Besnoitia darlingi (Apicomplexa,Sarcocystidae, Toxoplasmatinae): Transmission between Opossums and Cats1

ABSTRACT. Opossums (Didelphis marsupialis), act as intermediate hosts for Besnoitia darlingi and could be infected orally with sporozoites (oocysts) and bradyzoites (tissue cysts), or intraperitoneally (i.p.) with tachyzoites. Infections could presumably be transmitted through cannibalism. Cats (Felis catus), the definitive host, could be infected only with bradyzoites but not sporozoites. Oocysts shed by cats measure about 12 × 12 μm, resemble similarly sized oocysts of Toxoplasma gondii and Hammondia hammondi, and must be differentiated by the appearance of tissue cysts after experimental infection of intermediate hosts. Cats did not form tissue cysts of B. darlingi. Tachyzoites from the related B. jellisoni could be used in the Sabin-Feldman dye test to determine the development of antibody to B. darlingi in opossums after infection.     

Cystolith Development and Structure in Pilea cadierei (Urticaceae)

Cystolith formation, structure and composition have been investigatedin leaves and stem internodes of Pilea cadierei (Urticaceae)using a variety of techniques at the light and electron microscopelevels. The development of lithocysts from epidermal cells hasbeen followed. These cells are cytoplasmically similar to otherepidermal cells but possess a much more active Golgi apparatusand more numerous mitochondria. The cystolith is a spindle-shapedbody composed of concentric layers of longitudinally orientatedcellulose microfibrils associated with pectins and other cellwall polysaccharides. At maturity it is heavily impregnatedwith calcium carbonate. Some cystoliths also contain siliconand are covered in a sheath of siliceous material. Cystolithformation occurs at the tip of a peg that grows in from thelithocyst wall. Evidence from ultrastructure suggests that thelithocytst cytoplasm transports carbohydrates to the cystolithvia Golgi vesicles, and organizes the deposition of cystolithcellulose microfibrils via a system of microtubules lying beneaththe plasma membrane that envelopes the growing cystolith. Thepeg is composed of heavily staining amorphous material likethat of an apoplastically sealed cell wall. It is incapableof supporting the migration of lanthanum ions into the cystolith.We conclude that cystoliths are isolated volumes of apoplastthat act as repositories for inorganic salts, principally calciumcarbonate. We propose that calcium ions move into the lithocystprotoplast from surrounding cells and are then transported acrossthe plasma membrane boundary into the cystolith. This proposalconflicts with previous suggestions that calcium enters by diffusionthrough the peg. Cystolith, lithocyst, cell wall, calcium, silicon, cytochemistry, electron probe analysis, Pilea cadierei     

The West African species of Bathygobius (Teleostei: Gobiidae) and their affinities

The circumtropical gobiid fish genus Bathygobius Bleeker, 1878 is discussed and defined in terms of external features, including the head lateral-line system, and osteology. Three West African species are recognized and redescribed: the amphiatlantic B. soporalor (Valenciennes, 1837) and two endemics, B. burtoni (O'Shaughnessy, 1875) and B. casamancus (Rochebrune, 1880). West African B. soporator differs significantly from western Atlantic material only in average values for predorsal scales and some body proportions, so that separation of eastern and western Atlantic populations as morphological species is not warranted. The affinities of the West African Bathygobius species are examined by means of phenetic (presence-only group-average clustering) and cladistic (Camin-Sokal, Dollo and Wagner) numerical processing of a binary database comprising 46 character states in 15 Operational Taxonomic Units (OTUs) formed by species of Bathygobius. Results do not indicate close common ancestry between the West African endemic species and B. soporator , which has probably colonized West Africa from the New World. The implications of various cladistic schemes for the relationships of certain other American species are also noted.     

The contribution of setal blades to effective swimming in the aquatic mite Limnochares americana (Acari: Prostigmata: Limnocharidae)

Two rows (anterior and posterior) of long fine setae inserted on the 3rd, 4th and 5th segments of the last two pairs of legs of L. americana form functional swimming blades. Each swimming setal is mounted in a mobile basal socket, and the structure of the setal base and socket configuration ensure that the blades will be passively erected during the leg's power stroke to provide increased thrust and collapsed during the recovery stroke to reduce water resistance. The erect swimming blades increase the effective area for thrust by approximately 500%, making it possible for the mite to lift itself off the bottom. The IVth legs contribute the greater proportion of the thrust developed during paddling, and the 4th segment (genu) bears the largest swimming blades on both legs.