1. Ossicles in body wall include anchors and three-armed anchor plates, spired tables. Phosphatic deposits present...........................................................................................Genus Heteromolpadia Pawson, 1963... 2
- Ossicles in body wall may include anchors and rosettes of racquet-shaped plates, fusiform rods, spired tables. No three-armed anchor plates. Phosphatic deposits present or absent...................................................................................................................................................................Genus Molpadia Risso, 1826... 4
2. Tables in tail less than 200 Μm long, with 6–12 perforations. Complete tables usually present, but sometimes scattered, in body wall; diameter of tables usually exceeds 150 Μm.................................................. 3
- Tables in tail approximately 300 Μm long, with 15–20 perforations. Tables in body wall 100 Μm in diameter with three larger perforations, tables almost always transformed into phosphatic deposits.................... ............................................................................................................ Heteromolpadia joyceae new species
3. Body wall tables of average diameter 300 Μm, usually with more than 3 large perforations.................................................................................................................................. Heteromolpadia pikei Pawson, 1965 b
– Body wall tables of average diameter 150 Μm, usually with only 3 large perforations................................. ................................................................................................... Heteromolpadia marenzelleri Théel, 1886
4. Phosphatic deposits absent or very rare; adult specimens gray, pink, or whitish. Body wall ossicles exclusively tables................................................................................................................................................ 5
- Phosphatic deposits present, usually numerous; adult specimens red to violet. Ossicles predominantly fusiform rods in body wall and tail. Spired tables and anchors with rosettes of racquet-shaped plates present in juveniles and young adults ........................................................ Molpadia musculus Risso, 1826
5. Spires of body wall tables single, solid, derived from 3 pillars fused together.......................................... 6
- Spires of tables always composed of 3 discrete pillars, joined by crossbars but never fused together......... ................................................................................................................ Molpadia antarctica (Théel, 1886)
6. Tail ossicles circular, 75–160 Μm in diameter, often with only three perforations....................................... 7
- Tail ossicles rod-like, exceeding 300 Μm in length, with up to 20 perforations. Ossicles in body wall tables of average diameter 121 Μm, with 3–8 perforations............................. Molpadia abyssicola Pawson, 1977
7. Ossicles in body wall and tail exclusively tables with 3 perforations...... Molpadia discors Pawson, 1977
- Ossicles in body wall and tail tables with 3–8 perforations.......................... Molpadia liska Pawson, 1977