Nannopus sinusalbi, Sciberras & Cazzaniga & Huys, 2021

Sciberras, Michel, Cazzaniga, Néstor J. & Huys, Rony, 2021, Description of a new species of Nannopus Brady, 1880 (Copepoda: Harpacticoida Nannopodidae) from Argentinean waters, including an updated key to species, Zootaxa 5051 (1), pp. 506-528 : 509-518

publication ID	https://doi.org/ 10.11646/zootaxa.5051.1.20
publication LSID	lsid:zoobank.org:pub:4E269ABA-BEA6-4971-ADE8-30885D06C8F5
DOI	https://doi.org/10.5281/zenodo.5781745
persistent identifier	https://treatment.plazi.org/id/FA571AE5-531C-4521-BF3E-1740A50B5FDB
taxon LSID	lsid:zoobank.org:act:FA571AE5-531C-4521-BF3E-1740A50B5FDB
treatment provided by	Plazi
scientific name	Nannopus sinusalbi
status	sp. nov.

Treatment

Nannopus sinusalbi sp. nov.

( Figs. 2–8 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 View FIGURE 8 )

urn:lsid:zoobank.org:act:FA571AE5-531C-4521-BF3E-1740A50B5FDB

Type locality. Argentina, Buenos Aires Province; middle fringe of the mid littoral beach at Arroyo Pareja (38°53´S, 62°07´W); silt-clayey sediment with Spartina alterniflora ( Fig. 1 View FIGURE 1 ) GoogleMaps .

Type material. Holotype: adult ♀ dissected and mounted on four slides (MACN-In 42865), collected April 9, 2014. Paratypes deposited in MACN: three adult ♀♀ dissected, mounted on seven, four and five slides, respectively (MACN-In 42867), collected February 24, 2015 ; five ♀♀ preserved in ethanol (MACN-In 42868), collected March 19, 2015; one adult ♂ dissected and mounted on five slides (MACN-In 42866), collected February 24, 2015; two adult ♂♂ dissected and mounted on four slides each (MACN-In 42867), collected February 24, 2015; seven ♂♂ preserved in ethanol (MACN-In 42868), collected March 19, 2015. Paratypes deposited in MLP: five ♀♀ preserved in ethanol (MLP-Cr 27317), collected March 19, 2015 ; three ♂♂ preserved in ethanol (MLP-Cr 27318), collected February 24, 2015. All material was collected from the type locality by the senior author.

Description of female (holotype). Body length 562 µm. Habitus fusiform ( Fig. 2a View FIGURE 2 ). Colour of preserved specimens pale yellowish to colourless. Rostrum prominent, fused to cephalothorax, recurved ventrally; anterior margin with long and slender setules and one pair of sensilla ( Fig. 2b View FIGURE 2 ). Cephalothorax anteriorly attenuated in dorsal view, representing 28% of total body length; with one pair of dorsal pores; posterior margin serrate. Sensillar pattern on cephalothorax and body somites as illustrated ( Figs. 2a View FIGURE 2 , 3a–b View FIGURE 3 ). Posterodorsal margins of each somite serrate except for that of anal somite ( Figs. 2a View FIGURE 2 , 3a View FIGURE 3 ). Somite bearing P4 with one pair of dorsal pores ( Fig. 2a View FIGURE 2 ). Genital and first abdominal somite fused forming genital double-somite; original segmentation marked by bilateral constriction and by transverse serrate ridge dorsally ( Fig. 3a–b View FIGURE 3 ). Second abdominal somite with row of spinules on ventral posterior margin ( Fig. 3b View FIGURE 3 ). Operculum well developed, with rows of setules ( Fig. 3a View FIGURE 3 ). Anal somite cleft medially in ventral view; ventral posterior margin with row of spinules; dorsal surface with one pair of sensillae and three pairs of pores ( Fig. 3a–b View FIGURE 3 ).

