Pseudonychocamptus setadefectus, Cho & Kim & Lee, 2025

Pseudonychocamptus setadefectus sp. nov.

Figs 1 View Figure 1 , 2 View Figure 2 , 3 View Figure 3 , 4 View Figure 4 , 5 View Figure 5

Type locality.

Gohado   GoogleMaps ( 34°45'56.04"N, 126°22'22.38"E), Mokpo, Jeollanam-do, Republic of Korea.

Type material.

Holotype. • 1 ♀ ( MABIK CR 00258872 ), preserved in a vial with 95 % ethanol, collected from washings of marine plastic debris (a gunny sack) at the type locality on 14 March 2022 by GH Han GoogleMaps . Paratypes. • 2 ♀♀ ( MABIK CR 00258874–00258875 ), each dissected and mounted on 2 H-S slides GoogleMaps ; • 2 ♀♀ (MinRB-Hr 104-L 001 ), preserved in a vial with 95 % ethanol GoogleMaps ; • 1 ♂ ( MABIK CR 00258876 ), dissected and mounted on 2 H-S slides GoogleMaps ; and • 1 ♂ (MinRB-Hr 104-L 002 ) and 1 ♂ ( MABIK CR 00258873 ), each preserved in a vial with 95 % ethanol GoogleMaps . All material was collected from the type locality.

Other material examined.

• 1 ♀ ( MInRB - Hr 104-S 004 ), dissected and mounted on 2 H-S slides, collected from washings of marine plastic debris (expanded polystyrene buoy) at Chagwido Port , Jeju ( 33°19'25.86"N, 126°09'56.88"E) on 20 September 2022 by GH Han GoogleMaps .

Description.

Female. Body length 441–535 μm ( n = 6; measured from anterior margin of rostrum to posterior margin of caudal rami). Habitus broad, moderately flattened and gradually tapering posteriorly in dorsal view, separation between prosome and urosome indistinct (Fig. 1 A View Figure 1 ). Cephalothorax bell-shaped, slightly broadening posteriorly, maximum width 197 µm at posterior margin; dorsally with several paired sensilla, diminutive spinules, and reticulation (observable under high magnification); posteriorly margin fringed with small spinules. Cephalothorax and pedigerous somites laterally ornamented with minute spinules. Free pedigerous somites with dense spinules and scattered sensilla along posterior margins; also, with particular reticulation (observable under high magnification). Urosomites (Figs 1 A View Figure 1 , 3 A View Figure 3 ) posteriorly fringed with minute spinules (except anal somite); dorsal and ventral surfaces ornamented with transverse rows of fine spinules. Genital double-somite with a transverse spinular row dorsally and laterally, indicating original segmentation; ventrally completely fused. Genital field located near anterior margin of genital double-somite; either side of genital field covered by lobe derived from P 6, bearing two setae; each lobe with a small triangular process medially. Anal somite subequal in length to caudal rami, with spinular ornamentation; anal operculum bearing rows of diminutive spinules and pair of sensilla.

Caudal rami (Figs 1 A View Figure 1 , 3 A View Figure 3 ) ~ 1.25 × as long as wide; each ramus with seven setae and a ventral tube pore: seta I bare and shortest; setae II and III bare, the latter 1.5 × as long as the former; setae IV and V well-developed, basally fused, and bipinnate; seta VI unipinnate, shorter than seta II; and seta VII tri-articulate, inserted in the distal third.

Rostrum (Fig. 1 B, C View Figure 1 ) completely defined basally, triangular, with a pair of sensilla subdistally; midventral tube pore in subapical position; dorsal surface with reticulate ornamentation.

Antennule (Fig. 2 A View Figure 2 ) 7 - segmented; segments 2–6 with several rows of diminutive spinules present on dorsal surface. First segment with several inner spinular rows; second and third segments with inner long spinules. Apical acrothek consisting of an aesthetasc basally fused to two slender setae. Armature formula: 1 - [1], 2 - [9], 3 - [8], 4 - [1 + (1 + ae)], 5 - [1], 6 - [2], 7 - [7 + acro].

