Pinna Goldilocks and the philosopher’s stone

By Dimitra Mylona.

In the past, when people snorkeled in the Mediterranean, in its shallow protected coves, chances were that they would see colonies of noble pen shells among patches of emerald Poseidonia oceanica plants.  These are large bivalve shellfish that stand erect, well-rooted in sandy or muddy seabeds. Today, this spectacle is rare and the noble pen shells are on the brink of extinction. This fate seems to be almost inevitable!  It is not only the disruption of their habitat by trawling, the greedy divers who wipe out whole colonies or the global warming that makes survival difficult for these magnificent shellfish. A fatal disease has hit the noble pen shells of the Mediterranean and wipes out their populations.

But the noble pen shell is not only part of our watery universe; it is part of our culture! This post pays homage to the magnificent, enchanting creature that left its mark on Mediterranean past.

The noble pen shell was given by Carl Linneus, father of modern taxonomy, the Latin name Pinna nobilis. Pinna is the Latin word for the auricle, the outer part of the ear, and nobilis means the noble. This particular species lives only in the Mediterranean, it is endemic there.  Other pen shells are found in other seas. A thick muscle holds the two valves of the shellfish together, opening to filter water and closing to protect the animal.  In the shell lives also a small shrimp or a pair of them (Pontonia pinnophylax), or a small crab (Nepinnotheres pinnotheres), that takes advantage of the protection and food that the pen shell provides. 

Many people on the islands of the Aegean, now middle aged, remember fighting with their siblings for the privilege to eat that shrimp when pen shells reached the family table.  People in certain parts on the Mediterranean coasts still like the taste of pen shell.  In a bizarre, yet sad way this craving for pen shell flesh found its way in marine science literature. Stelios Katsanevakis and a team of marine biologists reported on how an endangered species, the noble pen shell, thrives in Greek fish taverns! Noble pen shells along with triton shells, tun shells and undersized seafood are often served in fish taverns as delicacies.  They are caught by amateur fishermen, sold illegally and are not reported in any way. The damage to their populations is invisible in formal statistics, yet very real!

Not just food

The noble pen shell, like other bivalves, excretes mother of pearl that covers its valves on the inside. The process was explained by Roxani on her post about the “Pearls of others”.

This material is whitish near the tip of the shell and it becomes reddish brown towards its lips.  The brilliance of the mother of pearl has been appreciated from fairly early on, and for this reason, cut pieces of pen shells were used as inlays (for example for wooden furniture) or in jewelry already in prehistory.  

The shell found, other, less obvious uses in antiquity.  At one of the Balearic islands on the western Mediterranean, sea folk who lived off of the riches of the sea and produced the famous purple dye used the elongated shallow shells to pour molten lead and make ingots of a distinct marine character. That happened sometime in the 4^th or 3^rd c. BCE.

But what made the pen shells legendary was neither their flesh nor their mother of pearl.  It was the golden threads of its byssus, which, woven or embroidered, enchanted people!

Byssus is a bundle of keratinous fibers that some bivalves excrete, to give themselves a grip on the seabed, whether rocky or sandy/muddy. Mussels have it, the hairy arks have it, and the noble pen shells have the longest such “anchor” of all.  Byssus resembles a beard and has been harvested, processed, and used like any other fiber in weaving, knitting, and embroidery for centuries.  In older literature it is known by several names, such as sea silk, sea wool, or fish wool, all names alluding to its use by humans.

The Goldilocks aka Pinna nobilis.

Literature from 18^th, 19^th and early 20^th century describe how the noble pen shell byssus was processed and used, mostly in two places in the Mediterranean, Taranto and Sardinia. In Sardinia this art still survives.  The knowledge about byssus harvesting and weaving seems to have passed from one generation of females to the next and these days, one can notice a revival of interest.

Much ethnographic and historical research has been done on textiles, and recently a major project has been launched by the Natural History Museum in Basel, Switzerland. There, Francesca Maeder, a leading expert on Pinna nobilis byssus and its history, has led a team of researchers in an amazing effort to collect data about this fascinating topic and make it available to the public.  The results of this project have been published in academic venues but also, quite significantly, are available on the project’s website.  There, in a clear and straightforward manner, the marvels of the pina byssus are unravelled.  One can find many articles on the web about the sea silk, but if the reader wants reliable information, this web site is the place to go (and it is the source of much of the information in this post too, so do look it up for further details).

The pen shells were harvested either by diving and plucking, or from a boat using specialised tools.  In Greece such a tool is called pinnologos, while in southern Italy it is called pernonico. Undoubtedly more names existed in the past wherever fishers used this tool. George Leukaditis, in his 1941 book Fishing on the Greek Shores, he explains how this tool works

“(pinnologos is) an iron almond shaped  hoop made of a rod 6-8 mm in diameter, firmly attached to the end of a pole. The hoop is about 25 cm long and 7-8 cm wide. When it passes over a pen shell, and turned about 90 degrees, the pen shell gets stuck and when the fisherman pulls it upwards, it remains captured” (Leukaditis 1941, 167).

The keratinous fibres that attach the bivalve to the sea bed, the byssus, is then cut and processed.  After several stages of cleaning with sea and fresh tepid water, shells, mud, and sand are removed, the byssus is dried and the fibres are then combed and straightened.   At this stage the colour of the sea silk is revealed and it can range from light yellow-gold to bronze gold, to green and brown.  Ingredients such as lemon juice, spices and herbs were mixed in vials, bowls and other strange containers and real alchemy took place!

