 The third suborder , Sirenoidea , contains the four species of sirens , which are in a single family , Sirenidae . Members of this order are eel @-@ like aquatic salamanders with much reduced forelimbs and no hind limbs . Some of their features are primitive while others are derived . Fertilisation is likely to be external as sirenids lack the cloacal glands used by male salamandrids to produce spermatophores and the females lack spermathecae for sperm storage . Despite this , the eggs are laid singly , a behaviour not conducive for external fertilisation . 
