Paramesochra mirabilis, Back & Lee, 2013

Back, Jinwook & Lee, Wonchoel, 2013, Three new species of the genus Paramesochra T. Scott, 1892 (Copepoda: Harpacticoida: Paramesochridae) from Yellow Sea, Korea with a redescription of Paramesochra similis Kunz, 1936, Journal of Natural History 47 (5 - 12), pp. 769-803 : 784-791

Paramesochra mirabilis sp. nov.

(Figures 9–12)

Type locality

Off Pungdo Island , subtidale zone, west coast of Korea, Yellow sea (37 ◦ 5 ′ 21 ′′ N, 126 ◦ 27 ′ 10 ′′ E), depth 10–15 m, sand, salinity 32 psu .

Material examined

Holotype 1 ♀ dissected on five slides ( NIBRIV0000261349 ) . Paratypes. 1 ♂ dissected on five slides ( NIBRIV0000261350 ) . 1 ♀ on one slide (CR00173704). 1 ♂ on one slide (CR00173705). 6 ♀♀ (CR00173702) and 5 ♂♂ (CR00173703) in 70% ethanol in vials, 26 February 2008, Leg. J. Back.

Description of female

Body (Figure 9A,B). Cylindrical and depressed dorsoventrally; body length 370 µm (n = 8, mean = 345; measured from tip of rostrum of cephalic shield to posterior margin of caudal rami); largest width measured at posterior margin of cephalic shield (65 µm); gradually tapering posteriorly.

Rostrum (Figure 9A). Diminutive, bare, triangular, and fused with cephalic shield.

Prosome (Figure 9A,B). Four-segmented, comprising cephalothorax (bearing first pedigerous somite) and three free pedigerous somites; cephalothorax bell-shaped, with few sensilla as illustrated in Figure 9A,B; pleural areas weakly developed and posterolateral angles rounded.

Urosome (Figures 9A, 10E). Five-segmented, comprising P5-bearing somite, genital double-somite, and three free abdominal somites; genital somite and first abdominal somite completely fused forming genital double-somite; genital field with copulatory pore located in median depression; gonopores obscure; P6 (Figure 10E,F) represented by one plate, bilaterally armed with one longer, outer pinnate seta and two shorter, inner bare setae; anal operculum (Figure 9A,D) not present; however, pseudoperculum well developed and rounded without ornamentation.

Caudal rami (Figure 9D). Approximately 2.2 times as long as wide, each ramus with seven setae; seta I bare; seta II bare and close to seta I; seta III spine-like and pinnate, situated at outer distal corner; seta IV well developed and pinnate; seta V longest, distal half bent laterally and pinnate; seta VI small and bare situated at inner distal corner; seta VII triarticulated at base located on dorsal surface forming chitinous out growth.

Figure 9. Paramesochra mirabilis sp. nov. (♀). (A) Habitus, dorsal; (B) habitus, lateral; (C) antennule; (D) caudal rami, dorsal.

Figure 10. Paramesochra mirabilis sp. nov. (♀). (A) P1; (B) P2; (C) P3; (D) P4; (E) urosome, ventral; (F) P6.

Antennule (Figure 9C). Eight-segmented, short, and robust; segment 1 largest armed with one bare seta; segment 3 and segment 4 with sub-cylindrical pedestal; armature formula: 1–[1 bare], 2–[7 bare + 2 pinnate], 3–[4 bare + 2 pinnate], 4–[4 bare + 1 pinnate + (1+ae)], 5–[1 bare], 6–[2 bare], 7–[2 bare], 8–[4 bare + acrothek], apical acrothek consisting of small aesthetasc fused basally to two bare setae.

Antenna (Figure 11A). Coxa bare; basis approximately twice as long as wide. Exopod one-segmented with three lateral bare setae, one strong apical seta, and one bare seta on distal corner. Endopod 2-segmented; enp-1 with one bare abexopodal seta; enp-2 with four bare setae, three geniculate setae apically, and one long geniculate seta fused basally to one bare seta, and with row of spinules sub-apically.

Mandible (Figure 11B 1,B 2). Gnathobase (Figure 11B 1) well developed, bearing several cuspidate teeth distally and one bare seta; mandibular palp (Figure 11B 2) biramous and well developed; basis widening distally, with one small bare seta; exopod one-segmented with three lateral bare setae and one apical bare seta; endopod twosegmented; enp-1 with two bare distal setae; enp-2 with five basally fused setae at apex.

Maxillule (Figure 11C). With trapezoidal praecoxa; arthrite well developed, with two bare setae laterally, six apical spines, and two juxtaposed bare setae on anterior surface; coxa with cylindrical endite bearing four bare setae; basis cylindrical, with six bare setae; exopod one-segmented, small, squarish with two naked setae; endopod onesegmented with six bare setae near distal margin.

Maxilla (Figure 11D). Syncoxa with chitinous outer rim, and with three cylindrical endites; first endite bilobed, with two bare setae on each lobe; second and third endites with three bare setae distally; allobasis with two claw-like setae; endopod one-segmented, indistinctly subdivided, squarish and with five bare setae.

