Spathula

Abstract: Light and electron microscopic observations on the ampullary organs of Polyodon spathula (Chondrostei, Osteichthyes) reveal a sensory epithelium similar to that found in the Lorenzinian ampulla, an electroreceptor found in marine Elasmobranchs.

Abstract: The mean total length of young-of-the-year paddlefish (Polyodon spathula) from Lewis and Clark Lake (a main-stem Missouri River reservoir at the Nebraska-South Dakota border) was 215 mm on 31 August of the first summer of life and estimated to be 296 mm by the end of the first growing season; average growth rate was 2.7 mm/day. The diet in 1972 consisted of zooplankton and aquatic and terrestrial insects. Daphnia pulex was by far the most important food occurring in stomachs of all 79 fish 30-149 mm long. Aquatic insects were important in late June and early July, and in August. The kinds of insects found in the stomachs suggested that the young fish fed at night in open water, near the surface.

Abstract: DURING the springs of 1904 and 1905 I visited the regions ini which Polyodon attains its largest size and occurs in greatest abundance. I had been aware for several years of the existence of this fish in great numbers in the lakes bordering the lower Mississippi River. Oil mentioning this fact to Professor Bashford Dean, he suggested to me the desirability of visiting these lakes with the object of obtaining the eggs anf( developmental stages of this peculial fish. iM3y best thanks are due Professor Dean for this suggestion, and for placing at my disposal during both years the Dyckmnan Fund of the Zoological Department of Columnbia University with which to defray the expenses of the trips. Most vertebrate embryologists and particularly those familiar with the development of the ganoiclds will admit, I believe, that a knowledge of the development of Polyodon is greatly desired. The ganoicis at present furnish an almost complete and one of the most instructive comllparative embryological series. The series is incomplete, however, in that nothing is known of the developmnent of either member of the order Selachostomni. This order comprises only two species, Polyodoii spat hula anl(1 Psephut1 -1as gladcius. The former is found in the MAlississippi R iver and its tributaries; the latter is known only in some of the rivers of China. Thus they have a decidedly discontinuous geographical distribution. I spent from March first to April fifteenth, 1904, in Concordia ancd Catahoula Parishes of Louisiana, and from April first -until May eighteenth, 1905, in WAashington County, I\iississippi, and on the WAhite River in Arkansas. During this entire time efforts were made to obtain spawning Polyodon. Although unfortunately I failed to secutre any of the embryonic stages, I succeeded, curino. the three months on the lakes and rivers where this fish is so abundlant, in making many observations onl its habits. The present paper contains a brief account of the behavior of the fish

Abstract: A phylogenetic analysis was performed on the genera and subgenera within the freshwater triclad family Dugesiidae, based on 19 terminal taxa and 17 morphological characters. The phylogenetic tree proposed has length of 27 steps and consistency index of 0.66. This phylogenetic hypothesis implies that the current genus Dugesia is paraphyletic and that its subgenera Girardia, Schmidiea and Dugesia S.S. should be elevated to the rank of genus. The genera Cura, Spathula and Neppia are presumed monophyletic by default because the database was unable to provide autapomorphies for any of these genera. The genera Dugesia S.S. and Neppia share sistergroup relationship. Several characters are discussed which were previously considered to be of phylogenetic importance but were not included in the present analysis. It is emphasized that sensory organs form potentially useful set of phylogenetic characters for the Dugesiidae.