The Caribbean spiny lobster Panulirus argus (Latreille, 1804) is a decapod crustacean distributed in the Caribbean coasts of Colombia, including the insular regions of San Andrés, Providencia and Santa Catalina (^{Gracia and Díaz, 2002}). This lobster is considered one of the most important fishing resources for the populations of artisanal marine fishermen since it has the highest economic value within the crustaceans that are fished in the greater Caribbean and the Gulf of Mexico (^{Seijo, 2007}; ^{FAO, 2015}, ²⁰¹⁹).

In the departments of Magdalena, La Guajira and the Archipelago of San Andrés, Providencia and Santa Catalina, this lobster is socially and economically important, since its extraction is essential for the livelihood of artisanal fishing communities. However, it is considered as a vulnerable species in Colombia (^{Gracia and Díaz, 2002}; ^{Minambiente, 2017}), due to the overexploitation of its fishing stock and the systematic destruction of its habitat. Additionally, there are natural factors that have contributed to the decline of P. argus populations, such as diseases (e.g., Panulirus argus virus 1-PaV1) (^{Shields y Behringer, 2004}) and parasites (e.g., nemerteans) (^{Atherley et al., 2020a}). Specifically, the parasite Carcinonemertes conanobrieni^{Simpson, Ambrosio and Baeza, 2017} is a nemertean that feeds on the embryos that ovigerous females carry in their pleopods, causing negative effects on the reproductive performance of the lobster (^{Baeza et al., 2016}; Simpson et al., 2017).

In 2018, C. conanobrieni was recorded for the first time on the Caribbean coast of Colombia (^{Gonzalez-Cueto and Quiroga, 2018}), based on the morphological analysis of four individuals found in an ovigerous lobster from the Gulf of Salamanca (Magdalena). However, it was necessary to complement this information with genetic sequence data, essential to delimit cryptic species within the phylum (Sundberg et al., 2016). Furthermore, in the case of nemertean species associated with P. argus, molecular identifications are necessary since in this lobster there are at least two species of the genus Carcinonemertes (^{Atherley et al., 2020b}).

Ovigerous lobsters of the P. argus species were captured by artisanal fishermen from the Gulf of Salamanca (10.97982; -74.32758), Puebloviejo municipality (Magdalena) (Figure 1). Upon examination, nemerteans were isolated at different stages of development; some of which were fixed in 100 % ETOH.

Figure 1 Records of Carcinonemertes conanobrieni in the Gulf of Mexico and the Caribbean Sea. The circle indicates the type locality in the Florida Keys (24.7707; -80.7615 - 24.7325; -80.9121); the pentagon corresponds to the record for the Caribbean coast of Colombia (10.97982; -74.32758); and the square is the record for Saint Kitts, West Indies (see ^{Atherley et al., 2020b}). 

DNA from one of the individuals identified as C. conanobrieni was extracted using the QuickExtract ™ kit following the manufacturer’s protocol (Lucigen). The “^{Folmer” region was amplified with universal primers (Folmer et al., 1994}). DNA extractions were amplified using 2 μL of DNA in a PCR mix with a final volume of 23 μL containing 1.25 μL MgCl₂, 5 μL 5X Buffer (BIOLINE), 1 μL of each primer, 0.625 μL of dNTPs, 13.625 μL of H₂O and 0.5 μL of Taq polymerase (BIOLASE^TM, BIOLINE). The thermo-cycler program was: 1 min at 95 °C, followed by 35 cycles of 15 s at 95 °C, 1 min at 40 °C, 1.5 min at 72 °C and a final extension period of 5 min at 72 °C. The sequence obtained was edited with ProSeq 3.5 and aligned with all the C. conanobrieni sequences available in GenBank using the ClustalW algorithm in MEGA (^{Tamura et al., 2011}). Other sequences of Carcinonemertes sp. reported in P. argus by ^{Atherley et al. (2020b)} were included in the analysis. A matrix of intraspecific and interspecific evolutionary genetic distances was made (^{Hebert et al., 2003}), using the K2P model (^{Kimura, 1980}).

A sequence of 488 base pairs corresponding to the section of the genetic barcode of the COI gene was obtained, this was deposited in GenBank with the access code MW205898. The sequence obtained, possess a genetic distance that varies between 0 % and 0.2 % when compared with other individuals of C. conanobrieni and 22.5 % with other species of this genus found in P. argus (Table 1).

Table 1 Matrix of interspecific and intraspecific genetic distances based on 488 bp sequences of the Cytochrome Oxidase I (COI) gene using the K2P nucleotide substitution evolution model (^{Kimura, 1980}). The sequence generated in this study is highlighted in bold; the rest of the sequences were extracted from the GenBank genetic sequence database of the “National Center for Biotechnology Information” (https://www.ncbi.nlm.nih.gov/). 

These results lead to the confirmation of the presence of C. conanobrieni in Colombia, since the genetic distance found was less than 0.5 % when compared with other individuals of C. conanobrieni sequenced by ^{Simpson et al. (2017)} in their original description of the species. Within the Hoplonemertea group, which contains the genus Carcinonemertes, it is estimated that the interspecific distances are greater than 5 % (Sundberg et al., 2016).

The information herein provides tools that allow for correct identification of the species of nemerteans that can be found parasitizing the lobster. The results of this study indicate monitoring programs should be established to evaluate the effect of C. conanobrieni on the lobster populations of Colombia. In order to maintain the present and future fishing and market values of P. argus, emerging pathogens and parasites must be considered, particularly in light of a changing environment.