# A new species of the isopod genus Ancinus (Isopoda: Sphaeromatidae) from sandy beaches of the northern Yucatan Peninsula, Mexico

## TL;DR

A new species of isopod from the Yucatan Peninsula is described, adding to the known diversity of the genus Ancinus.

## Contribution

The paper introduces a new species of Ancinus isopod with detailed morphological characteristics.

## Key findings

- The new species is distinguished by a smooth, unpigmented body and specific morphological traits.
- This is the third Ancinus species identified in the Gulf of Mexico and the tenth globally.
- A comparison table highlights differences between the three known Gulf of Mexico Ancinus species.

## Abstract

A new species of the sphaeromatid isopod genus Ancinus is described and illustrated. It comes from the Cinvestav Merida research project, Invertebrate Benthic Diversity of the Yucatan Intertidal and Shallow Subtidal Zones. This genus is easily recognized by having an oval and flattened body; in males, the first two pereonal appendages are subchelate, while in females, only the first one is subchelate, the pleotelson is triangular, and the first pleopods and uropods are uniramous. This new species of Ancinus differs from all others by body surface smooth and unpigmented; eyes not elevated; suture between head and pereonite 1 complete, straight; mandible lacinia mobilis lateral margins parallel; 3 irregular teeth, 1 long, 2 short blunt sclerotized cusps; mandible palp third article inner margin with 12 blunt robust distal setae; 2 maxilliped coupling setae; coxae 5–7 visible in dorsal view; pleopod 2 endopod margin with 20 short setae; male appendix styliform, fluted, and shorter than endopod; curved tip. This is the third known species of Ancinus in the Gulf of Mexico and the tenth worldwide. A table with the main differences among the three known species in the gulf is also given.