Title : Identification of nine commercial sea cucumber species using their spicules as major taxonomic character
Abstract:
Sea Cucumbers (Class Holothuroidea of the Phylum Echinodermata) are very important elements in the benthic marine ecosystem as they play unique role in maintaining the stability of the ecosystem. They possess several chemical characteristics which are important in medicine and pharmaceutical industry. Proper identification of the Sea Cucumber species is essential in fisheries, population studies and conservation activities. Sea Cucumber species identification is practiced on the basis of their external morphology and calcareous spicules found in internal tissues. More importantly, each species has uniquely patterned calcareous spicules and therefore species descriptions can be made on the shape, distribution and abundance of calcareous spicules in their dorsal and ventral body walls, the papillae, the podia and the tentacles. Majority of Sri Lankan Sea Cucumber identification studies are solely based on external morphology. However, single use of external morphology is not reliable in Sea Cucumber species identification, as they have shown high degree of polymorphism and morphological plasticity which lead taxonomic confusion. Therefore, an obvious need is seen for a detailed spicules-based study on describing the commercially harvesting Sea Cucumbers in Sri Lanka. Therefore, the objectives of the current study were to produce: Clear photographs of live and processed Sea Cucumbers for photographic archives, Illustrations of the calcareous spicules found in their body tissues and a taxonomic key based on both spicules and external morphological features. Fresh Sea Cucumber samples were collected from Kalpitiya and in-between Puttlam to Mannar. From each sample, one small piece (1mm2 ) of tissue was removed from each the dorsal body wall, ventral body wall, tentacles and from a random podia. The tissue samples were placed in separate small vials and 1ml of Potassium Hydroxide was added to each vial. The samples were next kept for 30 minutes in order to dissolve the organic tissues bonded with the calcareous spicules. Next, the spicules were observed under the light microscope, they were illustrated on papers and were photographed. The Sea Cucumber samples were identified using illustrations of the calcareous spicules and standard taxonomic keys. Within the Order Aspidochirotida: a total of 9 Sea Cucumber species were identified including 6 species of Family Holothuriidae (Holothuria leucospilota, Holothuria atra, Holothuria scabra, Holothuria spinifera, Actinopyga palauensi and Actinopyga mauritiana) and 3 species of Family Stichopodidae (Thelenota anax, Stichopus chloronotus, Stichopus herrmanni). Family Holothuriidae was characterized by the features: (a) dominance of tables, buttons and rods spicules and (b) absence of C-shaped spicules. Dominance of Branced rods and C-shaped rod spicules as well as absence of button spicule were the characteristics of Family Stichopodidae. Key words: Sri Lanka, Sea cucumber, Spicules, Species Identification
