Anatomy & Physiology
Aim
The aim of this histological study was to examine the internal structure of Myzostoma sp. predominantly focusing on the digestive system.
Methods
A Crinoid species from the family Comasteridae was collected from the reef crest zone at Heron Island. The Crinoid species was initially observed under a microscope, before each Myzostomid specimen was removed and isolated. Two Myzostomid specimens (Myzostoma sp.) were found and isolated from the Crinoid. Photographic evidence regarding the external morphological traits of the Myzostomids were taken before the specimens were relaxed, fixed and preserved in ethanol (70%). Transverse and frontal sections were created from the two myzostoma sp. samples. Sections were examined under a microscope.
Results and Discussion
Nervous System
the nervous system within Myzostoma sp. is located throughout its body. Proboscis nerves, a compact ventral nerve mass, peripheral nerves and a circum-oesophageal nerve ring are the predominant parts of the nervous system (Grygier 2000). Within the Proboscis, the nerves travel to the buccal papillae and towards the base of the proboscis (Grygier 2000).
Digestive System
The digestive organs in Myzostoma sp. consist predominantly of the mouth, pharynx, stomach, digestive caeca and intestine (Grygier 2000)(Figure 1).
Pharynx
The pharynx in Myzostoma sp. is long and thin (Figure 2). The pharynx is lined with glandular cells and is surrounded by a muscle bulb that shows alternating circular and longitudinal muscles (Grygier 2000).
Stomach
The stomach is separated from the anterior pharynx and posterior intestine by sphincters. The epithelial cells of the stomach are ciliated (Grygier 2000). The beating of these cilia carry the food particles into the caecal areas. The stomach absorbs dissolved nutrients and stores lipids.
Intestine
The epithelial cells of the intestines are also ciliated (Grygier 2000). Intestinal cells absorb nutrients but are unable to store lipids.
Figure 1 Microscopic image displaying the internal anatomy of Myzostoma sp. from a frontal section. IP: introvert pouch, M: mouth, PH: pharynx, MB: muscular bulbous, CA:caecum, S: stomach, IN: intestines, PA: parapodia
Figure 2 Microscopic images of the pharynx and muscular bulbous of Myzostoma sp.PH: pharynx, MB: muscular bulbous
Figure 3 Microscopic image of the transverse section of ![]() Myzostoma sp. G: gut, PA: parapodia, C: chaete, T: male reproductive organs; testis. |