﻿A new species of Esola Edwards, 1891 (Crustacea, Copepoda, Harpacticoida, Laophontidae) from the Caribbean coast of Colombia

﻿Abstract A new species of the harpacticoid copepod genus Esola is described from specimens collected in Rodadero Beach, on Gaira Bay, on the Caribbean coast of Colombia. The species, E.wellsisp. nov., is described, illustrated, and compared with its congeners. Esolawellsisp. nov. differs from its known congeners in details of the armature of legs 1–4. It most closely resembles E.bulbifera (Norman, 1911) in the armature formula of P1–P5 but differs from the latter in several respects, including the female antennule segmentation (7-segmented in E.bulbifera but distinctly 6-segmented in E.wellsisp. nov.) and in the shape and size of the male P3ENP2 apophysis, among other characters. This is the second species of the genus known from the Caribbean and the second record of Esola in the Northwestern Tropical Atlantic. The genus now contains eight species. A key to the known species of the genus is also included.


Introduction
The family Laophontidae is one of the largest in the copepod order Harpacticoida; it contains over 320 species and 63 genera. Huys and Lee (2000) subdivided the family into two subfamilies: Esolinae and Laophontinae, with the latter containing 95% of the known laophontid species (Boxshall and Halsey 2004).
The knowledge on this harpacticoid family is practically non-existent for Colombian waters; a recent biological survey of the crustacean fauna of Rodadero Beach on Gaira Bay, a large embayment on the Caribbean coast of Colombia, yielded several male and female specimens of laophontid harpacticoid copepods. Some of these specimens were taxonomically examined and found to represent an undescribed species of Esola. The new species is here described, illustrated, and com pared with its known congeners.

Materials and methods
Biological samples of littoral habitats were obtained from Rodadero Beach, Gaira Bay, Magdalena, northern Colombia (11°12'30.120"N, 74°13'39.13"W) during fieldwork carried out from August 2015 to March 2016, mainly at inshore areas covered by mangrove vegetation and in an adjacent oyster bank. Water salinity, pH, and temperature were measured at each sampling site with the aid of a WTW 350i multiparameter equipment. Water samples were collected manually using a 25-L bucket at both littoral and limnetic habitats. Samples were filtered with a zooplankton net (mesh size = 45 μm) and preserved in 70% ethanol. Copepods were sorted from all the samples and then processed for taxonomic identification, including the examination of the whole specimen and the dissection of selected appendages. Dissected appendages were mounted on semi-permanent slides with glycerine and sealed with Canada balsam. Specimens were measured in ventral position, from the anterior end of the rostral area to the posterior margin of the caudal rami. Drawings were made with the aid of a camera lucida mounted on an Olympus BX51 compound microscope equipped with Nomarski DIC. Two female individuals were prepared for SEM examination with a JEOL LV 5900 microscope at the University of Aguascalientes (UAA), Mexico. The process included dehydration of specimens in progressively higher ethanol solution (70-100%), critical point drying, and gold coating following standard methods. The type specimens were deposited at the Centro de Colecciones Biológicas de la Universidad del Magdalena, Colombia (CBUMAG), where they are available for consultation and/or further examination.

Taxonomy
Water temperature at this mangrove site varies seasonally between 30 and 32 °C, salinity is 36.1 psu, and pH is 8.3.
Etymology. The species is named after Dr John B. Wells as a tribute for his longstanding, solid contributions to the taxonomic knowledge of harpacticoid copepods (Grieve et al. 2019; Huys 2021). It is a noun in apposition, gender masculine. Differential diagnosis. With characters of laophontid genus Esola, body covered by dense pattern of small spinules, closely resembling E. bulbifera as redescribed by Huys and Lee (2000) in most respects, including body length and armature of legs 1-4, but female antennule distinctly 6-segmented, male geniculate antennule 7-segmented, subchirocer. Male P3 apophysis distinctively pectinate.
Rostrum triangular in lateral view, rounded in dorsal view (Figs 5A, 6C). Genital double-somite with dorsal suture, somite completely fused ventrally (Fig. 1B). Cephalothorax slightly wider than free prosomites, with anterodorsal row of spinules. Cephalosome with dense pattern of small spinules ( Caudal rami (Figs 1D, 5C, 6A, B) subrectangular, length/width ratio = 2.6. Proximal half distinctly expanded, distal half narrow, concave. Outer margin furnished with spinules. Rami with 7 setal elements. Seta I small, spiniform. Seta II and III smooth and closely set, almost equally long, seta V about twice as long as seta IV, both lightly pinnate and with spinules at insertion point. Seta VI about ½ length of seta VII.
Anal operculum (Fig. 4B) stronger than in female, with 8-10 large spinules and small spinules on surface. Caudal ramus subrectangular, lacking bulbiform expansions as those observed in the female. Distal part about 1.5 times as long as wide.
The new species of Esola can be distinguished from its known congeners by a combination of characters including: 1) a relatively robust body; 2) female body length ranging from 616 to 630 μm; and 3) robust caudal rami. The most important characters of E. wellsi are: 1) mandibular palp with 4 setae 2) P1EXP2 with 3 geniculate setae, 3) P2 and P4 ENP1 with inner seta, 4) caudal rami length/distal width ratio = 2.0, and 5) outer apical length seta on female P5BENP short.
We followed Wells (2007) in identifying a group of morphologically similar species of Esola among which we compared E. wellsi sp. nov. According to our analysis, and following Wells (2007), the setal formula of the P2-4EXP3 (6:7:7), 2) the absence of an inner seta on P2-P4EXP1 (1-1-1), and the number of setae on P2-P4ENP (5-6-5) of E. wellsi sp. nov. are shared with several congeners: E. profunda, E. lobata, E. bulbifera, E. canalis, E. longicauda, and E. galapagoensis. Overall, the new species most closely resembles E. bulbifera in the armature formula of P1-P5 and the armature of the mandibular palp. These two species can be distinguished by the following characters: 1) female antennule indistinctly 7-segmented in E. bulbifera versus distinctly 6-segmented in E. wellsi sp. nov.  Fig. 3A with fig. 3A in Huys and Lee 2000), 5) the female P5 ENP outer seta is relatively shorter in E. wellsi sp. nov. than in E. bulbifera (compare Fig. 1F with fig. 3D in Huys and Lee 2000), 6) the spiniform process on the male antennulary segment 5 is simple and spiniform in E. wellsi sp. nov. versus bifid in E. bulbifera (compare Fig. 3E with fig. 5D Huys and Lee 2000), and 12) the dorsal caudal seta VII is as long as ramus in E. wellsi sp. nov. versus shorter than ramus in E. bulbifera (compare Fig. 6B with fig. 1D in Huys and Lee 2000). These differences are considered sufficient to justify the proposal of a new species of Esola.
Distribution and ecology. The new species is currently known only from the type locality, Rodadero Bay, Caribbean coast of Colombia. It was found in a mangrove system at a depth of 0.70 m, where the water temperature varies seasonally between 30 and 32 °C, salinity is 36.1 psu, and pH is 8.3. It is likely that it has a wider distributional range in similar habitats of the western Caribbean region.