Journal of the Marine Biological Association of the United Kingdom cambridge.org/mbi Original Article Cite this article: Fadl AEA, Yamaguchi S, Wakabayashi K (2021). Morphological observations and molecular confirmation of larvae of Levisquilla inermis (Crustacea: Stomatopoda) from the Seto Inland Sea. Journal of the Marine Biological Association of the United Kingdom 101, 801–810. https:// doi.org/10.1017/S002531542100076X Received: 15 June 2021 Revised: 19 October 2021 Accepted: 21 October 2021 First published online: 24 November 2021 Key words: 16S rRNA; cincinnuli; crustaceans; DNA barcoding; mantis shrimp; stomatopod larvae; taxonomy Author for correspondence: Kaori Wakabayashi, E-mail: kaoriw@hiroshima-u.ac.jp © The Author(s), 2021. Published by Cambridge University Press on behalf of Marine Biological Association of the United Kingdom Morphological observations and molecular confirmation of larvae of Levisquilla inermis (Crustacea: Stomatopoda) from the Seto Inland Sea Alyaa Elsaid Abdelaziz Fadl 1,2 , Shuhei Yamaguchi 3 and Kaori Wakabayashi 1 1 Graduate School of Integrated Sciences for Life, Hiroshima University, 1-4-4 Kagamiyama, Higashi-Hiroshima, Hiroshima 739–8528, Japan; 2 Department of Zoology, Faculty of Science, Kafrelsheikh University, Kafr Elsheikh, Egypt and 3 School of Applied Biological Science, Hiroshima University, 1-4-4 Kagamiyama, Higashi-Hiroshima, Hiroshima 739–8528, Japan Abstract Mantis shrimps are commercially important crustaceans in many areas of the world. In con- trast to the relatively common studies of adults, limited studies have been attempted of larvae because of a lack of identification keys. The objectives of this study were two-fold: (1) to link wild-caught larval specimens from the Seto Inland Sea to a certain species and (2) to present a detailed morphological description of the last larval stage. The resulting molecular phylogen- etic tree based on 16S rRNA gene sequences strongly implies that our larval specimens were linked to Levisquilla inermis, which was barcoded from a newly collected adult specimen with a morphological identification. K2P genetic divergence was found to be 0% among the larval and adult specimens. The congeneric species L. jurichi was the sister group of the L. inermis cluster, but the K2P distance between them was 3.4%, and it was considered a distinct species. Morphological observations provided five major distinguishing characteristics of the last-stage larva of L. inermis: (1) propodus of second maxilliped with three basal spines, (2) all five pleo- pods possessing an appendix interna with cincinnuli, (3) exopod of uropod longer than the endopod, (4) distal margin of the exopod of the uropod reaching the lateral tooth of telson, and (5) telson with nine intermediate denticles. Overall, our results reveal the importance of combining molecular and morphological analyses for solving stomatopod larval identification. This finding can be used to support and facilitate future research on the taxonomy and bio- diversity of stomatopod larvae. Introduction Mantis shrimps or stomatopods (Crustacea: Malacostraca) are predatory marine crustaceans, which are found mainly in tropical and subtropical coastal waters and are characterized by the remarkably developed second maxilliped that has been modified as a powerful raptorial appendage (Ahyong et al., 2008). Almost 500 species of stomatopods are known and divided into 17 families within seven superfamilies (Ahyong & Harling, 2000; Ahyong et al., 2008; Van Der Wal & Ahyong, 2017; Hwang et al., 2019; WoRMS, 2021). The life history of stomatopods involves a series of larval stages consisting of short propelagic and long pelagic phases. The last-stage larval metamorphosizes into a post-larva and settles into the adult benthic habitat after a single moult (Pyrne, 1972; Feller et al., 2013). Larval forms of stomatopods are highly specialized among crustacean larvae as they possess a remarkable set of morphological char- acteristics such as large, fully functional raptorial second maxillipeds and often large body size that can be up to 50 mm in total length (Ahyong et al., 2014; Wiethase et al., 2020). Stomatopods can exhibit a greater variety of ecological adaptations in larvae than in adults due to their distinct larval forms (Haug et al., 2016). While all stages of the stomatopod larvae can be clearly recognized from other crustacean larvae, identifying them to the species level based on their morphological characters is still dif- ficult. Only around 10% of known species could be identified in their larval stages (Diaz, 1998; Haug et al., 2016). Traditionally, the identification of stomatopod larvae has been performed either by hatching larvae from a known adult or by cultivating wild-caught larvae to adult- hood; however, these laboratory methods are time-consuming and extremely challenging (Provenzano & Manning, 1978; Diaz, 1998; Feller et al., 2013). Descriptions of the entire series of larval stages using those two methods exist for five of the 500 extant species: (1) Neogonodactylus oerstedii (Hansen, 1895) (as Gonodactylus oerstedii) (Manning & Provenzano, 1963; Provenzano & Manning, 1978), (2) Neogonodactylus wennerae Manning & Heard, 1997 (as Gonodactylus bredini Manning, 1969) (Morgan & Goy, 1987), (3) Pterygosquilla schizodontia (Richardson, 1953) (as Squilla armata H. Milne Edwards, 1837) (Pyne, 1972), (4) Heterosquilla tricarinata (Claus, 1871) (Greenwood & Williams, 1984) and (5) Oratosquilla oratoria (De Haan, 1833–1850) (Hamano & Matsuura, 1987). Even par- tial larval series are known only for a restricted number of species (Gurney, 1946; Alikunhi, 1967; Michel, 1968, 1970; Michel & Manning, 1972; Shanbhogue, 1975; Rodrigues & https://doi.org/10.1017/S002531542100076X Downloaded from https://www.cambridge.org/core. IP address: 3.231.220.57, on 13 Dec 2021 at 18:17:26, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms.