Discovering Sea Urchins

By Risidra Mendis | Published: 2:00 AM Jan 16 2021
Echo Discovering Sea Urchins

By Risidra Mendis 

A walk on the beach or a dip in the sea is what most of us know about the beach. But beneath the ocean lies a variety of interesting sea creatures yet to be discovered. For Dr. Malik Fernando, a retired scuba diver, his interest in knowing the unknown soon brought him to discover many interesting facts about Sri Lanka’s sea creatures that live many feet underwater. 

Though most of us have heard about sea urchins not much is known about these creatures. But Dr. Fernando after many years of research has finally discovered some amazing facts and mannerisms of these creatures which are most often heard about but not seen.      

“Sea urchins are members of a large group of exclusively marine animals that constitute the Phylum Echinodermata. This phylum is made up of five classes; Crinoidea (feather stars), Asteroidea (starfish), Ophiuroidea (brittle stars), Echinoidea (sea urchins) and Holothuroidea (sea cucumbers). All echinoderms have a body plan based on five radiating axes (though this may be obscured in some), a skeleton consisting of calcareous plates on the outside (reduced to spicules embedded in the skin in the sea cucumbers) and a system of tube feet. Both starfish and sea urchins possess spines:  immovable in the former, long, articulated and movable in the latter. The sea urchin skeleton of plates is termed the test,” Dr. Fernando explained.

Help to control algae

He said sea urchins are found in a variety of habitats that include sandy bottoms, rocky reefs and coral reefs. Some forms burrow in sand while others burrow into soft rock. “Many sea urchins are grazers and help control algal overgrowth. Most live in fairly quiet sub-tidal habitats but one species Stomopneustes variolaris lives in turbulent water on shallow rocky reefs and in inter-tidal pools - these are the animals familiar to most. Their tests are often washed up on beaches. The tests of some of the flattened forms called ‘Sand Dollars’ may also be found cast ashore on gently shelving beaches. Sea urchins come in a variety of shapes: the commonly seen animals are more or less spherical or hemispherical with their mouths underneath and anus at the top. These are termed regular sea urchins on account of their radially symmetrical shape with no definite anterior or posterior, right or left sides,” Dr. Fernando said.

He explained that depressed urchins are quite flattened and disc like (sand dollars) with the mouth and anus both underneath, while the irregular urchins, ‘Sea Potatoes’ and ‘Heart Urchins,’ are more or less shaped like eggs on their sides with the mouth underneath in front and the anuses at the rear. “These latter two forms possess a distinct anterior and posterior with right and left sides (bilateral symmetry) unlike the radial symmetry of the other echinoderms. The regular urchins and the depressed forms have five jaws ending in teeth that surround the mouth. These structures are called ‘Aristotle’s lanterns’ and are used to scrape the substrate for the organic matter that is their food,” Dr. Fernando explained. 

His research states that sand dwellers take in sand and extract the organic matter, passing the rest out through the anus and the arrangement of these structures vary with the genus and sometimes the species. “Spine character and colour are often required to separate species. It is generally possible to identify a bare test to genus level, but not always to species level. The echinoids of Sri Lanka and the Gulf of Mannar have been studied by many people since 1846. According to these studies there are 46 species of regular sea urchins and 37 species of irregular sea urchins. The total number of echinoid species (both regular and irregular) occurring in Sri Lanka stands at 77 species belonging to 48 genera. The diversity of irregular echinoids from Sri Lanka stands at 37 species representing 11 families in four orders with Peronella oblonga a new record for Sri Lanka,” Dr. Fernando said.

Spotted in Mount Lavinia

Among the List of regular sea urchins the Baguette Urchin or Imperial Urchin was first seen by the author in 1975, the encounter being described in a 1991 article as follows: “We have found this urchin wedged in between rocks at the foot of Bellangala, the rocky islet at Mount Lavinia, at a depth of about 3 metres. It is reported as using its large spines for locomotion. It was wedged in the rocks by its spines, resisting all attempts at extrication. One can well imagine how it picks its way amongst the rocks using its spines as three-dimensional stilts. Dozens of detached spines were found on a later dive in the shallows amongst other debris and shell grit in the Galle Harbour.” It is a nocturnal animal.

“The Astropyga radiata was obtained from the tanks of an exporter on 3 March 1995. It was collected from the sand bottom at a depth of 15 to 25 metres off Dehiwela. It was said to live gregariously and to move about rapidly as a group, but was ‘never found in the same place on two consecutive days’. It is also found in the same area with another sand dwelling species Salmacis virgulata. Many specimens had been collected ranging in colour from pale pink to a deep orange-red—one of the darkest coloured obtained and photographed, a very striking animal, especially in bright sunlight. It is attractively coloured,” Dr. Fernando explained.

The Venomous Sea Urchin, a colourful urchin was found on deeper sand bottoms, living gregariously. The first specimen was obtained in 2000 from an ornamental fish exporter’s aquarium and a subsequent one in 2003, said to be from Trincomalee. It was observed and photographed in situ at Kandakuliya. The Oval Sea Urchin, a medium sized sea urchin was found in and amongst rocks in reef habitats. An algal browser, it is oval shaped enabling it to get into crevices in its search for food. It was collected in Mount Lavinia, at 3 meters depth, on 13 December 1987 and in Trincomalee, at 2 meters in September 1995.

The Slate Pencil Sea Urchin is a rare sea urchin protected under the Fauna and Flora Protection Ordinance (FFPO). It has been seen alive only once by Dr. Fernando, at the Hikkaduwa National Park where the photograph was taken. The animal was in full view when first spotted but sensed the approaching diver and slowly withdrew into its cave. The image was made from about 2 metres away. The urchin gets its name from the thick, pencil-like primary spines with red tips. The bases are ringed with white and the membranes covering the articulations are striped in orange and black.

Pink Sea Urchin 

“The Common Black-spined Sea Urchin is a medium-sized sea urchin with stout black spines that lives on reefs with a lot of water movement. This animal is easily seen as it inhabits shallow reefs and rocks. It is often found under rocky ledges or lying in shallow depressions in rocks, rarely in large congregations in rock pools as on the Barberyn Reef at Beruwela. Its spines are thick and black in colour. They may be sharp or blunt, as they are used to scrape the rocks for algae,” Dr. Fernando said. 

The Pink Sea Urchin is a colourful sea urchin seen on the Colombo reefs at shallow depths below 3 metres. They are always found on rocks and appear to feed on red coralline algae, as observed in an aquarium. When algae-bearing rocks were not available in the tank the animal accepted fragments of boiled prawn that were ingested whole.

“The Purple-spined Sea Urchin was first collected in 1982 at Kinniya at a depth of 1.5 metres, it was next encountered off Colombo at a depth of 32 metres on the sand bottom seaward of Vatiya Parai (reef), off Dehiwela. A most attractive animal, the spines are coloured purple with white bases. They are sand dwellers. The first one collected at Vatiya Parai had a small commensal crab living on the oral aspect of the surface of the test. It had clipped a row or two of spines to create a path along which the crab travelled, from the peristome to the outer margin of the test. The Flower Urchin is so called because of the flower-like discoid structures that are prominent among the spines. They are uncommon and have been seen at Hikkaduwa and Colombo hiding in rock crevices, and also on the sand at Unawatuna in 1992, but not after the global warming event of 1998,” Dr. Fernando explained.

He said this species is reported as being venomous and the dangerous part of the animal appears not to be the spines, but the protective structures called pedicellariae. “All sea urchins possess these pincer-like structures on the ends of moveable stalks, which are used to pick off smaller animals, larvae and so forth that may attempt to colonise the surface of the urchin. The order Spatangoida contains the Oval or Heart Urchins, also called Sea Potatoes on account of their shape. They have egg-shaped tests and are covered in short spines. Lovenia elongata, the only species collected alive however, has long spines on its dorsal surface lying along the test surface. The irregular sea urchins flattened include the Two-slit Biscuit Urchin, the Open-slit Biscuit Urchin and Sand Dollars among others, 

“Dr. Fernando said.  

The website, is based on Dr. Fernando’s Marine Natural History and Marine Antiquities Collections. Having been a diver for many years, he was struck by the variety of animals and plants that had not been recorded or studied by other Sri Lankans in recent years. “I began collecting marine invertebrates for a home aquarium and for identification in the 1990’s as I was interested in the names of these animals. Over the years I built up a collection of dried specimens, photographs – both under water as well as ex situ images – drawings and a seaweed herbarium. I hope the site’s contents will stimulate others to document and research the unknown bounty beneath our seas around Sri Lanka as underwater diving is easy to learn and the facilities are widely available in Sri Lanka,” Dr. Fernando said. 

By Risidra Mendis | Published: 2:00 AM Jan 16 2021

More News