In this relaxing Minute, we would like to introduce you to a beautiful bottom dweller named the Blue-lined philinopsis. In scientific circles, it goes by the name Philinopsis cyanea. To make things even more complicated, Philinopsis cyanea is almost certainly a synonym of Philinopsis speciosa. This particular species was first described in 1860 in the Hawaiian Islands and was thought to be endemic to that region. However, upon further investigation, there are no anatomical features distinguishing P. speciosa from the widespread Philinopsis cyanea. On top of that, it shows an identical range of colour variation. It would appear that P. speciosa is a widespread Indo-West Pacific species which has been (mis)identified in most places as P. cyanea.  According to some scientists,  P. speciosa is the older name, as well as the type of the genus, and it should replace the more commonly used P. cyanea. So far, all rather confusing…

Let’s take a close look at the Blue-lined philinopsis and its habitat


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We hope science will clear this one up in the not-too-distant future. Philinopsis speciosa is a species of sea slug, a shell-less opisthobranch gastropod mollusc in the family Aglajidae. It has a widespread distribution in the tropical Indo-Pacific region, with a range extending from the east coast of Africa and the Red Sea to Japan, Hawaii and New Caledonia. It can be found in the subtidal zone, where it moves along sandy and clay bottoms, among seagrass and seaweeds, at depths down to about 20 m (66 ft).

Body features of Philinopsis speciosa

Philinopsis speciosa is basically a large slug, growing to a length of about 80 mm. It has a well-developed, broad head shield, of which the posterior edge has a tapering crest, which stands erect, and the body is cylindrical in shape. The head shield is used for gliding over and burrowing beneath the surface of the sand. Behind the head shield is a body shield consisting of two rounded lobes at the back. On either side of the body are lateral outgrowths known as parapodia. On the front of their heads, they have sensory bristles, that help them navigate, and detect their prey.

The hunting slug

Like other members of the Aglajidae, Philinopsis speciosa is a predator. Its diet consists mainly of other gastropod molluscs. It has no radula, which is typically used by molluscs for scraping or cutting their prey before the food enters the esophagus. Instead, they feed by partially everting their large muscular buccal bulb, or pharynx, to envelop their prey and swallow them whole. After digestion, the empty, unbroken shell of the prey is regurgitated, being too large to pass through the gut.

Reproduction of the blue-lined philinopsis

Philinopsis speciosa is a hermaphrodite. Reproduction occurs when two or more individuals form a circle or a short chain. The penis is on the right, level with the head, and the female genital opening is on the right side further back. The first individual acts as a female and receives sperm from the second, which acts as both male and female, giving sperm to the first, and receiving sperm from the third. The last slug in the line acts only as a male. The white eggs are wrapped in a thin layer of mucus and this strand is wound around the slug’s head in a tangled cylinder. The slug then removes its head from the cylinder and sticks the end of the filament to the substrate.

So much to learn and discover

What a beautiful freaky world we live in! This video was filmed at the dive site Siaba Besar in the Komodo Nationalpark (Indonesia). Take a good look at the sensory bristles! After all, this is what our minutes are for: Taking in the details and admiring nature’s glory.

For more visual meditation and marine information, watch the whole playlist on our YouTube channel or browse through the different clips on our designated page „Take a Minute“ on this website.

Did you spot the sensory bristles of Blue-lined philinopsis (Philinopsis speciosa)?

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