The integument is the scientific terminology for the skin. It comes from ‘integumentum’ meaning to COVER.

The killer whales’ skin has an exterior polish that no other mammals have. Its texture is similar to a thick rubber. To touch an orca’s skin is like touching a wet pair of Wellington. However this skin is very soft and very sensitive. Some areas are more sensitive than others, especially the stomach around the navel and the genital organs, as well as the area around the pectoral fins. It could be one of the reasons why, at certain time, the male in the Johnson Bay rub their belly against the pebbles covered bottom of the shore. This bay is also known as the ‘caress creek’ or ‘the pebbles’ bay’. It is one of the very few occasions where it is not recommended to approach the animals. They could make you understand that your presence is not welcomed. The caress bay is not for you!!!

The orca’s skin is extremely well adapted to the underwater movements. Actually it is active and reactive and will, according to the requirements, modify its structure. But let’s have a closer look…

THE SKIN IS MADE OF:

• THE EPIDERMIS (epi=above, derma=skin)
• THE DERMIS (OR CORIUM OR DERMA)

THE EPIDERMIS IS MADE OF 4 LAYERS:

• THE CORNEA LAYER (stratum corneum): is a thin, keratinised layer. It is at the same time hard and very fragile. It is the most external one.
• THE CLEAR LAYER (stratum lucidum): it’s a very thin, nearly invisible layer.
• THE MALPIGHI LAYER (stratum spinosum):
• THE BASAL LAYER or GERMINATING LAYER (stratum germinativum): it’s from there that the cells renewal for the mitosis starts. It’s the deepest layer of the epidermis.

The keratinocytes are the most numerous cells of the epidermis. They are going to suffer, from the basal (or germinating layer) a morphological and biochemical transformation that will lead to the creation of the cornea or keratinised (cornea layer) cells. The epidermis is also made of melanin that will generate the skin pigmentation. The keratinised layer is very thin and can be easily peeled of from recently died body.

Under this epidermis layer, we will naturally find the dermis.

The dermis is made of wrinkles parallel to the body axis, where dermis papillae are coming up, in a smaller number than on terrestrial mammals. It is a mattress of fabric support (parallel fibres) at the surface of the body. In depth the dermis becomes the lard.

The lard, also known as panniculus adiposus, or fat is made of a tight network of conjunctives bundles, keeping tightly together huge adipose cells. It is worth noting that the arterioles pass through this layer and create in the dermis little twigs that enter the papillae (where they become capillaries). Venules take the same route.

Let’s take some distance to go back to the surface of this skin. It is perfectly hairless. It is also free of integumentary glands (except mammals glands), sudoriferous glands and pores. This skin has a hydrodynamic secret though. During moves in the water, turbulences will be created on the body of the animal and will slow it down. The skin is going to react and absorb these turbulences. How?

Despite the appearances, tegument is not waterproof. The external layer is water permeable and recovers the fatty and hard inferior layer. It is made of a kind of very thin membrane, recovering a multitude of small vertical canals. These are full of a spongious filling that will absorb or expulse water according to the need. This skin is going to expulse the water so its final mass will only be 20% of its original (ie filled with water) weight. This system in fact reacts to pressure, and will absorb oscillations that form on the skin when the speed is high and the pressure stronger. In order to do so, the skin will contract itself to generate creases at the turbulence level. The shallow part of these creases will then break the oscillations and absorbs whirlpool allowing a better flow of the water.

This schema will show you the principle. On the left, slow speed, on the right, high speed. At the top, normal skin, at the bottom, orcas’ skin. At high speed the killer whale’s skin creases and absorbs vibrations in a way, it’s the addition of these creases and the expulsed water that will attenuate the vibrations.

On top of that, there is another ingenious system: lubrication. The skin secretes little drops of a slightly viscous liquid to minimise the frictions. After analysis, this liquid happens to be a high polymer of ethylene oxide.

Now, let’s take even more distance and look at the colour scheme with its so specific pattern.

The killer whale is black from the tip of the nose to the end of the caudal fin (including the superior side). The dorsal fin is totally black, just like the pectorals (on both side). Nearly all of the back area is black, except for the back of the fin, where a greyish mark goes down to the side of the animal for about 50 cm. This area is called the saddle. The white part is an irregular band that goes from the inferior jaw and carries on to the back, between the pectorals. It ends at the kidney level, in a trident shape in which the central part includes the uro-genital zone, the mammals’ zone and the anal zone. The extremity of the central dent is rounded with the males but is pointed with the females. The lateral dents go up from the kidney to the flanks. The white part reappears near the fluke. The fluke is white on the inferior side except for the black borders.

A white mark is visible on each eye. It is situated at the top back corner and is oval shaped.

During healing, it is not unusual to spot an inverted colour, i.e. a black scar on a white skin and vice versa. Albinism cases have been seen (the animal is then white all over).

The skin colours have the double role of hiding tool and combat weapon. Hiding tool because in the depth the colour black is invisible. By showing its superior side to its enemy (the totally black side), the orca is practically invisible. By swimming under or by the side of a prey (it will then slightly turn on its rotation axis), without emitting any noise, the killer whale becomes then a dangerous torpedo. However, the skin colour is also a fighting / hunting tool: by presenting its ventral side and powerfully screaming, our orca scares its prey, making them lose their sense of direction and becoming easier to hunt.