Family Isotomidae

Isotomid characteristics:

• unscaled
• elongated body and body segments of approximately equal length (c.f. Entomobryidae, abd4 more than twice as long as abd3)
• antennae with 4 segments of similar length
• 8+8 ocelli
• furca & PAO present
• no anal spines

The presence and positioning of macrosetae (long hairs) and bothriotricha (mechanoreceptive hairs) are important in separating these genera. However, these are easily lost and may be missing. In this case you have to check whether or not empty sockets of macrosetae are present on the skin surface (difficult). Bothriotricha are often difficult to see even if present, but the pits in which they sit may be visible.

Ocelli:


Desoria - covered in short setae (hairs); ocelli B-D-E in straight line; mucro has four teeth but does not possess a lateral seta, apical tooth is large (c.f. Isotomurus); no teeth on manubrium (c.f. Isotoma); Hopkin key #224

Isotoma - long macrosetae on all body segments; ocelli C-D-E in straight line; mucro has three teeth; bothriotricha absent; Hopkin key #220

Isotomurus - long macrosetae on abd4-6 only; ocelli B-D-E in straight line; mucro has four teeth, apical tooth smaller than the others (c.f. Desoria); bothriotricha present; Hopkin key #209 (pigmentation patterns).

Vertagopus - no long macrosetae but a fuzzy cover of short setae; mucro has four teeth; tibiotarsi (adjacent to claws) have clavate tenant (knobbed) setae; only two British species; Hopkin key #215

Desoria

Desoria - covered in short setae (hairs); simple (unforked) setae by the feet; mucro has four teeth but does not possess a lateral seta, apical tooth is large (c.f. Isotomurus).
Isotoma - long setae on all body segments; mucro has three teeth.
Isotomurus - long setae on abd5+6 only; mucro has four teeth, apical tooth smaller than the others (c.f. Desoria).


Genus Desoria:
Desoria infuscata - very rare, upland sphagnum bogs.
Desoria tigrina - common, widespread. Dorsal plus lateral pigment stripes. Macrosetae on abd5 <0.7 length of adb5. (All UK literature records for 'Isotoma olivacea' are probably Desoria tigrina.)
Desoria trispinata - probable horticultural import. No macrosetae on abd. Looks like Vertagopus arboreus but with blue rather than pale legs. Eight ocelli in a rectangular eyepatch, c.f. four in a square patch for Parisotoma notabilis. Nine setae around the feet c.f. eleven in Isotoma.
Desoria violacea - common, widespread. Dark colour with blue/violet iridescence. Macrosetae on abd5 approximately same length of adb5.


Desoria tigrina
"Desoria tigrina (formerly Isotoma tigrina) is widespread and common, with a tendency towards human-impacted soils or habitats rich in organic matter. Desoria tigrina is light to dark grey or brown (never white, dark blue or violet)."





- No macrosetae
- Ocelli B-D-E aligned
- Mucro with 4 teeth and no lateral seta
- Long setae on Abd5 <0.7 length of Abd5



Desoria trispinata - Photo Marie Huskens:





Desoria violacea: