Paramesochra parasimilis, 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 : 770-777

Paramesochra parasimilis sp. nov.

(Figures 1–4)

Type locality

Off Pungdo Island , subtidal zone, west coast of Korea, Yellow sea (37 ◦ 6 ′ 39 ′′ N, 126 ◦ 24 ′ 27 ′′ E), depth 20–25 m, sand, salinity 31 psu .

Material examined

Holotype 1 ♀ ( NIBRIV0000261347 ) dissected on five slides . Paratype 1 ♀ (CR00173700) preserved in 70% ethanol, 26 February 2008, Leg. J. Back.

Description of female

Body (Figure 1A,B). Cylindrical and depressed dorsoventrally; body length 300 µm (n = 2, mean = 295, measured from anterior tip of rostrum of cephalic shield to posterior margin of caudal rami); largest width measured at posterior margin of cephalic

Figure 1. Paramesochra parasimilis sp. nov. (♀). (A) Habitus, dorsal; (B) habitus lateral; (C) urosome, ventral.

shield (65 µm); gradually tapering posteriorly; body somites connected by arthrodial membranes, sensilla on dorsal surface as in Figure 1A.

Rostrum. Diminutive, bare, fused with cephalosome (Figure 1A).

Prosome (Figure 1A). Four-segmented, comprising cephalothorax (bearing first pedigerous somite) and three free pedigerous somites; cephalothorax (Figure 1A,B) bell-shaped, with sensilla; pleural areas weakly developed and posterolateral angles rounded; posterior margin smooth; cuticula between cephalothorax and first free somite distinctly pursed; three free prosomites with sensilla as figured.

Urosome (Figure 1A–C). 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; gonopores fused medially forming single genital slit covered on both sides by opercula derived from P6; P6 represented by one plate, armed with one bare seta; middle of plate well developed and protruded. Anal somite (Figure 2A) small, occasionally, telescoped inside penultimate somite; anal operculum not present but pseudoperculum developed and trapezoid.

Caudal rami (Figures 1C, 2A). Juxtaposed, oblong and approximately four times as long as wide; with spinular row around ventral distal margin; each ramus armed with six setae; Seta I obscure, vestigial, probably presented by one small pore; seta II bare, situated in proximal half; seta III stout, spine-like bipinnate; seta IV shorter than caudal rami, slightly bulbous proximally pinnate distally; seta V longest, well developed, pinnate distally; seta VI bare and smallest; seta VII triarticulated at base.

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

Antenna (Figure 3A). Four-segmented, comprising coxa, basis, one-segmented exopod, and free two-segmented endopod; coxa short and bare; basis approximately 2.2 times as long as wide; exopod one-segmented with four bare setae (apical element thick and modified); endopod two-segmented; enp-1 with one abexopodal bare seta; enp-2 with four bare setae laterally, one pinnate seta sub-apically, and five geniculate apical setae; outermost one fused basally to one bare seta.

Mandible (Figure 3B 1,B 2). With well-developed gnathobase bearing seven cuspidate teeth distally and one bare seta at dorsal corner; mandibular palp biramous, well developed; basis widening distally, with two bare setae; exopod one-segmented, with two lateral and two distal bare setae, with spinular row sub-apically; endopod twosegmented, enp-1 longest, as long as exopod, with two bare distal setae, enp-2 approximately three times as long as wide, with five basally fused setae (note that the distal setae with fused bases are often misinterpreted as the third endopodal segment).

Figure 2. Paramesochra parasimilis sp. nov. (♀). (A) Caudal rami, dorsal; (B) P5, anterior; (C) antennule.

Figure 3. Paramesochra parasimilis sp. nov. (♀). (A) Antenna; (B) mandible (B 1, gnathobase; B 2, palp); (C) maxillule; (D) maxilla; (E) maxilliped.

Maxillule (Figure 3C). Praecoxa trapezoidal, and inner edge with two long spinules; arthrite well developed with two lateral bare setae, six curved distal spines, and two anterior bare setae; coxa with cylindrical process bearing one stout bare and two bare setae; basis cylindrical process with one pinnate and five bare setae; exopod one-segmented, squarish, with two pinnate setae; endopod one-segmented, elongate, rectangular, with five bare setae distally.

Maxilla (Figure 3D). Syncoxa with chitinous outer margin, and three cylindrical endites; proximal endite bilobed, with two bare setae on each lobe; second and third endites closed to each other, with three bare setae; allobasis with two terminal stout setae and one bare seta near insertion of endopodal base; endopod two-segmented; enp-1 with spinular row laterally; enp-2 squarish, minute, with one stout bare seta and three bare setae distally.

Maxilliped (Figure 3E). Four-segmented; syncoxa bare; basis elongate, approximately twice as long as wide, without ornamentation; endopod two-segmented; enp-1 twice as long as wide, with one small bare inner seta and one geniculate distal seta; enp-2 small with two geniculate setae distally.

Swimming legs P1–P4 (Figure 4A–D). Well-developed coxae and bases with long setular row on anterior surface as figured except for P1. Bases of P2–P4 with one outer bare seta; exopod three-segmented and endopod two-segmented; P2–P4 with spinular row along outer margin of exopod and endopod.

P1 (Figure 4A). Coxa bare; basis with one inner and one outer bare seta; exopod two-segmented and much shorter than enp-1; exp-1 with one outer bare seta at distal corner; exp-2 with four pinnate setae; endopod two-segmented; enp-1 bare, 1.6 times as long as exp; enp-2 small, squarish, with two geniculate setae on distal margin.

P2–P3 (Figure 4B,C). Exp-1 with one outer spine; exp-2 with one outer spine and inner corner forming small spinous projection; exp-3 with two pinnate spines, one apical bare seta and one pinnate seta; enp-1 without seta (P2) or with one inner bare seta (P3); enp-2 with one apical pinnate seta.

P4 (Figures 4D). Exp-1 with one outer spine; exp-2 with one outer spine and inner corner forming spinous projection; exp-3 with one outer spine and one stout bare seta apically; enp-1 with one inner seta; enp-2 with one stout unipinnate seta and acute inner corner. Armature formula of P1 to P4 is given in Table 1.

P5 (Figure 2B), baseoendopods confluent, forming large plate, furnished with one basal seta each; endopodal lobe expanding beyond exopod, and bilobed at distal edge, with two small pinnate setae; exopod discrete, small, with three bare setae, and with inner row of spinules.

Etymology

The specific name makes reference to the close relationship with P. similis Kunz, 1936 .

Remarks

The new species is most closely related to P. similis Kunz, 1936 in the structure and armature formula of P1–P4, shape of P5, ratio of length to width in caudal rami, Figure 4. Paramesochra parasimilis sp. nov. (♀). (A) P1; (B) P2; (C) P3; (D) P4.

parasimilis sp. nov. and short caudal rami seta VI. However, the new species is clearly distinguished from its congener by the combination of the following characters: (1) antennary exopod arms with four setae in P. parasimilis (Figure 3A), but five setae in P. similis (Figure 14C); (2) well-developed caudal rami seta IV somewhat bulbous in proximal third (Figures 1A–C, 2A), P. parasimilis is the only species within the genus with a modified caudal seta IV; (3) caudal seta III with spinules instead of setules (Figures 1C, 2A); (4) median posterior margin of P6 protruded in P. parasimilis (Figure 1C) but plain in P. similis (Figure 14A); and (5) trapezoidal pseudoperculum in P. parasimilis (Figure 1A).