The Rhombus in Nature

Fig. 1

In geometry class back in secondary school, there was one happy day, at least—the day we talked about the rhombus. The rhombus is a parallelogram in which the angles of the opposite sides are equal: diagonals drawn through the center of these angles will intersect each other at right angles in the center of the rhombus (see fig. 1). It is a beautiful shape with a stylish name that everyone started saying in amused wonder. Meanwhile, off the coast of Cuba or Tenerife or Okinawa, divers sometimes chance upon a mysterious human-sized blob of diaphanous pink gelatin composed of delicate loops of exquisite pink spheres.  What is the connection between these disparate stories?

Mysterious pink blob in the ocean (photo by David Fleetham)

The pink alien blobs floating in the tropical and semi tropical seas of the world are the work of Thysanoteuthis rhombus, a.k.a. the diamond squid (which completely sounds like a crime boss name). The species is actually quite large for an invertebrate and some individuals can grow up to a meter (3 feet) in length and mass up to 30 kilograms (66 pounds). Thysanoteuthis rhombus is named for its huge fins which run along the entirety of its mantle and give it the appearance of a rhombus. If you draw diagonals through the center of its angles they would probably intersect at right angles too (although you shouldn’t do this in the real world since T. rhombus is a tremendous swimmer with ten strong tentacle arms–including two extra-long club arms covered with extra-rows of tentacles for grabbing prey or fighting).

The Diamond Squid (Thysanoteuthis rhombus)

Diamondback squid jet through the warm parts of the oceans in pairs and tiny schools hunting for swift and intelligent fish. They in turn are hunted by some of nature’s most fearsome predators: cetaceans, sharks, and the Japanese.

The squid hunt near the surface at night, and retreat to middle depths during the day. Somewhat uncharacteristically, they have no bioluminescence. The large enigmatic pink blobs I mentioned are their eggs. Once the female is fertilized, she lays a vast helix of eggs which are embedded in a stickly translucent line. These egg clusters look like salps or siphonophores (or extraterrestrials) but they are actually thousands of diamond squid eggs. When they hatch, they become adorable larval squid which head off into the phytoplankton to hunt.

Closeup of the eggs of Thysanoteuthis rhombus

Hatchling Diamond Squid

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Heliciculture

Escargot

Heliciculture is the farming of snails for human consumption (and for snail mucous used in make-up and skin cream in the Latino community). Garbage middens from prehistoric settlements contain large numbers of cooked shells–so snails have been utilized as food for a long time.  Sustained snail farming dates back at least to pre-Roman Phoenician colonies, however the ancient Romans took heliciculture and snail cooking to new levels. Romans gastronomes regarded snails as a particular delicacy and they introduced certain Mediterranean species to everywhere they conquered.  When the empire fell apart Gaul continued the Roman tradition of enjoying escargot.  Today the French alone consume 40,000 tons of snails per year.  Serious agricultural effort is required to keep up with that sort of appetite.

Snails at market

Roman heliciculture apparently involved building little islands from which the snails could not escape.  Today, however, snails are kept in carefully fenced garden plots.  A small gauge metal wall which extends into the earth is necessary to keep snail predators out (particularly mice, shrews, raccoons, skunks, and toads) while a second interior wall made of specially constructed material keeps the snails in.  A net can be added so that birds do not eat the tasty gastropods. Since pesticide and herbicide could injure the snails or the people eating them, organic greens are grown for the snails to consume.  Apparently snails operate by Tron-style rules and do not like to cross another snail’s slime path—which means that only 20 snails can be kept per square meter.  There are two principal species which are consumed as escargot. The smaller and more common Helix aspersa is also known as the “petit gris” or “escargot chagrine” whereas the larger, rarer Helix pomatia  is called the “Roman snail,” “apple snail,” or “escargot de Bourgogne”. Both of these Mediterranean species have been widely introduced around the world for agricultural purposes.  They are now endemic pests in Asia, Africa, Australia, New Zealand, North America and southern South America (and probably elsewhere).  It’s funny to think that the snail eating your cabbages is the descendant of a snail which escaped from some long-dead hungry French chef.  I can sort of imagine the scene as a black and white early Disney cartoon with giddy jazz playing in the background.

Snail Farming

Everybody and everything seems to enjoy eating snails including…other snails.  A particular source of difficulty for snail farmers is cannibalism.  Larger snails will eat eggs and hatchlings for the calcium.  If not eaten by something, snails can live a long time.  They hibernate in winter and Helix pomatia can live up to 35 years.

Helix pomatia