sp. (Tables 1���2, Figs 1���2) Material examined. Half Moon Bay, Akumal, Quintana Roo, M��xico, 15 specimens. Holotype: complete adult male (ZMUC-POL- 2435, stub-mounted for SEM), 13.3 mm long, 65 segments. Coarse sand, swash zone, 0.2 m depth, 20 �� 24.22 'N, 87 �� 18.28 'W. Collectors: B. C. Gonzalez & A. Mart��nez 19.06. 2014. Paratypes: 1 male (ZMUC-POL- 2436, stub-mounted for SEM), 4 females (1 stub-mounted for ZMUC-POL-2437, 3 preserved and stored in ethanol ZMUC-POL- 2439, ZMUC-POL- 2440), 4 incomplete specimens (ZMUC-POL- 2441), sex unknown (4.25���8.72 mm, 24���41 segments, stored in ethanol) and 4 specimens in bad condition (ZMUC-POL- 2442), sex unknown (7.88���17.75 mm, fixed in PFA, stored in PBS), same locality and sampling date as holotype. Diagnosis. Muscular and slender body, anteriorly and posteriorly tapering. One pair of anterior, basally fused antennae, two smooth lateral prostomial palps; one pair of ventral elongated cirri on segment 2, one pair of dorsal elongated cirri on segment 3. Pharynx eversible, with a terminal crown of 18 papillae and two pairs of hook-shaped jaws. Achaetous parapodia with distal glandular disc present from segment 8 onward. Males with one row of midventral pores from segment 11 to posterior end. One pair of club-shaped copulatory organs on segment 45. Description. All measurements from the holotype, parenthetical numbers from paratypes. Body slender, muscular, white to pale yellow (fixed specimens) (Fig. 1 A), with thick cuticle and smooth body surface. Length 13.3 mm (7.33���17.75 mm, n= 10), width including parapodia 0.45 mm (0.47���0.69 mm, n= 5), width excluding parapodia 0.34 mm (0.24���0.52 mm, n= 15), 65 segments (45���62, n= 5). Fused conical prostomium with segment 1, one pair of antennae fused at base (Fig. 2 A). One pair of palps, smooth, 0.28 mm long (0.22���0.34 mm, n= 7), emerging laterally from prostomium (Fig. 2 A). One pair of dorsal eyes in segment 2 (Fig. 1 B). Cerebral ganglion large, bilobed, extending from middle of segment 1 to segment 4. Mouth ventral with eversible pharynx, equipped with two pairs of hooked jaws (Fig. 1 C). Pharynx with a terminal crown of 18 digitiform papillae (Fig. 2 B), central papilla largest, decreasing in size laterally. Segments 1���3 lacking parapodia, segments 4-7 with rudimentary parapodia. Ventral cirri on segment 2 (buccal segment), long and tapering, similar in length to palps; dorsal cirri on segment 2 small, bottle-shaped (Fig. 2 A, C). Dorsal cirri on segment 3 (see Rouse and Pleijel 2001) longest among anterior appendages, approximately twice the length of palps (Fig. 2 A); ventral cirri on segment 3 small and bottle-shaped (Fig. 2 C). All anterior appendages smooth. From segment 4 posteriorly, dorsal and ventral cirri small with subdistal and distal cilia (Fig. 2 D). Rudimentary parapodia and cirri may be lacking in some specimens from segment 4 to segment 7 (Fig. 2 C). Parapodia initiating on segment 8, achaetous in mature specimens (unknown in juveniles). All parapodia cylindrical and slender, with subdistal tufts of compound cilia; distal disc with adhesive glands (Fig. 2 D). Notoacicula absent, neuroacicula straight (Fig. 1 D). Adult males with midventral line of segmentally repeated pores ca. 35 ��m wide (n= 2) from segment 11 to last segment prior to pygidium, pore diameter smaller on copulatory segment (ca. 10���15 ��m, n= 2) (Fig. 2 E); midventral pores lacking in females and juveniles. Paired lateral fields of ca. 35 epidermal pores (2-5 ��m) present between parapodia. Pygidium with one pair of cirri, short and cylindrical (Fig. 2 F). Anus dorsal. One pair of male copulatory organs, on segment 45 in holotype (42, n= 1), with short dorsal cirri, parapodia and ventral cirri absent. Copulatory organ approximately same length as body width (0.40 mm, n= 1), club-shaped, curved latero-ventrally, with subdistal node-shaped process (Fig. 2 G) and small papillae distally; tip slightly curled, with small terminal process (Fig. 2 H), but lacking cuticular hooks. Females appear to differ from males externally only in the absence of copulatory organs and mid-ventral pores. Molecular information. Newly generated sequences for Pisionidens ixazaluohae n. sp. included 1800 bp of 18 S rDNA (Gb accession number KX 