Klaus J. Müller & Dieter Walossek: External morphology and larval development of the Upper Cambrian maxillopod Bredocaris admirabilis
Abstract: Search for new material yielded more than ninety specimens of different growth stages of Bredocaris admirabilis Müller, 1983. It enables us to present an extended description of the largest stage, considered as adult, and of the larval sequence. Discovery of the tagma boundary of the cephalon behind the fifth pair of appendages led to the identification of the second maxilla, which has the same design as the thoracopods and is incorporated within the trunk limb series. The larval sequence comprises five successive metanaupliar instars, with delay of development of post-maxillulary limbs. Stages between larvae and the presumed adult have not been found. Bredocaris, about 0.85 mm long as adult, is assumed to have lived epihenthically, swimming closely above a flocculent bottom layer. Lack of special feeding structures on the trunk limbs and retention of the larval cephalic feeding apparatus in the adult suggest rather simple nutritory habits; filter feeding can be ruled out. The morphology, in particular the possession of seven pairs of thoracopods, and ontogeny indicate a systematic position of Bredocaris within the Maxillopoda and close alliance to the shield-bearing members of this subclass, the Thecostraca. Differences between Bredocaris and all known maxillopodan taxa are the basis for proposing the new order Orstenocarida and new family Bredocarididae. The major diagnostic characters of this new order include: a simple. posteriorly indented head shield, probably compound eyes, anterior three-head appendages of naupliar shape, a 1st maxilla with rudimentary exopod and specialized for trophic function, a 2nd maxilla of trunk-limb shape, a thorax composed of seven segments, each with a pair of biramous paddle-shaped thoracopods, and a uniform abdomen carrying inarticulate, unsegmented furcal rami.