Nuriaella mendezae, Gómez & Yáñez-Rivera & García-Vázquez, 2025

4.4. Nuriaella mendezae View in CoL gen. et sp. nov.: position and justification (see also Table S2)

The Paranannopidae was proposed by Por (1986) as a new family for Paranannopus Lang, 1936c View in CoL [note that Lang’ s genus name Paranannopus View in CoL was unavailable until Huys (2009) made the name available under his authorship as Paranannopus Huys, 2009 View in CoL ], and Cylindronannopus Coull, 1973b View in CoL . Huys et al. (1996) treated Paranannopidae as a synonym of Danielsseniidae (see above). The taxonomy of Pseudotachidiidae View in CoL is still controversial, and Walter and Boxshall (2024) regarded the family Danielsseniidae as a subfamily of Pseudotachidiidae View in CoL . With 19 valid species, Danielsseniinae View in CoL is the most species-rich subfamily of Pseudotachidiidae View in CoL .

Like many pseudotachidiid species, N. mendezae View in CoL gen. et sp. nov. is known from the female only, which makes its allocation to any known genus difficult. The belonging of N. mendezae View in CoL gen. et sp. nov. in the Donsiellinae View in CoL and Pseudotachidiinae View in CoL can be unambiguously ruled out by the specialized P1 of the two latter taxa. The first swimming leg of N. mendezae View in CoL gen. et sp. nov. resembles that of Pseudomesochra View in CoL , but the new species lacks the autapomorphies for that genus and for Pseudomesochrinae View in CoL [see Willen and Dittmar (2009: 296–297)]. Nuriaella mendezae View in CoL gen. et sp. nov. keys out as a danielsseniin in Wells (2007: 683), with three- and two-segmented P1 EXP and ENP, respectively, three-segmented P2–P4 EXP, three-segmented P4 ENP, P2 EXP3 with six setae in all, and three-segmented A2 EXP. However, the belonging of N. mendezae View in CoL gen. et sp. nov. in Afrosenia Huys and Gee, 1996a View in CoL , Archisenia View in CoL

Huys and Gee, 1993, Fladenia Gee and Huys, 1990 , Cylindronannopus , Mucrosenia Gee and Huys, 1994 , Danielssenia Boeck, 1873 , and Paranannopus can be ruled out given the autapomorphies for the females of these genera:

- Afrosenia View in CoL is a monotypic genus, and the female of its only species, A. spinipes ( Wells, 1967) View in CoL , is characterized by the five-segmented antennule, the elongate mandibular palp, and by the distinctive pseudoperculum ( Huys and Gee, 1996a). Huys and Gee (1996a) envisaged a scenario in which Afrosenia View in CoL would diverge from the basal node of the lineage that gave birth to the genera with oral aesthetascs.

- The females of Archisenia sibirica (Sars G.O., 1898) View in CoL , the only species of that genus, possess the following set of autapomorphies: i) presence of an outer extension on the female—and male—P3 ENP2, ii) female copulatory duct sigmoid and heavily sclerotized, and iii) inner seta of the female P5 EXP well separated from the other elements ( Huys and Gee, 1993) (but note also that the inner seta of the female P5 EXP of Mucrosenia kendalli Gee and Huys, 1994 View in CoL is also widely separated from the rest of the setae [see Gee and Huys (1994: 1029, Fig. 16E View Fig )].

- The genus Fladenia , with its only species, F. robusta (Sars G.O., 1921) , was defined by several aspects of the sexual dimorphism of the males [see Gee and Huys (1990): 1566] but also on i) the five-segmented female antennule, ii) the relative length of the mandibular EXP and ENP (endopod twice as long as exopod), iii) the presence of two accessory setae on the endopodal claw of the maxilliped, iv) relative length of the distal outer spine of P1 EXP3 (shorter that the middle outer spine), v) insertion site of the inner seta of P1 ENP2 (near the base of the segment), vi) transformation of the inner armature of P2–P3 ENP1 into a spiniform element, vii) shape of the female P5 EXP and BENP (rami fused), and viii) female P5 BENP with four setae [see Gee and Huys (1990)]. Gee and Huys (1990) suggested that Fladenia is the link between Paranannopus and the other danielsseniin genera.