282503), 1039 bp of 28 S rDNA (Gb accession number KX 282504), 510 bp of 16 S rDNA (Gb accession number KX 282502), and 582 bp of COI (Gb accession number KX 282505). In previous molecular analyses (Gonzalez et al. 2015), Pisionidens ixazaluohae n. sp. was recovered next to Pisionidens sp. (Norlinder et al. 2012), forming the well-supported sister clade of all the species of Pisione included in the analyses. The COI gene fragment of Pisionidens ixazaluohae n. sp. presents 83.4 % similarity to the COI of Pisionidens sp. (Acc. Num JN 852943), being the only Pisionidens sequence available in GenBank. This similarity accounts for 94 mutations, three of them non-synonymous. Remarks. Pisionidens ixazaluohae n. sp. is characterized by having only one pair of copulatory organs, while the previously described species possess two to four pairs. P. ixazaluohae n. sp. differs from P. indica (Aiyar & Alikuhni 1940) and Pisionidens tchesunovi, Tzetlin 1987 by lacking true parapodia on segments with copulatory organs. This feature is similarly found in Pisionidens maturata, Yamanishi 1976. However, P. ixazaluohae n. sp. is distinguished from P. m at ur a t a and P. indica by having one continuous series of midventral pores (versus two separate series of ventral pores). A comprehensive comparison of taxonomic characters and distribution of all described species of the genus Pisionidens is given in Table 2. Holotype ZMUC-POL- 2435 Ađult Male 1 13.3 mm 64 45 0.28 mm 0.35 / 0.43 mm 0.45 / 0.34 mm Paratype 1 ZMUC-POL- 2436 Ađult Female 1 11.0 mm 54 0.26 mm 0.34 / 0.44 mm 0.51 / 0.37 mm Paratype 2 ZMUC-POL- 2437 Ađult Male 1 10.6 mm 61 42 0.22 mm 0.22 / 0.35 mm 0.49 / 0.30 mm Paratype 3 ZMUC-POL- 2438 Ađult Female 1 4.2 mm 24 * 0.31 mm 0.30 / 0.36 mm 0.47 / 0.29 mm Paratype 4 ZMUC-POL- 2439 Ađult Female 1 13.4 mm 62 0.32 mm 0.33 / 0.38 mm */ 0.34 mm Paratype 5 ZMUC-POL- 2440 ?? 2 8.2 mm 45 0.25 mm 0.19 / 0.35 mm */ 0.30 mm Ađult? 17.7 mm 52 * * 0.69 / 0.52 mm Paratype 6 ZMUC-POL- 2441 Ađult? 4 14.1 mm * * * */ 0.45 mm Ađult? 16.5 mm * 0.30 mm 0.31 / 0.45 mm */ 0.45 mm ?? 7.9 mm * * * */ 0.28 mm Ađult? 8.7 mm 41 *?/ 0.39 mm */ 0.35 mm Paratype 7 ZMUC-POL- 2442 Ađult? 4 6.2 mm * * * */ 0.38 mm Ađult? 13.1 mm * * * */ 0.26 mm ?? 7.3 mm * * * */ 0.24 mm Ađult? 6.2 mm * * * */ 0.44 mm Type locality. Half Moon Bay, Akumal, Quintana Roo, M��xico. Habitat. Coarse sand in the swash zone of an exposed beach: 0���0.25 m depth. Several other annelids were found in the samples including Claudrilus cf. ovarium (Di Domenico et al. 2013), Saccocirrus sp., Polygordius sp., Microphthalmus sp., Macrochaeta sp., Pholoe sp., as well as high numbers of Ingolfiella sp. and otoplanid flatworms. Distribution. Caribbean Sea, Akumal, M��xico. Etymology. Named after the Mayan goddess of water, Ixazaluoh., Published as part of Petersen, H. Cecilie B., Gonzalez, Brett C., Mart��nez, Alejandro & Worsaae, Katrine, 2016, New species of Pisionidens (Sigalionidae, Annelida) from Akumal, M��xico, pp. 165-173 in Zootaxa 4136 (1) on pages 167-171, DOI: 10.11646/zootaxa.4136.1.8, http://zenodo.org/record/255493, {"references":["Rouse, G. & Pleijel, F. (2001) Polychaetes. Oxford university press, 353 pp.","Norlinder, E., Nygren, A., Wiklund, H. & Pleijel, F. (2012) Phylogeny of scale-worms (Aphroditiformia, Annelida), assessed from 18 SrRNA, 28 SrRNA, 16 SrRNA, mitochondrial cytochrome c oxidase subunit I (COI), and morphology. Molecular Phylogenetics and Evolution, 65 (2), 490 - 500. http: // dx. doi. org / 10.1016 / j. ympev. 2012.07.002","Aiyar, R. G. & Alikunhi, K. H. (1940) On a new pisionid from the sandy beach, Madras. Record of the Indian Museum, 42 (1), 89 - 107.","Tzetlin, A. B. (1987) Description of Pisionidens tchesunovi sp. n. (Polychaeta, Pisionidae) from the Red Sea. Zoologicheskii Zhurnal, 66 (9), 1408 - 1412.","Yamanishi, R. (1976) Interstitial polychaetes of Japan I. Three new pisionid worms from Western Japan. Publications of the Seto Marine Biological Laboratory, 23 (3 - 5), 371 - 385.","Di Domenico, M., Martinez, A., da Cunha Lana, P. & Worsaae, K. (2013) Protodrilus (Protodrilidae, Annelida) from the Southern and Southeastern Brazilian Coasts. Helgoland Marine Research, 67 (4), 733 - 748. http: // dx. doi. org / 10.1007 / s 10152 - 013 - 0358 - z"]}