https://doi.org/10.11646/zootaxa.4821.1.13 http://zoobank.org/urn:lsid:zoobank.org:pub:C655C5D9-B45E-4D8B-B17B-BF63795D4C9B ZOOTAXA ISSN 1175-5326 (print edition) ISSN 1175-5334 (online edition) Zootaxa 4821 (1): 196–200 https://www.mapress.com/j/zt/ Copyright © 2020 Magnolia Press Correspondence 196 Accepted by B. Neuhaus: 4 May 2020; published: 30 Jul. 2020 Echinoderes unispinosus (Kinorhyncha: Cyclorhagida), a new record from deep-sea sediments in the Gulf of Mexico LUCIA ÁLVAREZ-CASTILLO 1 , DIEGO CEPEDA 2* , FERNANDO PARDOS 2 , GERARDO RIVAS 1 & AXAYÁCATL ROCHA-OLIVARES 3 1 Departamento de Biología Comparada, Facultad de Ciencias, Universidad Nacional Autónoma de México, Ciudad Universitaria, Ciudad de México, Mexico � lucia.alvarezcastillo@ciencias.unam.mx; https://orcid.org/0000-0002-9700-2859 � gerard.rivas@gmail.com; https://orcid.org/0000-0003-0075-5609 2 Departamento de Biodiversidad, Ecología y Evolución, Facultad de Ciencias Biológicas, Universidad Complutense de Madrid (UCM), C/José Antonio Novais 2, 28040 Madrid, Spain � diegocepeda@ucm.es; https://orcid.org/0000-0002-5194-3346 � fpardos@ucm.es; https://orcid.org/0000-0002-6292-9793 3 Departamento de Oceanografía Biológica, Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE), Ensenada, Baja California, Mexico. � arocha@cicese.mx; http://orcid.org/0000-0002-2700-9086 * Corresponding author. Kinorhyncha is a phylum of exclusively marine, meiofaunal invertebrates (Sørensen & Pardos 2008). Currently, the knowledge about the worldwide distribution of most of its species is considerably patchy, as several taxa have been re- ported from a single or few localities, usually within a limited geographic area (Sørensen & Pardos 2008; Yamasaki et al. 2018a). This even becomes more evident for deep-sea kinorhynchs, as noticed by Sørensen et al. (2018). Given the particular value of new records from the deep-sea to increase our understanding in the distribution of meiofaunal organ- isms plus the observed relationship of morphological variation through the bathymetric gradient, we aim to report the first record of Echinoderes unispinosus Yamasaki, Neuhaus & George, 2018 in the southern edge of the Gulf of Mexico (GoM), and contribute with new information about the morphological intraspecific variation of this species. In Mexico, studies of kinorhynch biodiversity are limited to the northern Gulf of California (50–1570m depth) (Álvarez-Castillo et al. 2015, 2018; Cepeda et al. 2019) and the Yucatán Peninsula (Sánchez & Martínez 2019). The GoM is a semi-closed basin located in a transition zone with both subtropical and tropical weather. Deep-sea muddy sediment samples of the present study were collected during the expedition XIXIMI-5 (10–24 June 2016) and processed according to Cisterna-Céliz et al. (2019). Kinorhynch specimens were mounted, measured and photographed according to Cepeda et al. (2019). Two adult males were identified as E. unispinosus, one from station B11 (2298 m depth) and another from station B15 (3708m depth). Kinorhynch specimens were deposited at the Aquatic Invertebrates Collection of the Facultad de Ciencias, Uni- versidad Nacional Autónoma de México (UNAM), Mexico, under accession numbers: KGM.001 and KGM.002. The analyzed specimens agree quite well with those from the northeast Atlantic (type locality of the species) in their morphology (Figs. 2A–D) and measurements provided by Yamasaki et al. (2018b) (Tables 1 and 2). Although most posi- tions of cuticular structures are quite constant, some morphological differences regarding the sensory spots arrangement, length of lateroventral spines and width of sternal plates must be remarked. The differences among sensory spots arrangements were also detected by Sørensen et al. (2018) in specimens from the northwest Pacific. For instance, the Pacific specimens showed sub- lateral sensory spots in segments 3, 5–7 and 9, being this pattern different from those of the Mexican and northeast Atlantic spec- imens, which showed midlateral sensory spots in segments 5–7 only, and subdorsal sensory spots in segment 8 which were not detected in the specimens from the northwest Pacific. Middorsal and laterodorsal sensory spots of segment 2 were not detected in the Mexican specimens (Table 1), although reported in both the northeast Atlantic and northwest Pacific specimens. The measurements from the two male specimens from the GoM (Table 2) are quite similar to those of the type material. For instance, the total length (TL) of the Mexican specimens, the specimens reported by Sørensen et al. (2018) and the type material reported by Yamasaki et al. (2018b) overlap. On the other hand, the maximum sternal width was slightly larger in the Mexican specimens (51 µm) and the northwest Pacific ones (49–54µm) compared to that of northeast Atlantic specimens (44–48 µm), and so was the length of the lateroterminal spines (204–232 µm for GoM vs. 169–205 µm for north Atlantic vs. 198–237 µm for northwest Pacific specimens).