- With three species, Cylindronannopus primus Coull, 1973b , C. elongatus (Becker, 1979) , and C. bispinosus Schriever, 1985 , C ylindronannopus is characterized mainly by its vermiform habitus ( Coull, 1973b), but it also possesses long and densely setulated rostral sensilla, the female P5 EXP and BENP are fused into a single plate, and P3 and/or P2 ENP are three-segmented with reduced number of armature elements on the distal segment [see also Coull (1973b); Becker (1979); Schriever (1985)].

- The females of Mucrosenia [ M. kendalli , and M. kliei ( Smirnov, 1946) ], have been defined upon a set of autapomorphies: i) presence of a mucroniform process on the female P2 ENP2, reaching almost to the end of ENP3, ii) lack of inner armature on the female P2 ENP2, iii) posterior displacement of caudal seta II, iv) presence of bunch of long setules at the distal inner corner of caudal rami, iv) P2 ENP shorter than EXP, and v) lack of inner armature on P2–P4 EXP1 ( Gee and Huys, 1994: 1035).

- At present, the genus Danielssenia is composed of six species, D. quadriseta Gee, 1988 , D. reducta Gee, 1988 , D. spiridonovi Garlitska and Chertoprud, 2021 , D. spitsbergensis Gee and Huys, 1994 , D. typica Boeck, 1873 , and D. similis Chislenko, 1978 [the latter was regarded as taxon inquirendum by Huys and Gee (1993), but it was redescribed by Garlitska and Chertoprud (2021)]. Danielssenia has been diagnosed by several autapomorphies: i) rostrum ventrally deflected, ii) mandibular gnathobase with blunt teeth, iii) dorsal hyaline frill of P5-bearing somite incised, and iv) seminal receptacle with paired anterior, elongate cylindrical chambers reaching the posterior part of the P5-bearing somite ( Huys and Gee, 1993: 78).

- With 22 species, the genus Paranannopus is most probably an amalgam of several genera (Huys et al., 1996; Willen, 2005), and its species are all known from one sex only [see also Gee and Huys (1990: 1568) for the case of P. langi Wells, 1965 and P. triarticulatus Wells, 1965 , and P. variabilis Schriever, 1985 ]. All this makes a sound generic diagnosis difficult. In their diagnosis of the genus, Huys et al. (1996) mentioned the five- or six-segmented antennule in both sexes and only slightly modified in the male, P2–P4 ENP missing or two-segmented, male P2 ENP2 with an apophysis, and female and male P5 EXP and BENP completely fused and indistinguishable, both P5 not fused medially in the female, but fused in the male.

Moreover, except for few danielsseniin species, viz., Paradanielssenia confluenta Kornev and Chertoprud, 2008 , P. triseta Kornev and Chertoprud, 2008 (the latter two species with claviform aesthetascs on mouthparts, see below), Cylindronannopus bispinosus , C. primus , Paranannopus longithorax Becker, 1979 , P. reductus Becker, 1979 , P. uniarticulatus Schriever, 1985 , and P. variabilis , all other species possess the full complement of three outer spines on P1 EXP3.

