Pterosagitta Research Articles

Species groups in the zooplankton of eastern Australian slope waters, 1938-41

Some 1700 plankton net hauls (642 on the slope reglon of the continental shelf and 1100 in neritic waters) were made during surveys carried out by F.R.V. Wavreen (C.S.1 R., Division of Fisheries) in the eastern Australian Pacific Ocean area between latitudes 24�S. and 44�S from 1938 to 1941. The Tunicata. Euphausiacea, Hyperiidae. Chaetognatha, and Pteropoda totalling 118 species in the slope and shelf hauls were identified by various authors. In this paper 27 species which were frequently a part of each other's biological environment in the slope plankton, were assorted into groups: (1) by the use of an index derived from the corrected geometric mean of the joint occurrence of pairs of species, following Fager and McGowan (1963); and (2) by assessing the significance (using X 2 ) of the departure of a joint occurrence from an expected value calculated on the basis of empirical probability for each pair of species. Groups were set up according to the method of Fager (1957). The tests yielded similar results. Groups found, using test (2), and their tentative water mass affiliations were follows. (i) Central Tasman and south-west Tasman: GROUP A, Sagitta planctonis, S. lyra, S. minima, Krohnitta subtilis, Eukrohnia hamata; GROUP B, Thysanoessa gregaria, Euphausia recurva, N. dificilis, E. spinifera. (ii) South equatorial and Coral Sea: GROUP C, Oikopleura fusiformis, O. cophocerca, O. longicauda; GROUP D Stegosoma magnum, Megalocercus huxleyi, Oikopleura rufescens, Traustedtia multitentaculata, Doliolum denticulatum; GROUP E, Sagitta hexaptera, Pterosagitta draco, S. regularis, S. serratodentata pacifica, S. bipunctata, S. enflata, S. ferox, S. robusta, and Stylocheiuon carinatum. Recent references to the grouped species are discussed. The major affiliations and the temperature, chlorinity, and latitudinal ranges of the three forms of Sagitta serratodentata (tasmanica, atlantica, and pacifica) are set out and a tentative list of the water mass preferences of a number of the ungrouped species is given.

Investigations of Inner Continental Shelf Waters off Lower Chesapeake Bay. Part IV. Descriptions of the Chaetognatha and a Key to Their Identification

Ten species of chaetognaths were identified from plankton collections taken from the inner continental shelf waters off Virginia in 1960, including:Sagitta serratodentata, S. elegans, S. tenuis, S. enflata, S. helenae, S. minima, S. hispida, S. bipunctata, Pterosagitta draco, andKrohnitta pacifica. An artificial key to the identification of these species and descriptions based on the collected specimens are given. Tooth counts and seminal vesicle structure ofS. serratodentata revealed the presence of two subspecies in the western Atlantic. Virginian specimens are the cold-water vaviety,S. s. tasmanica, whereas Cuban waters are inhabited byS. s. atlantica. Published counts and descriptions of this species are lacking for intermediate waters. Specimens ofS. tenuis displayed an intermediacy and overlapping of several characters that have been used for the separation ofS. friderici andS. tenuis. Included among these characters are Tokioka’s TC values, maximum body length, number of teeth, extension of the ovaries, and size at maturity. The present collections ofK. pacifica constitute a northward extension of the known range of this species in the western Atlantic.

Pterosagitta besnardi Van. & Hosoe 1952 synonym of P. draco (Krohn 1853)

Tendo sido encontrado na regiao de Fernando de Noronha abundante material morfologicamente intermediario entre Pterosagitta draco e P. besnardi, proveniente esta ultima da regiao da Ilha da Trindade, os caracteres anteriormente considerados como disjuntivos foram reestudados em material proveniente de ambas as zonas. As conclusoes a que se chegou sao: P. besnardi e sinonimo de P. draco. 2.o - P. draco e muito provavelmente uma especie politipica. 3.o - Provavelmente existe um gradiante morfologico no Atlântico, representando o material da Trindade o extremo sul da area de dispersao da especie.