The 2009 Philippine Marine Biodiversity souvenir sheet on the cover depict six kinds of sea slugs.
Slug is a common name that is normally applied to any gastropod mollusc that lacks a shell, has a very reduced shell, or has a small internal shell. This is in contrast to the common name snail, which is applied to gastropods that have coiled shells that are big enough to retract into.
All slugs are descended from snails that gradually lost or reduced their shells over time.However, the shell-less condition has arisen many times independently during the evolutionary past, and thus the category "slug" is emphatically a polyphyletic one. The various groups of slugs are not closely related, despite a superficial similarity in the overall body form.
There are marine and terrestrial slugs, but the common name "slug" is most frequently applied to air-breathing land species, while the marine forms are known as sea slugs. Land gastropods with a shell that is not quite vestigial, but is too small to retract into (like many in the family Urocyclidae), are known as semislugs.
The other four 7P stamps are 2007 Wild Ducks issue showing Northern Pintail,Greater Scaup,Common Shelduck and Northern Shoveler.
Northern Pintail(Anas acuta) is a widely occurring duck which breeds in the northern areas of Europe, Asia and North America. It is strongly migratory and winters south of its breeding range to the equator. This is a fairly large duck, with a long pointed tail that gives rise to the species' English and scientific names. The male has a very distinctive brown, grey and white appearance, whereas the female has mainly light brown plumage and a shorter tail. The male's call is a mellow whistle, whereas the female quacks like a Mallard.
The Greater Scaup (Aythya marila), just Scaup in Europe, or colloquially known as "Bluebill", is a small diving duck. It breeds on the ground by lakes and bogs on the tundra and at the northern limits of the boreal forest across Arctic and subarctic regions of northern North America, Europe and Asia.
The gooselike Common Shelduck (Tadorna tadorna) is a striking bird with its red bill, white and chestnut body, dark green head and neck. Sexes are similar, but the female is duller. The male has a swollen red bill knob in the breeding season.
Northern Shoveler (Anas clypeata) is unmistakable in the northern hemisphere due to its large spatulate bill.