The fibres are pinched by hand and then spun into thread.  In this video,   Arianna Pintus, a young woman from Sardinia, who knows how to make sea silk and use it, demonstrates the process.  The end result is a thread that resembles gold, but it changes colour and brilliance under different light conditions.  What may seem a drab brown when seen indoors may transform into a sparkling, dazzling golden object under the sun.

The sea silk, or marine wool, or wool of fish as it was called in the past, would then be woven, knitted, crocheted or used in embroidery.  The “Inventory” chapter of the Sea Silk web site of the Natural History Museum at Basel exhibits a number of such objects.

During the Renaissance and also later, gloves, caps, scarves, belts and even whole precious garments made of sea silk were hyper-luxurious items, worn by wealthy people of high status. Yet, Chiara Viga, from Sant’Antioco, a small island of Sardinia, who is the last of 24 generations of women su maistu  “Masters” of the art of sea silk is adamant…  byssus cannot be sold or bought… it is only given as a gift. A sacred oath binds those who produce it. This BBC travel log of 2017 tells the story of Chiara Vigo and her magic relationship with the golden locks of the noble pen shell.

Linguistic and archaeological brain teasers

The sea silk of the noble pen shell has at times turned into an obsession, striking historians and archaeologists in subtle, yet, defining ways.

When was the byssus first used?  In Medieval times as most researchers always thought or in antiquity?  And how far back?

Felicitas Madder, the soul behind the Sea Silk Project, took it upon herself to untangle the labyrinthine ways of byssus misinformation and erroneous identifications.

The story she tells about the sponge that was discovered at Pompei  in 1941 and gradually turned into the earliest byssus in history is illuminating (for the complex history of the find, its identification and publication see Madder’s paper here).

The sponge, perfectly preserved due to the volcanic materials that buried it, was discovered in the House of M. Epidius Primus (I 8, 14) and was first recorded as such in the excavations notebook (“plant matter, fragments of sponge”).  Later, however, in the inventory of archaeological finds (inv. no. 7562) it was described as “(Bundle of raw fibers) really fine linen or marine silk”.  An in-depth analysis and SEM (Scanning Electron Microscope) photography in 1999 seemingly finalized the identification of the object. Despite the apparent misidentification and the doubts that some researchers had over the years, the sponge was called Pinna nobilis byssus until recently.

The SEM photographs below show the problem clearly.  The first photograph shows the micro-structure of the archaeological object Inv.no. 7562.  The fibers are branching and turning.  They are not smooth and straight as those shown in the second SEM photograph, which shows actual sea silk, but they do resemble the fibers shown in the third photograph, that depicts the microstructures of the sea sponge.

Part of the long-lasting confusion about the byssus of the noble pen shell stems from the word itself.   As mentioned above, today byssus is the zoological term for the fiber “beard” of some bivalves.  But what does the word actually mean?  Where was it first used? Did it have the same meaning always, in all cultures?  Here is another complex issue that confuses all but the most knowledgeable linguists of ancient Mediterranean languages.

Felicitas Maeder explains it as clearly as possible in the Sea Silk web site that is the source of all wisdom about sea silk.  Suffice it to say here that the word byssus stems from the Hebrew Būṣ, which was the word for fine linen. In the Old Testament we encounter it no less than 40 times.  The word was later adopted by the Egyptians and made it into Greek, Latin and eventually into early modern European languages. Significantly, the dissemination of the term involved an inspired translation of Aristotle’s Historia Animalium by Theodorus Gaza in the 15^th century. Gaza improved on Aristotle using the latest zoological knowledge of his time. Part of that knowledge was that the noble pen shell attaches itself to the sea bed with a beard which resembles fine linen threads (i.e. byssus). When Theodorus Gaza read the word βυσσος in the original text (a word to denote the sea bottom) he translated it as byssus, because of its association to the noble pen shell. His translation was extremely popular (having over 40 re-prints by the 16^th century).  That is how, in the Romance? languages of Europe and later its colonies, the word byssus (originally denoting fine linen fabric or threads) came to mean the filaments that rooted bivalves to the sea bed and byssion came to refer specifically to sea silk!!!

The sea silk, however, seems to have been known already in antiquity, at least in Roman times. Alkiphron, a sophist and epistolographer (letter writer), wrote in the 2^nd century AD about thalassis eria, sea wool. Diocletian’s Edict on maximum prices (301 AD) refers to a tunic made of sea silk that cost the exorbitant price of 40.000 denarii. Other Latin authors left us similar hints.

A most unexpected clue however, comes from China in a chronicle of the 2^nd or 3^rd century CE where the DaQuin, the Roman Empire, is described!  At the time, the Chinese believed that Roman travelers to those parts claimed that the Roman elites were descendants of immigrant descendants of ancient Chinese nobility, so the Roman empire had an extra allure to them.  Among the many features of the Roman Empire (listen here) there is this note: “They (the Romans) also have a fine cloth which some people say is made from the down of water sheep”.

The noble pen shell has certainly a long history in the Mediterranean, and it resonated as far away as China.  Will it continue to be part of our lives in the future? One can only hope!

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