Antenna (Fig. 2 B View Figure 2 ) 3 - segmented. Coxa (not figured) small. Allobasis with one abexopodal seta located at distal third of segment length, and with two rows of spinules. Endopod with a proximal inner tuft of spinules and two subapical frills; laterally with two spines and one slender seta; distally with two strong spines and three geniculate setae (of which most outer one basally fused to a short seta). Exopod 1 - segmented, small, ~ 3 × as long as wide, with four pinnate setae.

Mandible (Fig. 2 C View Figure 2 ) with well-developed gnathobase bearing several blunt teeth around distal margin and one pinnate seta at distal corner. Mandibular palp small, uniramous, with one (exopodal) bare and three (endopodal) pinnate lateral setae, and one (basal) plumose apical seta ~ 1.7–1.8 × length of palp.

Maxillule (Fig. 2 D View Figure 2 ). Praecoxa with few spinules along outer margin; arthrite with a slender seta on anterior surface and eight elements around distal margin; with one row of long spinules on posterior surface. Coxa and basis each with one cylindrical endite, two spinular rows on anterior surface. Coxal endite with one slender seta and one pinnate spine. Basal endite with two slender setae and one pinnate spine. Endopod incorporated into basis, represented by three setae (one pinnate, two bare). Exopod 1 - segmented, cylindrical, with two apical setae and two surface rows of fine spinules.

Maxilla (Fig. 2 E View Figure 2 ). Syncoxa; ornamented with one row of long spinules along distal outer edge, several rows of spinules on posterior surface, and minute spinules around inner margin; with two endites, each with one bipinnate spine (spine on proximal endite fused to segment) and two pinnate setae. Allobasis produced into a stout, distally pinnate claw, accompanied by one pinnate and two bare setae. Endopod incorporated into allobasis, consisting of two long basally fused setae and two short elements.

Maxilliped (Fig. 2 F View Figure 2 ). Syncoxa with two pinnate setae and several rows of spinules. Basis longer than syncoxa, outer margin slightly convex, with one transverse row of spinules; palmar margin bearing a longitudinal row of spinules. Endopod 1 - segmented, with a long, curved, proximally pinnate claw; with two anterior accessory setae (one small, one long) and one posterior tube pore.

P 1 – P 4 (Figs 3 B View Figure 3 , 4 A – C View Figure 4 ) with wide and narrow intercoxal sclerite (not figured for P 1); all legs with 3 - segmented exopods and 2 - segmented endopods.

P 1 (Fig. 3 B View Figure 3 ). Coxa large, longer than wide, with several spinular rows on surface. Basis as large as coxa, with one bipinnate seta on outer margin and several spinules, and with one bipinnate seta arising near insertion of endopod. Exopod reaching middle of enp - 1, 3 - segmented: exp - 1 with one bipinnate outer seta; exp - 2 with one serrate outer spine; exp - 3 with two bare outer spines and two geniculate apical setae. Endopod 2 - segmented; enp - 1 elongated, ~ 1.7 × as long as exopod, with long spinules along proximal half of inner margin sparsely; enp - 2 short, with one strong, serrate claw and one tiny seta; various-sized spinules along outer margin and few short spinules around inner distal corner.

P 2 – P 4 (Fig. 4 A – C View Figure 4 ). Praecoxae small, transversely elongated-triangular, with several spinules around outer corner. Coxae with several spinular rows along outer margin and on anterior surface. Bases with few spinules on inner margin, several spinules around outer distal corner, and one tube pore on anterior surface. Outer margin of basis with one bipinnate spiniform seta (P 2) or one bare seta (P 3 and P 4). Exopods longer than endopods, gradually tapering distally (especially in P 2 and P 3); each segment ornamented with spinules along outer and anterior margins; exp - 1 with inner spinules subdistally; exp - 3 longest. Enp- 1 shorter than enp - 2, with spinules along outer margin and few (P 2) or no spinules (P 3 and P 4) on inner margin, and with one inner seta in P 3 and P 4 enp - 1 (absent in P 2); enp - 2 with several spinules along outer margin and few spinules near insertion of proximal seta, and with one (P 4) or two (P 2 and P 3) inner setae, two apical setae and one outer seta in P 3 and P 4 (absent in P 2). P 3 and P 4 enp - 2 with a tube pore near distal margin.

