• journal_title：Journal of Paleontology
• Contributor：Tae-Yoon Park ; George D. F. Wilson ; Dong-Chan Lee ; Duck K. Choi
• Publisher：Paleontological Society
• Date：2012-
• Format：text/html
• Language：en
• Identifier：10.1666/11-131R.1
• journal_abbrev：Journal of Paleontology
• issn：0022-3360
• volume：86
• issue：4
• firstpage：626
• section：ARTICLES

The fossil isopod crustacean genus <span class="named-content genus-species" id="named-content-2">Archaeoniscusspan> has been known to occur in England, France and Germany during the Upper Jurassic, and in Mexico and Egypt during the Lower Cretaceous. The morphology of this genus is unique in having dorsoventrally compressed body, the cephalon set deeply into the first pereionite, pleon as wide as pereion, and a broad semicircular pleotelson. These features have resulted in placing the classification of the genus in the monotypic family Archaeoniscidae. However, due to the lack of detailed morphological data, suprafamilial classification of this genus has remained unclear, as well as its ecology and lifestyle. Here we report <span class="named-content genus-species" id="named-content-3">Archaeoniscus coreaensisspan> n. sp. from the Jinju Formation, Gyeongsang Basin, Korea. The occurrence of <span class="named-content genus-species" id="named-content-4">Archaeoniscusspan> in the East Asia implies that the genus may have had a worldwide distribution. The Gyeongsang Basin was a Cretaceous backarc basin, which consists of exclusively non-marine sedimentary sequences. The occurrence of this genus, therefore, indicates that <span class="named-content genus-species" id="named-content-5">Archaeoniscusspan> successfully adapted to a freshwater ecosystem as well. Detailed anatomy including antennulae, antennae, pereiopods, and uropods was observed from well-preserved multiple specimens, which allows better understanding of the morphology of <span class="named-content genus-species" id="named-content-6">Archaeoniscusspan>. The axial structure in the posterior part of the body, which was previously interpreted as a unique brood pouch characterizing the family, turned out to be a remnant of the hindgut. Females of all isopods and most of the members of the superorder Peracarida have a thoracic ventral brood pouch, modified from the thoracic coxal endites. Based on the morphology of the largely unmodified ambulatory pereiopods of <span class="named-content genus-species" id="named-content-7">A. coreaensisspan>, the possibility of <span class="named-content genus-species" id="named-content-8">Archaeoniscusspan> being ectoparasitic is discounted. Instead, the flattened body and the form of limbs of <span class="named-content genus-species" id="named-content-9">A. coreaensisspan> would have been suitable for a benthic lifestyle.