Euphrosinopsis ahearni, Neal & Wiklund & Gunton & Rabone & Bribiesca-Contreras & Dahlgren & Glover, 2022

Neal, Lenka, Wiklund, Helena, Gunton, Laetitia M., Rabone, Muriel, Bribiesca-Contreras, Guadalupe, Dahlgren, Thomas G. & Glover, Adrian G., 2022, Abyssal fauna of polymetallic nodule exploration areas, eastern Clarion-Clipperton Zone, central Pacific Ocean: Amphinomidae and Euphrosinidae (Annelida, Amphinomida), ZooKeys 1137, pp. 33-74 : 33

Euphrosinopsis ahearni sp. nov.

Figs 15B , 17A-F , 18A-F , 19A-I

Material examined.

NHM_0095, NHMUK ANEA 2022.644, coll. 11/10/2013, box core, 13.79335, -116.70308, 4081 m, UK-1, http://data.nhm.ac.uk/object/a351cb41-736c-4390-8ad8-02c0358b73e0; NHM_0888, NHMUK ANEA 2022.645, coll. 23/02/2015, EBS, 12.571333, -116.6105, 4198 m, UK-1, http://data.nhm.ac.uk/object/4d76b4e2-569d-4a17-9276-3ce721cbdf72; NHM_0551 (paratype, SEM), NHMUK ANEA 2022.646, coll. 17/02/2015, EBS, 12.386243, -116.54867, 4202 m, UK-1, http://data.nhm.ac.uk/object/241b828d-a574-47f2-995d-0bdef239c427; NHM_5042, NHMUK ANEA 2022.647, coll. 30/10/2020, box core, 10.92936, -116.26351, 4262 m, NORI-D, http://data.nhm.ac.uk/object/1662fd8b-54a5-4f97-9083-02dbb2df7e39; NHM_1737A, NHMUK ANEA 2022.648, coll. 11/03/2015, EBS, 12.17383, -117.19283, 4045 m, OMS, http://data.nhm.ac.uk/object/4f372c07-c466-4b6c-91a9-229cd7c7a17d; NHM_1876, NHMUK ANEA 2022.649, coll. 13/03/2015, EBS, 12.0415, -117.21717, 4094 m, OMS, http://data.nhm.ac.uk/object/6ad5c2b3-ece8-4195-a19f-3913de511e71; NHM_0550, NHMUK ANEA 2022.650, 17/02/2015, EBS, 12.386243, -116.54867, 4202 m, UK-1, http://data.nhm.ac.uk/object/92791783-35c2-4fbf-80b0-2b074ef70828; NHM_1302, NHMUK ANEA 2022.651, coll. 01/03/2015, EBS, 12.257333, -117.3021667, 4302 m, OMS, http://data.nhm.ac.uk/object/7aabe644-2ec6-4671-8c1a-f826eeeb0b46; NHM_1302A (holotype), NHMUK ANEA 2022.652, coll. 01/03/2015, EBS, 12.257333, -117.3021667, 4302 m, OMS, http://data.nhm.ac.uk/object/479933d3-9943-4d87-a1b8-ea120bd8f4ee; NHM_1737, NHMUK ANEA 2022.653, coll. 11/03/2015, EBS, 12.17383, -117.19283, 4045 m, OMS, http://data.nhm.ac.uk/object/2ca3e584-a68d-4ea5-98d2-75ce10515386;

NHM_1737C (paratype), NHMUK ANEA 2022.654, coll. 11/03/2015, EBS, 12.17383, -117.19283, 4045 m, OMS, http://data.nhm.ac.uk/object/efe95a8c-fc88-4849-ad26-1df3d292ef20; NHM_0616, NHMUK ANEA 2022.655, coll. 17/02/2015, EBS, 12.386243, -116.54867, 4202 m, UK-1, http://data.nhm.ac.uk/object/4758bf19-c6d0-42e0-b5ba-e83e203d2e18; NHM_0759, NHMUK ANEA 2022.656, coll. 20/02/2015, EBS, 12.53717, -116.60417, 4425 m, UK-1, http://data.nhm.ac.uk/object/b0f9162f-a861-4eb2-89a1-ce25c2bd09c4; NHM_1839, NHMUK ANEA 2022.657, coll. 12/03/2015, box core, 12.0999, -117.1966, 4051 m, OMS, http://data.nhm.ac.uk/object/02a5ace7-841e-4f50-bf03-57ba21f02f7c.

Diagnosis.