Nuriaella mendezae View in CoL gen. et sp. nov. also keys out as a member of the danielsseniin Sentiropsis Huys and Gee, 1996a View in CoL in Huys and Gee (1993: 79), or as Sentiropsis minuta ( Coull, 1969) View in CoL in Huys et al. (1996: 238). However, Sentiropsis View in CoL , along with Leptotachidia Becker, 1974 View in CoL , Micropsammis Gee and Huys, 1991 View in CoL , Paradanielssenia Soyer, 1970 View in CoL , Telopsammis Gee and Huys, 1991 View in CoL , Peltisenia Huys and Gee, 1996a View in CoL , Jonesiella Brady, 1880 View in CoL , and Nyxis Willen, 2009 View in CoL conform a well-defined group with sensory aesthetascs on the mandibular endopod, maxillulary basis, and maxillary endopod ( Gee and Huys, 1991; Huys and Gee, 1996a; 1996b, 1992; Willen, 2009). Of these, Leptotachidia View in CoL , Micropsammis View in CoL , Paradanielssenia View in CoL , and Telopsammis View in CoL conform a monophyletic group, and share i) the uniramous mandibular palp (without exopod), and ii) male P2 ENP3 with outer distal spine fused to segment ( Gee and Huys, 1991; Huys and Gee, 1996a), but also iii) the claviform aesthetascs on mouthparts. In their analysis, Huys and Gee (1996b) concluded that Peltisenia View in CoL , albeit with claviform aesthetascs on mouthparts, the possession of a biramous mandibular palp (with one-segmented endopod and two-segmented exopod) and the differently constructed male P2 ENP3 precludes its belonging to that monophyletic clade, and indicates that Peltisenia View in CoL occupies and intermediate position between that clade and the genera with setiform aesthetascs on mouth parts, viz., Jonesiella View in CoL , Sentiropsis View in CoL , and Nyxis View in CoL .

Prionos Huys and Gee, 1996b View in CoL , Anapophysia Huys and Gee, 1996b View in CoL , Psammis Sars G.O., 1910 View in CoL , and Bathypsammis Huys and Gee, 1993 View in CoL lack aesthetascs on mouthparts.

Prionos View in CoL with its only species, P. ornata Huys and Gee, 1996b View in CoL , was defined by the—autapomorphic—shape of the rostrum, somatic frills of the cephalothorax and free body somites (except P5-bearing somite), and shape of the armature elements of the female P5, and was hypothesized to occupy a basal position in the Psammis-Danielssenia-Mucrosenia clade ( Huys and Gee, 1996b). Prionos View in CoL and Anapophysia View in CoL , the latter with two species [ A. borealis ( Klie, 1939) View in CoL and A. segonzaci Huys and Gee, 1996b View in CoL ] possess three inner setae on P3-P4 EXP3 and P3 ENP3, and two inner setae on P2 ENP2. On the other hand, Willen and Schulz (2007: 56) characterised Bathypsammis View in CoL by the following set of autapomorphies: i) P1 ENP1 and ENP2 subequal in length, basal outer spine reaching at least proximal half of EXP2, EXP1 as long as ENP1, ii) shape and armature elements of female P5 EXP and BENP (EXP and BENP fused into large rectangular plate with basal outer seta short and pinnate, with four exopodal elements of which outermost spiniform pinnate, two long medial setae, and one short spiniform element shorter and thicker than outermost, endopodal lobe with one outer spiniform pinnate element, one distal outer bipinnate seta, two inner short spines with characteristic pinnae, and one moderately long spiniform bipinnate element), iii) caudal rami very elongate, iv) caudal seta IV and V with distal part flexible and tendril, and v) caudal rami with tuft of long fine setules at distal inner corner. Bathypsammis View in CoL with three species [ B. longifurca ( Bodin, 1968) View in CoL , B. polaris Willen and Schulz, 2007 View in CoL , and B. spinulosa Apostolov, 2011 View in CoL ] and Psammis View in CoL , with three species ( P. longipes Becker, 1974 View in CoL , P. longisetosa Sars G.O., 1910 View in CoL , and P. wellsi Kim, Lee and Huys, 2021 View in CoL ) also possess two inner setae on P2 ENP2 and other significant reductions on the segments of other swimming legs ( Huys and Gee, 1996b).

Nuriaella mendezae View in CoL gen. et sp. nov. does not match the autapomorphies for Danielssenia View in CoL proposed by Huys and Gee (1993: 78) (rostrum ventrally deflected, mandibular gnathobase with blunt teeth, dorsal hyaline frill of P5-bearing somite incised, and seminal receptacle with paired anterior, elongate cylindrical chambers reaching the posterior part of the P5-bearing somite), with which it seems to be more closely related (see below).

