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摘要： Dyopedos monacanthus inhabits self-constructed mud whips on marine soft-bottoms. Juveniles stay on the mud whip of their mother for extended time periods after they hatch from her brood pouch. During the main reproductive period in the spring, parental females have been observed in the aquarium and collected from the field. Specimens of D. monacanthus have been collected simultaneously from the intake filter from the seawater laboratory. Several consecutive clutches have been found on the whip of one female. Most juveniles are small (1 mm in size), but they grow to sizes of >2 mm on the whip of their mother. In the aquarium, juveniles usually hatched immediately after the females had been attended by males. They then clung to their mother's whip for about two weeks. Most parental females in the aquarium produced three broods during a time period of about six weeks. In the field an average of 36 parental females m(-2) were found in April, and an average number of 75 juveniles clung to each female's whip. The average number of juveniles found on the females' whips declined in May and lune. Many juveniles appeared in the sea-water intake filter starting in mid April. Most juveniles caught in the intake filter were between 2 and 3 mm in size which corresponds well with their size at leaving the female's whip. In mid May, all amphipods disappeared within a few days from the aquarium, when shrimp Crangon septemspinosa started to become more active again. Many big females disappeared in the field at that time too, and in mid June parental females were smaller than in the previous months. The amphipod D. monacanthus belongs in the category of epibenthic suspension-feeding amphipods. It is probably very susceptible to epibenthic predation and extended parental care is primarily a mechanism to lift very small juveniles above the viscous sublayer in the benthic boundary layer.

关键词： Animals   Echinodermata/genetics   Evolution   Evolution, Molecular   Evolution, Molecular   Homeodomain Proteins/genetics   Morphogenesis/genetics  

关键词： Animals   Evolution   Female   Fossils   Male   Mammals/anatomy & histology   Mammals/classification   Marsupialia/anatomy & histology   Marsupialia/classification   Monotremata/anatomy & histology   Monotremata/classification   Pelvic Bones/anatomy & histology   Pelvis/anatomy & histology   Pelvis/anatomy & histology   Pubic Bone/anatomy & histology   Reproduction  

摘要： Living mammals can be subdivided into the monotremes (which lay eggs), the marsupials (which nurture their young in a pouch) and the placentals (in which the young stay in the uterus until a comparatively late stage of development). Traditionally, the epipubis or so-called 'marsupial bone' has been associated with the suckling of young in a marsupial pouch: its absence from placental mammals supposedly reflected prolonged intrauterine development and birth at a stage when the individual could survive either in a nest or by keeping pace with the mother during lactation. Now, however, Novacek and colleagues (page 483 of this issue) have identified epipubic bones in fossil mammals which, by all other criteria, would be classed as placentals. Here we have a morphological conundrum.

标准号: NF V08-408-1997

标准号: NF V08-401-1997

标准号: NF V08-409-1997

标准号: NF V08-403-1997

关键词： magnetic stratigraphy   mammal evolution   biochronology   vertebrate paleontology  

摘要： Eleven sections have been sampled for magnetostratigraphy in the fossil mammal-productive late Neogene basins of eastern Spain. The characteristic direction of magnetization was determined through progressive thermal and alternating held demagnetization. It was possible to correlate the magnetozones from the various sections to the GPTS as well as to the fossil MN zones within the sediment. The MN zone boundaries based on this correlation are as follows: MN 11/12 similar or equal to 8.1 my. MN 12/13 similar or equal to 6 my;MN 13/14 similar or equal to 4.9 my;MN 14/15=4.18 my;MN 15/16=3.58 my, New fossil lists are presented for the Fuente del Vise and Loma del Castillo faunas in the Cabriel Basin. (C) 1997 Elsevier Science B.V.

关键词： 水产动物   病毒   生物学性质  

关键词： microcrustacean zooplankton   tropical limnology   biomass   production   empirical relationships  

摘要： Production, biomass and productivity of the microcrustacean zooplankton populations of three low-land reservoirs, Tissawewa (eutrophic), Ridiyagama (moderately eutrophic), and Muruthawela (mesotrophic) in South-east Sri Lanka were studied. The temporal variation of zooplankton production was studied in Tissawewa on basis of fortnightly sampling on five fixed sampling stations for 2 years. Zooplankton production was relatively high, mainly because of high copepod production predominantly realised due to two calanoid copepods, Phyllodiaptomus annae and Heliodiaptomus viduus. About half of the copepod production was contributed by the naupliar instar stages, whereas the contribution of the eggs was generally much smaller (<20%). In contrast, the cladoceran production consisted for ca 50-70% of egg production. The results of this study were compared with those from more than twenty other tropical and subtropical waterbodies reported in the literature by deriving empirical relationships between mean phytoplankton biomass and mean zooplankton biomass and production. Mean zooplankton biomass and annual zooplankton production were found to be positively related to mean phytoplankton biomass, and mean phytoplankton biomass proved to be a good predictor of mean zooplankton biomass (r(2) = 0.58) and a moderate good predictor of annual zooplankton production (r(2) = 0.43). However, the relationships between the mean phytoplankton biomass and zooplankton P/B were not significant neither for small-bodied and large-bodied cladocerans nor for copepods.