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?
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).
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.