Huys and Gee (1996b) recognized two major lineages within Danielsseniinae (former Paranannopidae ), the paranannopid branch ( Paranannopus , Cylindronannopus , Fladenia , Bathypsammis , and Anapophysia ) and the danielsseniid branch ( Leptotachidia , Micropsammis , Paradanielssenia , Telopsammis , Peltisenia , Jonesiella , Sentiropsis , Nyxis with aesthetascs on mouthparts which constitute a well-defined group, and Afrosenia , Archisenia , Mucrosenia , Danielssenia , Prionos , and Psammis without aesthetascs on mouthparts), with Fladenia as a link between them. Huys and Gee (1996b) characterized the paranannopid branch by the shape of the subapical element on the A2 ENP (modified into a large bi- or multipinnate—apomorphic—spine in the paranannopid branch, but setiform in the danielsseniid branch), but also by the relative length of the outer distal spine of P1 EXP3 (at most as long as the median outer spine in the paranannopid branch, but outer spines gradually increasing in size in the danielsseniid branch), and to some extent, by the fused female P5 EXP and BENP [see Huys and Gee (1996b: 247)].

Nuriaella mendezae gen. et sp. nov. is placed here in the danielsseniid branch sensu Huys and Gee (1996b) without aesthetascs on mouthparts by the combination of i) the subapical element on A2 ENP setiform, ii) the outer spines on P1 EXP3 gradually increasing in length, iii) shape of P1, iv) the three-segmented A2 EXP, and v) the distinct female P5 EXP and BENP.

Within the genera of the danielsseniid branch without aesthetascs on mouthparts, N. mendezae gen. et sp. nov. seems to be more closely related to Danielssenia by the combination of i) lack of aesthetascs on mouthparts, ii) armature formula of A2 EXP [1,1,120; also present in the monotypic Afrosenia and Prionos and in M. kendalli , in some taxa of the danielsseniid branch with aesthetascs on mouthparts, viz., Leptotachidia , Paradanielssenia christineae Gee and Huys, 1994 , P. kathleenae Gee and Huys, 1994 , P. kunzi Soyer, 1970 , Telopsammis secunda ( Mielke, 1975) and Jonesiella , but also in some species of the paranannopid branch ( Paranaannopus kunzi Schriever, 1985 and P. minutus Smirnov, 1946 )], iii) armature formula of the two-segmented P1 ENP (1,121) (present also in all other genera of the danielsseniid branch except for the three-segmented P1 ENP of Jonesiella eastwardae ( Coull, 1971) , but also in Fladenia , Anapophysia and Bathypsammis within the paranannopid branch), iv) armature formula of P2 EXP, 0,1,123 [unique for N. mendezae gen. et sp. nov., Danielssenia reducta and D. spiridonovi ; but EXP1 lacks inner armature also in M. kendalli , Sentiropsis and Nyxis of the danielsseniid branch with aesthetascs on mouthparts, and in C. primus , Paranannopus abyssi (Sars G.O., 1920b) , P. caheti Soyer, 1964 , P. longithorax , P. reductus , and P. variabilis ], v) P3–P4 EXP1 without inner armature (but also missing in M. kendalli , in Sentiropsis and Nyxis , and C. primus and some species of Paranannopus — P. abyssi , P. caheti , P. denticulatus Schriever, 1985 , P. echinipes Smirnov, 1946 , P. longithorax , P. plumosus Schriever, 1983 , and P. variabilis ), vi) armature formula of P3 ENP 0,1,121 as in D. quadriseta (but also M. kendalli of the danielsseniid branch without, and P. christineae of the danielsseniid branch with aesthetascs on mouthparts), and vii) female P5 EXP and BENP separated (this condition is also present in Afrosenia , Archisenia , and M. kendalli , but also in Paradanielssenia , Peltisenia , Jonesiella , Sentiropsis , and Nyxis of the danielsseniid branch with aesthetascs on mouthparts). Only few taxa lack inner armature on the second endopodal segment of the three-segmented P4 ENP, viz., Leptotachidia and Micropsammis , and Telopsammis galapagoensis ( Mielke, 1997) and T. secunda (all these also lack inner armature on P4 ENP1) of the danielsseniid branch with aesthetascs on mouthparts, and the armature formula 1,0,121 for P4 ENP is unique to P. christineae of the danielsseniid branch with aesthetascs on mouthparts, and to N. mendezae gen. et sp. nov. of the danielsseniid branch without aesthetascs on mouthparts.

