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Posterior Tip (posterior + tip)
Selected AbstractsSpermiogenesis and spermatozoon ultrastructure of the davaineid cestode Raillietina micracantha (Fuhrmann, 1909)ACTA ZOOLOGICA, Issue 2 2010Jordi Miquel Abstract Miquel, J., Torres, J., Foronda, P. and Feliu, C. 2010. Spermiogenesis and spermatozoon ultrastructure of the davaineid cestode Raillietina micracantha. , Acta Zoologica (Stockholm) 91: 212,221 The spermiogenesis and the ultrastructural organization of the spermatozoon of the davaineid cestode Raillietina micracantha are described by means of transmission electron microscopy. Spermiogenesis begins with the formation of a zone of differentiation containing two centrioles. One of the centrioles develops a free flagellum that later fuses with a cytoplasmic extension. The nucleus migrates along the spermatid body after the proximodistal fusion of the flagellum and the cytoplasmic extension. During advanced stages of spermiogenesis a periaxonemal sheath and intracytoplasmic walls appear in the spermatids. Spermiogenesis finishes with the appearance of two helicoidal crested bodies at the base of spermatids and, finally, the narrowing of the ring of arched membranes detaches the fully formed spermatozoon. The mature spermatozoon of R. micracantha is a long and filiform cell, tapered at both ends, which lacks mitochondria. It exhibits two crested bodies of different lengths, one axoneme of the 9 + ,1' pattern of trepaxonematan Platyhelminthes, twisted cortical microtubules, a periaxonemal sheath, intracytoplasmic walls, granules of glycogen and a spiralled nucleus. The anterior extremity of the spermatozoon is characterized by the presence of an electron-dense apical cone and two spiralled crested bodies while the posterior extremity of the male gamete exhibits only the axoneme and an electron-dense posterior tip. [source] Social Behavior of Larvae of the Neotropical Processionary Weevil Phelypera distigma (Boheman) (Coleoptera: Curculionidae: Hyperinae)ETHOLOGY, Issue 7 2004James T. Costa Socially gregarious behavior among free-living leaf-eating insect larvae occurs mostly among Lepidoptera, Symphyta, and a few Chyrsomelidae (Coleoptera). However, the Neotropical hyperine curculionid Phelypera distigma has also evolved this lifestyle, exhibiting a suite of social behaviors unique among beetles. The larvae are nomadic processionary foragers that punctuate foraging bouts with rosette-shaped resting formations (cycloalexy). Larvae also vibrate or bob their heads rapidly when moving, especially when in contact with conspecifics, and this suggests acoustic or vibrational communication. In this study we used observational and experimental approaches to investigate the basis of processionary, cycloalexic,and head-vibration behavior of this species. Larvae used both trail pheromones and thigmotactic signals to organize themselves into head-to-tail processionary columns. The trail pheromone, produced from the center of the abdomen, remains active for up to 4 h. Processions are not consistently led by particular individuals, but dynamically change over time and often temporarily break into two or more subprocessions. Subprocessions reunite through use of the trail pheromone. We found no evidence that head-bobbing generates attraction through substrate-borne or acoustic signals, but this behavior functions in direct contact to excite group activity. Time-lapse videography used to analyze cycloalexic group formation showed that larvae transition from feeding in a line along the leaf margin to cycloalexic formations on the upper leaf surface via a coordinated back-up movement that brings the posterior tip of their abdomens into contact. We identify three phases of cycloalexic formation: line-up, back-up, and an adjustment phase. Complete assembly can be achieved in as little as 5 s, but often the two phases establishing the basic rosette lasts 5,10 min, while the adjustment phase slowly tightens the group over a period of up to an hour. Collectively these studies present the first documented case of chemical trail marking in a beetle, and provide insight into a remarkable social-behavioral repertoire convergent in key respects with the better-studied social caterpillars and sawflies. [source] The fine structure of the muscle system in the female of the orthonectid Intoshia variabili (Orthonectida)ACTA ZOOLOGICA, Issue 2 2003George S. Slyusarev Abstract The contractile system of the female Intoshia variabili (Orthonectida) consists of smooth muscles. The attachment of the longitudinal muscle fibres at the anterior and the posterior tips of the body is rather peculiar, accomplished by means of elongated terminal muscle cells piercing through several ciliated cells. In the last ciliated cell, the muscle cell invaginates the ciliated cell basal membrane almost up to the ciliated cell surface. Here, around the protrusion terminus, there is an electron-dense zone in contact with the cilia rootlets. [source] Correlation of fluorescence and electron microscopy of F-actin-containing sensory cells in the epidermis of Convoluta pulchra (Platyhelminthes: Acoela)ACTA ZOOLOGICA, Issue 1 2002R Pfistermüller Abstract Phalloidin-stained whole mounts of acoel turbellarians show brightly fluorescing club-shaped structures distributed over the epidermis and concentrated especially at the anterior and posterior tips of the body. By correlating electron micrographic images and fluorescence images of Convoluta pulchra, these structures can be seen to be sensory receptors with a central cilium surrounded by a collar of microvilli. The other candidate for showing fluorescence in the epidermis, namely gland necks, can be ruled out since their distribution is too dense to resemble the distribution of the fluorescent structures seen here. The collared sensory receptors were inserted between epidermal cells, and each bore a central cilium surrounded by a collar of 6,18 microvilli and an additional centrally positioned 2,7 microvilli of which 2 or 3 were associated with a modified rootlet called the swallow's nest. Confocal scanning laser microscopy resolved the core of actin filaments within the microvilli of the collar and their rootlet-like connections to the base of the sensory cell. Such receptors could also be identified by fluorescence microscopy in several other species of acoel turbellarians. [source] | ||||||||||