Nannopus bulbiseta sp. nov.

(Figs. 32–38)

Type locality. Intertidal mudflat, Yangdo-myeon, Ganghwa Island, South Korea, Yellow Sea, 37°40'08.4"N 126°24'20.9"E (Fig. 1A, B).

Type material. Holotype: dissected on 2 slides (NIBRIV0000753987). Allotype: dissected on 2 slides (NIBRIV0000810823). Paratypes: 3 females dissected on 2, 2 and 1 slides (NIBRIV0000810820, 22, 24), and 1 male dissected on 1 slides (NIBRIV0000810827), 1 female in 70% ethanol (NIBRIV0000810821), 1 male in 70% ethanol (NIBRIV0000810826), and 2 females and 2 males together on SEM stub (NIBRIV0000810825). All samples were collected from the type locality by Vinod Vakati, 5 March 2015.

Etymology. The specific epithet refers to the bulbous shape of caudal seta V in female.

Description of female (based on holotype and paratypes). Body (Fig. 32A) fusiform, total body length ranged from 416 to 455 µm (mean = 437 µm, n = 4; holotype: 455 µm, measured from tip of rostrum to posterior margin of caudal rami). Maximum width ranged from 161 to 152 µm (mean = 159 µm, n = 4; holotype: 165 µm, measured at posterior margin of cephalothorax). Boundary between prosome and urosome clearly present, urosome/prosome length ratio 0.36, and body length/width ratio about 2.6. Surface ornamentation as in N. parvus . Cephalothorax (Fig. 32A) almost as long as width, comprising 34.1% of total body length, posterior margin serrated, and with several sensilla, and denticles.

Rostrum as in N. parvus .

Prosome (Fig. 32A, B, 33A) 4 segmented, comprising cephalothorax, and 3 pedigerous somites. All prosomites subequal, serrated posterior margins, and with row of sensilla. P2 and P3 bearing prosomites with very long sensilla on either side of dorsolateral margins, and P2-bearing somite with 1 row of short frills along anterior margin (Figs. 32A, arrowed in 33A).

Urosome (Figs. 32A, B, 33B, 35C) 5-segmented, posteriorly tapering, comprising P5-bearing somite, genital double-somite, 2 free abdominal somites, and anal somite. Posterior margins of urosomites serrated dorsally and ventrally. Row of sensilla along posterior margins dorsally except for penultimate somite. Row of spinules on third somite ventrally.

Genital double-somite (Figs. 32B, 33B, 35C) 2.4 times wider than long (ventral view), with original segmentation indicated by transverse, serrated surface ridge dorsally, and completely fused ventrally. Copulatory pore located medially, and with round shape.

Anal somite (Figs. 32A, 33D) twice wider than long, with well-developed operculum presenting row of dense setules along distal margin, 1 pair of dorsal sensilla, and denticles scattered randomly.

Caudal rami (Fig. 35A–C) nearly incorporated into anal somite but with clear separation between anal somite and each ramus. Medial spinular row located midway of outer margin laterally and ventrally. Distal spinular row dorsally and ventrally, and 0.9 (dorsal view) and 1.9 (ventral view) times as long as width. Caudal ramus bearing 7 setae: seta I naked, shorter than ramus width, and located dorsolaterally at anterior region; seta II naked, almost as long as ramus length, and located anterodorsally; seta III naked, almost as long as ramus length, and located laterally along posterior region; seta IV naked, 0.3 times as long as seta V, located at outer posterior margin, and proximal area slightly inflated; seta V longest, pinnate, bulbous anteriorly, and extremely thin posterior half; seta VI pinnate, almost as long as seta II and III; seta VII biarticulate, pinnate, and located at midway along inner margin.

Antennule, Antenna, and mouth parts as in N. parvus .

