Anatomy & Physiology

Defining anatomical traits of Elysiidae (=Plakebranchidae) include a narrow foot and a pair of lateral, leaf-like parapodia that wrap along the body, and a coloured margin along the parapodia is not uncommon (Williams & Walker 1999). These opisthobranchs also feature an anus and oviducal opening close together in a lateral groove on the right side of the body. Specimens are also often green, with this colour provided from ingested chloroplasts. Most opisthobranchs also have gills towards the rear of the body. Sacoglossans usually have two pairs of tentacles on their head, one pair of oral tentacles, and one pair of rhinopores (which are used as chemosensory organs). There is also a primitive eye found at the base of the tentacles, with the function of it being more so in orientation rather than object discrimination (Williams & Walker 1999). Sacoglossans also possess highly modified uniseriate radula, forming a continuous single row of teeth, which may be used for identification of genera. 

Figure 1 below illustrates the chloroplasts within the parapodia of E. obtusa. Within the prepared slide, intact chloroplasts are observable, alongside ruptured cells which are in the process of being digested. A distinct band occurs where the chloroplasts are no longer present and the margin of the parapodia, which would indicate the limits of the digestive glands. 

Figure 1. Sagittal cross section of the parapodia of an E. obtusa at 100x magnification.