Caudal ramus ( Fig. 3a–b View FIGURE 3 ) cylindrical and elongate, clearly separated from anal somite; with seven setae. Seta I naked, inserted closely to anterior margin of ramus. Seta II naked, as long as seta I; located dorsolaterally. Seta III bipinnate in distal half, inserted about halfway down outer margin. Seta IV naked, as long as ramus (in dorsal view); located at outer distal corner. Seta V strongest, bipinnate in middle section; slightly inflated proximally, with few spinules along outer margin; seven times as long as seta IV. Seta VI naked, as long as seta IV; located at inner distal corner. Dorsal seta VII bi-articulate at base; bipinnate; located close to inner margin. Ventral posterior margin of ramus with row of spinules; one pore on dorsal surface.

Antennule ( Fig. 2c View FIGURE 2 ). Short, compact, 5-segmented. First and second segments strong and wide; first and third segments with row of spinules. Segment 2 with tri-articulate seta (marked by arrow). Segment 3 with aesthetasc (length 38 µm) fused basally to short seta. Segment 5 with acrothek consisting of three setae, distinctly fused at base forming a minute pedestal. Armature as follows: 1-[1], 2-[4 + 5 bipinnate], 3-[5 + (1 + ae)], 4-[1], 5-[8 + acrothek].

Antenna ( Fig. 2d View FIGURE 2 ). Relatively short, composed of allobasis, 1-segmented endopod and 1-segmented exopod; coxa not observed. Allobasis with row of setules and two pinnate setae on abexopodal margin. Endopod with transverse row of setules in proximal half; row of robust spinules near inner and outer corner; armed with five strong, naked spines and one naked setiform element. Exopod with four elements, one of them bipinnate.

Mandible ( Fig. 4a View FIGURE 4 ). Gnathobase well developed; cutting edge provided with three rigid, multicuspidate teeth. Mandibular palp 1-segmented with rami completely incorporated into basis; outer margin with row of spinules; armed with four bipinnate setae, one of which (derived from the basis) originating from subcylindrical pedestal.

Maxillule ( Fig. 4b View FIGURE 4 ). Praecoxal arthrite with two setae on anterior surface; distal margin with five stout spines and two slender elements. Coxal endite with two setae. Basis and rami fused; armed with five naked and two bipinnate setae (homology and origin of these elements unconfirmed).

Maxilla ( Fig. 4c View FIGURE 4 ). Syncoxa bearing two endites, each with three elements, all of which confluent with segment. Allobasis with row of spinules, a strong claw with one long spinule along outer margin, and one accompanying seta. Endopod incorporated into basis, represented by two setae.

Maxilliped ( Fig. 4d View FIGURE 4 ) subchelate, 3-segmented. Syncoxa shorter than basis with rows of spinules and one short seta (marked by arrow). Basis unarmed; with rows of spinules as illustrated. Endopod with strong, curved claw ornamented with spinules in distal half and two naked accessory setae.

Swimming legs ( Figs. 5a–b View FIGURE 5 , 6a–b View FIGURE 6 ) with 3-segmented exopods and 2- (P1–P3) or 1-segmented (P4) endopods; exopods longer than endopods. Coxae with a row of spinules on anterior surface and a row of strong spinules along outer margin (only illustrated for P2–P4; Figs. 5b View FIGURE 5 , 6a–b View FIGURE 6 ). Bases with naked (P1–P2) or plumose (P3–P4) outer seta; with rows of spinules near insertion of exopod and endopod. First and second exopodal segments with anterior row of tiny spinules near inner distal corner; outer margins of exopodal and endopodal segments with spinular ornamentation, except for P4 endopod; inner margin of exp-2 with sparse setules; exp-3 with one anterior pore; inner seta of exp-2 plumose.

P1 ( Fig. 5a View FIGURE 5 ) smaller than other legs. Basis with row of spinules near insertion of inner spine; inner basal spine naked. Outer exopodal spines of exp-1 and -2 naked; exp-3 with two outer spines, proximal one naked and distal one with few spinules, and two terminal elements, outer one bipinnate and inner one plumose. Enp-1 with anterior row of tiny spinules near inner distal corner; inner margin of enp-2 with few setules; outer element of enp-2 naked, terminal element bipinnate and inner seta short and plumose.

