On the Mysid Crustacean Genus Deltamysis (Mysidae: Heteromysinae), with a New Species and a New Record from Australia Author Daneliya, Mikhail E. text Records of the Australian Museum 2023 Rec. Aust. Mus. 2023-12-06 75 4 413 430 http://dx.doi.org/10.3853/j.2201-4349.75.2023.1881 journal article 10.3853/j.2201-4349.75.2023.1881 2201-4349 65F4EF7E-9AD1-4867-AAA5-956B29A17042 Deltamysis nana ( Murano, 1998 ) Heteromysoides nana Murano, 1998: 32–37 , figs 4, 5.— Hanamura & Kase, 2001: 65 , 70, fig. 3d; 2004: 2151.— Lowry & Stoddart, 2003: 450 .—Yolanda et al ., 2019: 535, 541. Deltamysis nana .— Daneliya, 2021: 4 . Holotype : Female (with embryos), 3.3 mm , Australia , Northern Territory , Channel Island , mud around mangroves, coll. K. Coombes , 2 Jul 1991 , NTM Cr. 008032 ( Murano, 1998 ). Diagnosis . Anterior margin of carapace angular, apically rounded. Cornea narrower than stalk (0.8 times as wide). Telson rather long, trapezoidal, with tapering lateral margins, 1.5–1.6 times as long as wide anteriorly; apically with barely visible cleft, 0.02 of telson length, with two spinules, less than half as long as lateral terminal spiniform setae; its lateral margins with five spiniform setae; subterminal spiniform setae about twice as long as preceding lateral and about as long as terminal; terminal spiniform setae 0.12 of telson length. Maxilla 2, exopod rather small, not reaching endopod segment 2, with numerous short lateral setae; endopod with lateral setae. Maxilliped 2 without lateral processes on carpus and propodus. Pereopod dactylus rather thin, about twice as long as wide. Pereopod 3–6 carpopropodus 4–5-segmented, segments thin, prolonged; segment 1 significantly shorter than other segments combined. Body length . Only known female holotype is 3.3 mm ( Murano, 1998 ). Comparison . Deltamysis nana is distinguished from other species of the genus by the narrowest telson. Other specific differences can be consulted in Table 1 . Distribution . So far known only from its type locality by the Australian coast of the Timor Sea, Northern Territory , near Channel Island ( Murano, 1998 ). Habitat . Found among the mangroves in mud ( Murano, 1998 ). Remarks . Murano (1998) described and illustrated this species in detail, and assigned it to the genus Heteromysoides . He did not mention any particular reason for such an assignment, but presumably for the somewhat subquadrate, flattened eyes. It was already noted that H. nana had the shape of the eyes, telson, mandibular palp and pereopods similar to Deltamysis , and the species was transferred to this genus ( Daneliya, 2021 ). Here I compare it with all known species of Deltamysis and revise its diagnosis.