Armature formula of P 1 – P 4 as follows:

P 5 (Fig. 3 C View Figure 3 ). Baseoendopod and exopod separate; anterior surface of both segments covered with spinules (ornamentation of exopod denser than that of baseoendopod). Baseoendopod with one bare basal seta arising from a short and thick setophore; endopodal lobe reaching to proximal fifth of exopod, bearing five bipinnate setae, outermost shortest. Exopod oval-shaped, ~ 1.8 × as long as wide, bearing one bare and five pinnate setae, of which bare one longest and located terminally.

Male (based on the paratypes). Body (Fig. 1 D View Figure 1 ) smaller than female. Body length 349–400 μm ( n = 3; measured in the same way as in females), maximum width 148 µm at posterior margin of cephalothorax. Sexual dimorphism present in genital segmentation, antennule, P 2 – P 6.

Urosome (Fig. 3 D View Figure 3 ) narrower than in female, 6 - segmented; genital somite and first abdominal somite completely separate. Second to fourth abdominal somites with a row of strong spinules along posteroventral margins. Caudal rami as in female.

Antennule (Fig. 5 A View Figure 5 ) 8 - segmented, subchirocer, geniculate between segments 5 and 6. First segment as in females; second segment with nine setae, including two pinnate; fifth segment swollen (Fig. 5 a View Figure 5 ); eighth segment triangular. Armature formula: 1 - [1], 2 - [9], 3 - [8], 4 - [2], 5 - [9 + 2 pinnate + 2 modified + 2 teethlike elements + (1 + ae)], 6 - [3 elements], 7 - [1], 8 - [8 + acro].

Swimming legs. P 1 and P 2 similar to those of female, except for P 2 enp - 1 and enp - 2 subequal in length ( enp - 2 relatively shorter than that of female), with one inner and two apical setae (Fig. 5 B View Figure 5 ).

P 3 and P 4 (Fig. 5 C, D View Figure 5 ). Exopods more robust than those of females. P 3 exp - 3 considerably shorter, with thicker spines. P 3 endopod not reaching to distal margin of exp - 2; enp - 1 without inner seta; enp - 2 with one inner and two apical setae and one anterior tube pore; outer lateral margin produced into a short apophysis bearing distal cuspidate tip; coarse spinules present near at base of apophysis. P 4 endopod reduced, 1 - segmented, with two apical setae and one anterior tube pore.

P 5 (Fig. 3 D, E View Figure 3 ). Left and right baseoendopods fused medially, each with one outer basal seta; endopodal lobe vestigial, represented by two bare setae; posterior margin with two tube pores. Exopod 1 - segmented, oblong, with one inner, one apical and two outer setae; inner seta shortest; spinules present on outer margin and anterior surface.

P 6 (Fig. 3 D View Figure 3 ) asymmetrical, one side functional, the other fused to somite; outer sides of both plates produced into cylindrical processes, each bearing one inner pinnate and one outer bare seta.

Variability.

Morphological variation was observed in the armature formula of the thoracopods in P. setadefectus sp. nov. In females, the P 2 enp - 2 typically bears two inner setae; however, in one of the five specimens examined, three inner setae were present.

Etymology.

The species name setadefectus is derived from the Latin words seta (bristle) and defectus (lacking, missing), referring to the absence of the proximal endite bearing a seta of maxilla — a distinguishing feature of this species among its congeners. It is an adjective in the singular nominative, gender masculine.