Holotype (NHMUK ANEA.2022.652) complete (except for tissue sampled for DNA), 2.2 mm long and 0.8 mm wide without chaetae for 12 chaetigers (Fig. 17A-F ). Paratype (NHMUK ANEA.2022.654) complete (except for tissue sampled for DNA), 2.8 mm long and 1 mm wide for 12 chaetigers (Fig. 18A-F ). Paratype (NHMUK ANEA.2022.646, SEM specimen) anterior fragment only (Fig. 19A-I ). Body short, oval, flattened, pale yellow in alcohol (Figs 17A , 18B ), with a patch of light brown pigmentation on prostomium (Fig. 18C ). Live specimen pale with blueish hues (Fig. 18A ). Prostomium longer than wide, with 5 prostomial appendages (Fig. 15B ). Pair of short slender palps (Figs 17C , 18D ); pair of slender lateral antenna (at least twice the length of palps) (Figs 17C , 18D ) and median antenna of caruncle with long thick ceratophore and very long slender cirrus reaching dorsally to chaetiger 7 (Fig. 17F ). Caruncle as oval lobe reaching to anterior margin of chaetiger 4, mostly free of body wall, with median keel and two pairs of lateral ridges, median keel slightly thicker than the lateral ones. Single pair of large, spherical eyes, deeply embedded, lateral to median antenna and caruncle (Figs 15B , 18A ).

Parapodia biramous, two rami well separated. Parapodia of chaetiger 1 well developed, not reduced, parapodial cirri, branchiae or ringent chaetae not observed. In subsequent parapodia, parapodial appendages in the following dorsoventral order: dorsal cirrus, 1st branchia, lateral cirrus, 2nd branchia, ventral cirrus (Fig. 15E ). Dorsal cirrus as a single very long filament (extending over two chaetigers in mid-body segments) (Fig. 18F ); the lateral cirrus as a shorter, stouter filament (Fig. 17D, E ); ventral cirri often missing, when observed, very slender (Fig. 18E ). Branchiae up to two pairs present per segment in mid-body, first branchia attached laterally to dorsal cirrus (Figs 15E , 18F ), second branchia attached laterally to lateral cirrus (Figs 15E , 17D ), both branchiae branched with 2-4 very long and slender branches (Figs 15E , 17D, E , 18E, F ).

Chaetae fragile, prone to breakage, of two main types: 1. Numerous, bifurcate chaetae arranged in three rows in notopodia; their shafts of various length and thickness (Fig. 19A ); their prongs variable in length with short furcate chaetae in anterior tier having the ratio of short to long prong ca. 1:3.5 (where possible to establish), the prong ratio of longest chaetae in the mid tear 1:4-5 (where possible to establish); prongs mainly smooth or with faint serration (Fig. 19C-E ); 2. Ringent chaetae (sensu Kudenov 1993) present in notopodia only, numerous (ca. 20 per notopodium) (Fig. 19A, B ), composed of two curved prongs of unequal length and thickness, both with distinct serration, the long prong distally with slender tip, short prong broad and distally rounded (Fig. 19F-I ). Neurochaetae numerous, but thinner than notochaetae, all bifurcate, of varying lengths prongs appearing smooth. Pygidium with paired anal cirri, resembling cylindrical tube feet (Fig. 17A, B ).

Molecular Information.

Specimen (NHMUK ANEA.2022.644) was sequenced for 16S and 18S while 14 other specimens were sequenced for 16S only. There were no identical sequences for 16S on GenBank (Table 1 ). The relationships between Euphrosinella and Euphrosinopsis in the phylogenetic tree is unresolved (Fig. 5B ). As COI sequencing was not successful in this study, all euphrosinid species are represented by only 16S and 18S.

Remarks.

The CCZ species agrees well with the genus Euphrosinopsis in having five prostomial appendages, caruncle partially free from the body wall and the presence of large, deeply embedded eyes lateral to median antenna and caruncle. However, this species shows differences from all known species in this genus, suggesting it belongs to a new species. Euphrosinopsis crassiseta (type locality: Weddell Sea, 3697 m) can be easily distinguished by having only small, cirriform branchia per segment rather than two pairs of branched branchiae, by the absence of ringent chaetae and presence of coarsely serrated neurochaetae. Euphrosinopsis horsti (type locality: Pacific Antarctic Ridge, 3219-3255 m) also has only one very small, cirriform branchia per segment. Ringent chaetae are present in the known species, but they possess a distal tooth in the gap, which is absent in the new species. Finally, the most similar species, Euphrosinopsis antarctica can be distinguished by having up to three branchiae per segment, the first branched, but the others cirriform and style of median antenna of similar length to caruncle, rather than much longer as in the new species.

