First Record of Holothurian Symbiotic Crab Asthenognathus inaequipes (Decapoda: Brachyura: Varunidae) from Korea

Abstract

A hole dwelling holothurian symbiotic crab was collected in the low tidal mark in Namhae Island. The crab was identified as Asthenognathus inaequipes Stimpson, 1858 and found to be new to Korean waters. The species was briefly illustrated and described. Remarks. The specimen agrees closely with the description of Sakai (1939) except in the number of the tooth on the inner margin of the movable finger in the male cheliped. It had an obtuse tooth in his description and a figure of Takeda and Konishi (1991) and two small teeth was described in the key of the Indo-Pacific species of Asthenognathus by Yang and Tang (2008). However, the present male specimen has three teeth, therefore, the number of tooth seems to be variable according to the specimens.Habitat. Muddy bottom in intertidal region. Distribution. Japan, East China Sea (Sakai, 2004), and now Korea. ACKNOWLEDGEMENTSThis work was derived from the "Flora and Fauna of Korea" project supported by on the National Institute of Biological Resources, the Ministry of Environment, Korea. REFERENCES

Phylomitogenomics elucidates the evolution of symbiosis in Thoracotremata (Decapoda: Cryptochiridae, Pinnotheridae, Varunidae)

“… Sun et al (2022) included A. inaequipes and T. horvathi (Varunidae) in their dataset, but did not recognise the species as symbiotic. Astenognathus inaequipes is symbiotic with holothurians ( Lee, Lee & Ko, 2010 ), whereas T. horvathi associates with the polychaete Loimia medusa (Savigny, 1822) ( Sakai, 1976 ; Otani, Takahashi & Matsuura, 1996 ). Tsang et al (2022) considered T. horvathi as free-living in their analyses, a decision we disagree with based on Sakai (1976) and Otani, Takahashi & Matsuura (1996) .…”

“…The different mitochondrial gene rearrangement scenarios are perhaps related to their evolutionary history associating with different invertebrate hosts. Gall crabs are obligate symbionts of scleractinian corals, pea crabs associate with a range of invertebrate hosts (but not scleractinian corals), A. inaequipes associates with holothurians, whereas T. horvathi associates with polychaetes ( Fize & Serène, 1957 ; Sakai, 1976 ; Lee, Lee & Ko, 2010 ; Castro, 2015 ; Palacios Theil, Cuesta & Felder, 2016 ; De Gier & Becker, 2020 ). Sun et al (2022) proposed that mitochondrial gene rearrangements may correlate with the specialised lifestyles within the Thoracotremata, however, this does not agree with our results of the MGOs being mostly linked to the various thoracotreme clades ( Fig.…”

“…Symbionts within Thoracotremata are also found in Varunidae (superfamily Grapsoidea): e.g. , Sestrostoma balssi (Shen, 1932), S. depressum (Sakai, 1965), and S. toriumii (Takeda, 1974) reside in the tubes of callianassids, upogebiids, echiurans, and polychaetes ( Castro, 2015 ); Asthenognathus inaequipes Stimpson, 1858, inhabits holothurians ( Lee, Lee & Ko, 2010 ); and Tritodynamia horvathi Nobili, 1905, associates with polychaetes ( Sakai, 1976 ; Otani, Takahashi & Matsuura, 1996 ).…”