In their study of 1993, Huys and Gee (1993) concluded that Danielssenia was the most advanced genus within the Danielssenia-Psammis - Bathypsammis lineage ( Danielssenia and Psammis were the only genera of the, at the time, undiagnosed danielsseniid branch, and Bathypsammis would later be included in the paranannopid branch) by the lack of a seta on the first exopodal segment of the antenna, the mandibular basis, P2–P4 EXP1, and P2 ENP2, and that it was closely related to Psammis . More recent advances show that within the danielsseniid branch ( Archisenia , Psammis , Afrosenia , Mucrosenia , Danielssenia , Prionos , and N. mendezae gen. et sp. nov.), Archisenia and Psammis display the plesiomorphic bisetose condition of A2 EXP1, and P2–P4 EXP1 with an inner seta, but Archisenia retained the—plesiomorphic—separate female P5 EXP and BENP (fused in Psammis ), the two-segmented mandibular exopod (one-segmented in Psammis ), and nine setae on the mandibular endopod (three or four setae in Psammis ). Afrosenia and Prionos underwent reduction in the armature of A2 EXP2 from two to one seta, Afrosenia kept the two segmented mandibular exopod (one-segmented in Prionos ), and both retained the inner seta on P2–P4 EXP1, and the separated female P5 EXP and BENP. Mucrosenia , Danielssenia , and N. mendezae gen. et sp. nov., seem to be more advanced in that they all lack one seta on A2 EXP1 and inner armature on P2–P4 EXP1. Mucrosenia kliei and N. mendezae gen. et sp. nov. are similar in the tetrasetose P1 EXP3, and armature formulae of P2 EXP. Mucrosenia kendalli and N. mendezae gen. et sp. nov. are similar in the P3 ENP with one, one, and four setae on the first to third segments, respectively, and in the separate female P5 EXP and BENP. Nuriaella mendezae gen. et sp. nov. is similar to D. quadriseta in the armature formula of P3 ENP (1,1, 121) and in the separate female P5 EXP and BENP, but it seems more closely related to D. reducta and D. spiridonovi in the armature formula of P2 EXP (0,1,123), in the lack of an inner seta on P3 EXP3 (armature formula 0,1,123; 0, 1,223 in D. quadriseta , but also in M. kendalli ), in the pentasetose female P5 EXP (with four setae in Mucrosenia and D. quadriseta ), and in the separate female P5 EXP and BENP. Unfortunately, the female of D. spitsbergensis still awaits discovery. Overall, N. mendezae gen. et sp. nov. is unique in the—apomorphic—loss of one outer spine on P3–P4 EXP3, in the thin and elongate outer spines of P1–P4, the latter similar to Paranannopus and Cylindronannopus but much thinner, and in the large surface pores on pro- and urosomites.

Funding

This work was supported by the Programa de Apoyo a Proyectos de Investigaci´on e Innovaci´on Tecnol´ogica (PAPIIT) of the Direcci´on General de Asuntos del Personal Acad´emico of the Universidad Nacional Aut´onoma de M´exico (DGAPA-UNAM) (grant number IN202116) and Consejo Nacional de Ciencia y Tecnología (CONACyT) (grant number 31805-N), and Ocean Census through the Ocean Census Awards initiative.

CRediT authorship contribution statement

Samuel Gomez ´: Writing – review & editing, Writing – original draft, Methodology, Investigation, Funding acquisition, Conceptualization. Beatriz Ya´nez-Rivera ˜.: Writing – review & editing, Writing – original draft. Leonardo García-V´azquez: Writing – review & editing, Writing – original draft.