An account of a group of 66 species of minute mites found in marine and freshwater habitats.

Generally speaking, any mite found swimming or totally immersed in sea-water is likely to be a halacarid. In fresh water, it is more likely to be a Hydrachnid (Water Mite) especially if bright coloured.

Cleared and mounted for microscopy. It is sometimes necessary to examine both dorsal and ventral surfaces under x100 oil immersion.

Specimens should be cleaned of attached debris by letting them crawl around in clean water and in a thin layer of clean sand for an hour or two. It may be necessary to change the sand and water after an hour.

The mites must then be killed in 70% alcohol (also for storage) and cleared prior to making microscope preparations. Before clearing measure the specimen, then place in a small drop of lactic acid, puncture the side of the body between 2nd and 3rd legs using a tungsten needle (see below), and gently squeeze out the contents by pressing a blunt needle on the dorsal surface. Repeat a few times in fresh lactic acid until the body is clear enough to see the details of the plates. Gentle warming for 10-15 mins may also help.

Mount temporarily in lactic acid, or rinse twice in 70% ethanol and preserve in Glycerine Jelly or Modified Hoyer’s Fluid. Mount between two coverslips so the animal can be examined from both sides. The x100 oil immersion objective is often necessary.

Tungsten needles can be made by dipping the end of a short length of tungsten wire (c.0.2mm thick =No. 35 or 36 S.W.G.) in hot molten sodium nitrite. The latter can be heated over a spirit lamp in a very small brass or iron container in a well-ventilated space (danger: don’t spill or touch the molten liquid). When the nitrite is hot enough the end of the wire will glow and erode to leave an extremely sharp point. The wire can be glued to a matchstick for easier handling.