Taenioides

Abstract: This study describes a new Protodrilidae that lives in the coral sands of the Island of Moorea (French Polynesia). Astomus taenioides n.gen., n.sp. has no gut, mouth, anus, pharyngeal bulb, nor salivary glands. However, a thin median cord of cells rich in refringent granules takes the place of a gut and probably represents an endodermal vestige and a stocking location for reserve substances. The surface of the epidermis is increased due to an enlargement of the segments into lateral lobes; cilia are abundant and the cuticle well developed. These characteristics might favor considerable exchanges between the organism and its surroundings. The absorption of dissolved organic substances, well known in other marine invertebrates, seems to be developed in this case to the point that this annelid, like the pogonophores, can survive without any gut. If, compared with Annelida, the principal trait of the Pogonophora is regarded to be the absence of a gut and the absorption of nutritive elements solely through the...

Abstract: Examination of thin sections of trunk wall in an old specimen of Ikeda taneioides from Misaki, Sagami Bay revised previous false information about the wall musculature, actually consisting of outer circular, middle longitudinal, and inner-most oblique layers, like all other echiurans. This finding, together with the reexamination of relevant museum specimens, led to some taxonomic changes. These include that the definition of the genus Ikeda was amended to be a senior synonym of Prashadus; the family Ikedidae was regarded as a junior synonym of the family Echiuridae; and the order Heteromyota, erected virtually for I. taenioides, was abolished. Non-discovery of males and some other features in the amended genus Ikeda were noted with reference to its possible relationship with the family Bonelliidae.

Abstract: An ultrastructural investigation of the mouthless protodrilid Parenterodrilus taenioides shows that the residual gut, with its very narrow ciliated lumen, has lost any digestive function. Salivary glands are retained in some anterior segments and their canals converge in a ventral area of the prostomium and open at the epidermal surface. The epidermal ciliation is much more developed than in any other protodrilid species. In the middle and posterior body segments the enlarged epidermal surface area is covered by a cuticle bearing an array of epidermal microvilli which are probably the site of active transport of dissolved organic compounds. The presence of numerous subcuticular coated vesicles and lysyosomes in the support cells suggests that particulate material from the ambient milieu is taken up by endocytosis and finally digested in the epidermis. The origin and nature of the organic substances that constitute the food of P. taenioides are still unknown. There are no symbiotic bacteria in the cuticle,...

Abstract: Tsunamis associated with the 2011 off the Pacific Coast of Tohoku Earthquake seriously disrupted the shallow marine ecosystem along a 2000 km stretch of the Pacific coast of Japan. The effects of the 2011 tsunamis on the soft-bottom benthic community have been relatively well studied in the intertidal zone, whereas tsunami effects on the subtidal benthos remain poorly understood. Here, we investigated populations of the world’s largest spoon worm Ikeda taenioides (Annelida: Echiura: Ikedidae) in subtidal zone of Funakoshi Bay, Tohoku District, northeastern Japan. Subtidal scuba-diving surveys at two sites in the bay showed extremely long proboscises frequently extending from small holes in the sandy seafloor shortly before and soon after the tsunami disturbances. Based on morphological and molecular identification, the proboscises were revealed to be parts of I. taenioides. On 30 November 2011, 265 days after the tsunami event, many large-sized individuals with >1 m long proboscises were observed; these individuals were probably not derived from post-tsunami larval recruitment but more likely survived the tsunami disturbances. This is surprising because other sympatric megabenthos (e.g. spatangoid echinoids and venerid bivalves) and seagrass beds were almost completely destroyed (although they later recovered) by the tsunamis in this bay. The burrows of I. taenioides are known to be very deep (70–90 cm), which may have sheltered them from the impacts of the tsunamis. Our observations suggest that the effects of the 2011 tsunamis on benthos in soft sediments may differ depending on their burrowing depth.