Emertonia serrata Mathiske & Veit-Köhler, 2021

Mathiske, Annabel, Thistle, David, Gheerardyn, Hendrik & Veit-Köhler, Gritta, 2021, Deep sea without limits-four new closely related species of Emertonia Wilson 1932 (Copepoda: Harpacticoida: Paramesochridae) show characters with a worldwide distribution, Zootaxa 5051 (1), pp. 443-486 : 447-455

Emertonia serrata Mathiske & Veit-Köhler sp. nov.

http://zoobank.org/ urn:lsid:zoobank.org:act:5EFC895C-8621-473C-AAF0-164D3A2D0E1B

Type material. The examined specimens are registered and deposited in the Senckenberg Forschungsinstitut und Naturmuseum Frankfurt ( SMF), Germany. All specimens were collected in the Atlantic Ocean and in the Atlantic and Indian Ocean sector of the Southern Ocean. Station numbers indicate “Expedition, station number (plus - deployment number for SYSTCO and DIVA- 1), depth, core number, sediment horizon”.

Female holotype, SMF 37235 (adult female on 1 slide) : RV Polarstern PS 71 — SYSTCO, St. 85-7, 2,964 m, MUC8, 0–1 cm .

Male allotype, SMF 37236 (adult male on 1 slide): RV Meteor 48/1 — DIVA-1 , St. 346-7, 5,389 m , R7 , 0–1 cm .

Female paratype 1, SMF 37237 (adult female on 8 slides) : RV Polarstern PS 71 — SYSTCO, St. 85-7, 2,964 m, MUC8, 0–1 cm .

Male paratype 2, SMF 37238 (adult male on 3 slides): RRS Discovery 226—PAP, St. 13077#24, 4,844 m, 0–1 cm .

Etymology. The species name refers to the conspicuous serrations on the spines of the swimming legs P2–P4. Spines of this type are not known from any other species of Paramesochridae .

Description of female. Habitus ( Fig. 3A, B ). Total body length measured from anterior tip of rostrum to posterior margin of anal somite (holotype) 0.22 mm, including caudal rami 0.24 mm. Body cylindrical, slightly depressed dorsoventrally, with prosome slightly wider than urosome. Pores present in small numbers, distributed dorsally and laterally on cephalothorax and most of free somites. Most sensilla visible on cephalothorax, some on third and fourth pedigerous somite. Entire posterior margin of first urosomal somite ornamented with two rows of microspinules. Genital double-somite ornamented with row of micro- and row of spinules on posterior margin. Third urosomite with row of micro- and row of different sized spinules along posterior margin. Fourth urosomite ventrolaterally with same-sized spinules as anterior urosomite. Fourth urosomite with thin, well developed pseudoperculum. Anal somite short, with minute spinules ventrally and ventrolaterally along posterior margin ( Fig. 3B, C ).

Caudal rami of adult female ( Fig. 3C ) cylindrical, approximately two to three times longer than wide, with five setae: seta I absent; seta II slender, dorsally displaced; seta III slender, unipinnate, spine-like, situated dorsolaterally, near posterior end; seta IV shorter, naked, and more slender than III, V long and slender, bipinnate in posterior half; seta VI absent; seta VII slender, on dorsal surface.

Antennule ( Fig. 4A, B ). Eight-segmented. Armature formula:

I (0)

II (7) six slender naked setae of different sizes, one seta with three spinules near posterior end III (3) three naked setae

IV [1 + (2 + aes)] three naked setae, two of which situated on small protrusion with one aesthetasc

V (1) one slender seta

VI (0) unarmed

VII (3) three naked setae, two of which long

VIII [6 + (1 + aes)] seven slender naked setae, one of which fused at base with aesthetasc

Antenna. See male ( Fig. 5A ).

Mandibular palp ( Fig. 5B ). Palp biramous. Endopod two-segmented, proximal segment unarmed, distal segment apically with five naked, basally fused, slender setae. Exopod one-third length of endopod, one-segmented, with one dorsally displaced and two apical setae.

Maxillule ( Fig. 5C ). Praecoxal arthrite with two juxtaposed strong, stout setae on anterior and one seta on anterior surface. Arthrite with one short and flexible, four stout and two spine-like setae. Coxal endite bearing six slender setae. Endite of basis with four slender, naked setae. Endopod one-segmented, bearing two slender naked setae. Exopod with three slender naked setae.

Maxilla ( Fig. 5D ). Praecoxa and coxa fused forming syncoxa with three endites. No separation with basis visible. Proximal endite with two slender, unipinnate setae. Middle endite with two slender, unipinnate setae. Distal endite with two slender, naked setae. Allobasis with one naked and one unipinnate seta. Endopod with six naked setae, one of which broken off.

Maxilliped ( Fig. 5E ). Syncoxa with one long, naked seta. Basis with row of spinules. Endopod one-segmented, apically with one long, geniculate seta and one naked seta accompanied by three small spinules.

Swimming legs ( Fig. 6 ; Table 2 ). With rami characteristic for Emertonia species belonging to the andeep - group; intercoxal sclerites without ornamentation.