P2–P3 ( Figs. 5b View FIGURE 5 , 6a View FIGURE 6 ). Basis with a row of long setules along inner margin. Inner margins of all segments with setular row; outer exopodal spines of all segments naked, except for distal spine of exp-3 displaying few distal spinules. Outer terminal spine of exp-3 with outer spinules and inner setules; inner terminal element plumose; inner setae plumose. Inner margins of endopodal segments with setular row; outer element of enp-2 spiniform and naked, terminal and inner elements setiform and plumose.

P4 ( Fig. 6b View FIGURE 6 ). Inner margins of exopodal segments with sparse setules. Outer spine of exp-1 with small apical setule; outer spine of exp-2 naked; outer spines of exp-3 naked, except for distal one having a few distal setules; outer terminal spine of exp-3 with outer spinules and inner setules; inner terminal element of exp-3 plumose; inner distal seta shortest and pectinate; inner proximal seta plumose. Endopod with long plumose apical seta and short, naked inner element.

Armature formulae as follows:

Exopod Endopod

P1 0. 1.022 0.111 P2 0. 1.123 0.111 P3 0. 1.223 0.111 P4 0.1.223 110

P5 ( Fig. 7a View FIGURE 7 ). Baseoendopod represented by transversely elongate plate with spinules along inner distal corner and near articulation with exopod; endopodal lobe with four bipinnate elements; outer expansion with bipinnate basal seta. Exopod articulating with baseoendopod; semicircular and about as long as wide; with five elements: innermost bipinnate element strongest and articulating at base; next two elements pinnate; two outermost elements naked.

P6 ( Fig. 3b View FIGURE 3 ) closing off paired genital apertures, semi-triangular with protruding outer distal edge bearing one short bipinnate element.

Description of male. Body length 537 µm. Sexual dimorphism expressed in antennule, P2, P3, P5, P6, urosomal segmentation and caudal ramus setae.

Ornamentation of body generally as in female, except for minor differences such as the presence of a ventral row of long spinules on the genital and three abdominal somites ( Fig. 7b View FIGURE 7 ).

Armature of caudal ramus almost as in female except for seta IV being twice as long and seta VI being shorter ( Fig. 7b View FIGURE 7 ).

Antennule ( Fig. 7c View FIGURE 7 ) short, 6-segmented; geniculation located between segments 5 and 6. All segments strongly chitinized. First and third segments with a row of spinules. Segment 5 and 6 with aesthetasc fused basally to a short seta. Armature formula as follows: 1-[1], 2-[7 + 2 bipinnate], 3-[1], 4-[6], 5-[7 + (1 + ae)], 6-[5 + (1 + ae)].

P2–P3 ( Figs. 8a–b View FIGURE 8 ). Exp-2 and -3 with outer spines stronger than in female; outer terminal spine of exp-3 with inner spinules and stronger than in female. P3 enp-2 ( Fig. 8b View FIGURE 8 ) with outer spine forming basally fused, robust apophysis; terminal and inner element shorter than in female; inner element naked.

P5 ( Fig. 7d View FIGURE 7 ). Baseoendopod and exopod fused forming basally fused common plate with four rows of spinules. Endopodal lobe armed with two pinnate elements and two shorter naked elements. Outer setophore with plumose basal seta. Exopodal lobe with three naked and two plumose elements.

P6 ( Fig. 7e View FIGURE 7 ). Sixth pair of legs asymmetrical with functional left leg forming a simple flap; confluent with somite; with spinules along distal margin and armed with one naked and two plumose elements. Single spermatophore observed underneath left flap.

Variability. Female body length varied between 552 and 643 µm (n = 10; mean = 597.4 µm; standard deviation = 33.81 µm), while males measured 546 to 611 µm (n = 10; mean = 577.7 µm; standard deviation = 22.72 µm).

Etymology. The specific name sinusalbi is the genitive form of the Latin compound translating the name of the type locality (Bahía Blanca, i.e., White Bay): sinus, us (4 th declension, masculine: bay) and albus (white).