External morphology and larval development of the Upper Cambrian maxillopod Bredocaris admirabilis

Bredoearis admirabilis Müller, 1983. It enables us now 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 maxilIa, 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. Bredoearis, about 0.85 mm long as adult, is assumed to have lived epibenthically, swimming closely above a nocculent 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 ol1logeny indicate a systematie position of Bredoearis within the Maxillopoda and close alliance to the shicld-bearing members of this subclass, the Thecostraca. Differences between Bredoearis and all known maxillopodan taxa is 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 I st maxi Ila with rudimentary exopod and specialized for trophic function, a 2nd maxilIa of trunklimb 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.