Euphrosinopsis halli, 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 halli sp. nov.

Figs 15C , 20A-E , 21 A-E

Material examined.

NHM_0779, NHMUK ANEA 2022.641, coll. 20/02/2015, EBS, 12.53717, -116.60417, 4425 m, UK-1, http://data.nhm.ac.uk/object/1a683870-d904-4c2c-bf1a-a34ead0a42fc; NHM_4339 (holotype), NHMUK ANEA 2022.642, coll. 11/03/2020, box core, 12.17997, -117.065277, 4117 m, UK-1, http://data.nhm.ac.uk/object/670dfd34-338d-4edc-8856-b0a9a728efc9; NHM_6018 (paratype), NHMUK ANEA 2022.643; coll. 13/11/2020, box core, 10.35780, -117.15931, 4284 m, NORI-D, http://data.nhm.ac.uk/object/ab26e2ea-ab87-4013-8106-e817c0485cc9.

Diagnosis.

Holotype (NHMUK ANEA.2022.642) complete (except for tissue sampled for DNA), 1.3 mm long and 0.75 mm wide without chaetae for 11 chaetigers. Paratype (NHMUK ANEA.2022.643) complete (except for tissue sampled for DNA), 1.5 mm long and 0.75 mm wide for 12 chaetigers. Body short, oval, flattened, pale yellow in alcohol (Fig. 20A ). Prostomium longer than wide, with 5 prostomial appendages (Fig. 15C ). Pair of short slender palps; pair of slender lateral antenna; median antenna of caruncle with long thick ceratophore and slender cirrus of similar length to caruncle (Figs 15C , 20B ). Caruncle as oval lobe reaching to chaetiger 2, mostly free of body wall, with median keel and two pairs of lateral ridges, median keel slightly thicker than the lateral ones (Fig. 20B ). Single pair of large, spherical eyes, deeply embedded, lateral to median antenna and caruncle (Figs 15C , 20A ).

Parapodia biramous, two rami well separated. With parapodial appendages observed dorso-ventrally as follow (Figs 15F , 20C ): long slender dorsal cirrus, often curved into S-shape in middle chaetigers; single cirriform branchia attached laterally to dorsal cirrus; lateral cirrus similar to branchia in form, but more robust; slender cirriform ventral cirrus.

Chaetae fragile, prone to breakage, of two main types: 1. Numerous, bifurcate chaetae arranged in approximately three rows in notopodia; their shafts of various length and thickness (Fig. 21A ); development of filelike teeth on shafts ranging from smooth (Fig. 21C ) to well developed (Fig. 21D, E ); their prongs variable in length with short furcate chaetae in anterior tier having the ratio of short to long prong ranging from 1:2-2.5 (where possible to establish), the prong ratio of longest chaetae in the mid tear ranging from 1:3.5-4 (where possible to establish); prongs mainly smooth or with extremely faint serration only visible under high magnification (Fig. 21B ). 2. Ringent chaetae (sensu Kudenov 1993) present in notopodia only, few in numbers (ca. 5 per notopodium), composed of two curved prongs of unequal length and thickness, both with indistinct serration, the long prong distally with slender elongated tip, short prong broad and distally rounded (Fig. 20D, E ). Neurochaetae similar less numerous, thinner, and shorter than notochaetae, all bifurcate, prongs appearing smooth, often broken off. Pygidium with pair of cirri resembling cylindrical tube feet.

Molecular information.

Specimen NHMUK ANEA.2022.641, was sequenced for 16S and 18S while paratype NHMUK ANEA.2022.643 and holotype NHMUK ANEA.2022.642 were sequenced for 16S only (Table 1 ). There were no identical sequences for 16S on GenBank. 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, and in the case of the species from GenBank, only 16S.

Remarks.

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. The presence of single, small, unbranched cirriform branchia per parapodium suggest affiliation with E. crassiseta and E. horsti , which share the same character. However, the new species differs from E. crassiseta in possessing the ringent chaetae and lacking the coarse serration on neurochaetae. The most similar species, E. horsti can be easily separated by having anal cirri fused instead of typical cylindrical tube feet as in the new species. For comparison with another new Euphrosinopsis species also described in this study see the remarks section for E. ahearni sp. nov.

Distribution.

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

Etymology.

This species is named for Preben Hall, the captain onboard the ship Maersk Launcher that was used in NORI-D expeditions in 2020 and 2021.

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 20. Euphrosinopsis halli sp. nov. A preserved holotype NHMUK ANEA. 2022.642, eye spots visible B holotype NHMUK ANEA. 2022.642 stained with Shirlastain, showing caruncle (car) and median antenna (Ma) C specimen NHMUK ANEA. 2022.641 stained with Shirlastain, showing branchiae (Br) and dorsal cirri (Dc) and lateral cirrus (Lc) D, E ringent chaetae from specimen NHMUK ANEA. 2022.641. Scale bars: 500 µm (A, C); 25 µm (D); 50 µm (E). Abbreviations: Ma - median antenna, Car - caruncle, Br - branchiae, Dc - dorsal cirrus, Lc - lateral cirrus.

Figure 21. Euphrosinopsis halli sp. nov. (holotype NHMUK ANEA. 2022.642) A long and short furcate notochaetae B faint serration of long prong (marked by arrow) C smooth shafts of dorsalmost notochaetae D shafts with file-like teeth of middle chaetae E shafts with file-like teeth of ventralmost chaetae. Scale bar: 250 µm.