The biology and morphology of the pelagic annelid Poeobius meseres Heath

• Published in: Proceedings of the Zoological Society of London
• Main Author: Robbins, Diane E.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1965
• Subjects: Arctic
• Online Access: http://dx.doi.org/10.1111/j.1469-7998.1965.tb05209.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1469-7998.1965.tb05209.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-7998.1965.tb05209.x; https://zslpublications.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-7998.1965.tb05209.x

Poeobius meseres Heath was found off Southern California in tows which reached depths from 350 to 1300 metres. It is not strictly confined to the sub‐Arctic water mass. Sensory papillae are found randomly scattered over the anterior and posterior ends of the gelatinous sheath. Isolated sensory cells are distributed over the head epidermis. A group of projections which are granular depositions from the epidermis encircles the extended head. The coelom is divided into three parts by two complete septa. The coelomic diverticula are branched extensions of the anterior coelom into the gelatinous sheath. The palpal coelom is a paired, tubular structure which lies in the head region and reaches between the ventral cavities of each palpus. The coelomic funnels are a pair of lateral tubes placing the middle coelom in communication with the exterior and probably function in gamete emission. The coelomocytes are associated with excretion. They are capable of spreading out within the epidermis of the head regions to dispose of excretory wastes. The nephridiopores are anterior to the tentacles. Excretory concretions may be found within the nephridia. The buccal pad is composed of an anterior tongue‐like portion and a more posterior bulb. The bulbous portion governs food intake by controlling the extent to which the oral aperture is opened. Absorption spectra show that the blood is a haem‐protein and probably a chlorocruorin. Respiration is achieved by the tentacles which contain a vascular loop, and is possibly aided by the highly ciliated and vascular anal area. The septa are ruptured when animals are fully ripe so that the gametes extend throughout the entire coelomic system (except the palpal coelom). Gametes escape through the coelomic funnels. The first two cleavages are holoblastic. Some eggs show an abnormal tri‐astral formation in the second meiotic division. Some gravid females are found in a disintegrated condition due to an unknown cause. The sperms of Poeobius are of the primitive type. Fertilization is external. ...