P1 ( Fig. 6A ). Basis with one pinnate inner seta and one naked outer seta. Endopod slightly longer than exopod, both rami two-segmented. Enp1 armed with spinules on outer margin and three pinnules near inner distal corner. Enp1 unarmed. Enp2 terminally with one long bipinnate seta, one shorter, naked, slighty displaced outer seta, and one spine-like spinule near inner distal corner. Exp1 with one unipinnate outer spine. Exp2 with all elements arranged around distal margin: one unipinnate and one bipinnate spine, and two setae, the outermost being bipinnate with short outer pinnules, the inner one with pinules on inner margin.

P2–P4 ( Fig. 6B–D ). Surface of coxae naked. Bases of P2–P4 bearing one naked outer seta accompanied by a short row of spinules. Three-segmented exopods slightly longer than endopods, with spinules along outer margin. P2–P4 exp1 and exp2 with one strong serrated spine; exp2 with one inner spinule situated on pronounced ledge. P2–P3 exp3 with four elements. P2 exp3 with two serrated outer spines, and apically with one long, serrated outer spine and one long inner seta with two long pinnules. P3 exp3 as in P2, but long seta with four long pinnules. P4 exp3 with two serrated spines (outer one short and strongly serrated, inner one long); inner distal corner with few spinules. Endopods P2–P3 one-segmented with spinules along outer margin and an additional terminal spinule row. Endopods P2–P3 bearing two spinules on inner margin, one of which positioned on a ledge; apically with long, rigid, spine-like bipinnate seta. Endopod P4 two-segmented, armed with spinules along outer margin; enp1 apically with one inner spinule, and spinule row on posterior surface; enp2 with a row of inner spinules. P4 enp2 apically with two short spinous processes and one spine-like seta with distally jagged tip.

P5 ( Fig. 7A ). Baseoendopods fused medially; completely separated from small exopods. Baseoendopod with long outer basal seta (with two pinnules) and short spinule row near outer margin on anterior surface. Endopodal lobes well developed, separated by medial cleft; each with halfmoon-shaped spinule row and two stout setae, the outer unipinnate and the inner one bipinnate. Exopod with several spinules along inner margin and three spinelike setae, the inner one being shortest, the outer one being longest and unipinnate, and the middle one being more flexible, outwardly directed and arising from a minute protrusion.

P6 and genital field see Fig. 7B . Sixth pair of legs represented by small fused outgrowths bearing two minute spinous processes.

Description of male. Habitus ( Fig. 8A–C ). As in female but second and third urosomites not fused. Total body length measured from anterior tip of rostrum to posterior margin of anal somite (allotype) 0.20 mm, including caudal rami 0.22 mm. Mouthparts and swimming legs as in female, sexual dimorphism in antennule, P5, P6 and urosomal segmentation.

Antennule ( Fig. 9 ). Seven-segmented. Segment III small, segment V rounded and bulbous ( Fig. 9 A, B ). Armature formula:

I (0)

II (5) five slender naked setae

III (2) two naked setae

IV (3) three slender naked setae

V (6 + aes) three slender naked setae, three spine-like setae and one aesthetasc VI (2) two naked setae

VII (6 + aes) six slender naked setae and one aesthetasc

Antenna ( Fig. 5A ). Endopod two-segmented; enp1 unarmed; enp2 subapically with one seta; apical margin of enp2 with four slender naked setae, two of which geniculate. Exopod one-segmented with one naked inner seta and a small spine adjacent to two naked setae.

P5 ( Fig. 7C ). Baseoendopods fused medially; with outer basal seta (lost on one side) and short row of spinules near outer margin; endopodal lobes weakly developed, separated medially by indentation. Exopod discrete at base; with several spinules on inner margin; armed with three spine-like setae, the innermost being shortest and naked, the outer being longest and with two pinnules, and the middle one being flexible, naked, originating from a minute protrusion and outwardly directed.

P6 ( Fig. 7D ). Sixth legs represented by small, medially fused plates separated by deep cleft, each with two small, unipinnate setae and a short row of spinules on anterior surface.

Figures

FIGURE 3. Emertonia serrata sp. nov. Female (holotype). A, habitus, dorsal view; B, habitus, lateral view; C. caudal ramus, ventral view. Scale bars = a, b, 0.05 mm; c, 0.02 mm.

FIGURE 4. Emertonia serrata sp. nov. Female (paratype 1). A, antennule, overview (armature omitted); B, disarticulated antennulary segments showing armature. Scale bar = 0.02 mm.

FIGURE 5. Emertonia serrata sp. nov. Male:A, antenna (paratype 2); B, mandibular palp (allotype); C, maxillule, disarticulated (allotype). Female: D, maxilla (paratype 1); E, maxilliped (paratype 1). Scale bar = 0.01 mm.

FIGURE 6. Emertonia serrata sp. nov. Female (holotype). A, P1; B, P2; C, P3 with intercoxal sclerite; D, P4. Scale bar = 0.05 mm.

FIGURE 7. Emertonia serrata sp. nov. Female (paratype 1): A, P5; B, P6 and genital field. Male (allotype): C, P5; D, P6. Scale bar = 0.01 mm.

FIGURE 8. Emertonia serrata sp. nov. Male (allotype). A, habitus, dorsal view; B, habitus, lateral view; C, caudal ramus, ventral view. Scale bars = a, b, 0.05 mm; c, 0.02 mm.

FIGURE 9. Emertonia serrata sp. nov. Male (paratype 1). A, antennule, overview (armature omitted); B, disarticulated antennulary segments showing armature. Scale bar = 0.02 mm.