Oogenesis in the articulate brachiopodTerebratulina retusa

Abstract

A detailed ultrastructural description of oogenesis is presented for the articulate brachiopod Terebratulina retusa (Linnaeus), based on collections made between October 1985 and October 1986 from the Firth of Lorn, west coast of Scotland. Oogenesis has been divided into six stages, defined according to ultrastructural changes, which are thought to be important steps in the process of vitellogenesis. Special attention has been given to the possible mechanisms involved in the acquisition and assimilation of nutrients within the differentiating oocyte. Each vitellogenic oocyte is contained within a follicular envelope which is attached to a genital lamella. As maturation proceeds, accessory cells proliferate within the follicular envelope. A variety of intra-accessory cell and oocyte/accessory cell communications were identified. The process of elaboration of the oolemma is reported in detail. Lipid was identified as the major nutrient reserve of the oocyte. Late mature oocytes measure ,-~ ] 30 ~tm in diameter when spawned. The process of oosorption is also documented.

Variance in protegular size: a correlate of larval trophic mode in Early Palaeozoic brachiopods

“…Measurements of egg size in a sample of Terebratulina retusa (James et al 1991) show a narrow range of variation and this pattern has been frequently observed in other living taxa. Thus, all modern rhynchonelliform brachiopods have lecithotrophic larvae.…”

Structure of the ovary of the articulate brachiopodHemithyris psittacea(Rhynchonelliformea, Brachiopoda) with special reference to connective tissue pillars

“…Mixed vitellogenesis. In Terebratulina retusa there are special accessory cells located between the follicular cells and the oolemma (James et al, 1991b).…”

“…Some authors (James et al, 1991b;Williams et al, 1997) suggest that the follicular envelope of brachiopod oocytes may regulate the flow of nutrients into the oocyte, but experimental evidence to support this assumption is needed.…”

“…Extant species are relatively few in number compared to extinct species (Hyman, 1959). There are only a few studies of the gonad structure of brachiopods (Hancock, 1859;Joubin, 1886;Blochmann, 1892Blochmann, , 1900Senn, 1934;Ivanov et al, 1985), and even fewer that are devoted to the ultrastructure of their reproductive systems (Chuang, 1983a(Chuang, , 1983bJames et al, 1991aJames et al, , 1991b. Chuang (1983b) identified four main types of gonads in articulate brachiopods: unbranched, arborescent, reticulate and ovoid.…”

Early Ordovician molluscs with preserved colour pattern from the Timan-Pechora Basin of Russia

“…Pigments are usually metabolic products transferred from food. The most common pigments for the colouration of marine organisms are carotenoids, which give a brownish to orange colour to both the soft tissue and the shell (James et al 1991). The colouration of the shell is thought to be the disposal of such waste by products of metabolism (Kelley & Swann 1988).…”