What makes a good Leech Observation.

First of all: get up close - as close as you can.
Then crop your photos, so that the Leech is fully in the frame.
Take lots of pictures.

Best out of water (but not wet), or if in the water, then well down and out of the meniscus - which causes a shine that hides any colours and features.

Things to focus on:

Eyes

The eyes are crucial, especially for the Glossiphoniidae and Salifidae. the eyes may be in 2-4 pairs in various arrangements: and are diagnostic for species.
• The more typical families have 5 pairs of eyes on the outside of the head (in a parabolic arch).

Shape:

take several pictures of the rest state, and while stretched. Fully engorged leeches will be distorted: find some hungry ones.
• long and evenly slender: Salifidae
• tubular - most families
• flattened and varied shapes: Glossiphoniidae - some species can immediately be identified just by their shape - when at rest. Shape can be different if breeding or non-breeding - if more than one shape is present, get all the shapes.

Colouring:

Leeches are brightly coloured and the pattern and colour is useful for identification. Some species have more than one colour "morph". Photographs can record the colours beautifully: do them justice! In fact, some species cannot be identified without their patterns! Patterns may be spotted, longitudinally striped, or transversely banded. Make sure any reflection or sheen does not obscure the patterns.
The best colours appear to be in about 10mm of water - out of water many leeches appear blackish, even when they are colourful.

Guts:

In some groups the number of gut segments (caecae) are useful: these can easily be photographed with back lighting. Try and get a few backlit shots showing the internal organs. Well-fed beasts are best.

Segments.

The segments in leeches are folded into annuli (rings). There can be 3-14 rings per segment. In s Afr we have 3- 5- or 7- rings per complete segment. The easiest way to tell is to look at the ornaments (see next), which are usually on the middle ring of each segment. Crucial are the number of rings in each of the first 6 segments, with fewer rings towards the head, and #7 (from ring 7 onwards the rings are usually constant or "complete"). Where there is no ornamentation, this can be complicated and a ventral view closeup should show the nephropores (kidney ducts), which is much easier with bigger specimens. In some Glossiphoniidae and Salifidae one cannot determine the rings without dissection, but they have other useful features, so dont fret about it.

Ornamentation.

All leaches have sensillae on the middle ring of each segment - these taste and feel. They are usually hard to photograph. There are usually 3-4 pairs of sensillae dorsally and 3 ventrally. Fortunately in some groups these sensillae are on smooth domes (called papillae), or cones (called tuberculae) comprizing several domes on their tips. The pattern and arrangemnt of these is most useful.

If you get the eyes, body shape, annulation, colouring and ornamentation then you are 90% of the way to getting an easy ID ...

Posted on January 2, 2024 09:28 PM by tonyrebelo