Remarks.

Species of the genus Pseudonychocamptus exhibit marked sexual dimorphism, particularly in the following: the inner seta on P 3 – P 4 enp - 1, present in females, is absent in males; and the two-segmented P 4 endopod in females is reduced to a single segment bearing two setae in males. Notably, the latter trait represents the most prominent apomorphy of the genus ( Huys and Lee 2009). The newly discovered species from Korea exhibits both of these sexually dimorphic characteristics, thereby supporting its assignment to this genus.

The most distinctive feature of P. setadefectus sp. nov., which sets it apart from its six congeners, is the presence of only two endites on the maxilla, lacking the proximal endite represented by a single seta that is present in all other species of the genus. This condition represents a unique and highly unusual trait within Pseudonychocamptus .

The new species, P. setadefectus sp. nov., shares the presence of two inner setae on the female P 3 enp - 2 with four of the six valid species in the genus. These species are P. abbreviatus (Sars G. O., 1920) , P. colomboi Ceccherelli, 1988 , P. marinovi Apostolov & Petkovski, 1980 , and P. proximus (Sars G. O., 1908) . Conversely, P. koreni (Boeck, 1873) and P. spinifer Lang, 1965 possess only one inner seta on the female P 3 enp - 2. Among these, P. setadefectus sp. nov. is most similar to P. colomboi in that the male P 2 – P 3 enp - 2 bears only a single seta. It should be noted, however, that the male of P. marinovi has not yet been described. Previous studies (e. g., Ceccherelli 1988; Huys and Lee 2009) indicate that P. marinovi can be distinguished from the other three species ( P. abbreviatus , P. colomboi , and P. proximus ) by the broader than long caudal rami.

Although the morphological differences between females of P. setadefectus sp. nov. and P. colomboi are relatively subtle, the new Korean species can be readily distinguished by several characters. The fourth outermost seta on the P 5 exopod is ~ 1.5 × longer than the third outermost seta in P. setadefectus sp. nov. (Fig. 3 C View Figure 3 ), whereas these setae are subequal in length in P. colomboi ( Ceccherelli 1988: fig. 8 F). Additionally, the apical (basal) seta on the mandibular palp in P. setadefectus sp. nov. is 1.7–1.8 × as long as the total length of the palp (Fig. 3 D View Figure 3 ), compared to P. colomboi , in which it exceeds twice the palp length ( Ceccherelli 1988: fig. 7 H). In males, the P 5 exopod of P. setadefectus sp. nov. possesses an inner seta (Fig. 3 D View Figure 3 ), which is absent in P. colomboi ( Ceccherelli 1988: fig. 9 G). Furthermore, the P 6 is asymmetrical in P. setadefectus sp. nov. (Fig. 3 D View Figure 3 ), whereas it is symmetrical in P. colomboi ( Ceccherelli 1988: fig. 9 A).

In addition to the aforementioned differences, several minor features further distinguish P. setadefectus sp. nov. from P. colomboi : the maxillary endopod bears four setae in P. setadefectus sp. nov., but three in P. colomboi ; the maxillipedal claw is accompanied by two accessory setae in the new species, versus one in P. colomboi ; the inner setae on the female P 2 enp - 2 differ in relative length — the distal seta is ~ 2 × as long as the proximal in P. setadefectus sp. nov., whereas their length ratio is ~ 3: 1 in P. colomboi ; all setae, except for the longest apical seta, on the female P 5 exopod are ornamented in P. setadefectus sp. nov., but all are bare in P. colomboi ; the two setae of the female P 6 differ in length by more than twofold in P. setadefectus sp. nov., but they are subequal in P. colomboi ; the male P 2 enp - 1 and enp - 2 are subequal in length in P. setadefectus sp. nov., whereas the enp - 2 is slightly shorter in P. colomboi ; and P. setadefectus sp. nov. possesses a single pair of sensilla near the apex of the rostrum, compared to two pairs in P. colomboi .