ISSN 2816-6531

First record of the Harlequin crab Lissocarcinus orbicularis, an obligate symbiont of sea cucumbers, from the Red Sea

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Tags: Arthropoda, Caphyrinae, Decapoda, Lissocarcinus orbicularis, Malacostraca, Portunidae, Red Sea
Number 15, 
16 August 2023


The Harlequin crab, Lissocarcinus orbicularis Dana, 1852, (Decapoda: Portunidae) is one of the most common echinoderm symbionts in the Indo-West Pacific (IWP). It is typically found as a single individual or heterosexual pair on sea cucumbers of the genera Stichopus, Thelenota, Actinopyga, Bohadschia, and Holothuria, where it feeds on host integument and detritus (Ng & Jeng 1999; Caulier et al. 2012, 2014). These crabs have a striking color pattern of white spots on a dark red-brown background, or dark spots on white, that often complements their hosts (Caulier et al. 2012).

Lissocarcinus orbicularis has been reported across the IWP from Africa to Hawaii and French Polynesia (Vannini & Innocenti 2000). It has been listed from the Red Sea but without reference to specific specimens or localities (Laurie, 1915; Shankarankutty & Thomas, 1963). The first record, and likely the second, can be attributed to Nobili (1906), which documented a specimen collected at the Banc de La Clocheterie reef, Obock, Djibouti (outside of the Red Sea). All other authors have excluded the Red Sea from the distribution of L. orbicularis (e.g., Guinot 1967, Vannini & Innocenti 2000, DiBattista et al. 2016). Here we provide the first records of L. orbicularis from the Red Sea.

Results and Discussion

Lissocarcinus currently includes nine species, all putatively symbiotic, primarily on echinoderms, cerianthids, sea anemones, and possibly salps and some corals (Caulier et al. 2012; Evans 2016, 2018; Stephenson, 1972). Lissocarcinus orbicularis, L. holothuricola (Streets, 1876), and L. ornatus Chopra, 1931 are all symbionts of sea cucumbers and exhibit similar colorations (Fig. 1), but they are easily distinguished by differences in their frontal margin, epibranchial ridge, and fifth pereopod (Stephenson, 1972).

During an expedition to Saudi Arabia, an ovigerous female (UGI 3135) was collected from Majjde Reef, Red Sea, near the mouth of the Gulf of Aqaba. Together with three specimens at the Florida Museum (UF) from the Gulf of Aqaba (UF 47297) and Wasaliyat Islands (UF 48601, UF 48625), we report this species across much of the extent of the Red Sea. Recent expeditions to Oman and Djibouti resulted in additional specimens from the region (see


This research was supported by NEOM (grant 5209 - Biodiversity Baseline Assessment and Monitoring), the National Science Foundation (GECCO 1457769, DEB 1856245), and a Japan Society for the Promotion of Science (JSPS) post-doctoral fellowship (P22078).




Caulier, G., Lepoint, G., Van Nedervelde, F., & Eeckhaut, I. (2014). The diet of the Harlequin crab Lissocarcinus orbicularis, an obligate symbiont of sea cucumbers (holothuroids) belonging to the genera Thelenota, Bohadschia and Holothuria. Symbiosis, 62: 91-99.


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Figure. Lissocarcinus orbicularis, ovigerous female (UGI 3135), Majjde Reef, Gulf of Aqaba, Red Sea. Left: dorsal view; Right: map of new Red Sea records.