Thus, Euphrosinopsis ahearni sp. nov. can be distinguished mainly by having two pairs of branched branchiae in midbody chaetigers, both with very long thin branches. That is also the main distinguishing character from its congener from the CCZ, E. halli sp. nov. also described in this study, which possess only single cirriform branchia in each parapodium. Both new species possess ringent notochaetae, that can be distinguished as follow: 1. They are numerous (ca. 20 per notopodium) and easily observed in E. ahearni sp. nov., whilst only few (ca. 5 per notopodium) can be found in E. halli sp. nov.; 2. The serration of inner margin is more pronounced in E. ahearni sp. nov. and 3. The distal tip is shorter and stubbier in E. ahearni sp. nov. Further, the caruncle is more developed in E. ahearni sp. nov. reaching to chaetiger four, not two as in E. halli sp. nov., and style of median antenna is much longer than caruncle in the former species, whilst they are ca. the same length in the latter.

Distribution.

Central Pacific Ocean, Eastern CCZ, the exploration areas UK-1, OMS, and NORI-D (Fig. 1 ).

Etymology.

This species is named for Patrick A’Hearn, technician from the University of Washington onboard the RV Thomas G Thompson.

Figures

Figure 1. Map of CCZ of exploration areas and areas of particular interest, with targeted areas where samples of this study were collected highlighted in colours (see legend for explanation).

Figure 5. Majority-rule consensus trees from the Bayesian analyses with posterior probability values on nodes. Taxon names highlighted in blue are news species or new sequences for already known species. A Amphinomidae phylogenetic tree using a combined datasets for COI, 16 S, and 18 S with 26 terminal taxa of which Euphrosine foliosa (Euphrosinidae) was used as a root B Euphrosinidae phylogenetic tree using a combined datasets for 16 S and 18 S with nine terminal taxa of which Paramphinome jeffreysii (Amphinomidae) was used as a root.

Figure 15. Diagrammatic representation of prostomial (A-C) and parapodial appendages from mid-body chaetigers (D, E) of CCZ-collected Euphrosinidae species (relative lengths preserved, but not drawn to scale) A Euphrosinella georgievae sp. nov. B Euphrosinopsis ahearni sp. nov. C Euphrosinopsis halli sp. nov. D Euphrosinella georgievae sp. nov. E Euphrosinopsis ahearni sp. nov. F Euphrosinopsis halli sp. nov. Abbreviations: P - palps, La - lateral antennae, Ma - median antenna, Car - caruncle, E - eyes, DC - dorsal cirrus, LC - lateral cirrus, VC - ventral cirrus, Br - branchiae.

Figure 17. Euphrosinopsis ahearni sp. nov. (holotype NHMUK ANEA. 2022.652) A preserved specimen in dorsolateral view, pygidial cirri marked by arrows B specimen Shirlastained in dorsolateral view, pygidial cirri marked by arrows C detail of prostomium in dorsal view with palps (p) and lateral antennae (la) marked by arrows D, E branched branchiae (br) and lateral cirrus (cir) of midbody chaetigers F detail of midbody chaetigers, median antenna (ma) marked by arrow. Scale bars: 1 mm. Abbreviations: P - palps, la - lateral antennae, cir - cirrus, br - branchiae, ma - median antenna.

Figure 18. Euphrosinopsis ahearni sp. nov. (paratype NHMUK ANEA. 2022.654, unless stated otherwise) A live image of paratype (NHMUK ANEA. 2022.646), with eyespots (E) marked by arrows B preserved specimen in dorsolateral view C anterior end in dorsolateral view D detail of prostomium (specimen stained with Shirlastain) with palp (P) and lateral antennae (La) marked by arrows E two pairs of branched branchiae (Br), lateral cirrus (LC) and ventral cirrus (VC) of midbody chaetigers F dorsal cirrus (DC) and branchia (Br) of midbody chaetigers. Scale bars: 1 mm. Abbreviations: E - eyes, P - palps, La - lateral antennae, Br - branchiae, LC - lateral cirrus, VC - ventral cirrus, DC dorsal cirrus.

Figure 19. Euphrosinopsis ahearni sp. nov. (paratype NHMUK ANEA. 2022.646) A mid-body parapodium B notochaetae - anterior tier bifurcate and mid-tier ringent chaetae C bifurcate notochaetae posterior tier D, E details of variously serrated bifurcate notochaetae F, G examples of non-pigmented ringent notochaetae H details of pigmented ringent chaeta I SEM micrograph of ringent chaeta. Scale bars: 250 µm (A); 100 µm (B-D); 50 µm (E-H); 20 µm (I).