Telson

Abstract: A detailed description and reconstruction of Canadaspis perfecta demonstrates its status as the earliest well-preserved crustacean. The cephalon consisted of five somites (in addition to the eyes), the thorax eight, and the abdomen seven, excluding the telson. Two pairs of apparently uniramous antennae flanked a median cephalic spine. The mandible bore a massive incisor process posterior of a molar area made up of finer spines, and apparently lacked a palp. The first and second maxillae were essentially similar to the eight pairs of thoracopods, with a multisegmented inner ramus, and foliaceous outer ramus made up of wide filaments attached to a proximal lobe. A bivalved carapace covered the thorax; no rostral plate was present. The abdomen lacked appendages, apart from a pair of spinose ventral projections of the pre-telson somite. There was no caudal furca. The evidence suggests that C. perfecta fed on coarse particles, possibly with the aid of currents set up by the biramous appendages. The erection of a new order Canadaspidida and family Canadaspididae Novozhilov (in Orlov 1960) to include Canadaspis is vindicated, and they are re-defined and the subclass Phyllocarida amended to include them.

Abstract: A new species of protosquillid mantis shrimp is described from the coastal waters of Korea and Japan Chorisquilla orientalis n sp is distinguished from congeners by the combination of deep grooves and pits on the dorsal surface of abdominal somite 5, 8-14 spines on lateral margin of the telson, numerous minute dorsal spines on the telson and abdominal somite 6, and large, pyriform submedian bosses on the telson preceded by a small rounded boss Chorisquilla orientalis is morphologically closest to C mehtae Erdmann Manning, 1998, from Indonesia, but differs chiefly in the dorsal ornamentation of abdominal somite 6 and the telson and reaches a considerably larger size Chorisquilla orientalis n sp shows developmental changes from juvenile to adult in the shape of the ocular scales and anterior margin of lateral plates of carapace, and in the number of lateral spines on telson Also, C mehtae Erdmann Manning, 1998, which, to date has not been adequately illustrated, is redescribed and figured A key to the Korean gonodactyloids is presented

Abstract: Extant arthropods are diverse and ubiquitous, forming a major constituent of most modern ecosystems. Evidence from early Palaeozoic Konservat Lagerstatten indicates that this has been the case since the Cambrian. Despite this, the details of arthropod origins remain obscure, although most hypotheses regard the first arthropods as benthic predators or scavengers such as the fuxianhuiids or megacheirans (‘great-appendage’ arthropods). Here, we describe a new arthropod from the Tulip Beds locality of the Burgess Shale Formation (Cambrian, series 3, stage 5) that possesses a weakly sclerotized thorax with filamentous appendages, encased in a bivalved carapace, and a strongly sclerotized, elongate abdomen and telson. A cladistic analysis resolved this taxon as the basal-most member of a paraphyletic grade of nekto-benthic forms with bivalved carapaces. This grade occurs at the base of Arthropoda (panarthropods with arthropodized trunk limbs) and suggests that arthrodization (sclerotization and jointing of the exoskeleton) evolved to facilitate swimming. Predatory and fully benthic habits evolved later in the euarthropod stem-lineage and are plesiomorphically retained in pycnogonids (sea spiders) and euchelicerates (horseshoe crabs and arachnids).

Abstract: The original type species of Australimnadia is made a junior synonym of A. grobbeni , originally described as Limnadia grobbeni Daday, 1925. A second species of Australimnadia is described from Onslow, Western Australia; it differs in having unique egg morphology and is distinct in many morphological characters, including those of the telson and cercopod, but also of the thoracopods. Its validity is confirmed by molecular differences between the two species in COI and EF1α. A third species from southwestern Western Australia is separated morphologically by unique spination of the telson and setation of the cercopod, and by its egg morphology.