Distribution and Microhabitat Associations of an Apodous Holothurian: Synaptula recta (Semper, 1868) in the Shallow Coastal Waters of Selected Islands, Sri Lanka

Abstract

Apodous holothurians lack tube feet and are characterized by their vermiform retractable bodies. Even though a few species of apodous holothurians were recorded from Sri Lankan waters a long time ago, there was no record available on their micro-habitats or on their distribution in the Northern coastal waters. Therefore, the present study was conducted to identify the distribution and microhabitat association of apodous holothurians in the shallow coastal waters of selected islands such as Mandaitivu, Velanai, Karainagar, Eluvaitivu and Punkudutivu, during October 2020 to December 2022. Sampling was performed in eight locations among the marine sponges and algae at a maximum depth of 0.5 m. Species identification was done using morphological characteristics and ossicle types. In this study, Synaptula recta (Semper, 1867), a tube-feetless sea cucumber species that belongs to the Family Synaptidae was recorded for the first time from the northern shallow coastal waters of Sri Lanka that associated with 13 species of sponges and four species of algae. S. recta were collected from the external surface, osculum and spongocoel of the sponges. Also, this species showed camouflage with that of respective sponge species. Results suggest that S.recta prefers marine sponges and algae as their microhabitats and is not found in the bottom sediments. Therefore, it is essential to protect the marine benthic communities such as algae and sponges to preserve the S. recta in the coastal waters of Sri Lanka.