Tardigrade (water bear) (Echiniscus sp.). Tardigrada is an obscure phyla of invertebrates located between the nematodes (roundworms) and the arthropods (crustacea, insects, and ticks). Tardigrades are microscopic aquatic animals that need water to live. Without water they shrivel into a cask stage and survive long periods of desiccation in a stage called cryptobiosis. Tardigrades are found in marine, freshwater, and semi-aquatic terrestrial habitats. Mosses, lichens, leaf litter, soil, and even the grains of sand on a beach are examples of such habitats. They are small, 0.2-0.5 mm in length, with 5 body segments and 4 pairs of legs. They breathe through their cuticle and have a hemocoel for circulation. Water bears feed on the fluids of plant and animal cells. They have stylets which allow them to pierce plant or animal cells. Cryptobiosis is of great interest in the study of cryogenics and tardigrades have been subjected to laboratory experiments which have verified their ability to survive.
Petrified redwood / sequoia (Sequoia affinis, longitudinal section). Note the bordered pits in vertical vessel elements and also in the perpendicular ray cells.
Goblet cell in the mucosal lining of the small intestine
Goblet cell (green) in the mucosal lining of the small intestine (part of the digestive tract). A goblet cell secretes the mucus to protect the lining of the intestine and helps neutralize stomach acid. Inside the goblets cells are many mucigen granules (steel blue). When these are released into the intestine they will combine with water to form mucin, the main constituent of mucus. Surrounding the goblet cell are columnar epithelial cells (purple cell membrane outline; turquoise nucleus; red mitochondria). The brush-like surface of the columnar epithelial cells consists of microvilli (orange), tiny finger-like projections, which increase the surface area available for absorption of nutrients such as lipids, proteins and fat-soluble vitamins. The microvilli have a rapid turnover of 3-4 days. The intestinal lining is supplied with a rich network of blood vessels (not seen) to transport the nutrients around the body.
Watch cogs and gears from a 7-jeweled watch escapement. The red area is a ruby jewel used in a bearing. An escapement is a device within a watch that provides periodic impulses to the balance wheel that helps to regulate time- keeping. Jewels (natural or man-made) were used in watch bearings because their smooth surfaces offer little friction and slow wearing. Due to the age of the watch there has been some corrosion of the metal gears.
Vorticella spp. -ciliated protozoan. Shown is the main cell region of this stalked (attached) protozoan. The mouth is partially open with cilia protruding.
Gecko (lizard) foot / toe hairs (Hemidactylus frenatus). A lizard's foot has at least a half a million microscopic hairs, (one-tenth the thickness of a human hair). The end of each hair is split into smaller hairs. At the frayed ends these smaller hairs have spatula-shaped structures -- about a billion per gecko. This spatula-shaped tip can flatten over rough or smooth surfaces and increases the area with which the hair can make contact. The geckos movement is accomplished by rolling and un-rolling these hairs onto the surface.
