Description In this study, we analyzed the haline tolerance of the stomatopod (Crustacea) larvae collected in an estuary from the southern Gulf of Mexico. The chosen study area was the Sontecomapan lagoon, which shows great variability in the salinity gradient throughout the year. The Sontecomapan estuary was visited five times (June 2018, October 2019, May 2021, November 2021, and June 2022) and zooplankton samples were collected with a conical net (50 cm mouth diameter and 333 µm mesh size); to measure the volume of filtered water a flowmeter was attached to the net mouth. During the fieldwork, the number of sampling stations varied between 11 and 20, depending on weather conditions and logistic facilities. Sampling grid comprised the lagoon and the adjacent marine zone. In total, 69 samples were obtained, all of them fixed in a 4% formaldehyde solution and neutralized with sodium borate. Besides, at each sampling station, salinity was measured with a YSI brand salinometer, with a precision of 0.01. In the laboratory, stomatopod larvae were sorted from each sample and morphologically examined based on the criteria of Ahyong et al. (2014). Afterward, the standardized number of larvae (individuals per 1000 m3 of filtered water), was plotted over a salinity gradient graphic to examine the larvae distribution and their salinity tolerance. Results indicated the presence of two kinds of larvae at different developmental stages: antizoea and alima. The morphological characteristics of the antizoea larvae correspond to the superfamily Lysiosquilloidea, whereas those of the alima larvae, match with the superfamily Squilloidea. The antizoea larvae were recorded in salinities as low as 21.9 psu and the alima at 23.2 psu. The occurrence of alima larvae, a late developmental stage, suggests the presence of an adult population in the Sontecomapan lagoon, perhaps Squilla empusa, the commonest squilloid species in the western Atlantic.  The tolerance to salinity conditions of stomatopod larvae is indicative of their potential to enter into estuaries.   Sampling locality The Sontecomapan lagoon is a Ramsar site (number 1342) located within Los Tuxtlas Biosphere Reserve, between 18.51 – 18.57° N and 94.99 – 95.04° W, in the southern Gulf of Mexico. The lagoon has an irregular shape and permanent connection with the sea through a narrow channel; it is 7 km long and, on average, 1.5 m depth. The lagoon exhibits variable salinity gradients throughout the year depending on seawater intrusion, the tides, and discharges of rivers, such as Coxcoapan, Las Palmas, and Basura.   Sampling date - Expedition SONTE 1: June 2018. - Expedition SONTE 2: October 2019. - Expedition SONTE 3: May 2021. - Expedition SONTE 4: November 2021. - Expedition SONTE 5: June 2022. Structure of the information - Data are organized in five Excel sheets containing 9 columns: - Column 1: Expedition - Column 2: Year - Column 3: Month - Column 4: Sampling station - Column 5: Longitude in decimal degrees - Column 6: Latitude in decimal degrees - Column 7: Salinity (psu) - Column 8: Antizoea density (individuals per 1000 m3) - Column 9: Alima density (individuals per 1000 m3)