P1–P4 (Fig. 34A–E) with smooth and short concave intercoxal sclerite (not illustrated). Praecoxa somewhat triangular, shorter than coxa, and ornamented with row of spinules in P1. Coxa with 1 spinular row (P1, P2 and P3) on anterior surface, and row of strong outer spinules (P1, P2 and P4). Basis with row of strong outer spinules near insertion of exopod, and row of distal spinules near insertion of endopod (P1, P2, P3 and P4). Row of inner spinules (P1) or setules (P2 and P3). Basal outer seta naked (P1 and P2) or bipinnate (P3 and P4). Basal inner robust spine present on P1. P3 outer basal setae very robust and reaching to distal margin of exp-3. Exopod 3- segmented, and all segments sub-equal. Exp-1 to -2 (P1) and exp-1 to -3 (P2, P3 and P4) with robust outer spinules. Exp-1 to -2 (P1, P3 and P4) and exp-1 (P2) with row of inner setules. Exp-1 to -3 (P1–P3) with pinnate outer spines. Exp-2 (P2 and P3) with pinnate inner setae. Exp-3 (P1, P2, P3 and P4) with pinnate inner subdistal, distal and outer terminal setae. P4 exp-3 with short inner subdistal pectinate spine (Paratype presenting 1 minute spinule along inner margin near distal end, fig. 34D). Endopod 2-segmented in P1, P2 and P3 or 1-segmented in P4. Enp-2 (P1 and P3) with robust outer distal spinules, and enp-2 (P1 and P3) with row of inner setules. Setae on endopods of P1–P4 mostly pinnate except for 2 naked inner setae on enp-2 of P2–P3, and inner apical small seta of P4 endopod. Armature formula as follows:

P5 (Fig. 35D) almost as in N. parvus except for endopod with 2 inner sub-equal pectinate spines, and 2 small sub-equal naked setae. Exopod with 2 pinnate and 2 naked setae.

P6 (Fig. 35C, E) as in N. parvus .

Male (based on allotype and paratypes). Body (Fig. 36A) smaller than female, body length ranged from 411 to 386 µm (mean = 401 µm, n = 3; allotype: 408 µm, measured from tip of rostrum to posterior margin of caudal rami). Maximum width ranged from 137 to 152 µm (mean 149 µm, n = 3; allotype: 137 µm, measured at posterior margin of cephalothorax). Urosome/prosome length ratio 0.5 and body length/width ratio about 2.8. Cephalothorax (Fig. 36A) almost as in female, as long as wide, and comprising 36.2% of total body length. Body ornamentation (Fig. 36A), anal somite (Fig. 36A), rostrum (not illustrated), P1–P2 (not illustrated) as in female. Antennule (not illustrated) as in male N. parvus, antenna (not illustrated), and other mouth parts (not illustrated) as in N. parvus .

Prosome 4-segmented (Fig. 36A), comprising of cephalothorax (bearing first pedigerous somite), and 3 free somites. Posterior margin of prosomites serrated, and with sensilla as in female.

Urosome 6-segmented (Fig. 36A, B), comprising of P5-bearing somite, genital somite, 3 free abdominal somites and anal somite. Posterior margin of urosomites serrated except for anal somite, and with sensilla as in female. Urosomite 3 to 5 with longitudinal row of spinules near ventral posterior margin.

Genital somite (Fig. 36A) homologous to anterior part of genital double-somite in female, second and third urosomites well segmented in ventral view.

Caudal rami (Fig. 36B, D) almost as in female except for seta V inflated with globular expansion at its insertion site.

P3–P4 (Fig. 38A–F) intercoxal sclerite, praecoxa, coxa, basis, and ornamentation of setae on endopods as in female. P3 outer basal seta reduced (half as long as in female), P3 enp-2 outer spine fused to segment forming apophysis armed blunt tip, slightly curved along outer margin (arrowed in Fig. 38A, B), and 2 pinnate setae (1 long, and 1 short arrowed in Fig. 38A, B). P4 basal seta naked, endopod distal pinnate seta shorter than in female, and only reaching distal margin of exp-3 (Fig. 38C).

P5 (Fig. 38D) fused with somite, exopod and baseoendopod fused, and both baseoendopods confluent. Endopodal lobe with 2 sub-equal small pectinate spines, 2 sub-equal small naked setae, and rows of spinules near posterior margin. Exopodal lobe bearing 2 pinnate and 2 naked setae.

P6 (Figs. 36B, 38E) asymmetrical, with functional flap located at left side, with some spinules along posterior margin, with 3 setae (1 bipinnate and 2 naked), and median one twice as long as remaining 2 setae.