Maxilliped (Figure 11E). Four-segmented; syncoxa bare; basis elongate approximately three times as long as wide, without ornamentation; endopod two-segmented; enp-1 with one geniculate seta on distal margin and one small bare seta laterally; enp-2 with two geniculate setae distally and one small bare seta on lateral margin.

P1–P4 (Figure 10A–D). Well-developed coxae and bases with spinules rows as illustrated; P2–P4 basis with one outer bare seta; P2–P4 exopod three-segmented and endopod two-segmented; P2–P4 with row of spinules along outer margin of exopod and endopod.

P1 (Figure 10A). Basis with one outer and one inner bare seta; exopod twosegmented; exp-1 longer than exp-2; exp-1 with one pinnate outer seta; exp-2 with four pinnate setae; endopod two-segmented; enp-1 bare and elongate approximately twice as long as exopod; enp-2 small, squarish, and with two stout distal setae.

P2–P3 (Figure 10B,C). Exopod longer than endopod; exp-1 with outer spine; exp-2 with one outer spine, and inner corner forming small spinous projection; exp-3 with two outer spines, one apical strong seta and one bare distal seta at inner corner; enp-1 without seta (P2) or with one inner bare seta (P3); enp-2 with one apical cylindrical bare seta.

Figure 11. Paramesochra mirabilis sp. nov. (♀). (A) Antenna; (B) mandible (B 1, gnathobase; B 2, palp); (C) maxillule; (D) maxilla; (E) maxilliped.

P4 (Figure 10D). Exp-1 with one outer spine; exp-2 with one outer spine and inner corner forming small spinous projection; exp-3 with one outer spine and one stout bare seta apically. Enp-1 with one inner bare seta; enp-2 with one modified unipinnate seta. Armature formula of P1 to P4 is shown in Table 3.

mirabilis sp. nov.

P5 (Figure 10E). Baseoendopods confluent, forming large plate, and with one basal bare seta each; endopodal lobe reaching genital field, bilobed at median distal margin, and with two small pinnate setae; exopod small, clearly distinct, with one pinnate and two bare setae, and with row of spinules along outer distal margin.

Description of male

Body (Figure 12A). Slightly smaller and more slender than female, body length 290 µm (n = 7, mean = 291; measured from tip of rostrum of cephalic shield to posterior margin of caudal rami), largest width measured at posterior margin of cephalic shield: 55 µm; general body shape and ornamentation as in female except for double-genital somite; additional sexual dimorphism in A1, P5, and P6.

Antennule (Figure 12B 1 –B 3). Seven-segmented, subchirocer; segment 2 formed from fusion of two ancestral segments indicated by incomplete surface hinge, with triangular process along distal posterior margin. Segment 5 swollen, largest. Aesthetascs on fifth and seventh segments. Armature formula: 1–[1 bare], 2–[11 bare + 3 pinnate], 3–[6 bare + 1 pinnate], 4–[2 bare], 5–[10 bare + 1 pinnate + 1 modified stout + (1 + ae)], 6–[3 bare], 7–[7 bare + acrothek], apical acrothek consisting of small aesthetasc fused basally to two bare setae.

P5 (Figure 12C). Baseoendopod confluent, each side with one slender pinnate basal seta; endopodal lobe bilobed and bare; exopod subcircular and discrete, ornamented with row of long spinules along inner margin, armed with two outer pinnate setae laterally, two apical naked setae; innermost one longest; one large pore in median surface.

P6 (Figure 12C). Pair of P6 asymmetrical, not confluent; each P6 with one naked outer and two pinnate setae.

Etymology

The specific name, “ mirabilis ” refers to characteristic shape, laterally bent distal half of caudal seta V in the female.

Remarks

This new species is most closely related to P. mielkei in the armature formula of P1–P5, shape of P5 baseoendopod, and presence of seven setae in the caudal ramus. However,

Figure 12. Paramesochra mirabilis sp. nov. (♂). (A) Habitus, dorsal; (B) antennule (segments 2 and 5 shown as separate inserts B 2 and B 3); (C) P5 and P6.

the new species is clearly distinguished from P. mielkei by the combination of the following characters: (1) the modified, laterally bent caudal seta V as illustrated in Figure 9D, P. mirabilis sp. nov. is the only species in the genus female having modified caudal seta V ( Wellsopsyllus (Intermedopsyllus) intermedius (Scott and Scott, 1895) and Emertonia miguelensis (Kunz, 1983) share the modified seta V with the new species); (2) P5 baseoendopodal lobe with two setae of almost the same length (Figure 10E), the outer seta is longer than inner one in P. mielkei ; (3) smooth median margin of confluent P6 plate in the female (Figure 10E,F), whereas it is crenated in P. mielkei (see fig. 5A in Huys 1987); (4) the bilobed median margin of male P5 baseoendopod (Figure 12C), P. mielkei has plain median distal margin, and show no distinct median depression between both plates of baseoendopod of male P5; and (5) asymmetrical and quadrilateral shape of P 6 in the male (Figure 12C), trianglar shape of P 6 in P. mielkei .