﻿A new species of Nitokra Boeck, 1865 (Copepoda, Harpacticoida, Ameiridae) from the Caribbean coast of Colombia

﻿Abstract Biological samples obtained from a coastal system of northern Colombia yielded male and female specimens of an undescribed harpacticoid copepod of the diverse ameirid genus Nitokra Boeck, 1865. The new species is a member of the genus group III. We describe the new species based on adult male and female individuals. Nitokrapuebloviejensissp. nov., appears to be most closely related to N.vietnamensis Tran & Chang, 2012, but they can be separated by the following characters: 1) number of setal elements on second segment of mandibular palp, 2) P1ENP/EXP ratio, 3) relative lengths of P2, P3ENP/EXP, 4) number of elements on male P5EXP and ENP, and 5) segmentation of male antennule. In addition, N.puebloviejensissp. nov. can be confused with two other congeners: N.taylori Gómez, Carrasco & Morales-Serna, 2012 from South Africa and Colombia and N.kastjanensis Kornev & Chertoprud, 2008 from the White Sea, but the new species can be distinguished from them by: 1) number of setae on the maxillule coxa, 2) P1ENP/EXP ratio, 3) P2,P3ENP/EXP ratio, 4) female and male P5 setophore, 5) setation pattern of female P5EXP and ENP, 6) structure of female P6, 7) ornamentation of female anal operculum, 8) number of setae on male P5EXP, and 9) the male antennule segmentation. Most importantly, the presence of a group of five short setae on the medial surface of the maxilliped syncoxa allows the new species to be readily distinguished from its congeners. Only two subspecies and one species of this genus have been hitherto recorded from Colombia. A key to the 23 known American species of Nitokra is provided.

The knowledge on the diversity of Nitokra in Colombia is still scarce. Hitherto, only one species and three subspecies have been recorded in the country: N. lacustris colombianus from Bahía Solano, Choco, N. l. sinoi from Ciénaga Grande de Santa Marta, Magdalena and Laguna Navío Quebrado, la Guajira, and N. affinis colombiensis and N. taylori from Laguna Navío Quebrado, La Guajira (Reid 1988;Fuentes-Reinés and Suárez-Morales 2014a, b).
The Ciénaga Grande de Santa Marta, a large costal system of northern Colombia, was biologically surveyed during 2017 as part of an ongoing effort aiming to increase our knowledge of the Colombian aquatic biodiversity. The samples obtained yielded male and female specimens of an undescribed species of Nitokra. The new species is described and compared it with its closest congeners. A key to the 23 species of Nitokra known to occur in the Americas is also provided.

Materials and methods
Biological samples were obtained monthly from littoral habitats of the Ciénaga Grande de Santa Marta, northern Colombia (10°52'11.25"N, 74°19'31.64"W) in July, 2022; samples were collected manually from areas with mangrove vegetation using a 25 L bucket. Water salinity, pH, and temperature were measured in situ with a WT-W350i Multimeter.
Samples were filtered with a plankton net (45 μm mesh size) and then fixed and preserved in 70% ethanol. Copepods were sorted from the original samples and then processed for taxonomical identification, including dissection and mounting of taxonomically relevant appendages. Dissected specimens were mounted in glycerin and sealed with Canada balsam. Drawings of the mounted appendages were prepared with a camera lucida; they were also photographed using a Kodak Easy Share C140 digital camera adapted to a compound microscope. Two adult male individuals were prepared for SEM examination with a JEOL LV 5900 microscope at the University of Aguascalientes (UAA), Mexico; one female individual was prepared for SEM examination with a JSM-6010LA microscope at El Colegio de la Frontera Sur, Chetumal, Mexico. The whole specimens were measured in lateral position, from the tip of rostrum to the posterior margin of the caudal rami. Morphological nomenclature follows Huys and Boxshall (1991). The following abbreviations were used in the morphologic description and tables: P1-P6, first to sixth swimming legs; EXP, exopod; ENP, endopod. Setae or spiniform setae are referred to as setal elements. The type specimens were deposited in the collection held at Museo De Historia Natural Marina De Colombia -MAKURIWA. Additional material. Six adult females, four adult males in first authors' collection. One female and two male individuals prepared for SEM analysis.

