Is the fertilization of chondrichthyes internal or external?

Answer 1

Orthologues of many of the eutherian sperm membrane proteins related to fertilization40 are present in platypus (and marsupial) genomes. These include the genes for a number of putative zona pellucida receptors and proteins implicated in sperm-oolemma fusion. Testis-specific proteases, which in eutherians participate in degradation of the zona pellucida during fertilization, are all absent from the platypus genome assembly. Monotreme spermatozoa undergo some post-testicular maturational changes, including the acquisition of progressive motility, loss of cytoplasmic droplets and aggregation of single spermatozoa into bundles during passage through the epididymis11. Nevertheless, maturational changes in the sperm surface that are both unique and essential in other mammals for fertilization of the ovum have yet to be identified. Also, the epididymis of monotremes is not highly adapted for sperm storage as in most marsupial and eutherian mammals. Consistent with these findings is the absence of platypus genes for the epididymal-specific proteins that have been implicated in sperm maturation and storage in other mammals. The most abundant secreted protein in the platypus epididymis is a lipocalin, the homologues of which are the most secreted proteins in the reptilian epididymis41. Notably, ADAM7, a protease that is secreted in the epididymis of eutherians, has an orthologue in the platypus. This is a bona fide protease with a characteristic Zn2+-coordinating sequence HExxH in the platypus, in the opossum and the tree shrew (Tupaia belangeri). However, loss of its proteolytic activity is predicted in eutherians42 owing to a single point mutation within its active site (E to Q).

Answer 2

Internal, since it lays eggs, the platypus would have to be fertilised internally. Raphael Yee Singapore

Answer 3

Not sure how a sperm could negotiate an egg-shell, shell mebranes, egg-white.......................... Fertilisation takes place internally

Answer 4

The platypus is hatched, despite being a mammal.