Remarkable sea creature found at Clachtoll
November 15th 2020 was such a beautiful day of autumn sunshine that I went for a walk along the beaches at Clachtoll, hoping to find some interesting shells. There were none, but on the small beach south of the Split Rock (NC040266), next to the strandline of seaweed and plastic, I found what I thought was a sea gooseberry. There appeared to be a dead shrimp inside the transparent ‘barrel’.
When I got home, I washed the sand from the find and discovered that the ‘shrimp’ had emerged and was alive. It had a long pair of appendages with pincers, so I assumed it was the larval stage of a langoustine or lobster. By then it was dark, but I had to get some seawater from somewhere, so I drove into Lochinver and collected some from the shore by way of the steps in the main street.
The remarkable sea creature and its ‘barrel’ were left in the seawater overnight in the cold conservatory, but sadly, it was dead the next morning. The next day I showed them to Ian Evans, who now takes up the story.
I had never before seen anything like this.
The ‘barrel’ is transparent, 25 mm long and 20mm wide, with a larger aperture at one end than the other, gelatinous, but thick enough to maintain its shape. It is roughly square in section, but with rounded sides and ridged corners. Two of the sides have two longitudinal creases, the other two just one, with horizontal pleats throughout.
The creature that was inside it is 25mm long and obviously a crustacean, possibly an amphipod, related to sand-hoppers, since its body is compressed side-to-side. In life it was strikingly transparent, except for four pigmented eyes. Closer inspection reveals a heavy, bulbous head, with the eyes well-down towards its mouthparts. There appear to be eight pairs of appendages, the first five leg-like, but with internal branches, and then three more flattened ones towards the tail. The third pair are longer than the others, and bear huge ‘toothed’ pincers, with overlapping points.
There was nothing remotely like this in any of our books on marine life. Dredging my memory produced the term ‘salp’ for the ‘barrel’ and we then searched on-line for ‘amphipod and salp’, with immediate results. The crustacean is indeed an amphipod, called Phronima sedentaria, which has a remarkable life-story.
Film star material
At an earlier stage in its life this remarkable sea creature hijacks one section of a salp, one of several kinds of colonial pelagic tunicates, related to the sedentary sea squirts. To quote the source mentioned below, ‘It attacks salps and other similar animals, and from them, by eating away parts, fashions a gelatinous barrel-like house in which it shelters and rears its young. One may sometimes be seen swimming and pushing a barrel full of young ones in front of it.’ So, the ‘barrel’ is the hollowed-out test of the salp, which we have not, so far, managed to name. Phronima has acquired, amongst marine biologists (mainly American), the colloquial names of ‘monster-in-a-barrel’ and ‘pram bug’. It is also credited with providing the inspiration for the predatory creature (rather larger) in the 1979 film Alien.
The best account of this remarkable animal in British waters is to be found in one of the classics of the New Naturalist series, The Open Sea. Its Natural History: The World of Plankton (Alister C. Hardy, 1956, pp.169-170). ‘A very rare visitor to our seas – one of the exotic Lusitanian forms found by Dr Fraser to the north of Scotland – is the remarkable Phronima which is so common in the Mediterranean and subtropical Atlantic.’
A very few other records
Several occurred on the beach at Kilmory on the north side of Rum (NG3604) on 25th December 2019 and are described by Alison Wilson in The Highland Naturalist (16, 26, 2020). There are three additional records in NBN: Portrush, N. Ireland (C8540) 10th January 2019; Traigh Iar, Harris (NG0396), 14th January 2019; Kilchonan Beach, Islay (NR2063), also 14th January 2019. We have not so far traced any records from mainland Scotland. A fascinating addition to the list of creatures washed up on the shores of Assynt, well-spotted by Gwen amongst the usual tidal debris.
All photos by G. Richards