The nomenclature and taxonomy for the freshwater annelids is undergoing major revision.  The commonly used terms Hirudinea and Oligochaeta have little standing accordingly for level 1 testing we only require identifcation of the Annelida to the Phylum and Class levels. The answers will therefore be: 

Phylum Annelida - Class Clitellata Subclass Hirudinida

Phylum Annelida - Class Clitellata Oligochaetous Clitellata

 

The most recent hierarchy for these two groups is:

Leeches

Phylum Annelida

Class Clitellata

Subclass Hirudinida

Order Acanthobdellida

Order Arhynchobdellida

Family Haemopidae Sawyer, 1986

Family Hirudinidae Whitman, 1886

Family Erpobdellidae R. Blanchard, 1849

Family Salifidae Johansson, 1910

Order Rhynchobdellida Blanchard, 1894

Family Glossiphoniidae Vaillant, 1890

Family Piscicolidae Johnston, 1865

The hierarchy for the leeches is (from Classification and Checklist of the Leeches (Phylum Annelida: Class Clitellata: Subclass Hirudinida) occurring in North America North of Mexico. Compiled by Donald J. Klemm, William E. Moser, and Mark J. Wetzel.

 

Oligochaetes 

Phylum Annelida

Class Clitellata Oligochaetous Clitellata [= 'Oligochaeta'] -)(- Superorder Microdrili

Order Haplotaxida

Family Haplotaxidae

Order Lumbriculida

Family Lumbriculidae

Order Tubificida

Family Naididae

Subfamily Naidinae
Subfamily Pristininae
Subfamily Tubificinae
Subfamily Telmatodrilinae
Subfamily Rhyacodrilinae
Subfamily Phallodrilinae

Family Opistocystidae

Family Parvidrilidae

Order Enchytraeida

Family Enchytraeidae

Family Propappidae

From Classification and Checklist of the Freshwater Oligochaetes Occurring in North America North of Mexico
Compiled by M.J. Wetzel, R.D. Kathman, S.V. Fend, and K.A. Coates.