Characteristics: In all sea slugs (formerly known as Opisthobranchia) you will find the gills behind the heart. The sea slugs originate from the sea snails which have the gills in front of the heart. The shell is usually internal or completely lost at some point during evolution.The name Heterobranchia means different-gilled snails.he sea slugs originate from the sea snails which have the gills in front of the heart. The shell is usually internal or completely lost at some point during evolution. The name Heterobranchia means different-gilled snails.
The twelve thoracic vertebrae are numbered T1 to T12. The range of motion in the thoracic spine is limited. Lumbar (low back) - the main function of the lumbar spine is to bear the weight of the body. The five lumbar vertebrae are numbered L1 to L5.
The_human_spine_has_7_cervical,_12_Thoracic_and_5_Lumbar_vertebrae_as_well_as_5_(fused)_in_the_sacrum_and_another_4_(fused)_in_the_coccyx_which_totals_33. The human spine has 7 cervical, 12 Thoracic and 5 Lumbar vertebrae as well as 5 (fused) in the sacrum and another 4 (fused) in the coccyx which totals 33.lmost all humans are born with 33 separate vertebrae. By adulthood, most have only 24. This is due to the fusion of the vertebrae in certain parts of the spine during normal development.