Morphological description of the zoeal stages of Metopograpsus thukuhar (Owen, 1839) (Decapoda: Brachyura: Grapsidae) reared under laboratory conditions

Two species have been recorded from the Yemeni coastal waters of the Gulf of Aden: Metopograpsus thukuhar , and M. messor . Some species of Metopograpsus has been known the complete larval development described, such as M. latifrons , M. frontalis (as M. maculatus ). This study aimed to describe the zoeal stages of M. thukuhar . Two Ovigerous M. thukuhar were collected by hand from a mangrove habitat in Mukalla, Gulf of Aden, and maintained in laboratory aquaria without being fed until hatched. Around 500 larvae hatched. Every 50 larvae were reared under controlled conditions, with ten larvae from each zoeal stage preserved in 70% ethanol. Larvae were dissected and examined using stereoscopic and compound microscopes with differential interference contrast. Morphological features were drawn with a camera lucida, and measurements of various appendages and body parts were taken from ten larvae per stage, with average values recorded. The larval stages of M. thukuhar were successfully reared under laboratory conditions for the first time. Over a period of 30 days, five zoeal stages were observed and described in detail. The study provides the first comprehensive morphological description of the zoeal stages of M. thukuhar , highlighting the absence of cephalothorax lateral spines across all stages, present simple setae on the dorsal spine a feature not previously documented in the genus Metopograpsus except M. messor in the Red Sea. The morphological characteristics of M. thukuhar larvae were found to be consistent with those of other grapsid crabs, although some unique traits were identified, such as no lateral carapace spine and absence of exopod antenna. This study describes the development of M. thukuhar larvae through five stages, highlighting features that distinguish it from related species, such as the absence of a lateral spine in the cephalothorax in all zoeal stages and exopod of the antenna.