Etymology.
The new species is named in reference to the type locality of the new species by adding the toponimic suffix in singular. The gender of the species suffix is feminine to match that of the genus. Differential diagnosis. Nitokra with 1 inner seta and 5 setae on P1EXP2 and EXP3, respectively and 455 and 777 elements on P2-P4ENP3 and P2-P4EXP3, respectively, plus 111 inner setae on P2-P4ENP1, respectively. Female rostrum hourglass-shaped, distal segment of mandibular palp with 6 setal elements. P1ENP1 almost reaching distal margin of P1EXP3. Modified, club-shaped inner basipodal seta on leg1. Maxilliped with distinctive group of 5 setae inserted medially on the syncoxa.
P6. With 2 unequal setae, inner one about 3× as long as outer seta. Caudal rami as in female.
Variability. One male with 3 setal elements (instead of 4) on P5ENP. Another male was observed to possess 6 setae instead of 5 on P5EXP.
Habitat. The new species is known only from the type locality, Puebloviejo, Ciénaga Grande de Santa Marta (northern Colombia). The site where it was collected is a shallow mangrove area, 0.7 m deep, with water temperature 26-31 °C; local salinity was 15-20 PSU, and pH values was 7.5-8.1.
In a partial revision of Nitokra, Gómez et al. (2012) divided the genus into three morphological groups based on the combination of the armature formula of the P1EXP2 and 3. Species in the first group carry one inner seta and four elements on P1EXP2 and EXP3, respectively. The second group is distinguished by the absence of an inner seta on P1EXP2 but bears five setae on P1EXP3. The third, most diverse group contains species bearing one inner seta and five setae on P1EXP2 and EXP3, respectively (as in Fig. 5A). Up to 13 species and subspecies have been assigned to this group, whose members also share a pattern of 4,5,5 and 7,7,7 setal elements on P2-P4ENP3 and P2-P4EXP3, respectively, plus 1,1,1 inner setae on P2-P4ENP1, respectively. The group includes: N. spinipes Boeck, 1864, N. fragilis fragilis Sars, 1905, N. fragilis paulistana Jakobi, 1956, N. spinipes orientalis Sewell, 1924, N. pietschmanni Chappuis, 1933, N. australis Soyer, 1974, N. intermedia Pesce, 1983, N. laingensis Fiers, 1986, N. husmanni Kunz, 1976, N. koreanus Chang, 2007, N. taylori Gómez, Carrasco & Morales-Serna, 2012, N. vietnamensis Tran & Chang, 2012. Within this group, the new species most closely resembles N. vietnamensis because they share of several characters including the number of elements on the maxillule coxa, the setation pattern on female P5EXP and P1-P4, relative length of female P5 setophore, number of spines on anal operculum, and relative length of P5ENP inner seta. These two species can be distinguished by the following characters: 1) the distal segment of the mandibular palp has 6 elements in N. puebloviejensis (Fig. 2C) vs.\ only 4 in N. vietnamensis (Tran and Chang 2012: fig. 4E), 2) in the new species, N. puebloviejensis, the P1ENP1 almost reaches the distal margin of P1EXP3, whereas in N. vietnamensis the P1ENP1 is relatively shorter, barely reaching halflength of P1EXP2 (Tran and Chang 2012), 3) in N. puebloviejensis sp. nov. both the P2ENP and P3ENP reach about half of P2EXP3 and P3EXP3, respectively (Fig. 5B, E), whereas in N. vietnamensis these rami are relatively shorter, barely reaching the proximal 1/3 of P2EXP3 and P3EXP3, respectively (Tran and Chang 2012), 4) the female P5EXP is subquadrate, robust in N. puebloviejensis (Fig. 4C) vs clearly narrower and elongate in N. vietnamensis (Tran and Chang 2012), 5) the male P5EXP and P5ENP are armed with 5 or 6 and 4 elements, respectively, vs 3 and 6 elements, respectively, in N. vietnamensis (Tran and Chang 2012), 6) the male antennule is 10-segmented in N. puebloviejensis (Fig. 6A, B) vs 8-segmented in N. vietnamensis (Tran and Chang 2012).
The diversity of the ameirid harpacticoid fauna could be underestimated and deserves further study in the Caribbean region.