First Report of an Interstitial Semicytherura (Crustacea: Ostracoda: Cytheruridae: Cytherurinae) : a New Species from Central Japan

Abstract

A new species of ostracod, Senitqytherura scrgittijbrmis sp. nov., is described from a sandy beach in Shizueka Prefecture, centrai Japan. It lives in pore-waters of marine sandy sedirnents and is eeologically associated with other interstitial ostracods (e,g., Parmpolycope and Microloxoconcha). Semiqytherura sagittijbrmis is one of the smallest species in the genus Semicytherura, and its carapace size is comparable witih those of some large interstitial ostracods. This fact suggests that a small carapace is the most important charaeter for adaptation of ostracods to an interstitial environment,

Molecular phylogeny of interstitial Polycopidae ostracods (Crustacea) and descriptions of a new genus and four new species

“…Like other interstitial animals, these ostracods often show specialized morphological characters (Hartmann, ; Maddocks, ; Gottwald, ; Higashi & Tsukagoshi, ), e.g. they are much smaller than their surface‐dwelling relatives (Danielopol & Bonaduce, ; Yamada & Tanaka, ) and have reduced or absent eyes (Kaji & Tsukagoshi, ). Reduction of body size often results in convergent evolution of many characters both of the carapace and soft parts, and therefore it is sometimes hard to reveal the true phylogenetic relationships amongst closely related taxa based on morphological characters alone (Gottwald, ).…”

A New Species of <i>Semicytherura</i> (Crustacea: Ostracoda: Cytheroidea) from Obitsu River Estuary (Central Japan) and Its Microhabitat

“…This new Semicytherura species is the twenty-second species reported from the area. Yamada and Tanaka (2011) reported Semicytherura sagittiformis as the first interstitial Semicytherura species from Japan. Besides the small carapace size, both carapace and appendage morphology of S. sagittiformis resembles that of other, non-interstitial Semicytherura species.…”

“…More than 30 species of the genus Semicytherura Wanger, 1957 including both living and fossil specimens, have been reported from Japan and its adjacent areas (Yamada and Tsukagoshi 2010). Moreover, Tanaka (2011, 2013) reported three interstitial species, i.e., S. mukaishimensis Okubo, 1980, S. sagittiformis Yamada and Tanaka, 2011, and S. uzushio Yamada and Tanaka, 2013. Yamada and Tanaka (2011 emphasized the importance of small carapace size in the genus Semicytherura for adaptation to the interstitial environment, and suggested that S. hanaii Ishizaki, 1981, S. okinawaensis Nohara, 1987, S. polygonoreticulata Ishizaki and Kato, 1976, S. ryukyuensis Nohara, 1987, S. sabula Frydl, 1982 (Hanai, 1957), and S. yajimae Published online 1 January 2020 DOI: 10.12782/specdiv.25.1 Ikeya and Zhou, 1992 would be interstitial species based on their small carapace size.…”

“…Yamada and Tanaka (2011 emphasized the importance of small carapace size in the genus Semicytherura for adaptation to the interstitial environment, and suggested that S. hanaii Ishizaki, 1981, S. okinawaensis Nohara, 1987, S. polygonoreticulata Ishizaki and Kato, 1976, S. ryukyuensis Nohara, 1987, S. sabula Frydl, 1982 (Hanai, 1957), and S. yajimae Published online 1 January 2020 DOI: 10.12782/specdiv.25.1 Ikeya and Zhou, 1992 would be interstitial species based on their small carapace size. Contrastingly, some Semicytherura species were reported as epifaunal species (Tanaka 2009;Yamada and Tanaka 2011). Although Semicytherura species have been reported from various environments (e.g., tidal flat, rocky shore, inner bay, estuary, and infralittoral zones), no species have until now been strictly referred to as infaunal species.…”

The mating behaviour of the seed shrimpParapolycope spiralis(Ostracoda: Cladocopina), with insight into the evolution of mating systems in cryptic interstitial habitats

“…The interstitial environment can be regarded as a cryptic habitat, which is dark, has restricted spaces, and has a three‐dimensional, maze‐like structure. Most marine interstitial ostracods are characterized by being much smaller than surface‐dwelling species (Hartmann, ; Maddocks, ; Yamada & Tanaka, ), and a reduced or absent naupliar eye (Hartmann, ; Kaji & Tsukagoshi, ). All parapolycopid species exhibit some characteristics of interstitial species: small body size (0.2–0.4 mm in adult) and lack of eyes and a frontal organ (which has been suggested to be a photoreceptive structure: Müller, ; Hartmann, ).…”