Echinoderms Bahamas | ROLLING HARBOUR ABACO

ECHINODERMS, DOLLAR DOVES & PETRIFIED BISCUITS

Echinoderms (Gr. ‘Hedgehog Skin’) comprise a large variety of sea creatures characterised (mostly) by radial symmetry. In a nutshell a creature with radial (as opposed to bilateral) symmetry can be divided into equal portions from the centre, like a cake. It has no left or right side and no definable front or back. It is multidirectional from the centre, where the mouth is located. It obviously has a distinct upper side and an underside, but that has no bearing on this form of symmetry.

Within the family of radially symmetrical animals, echinoderms (starfish, sand dollars and sea urchins) are unique in having five-point radial symmetry. These are the creatures you are most likely to come across in Abaco. There are two particular aspects of dollars and biscuits that merit a closer look (made more difficult by me stupidly taking photos of white things on a white background).

DOLLAR DOVES

I’m sure all Bahamians know or are aware of at least one version of the famous ‘Sand Dollar’ poem, in which the various characteristics of the test (the skeleton of the creature) are given religious significance. One verse of the poem may be puzzling: “Now break the centre open And here you will release The five white doves awaiting To spread good will and peace”.

The Sand Dollar Legend

A few years back, Senior Granddaughter was looking at some Abaco sand dollars I’d given her for her growing collection of shells. She picked one up, shook it and it rattled. She said a friend at school had told her that a rattling sand dollar has ‘doves’ inside it, and asked if we could break it open and see. I’ve learnt that it is useless to argue with her – she has the tenacity of a trial lawyer – so we did. This is what we found.

Sand Dollar with a spiky interior like a white cave with stalagmites and stalagtites

Five white doves (in fact, the separated parts of the creature’s feeding apparatus)

Two broken pieces showing where the doves are centrally located

A regrettably poor photo of a single dove

The image below, from Pinterest, shows the ‘mouth’ with its dove-parts intact, in an arrangement called ‘Aristotle’s Lantern‘, a five-sided globular structure that supports the mouth and jaws of an echinoderm.

PETRIFIED BISCUITS

In common parlance ‘petrified’ is an extreme version of ‘terrified’. Literally, it means ‘turned to stone’ (L. petrus, a rock). It is descriptive of a state of fossilisation, where an animal skeleton or dead wood or plant matter turns over aeons into stone. Senior GD (a most inquisitive girl) followed up on the doves research after discovering a box containing random stones and fossils. She found these two items:

Fossilised sea biscuits Petrified / Fossilised Sea Biscuit (Keith Salvesen)

A closer look at the pair of rocks Petrified / Fossilised Sea Biscuit (Keith Salvesen)

The undersides of the fossils above – looking like stones but with some tell-tale small holes Petrified / Fossilised Sea Biscuit (Keith Salvesen)

A close-up of the pale biscuit Petrified / Fossilised Sea Biscuit (Keith Salvesen)

Sea biscuits on the beach at Delphi – familiar white skeletons (‘tests’) but not yet fossils

A ‘modern’ non-Jurassic Abaco sea biscuit in close-up

FUN FACT

Florida has an unofficial but proposed State Fossil, the ‘Sea Biscuit (Eocene Age)’. I didn’t know it before, but it turns out that more than 40 US States have State Fossils. Whatever next? State Bacteria? State Viruses?

SO HOW OLD MIGHT A PETRIFIED BISCUIT BE?

The fossil biscuits I have looked at, from Florida to Madagascar (see small image above), are said to come from three specific historic epochs – from the oldest, Jurassic (145m – 201m years ago), to Eocene (34m – 56m) and Pleistocene (0.01m – 2.6m).

HOW DOES THAT HELP ANYBODY? BE MORE PRECISE

By all means. Here is an excellent Geochart that gives an idea of the time span. A Jurassic sea biscuit would be more than 145m years old. This chart also helpfully helps avoid confusion with the Eon Era Period Epoch ordering.

geotimescale

You will find more echinoderm entertainment using this link to my fellow-blogger ‘Dear Kitty’ https://dearkitty1.wordpress.com/2007/01/01/big-hedgehog-small-sand-dollars-diving-schools/

All photos ‘in-house’ except the Delphi biscuits, Clare Latimer; & the single biscuit Rhonda Pearce; Sand Dollar poem on Postcard, Dexter Press; the Geochart was in my ‘useful chart photos’ folder but I can’t now find the source. I did try.

SEA URCHINS & SEA BISCUITS – BEACHCOMBING TREASURES ON ABACO

It’s time we had some more shells and other beach treasures on these pages. In the absence of star Abaco beachcomber and blog-contributor KASIA I have taken a closer look at the Delphi Club collection. This has been casually accumulated by the Club, its members and guests during the past 3 years whenever a good specimen has been encountered, and is displayed in the Great Room. The first items to catch my eye were the ECHINODERMS, a family that includes sea urchins, sand dollars, sea biscuits and star fish. Their sun-bleached tests are often found, though in my limited experience the larger they are, the rarer. The link above is to the Wiki-blurb, which has the unpromisingly daunting heading “This article may be too technical for most readers to understand…”. Now there’s a challenge!

First up is a very large SEA URCHIN, a thing of great delicacy and fragility that weighs next to nothing. I have never seen a bigger one. Looking at the fine detail, it is hard to believe that such perfection of symmetry and intricacy can exist in a creature so very painful to tread on.

This SEA URCHIN is smaller, with more prominent nodules and a much more random pattern – reminiscent of a cartoon of some distant white planet. It has cast a fine knobbly shadow.

SEA BISCUITS have similar five-way symmetry to their first cousins SAND DOLLARS but are generally pebble-shaped rather than disc-shaped. I have included 2 close-ups to show the fine details of the pattern – almost like lace-work

This SEA BISCUIT is a different type, with the 5 radials reaching right round it. For some reason it only has 4 and not 5 small holes (as one might expect) at the centre. Unlike SAND DOLLARS they tend to be more oblong than round.