Abstract
M.Sc.
At present 35 species of Argulus are recognized in Africa. From a summary of
the literature available for Argulus species in Africa it is clear that species
descriptions are often the only information available for the majority of
species. Information on the anatomy and histology of African Argulus species
is even more scant. However, previous literature reveals that the anatomy and
histology of the digestive system is similar in most branchiurans. The first
study includes a description of a poorly known Argulus species described
using SEM. Sixteen male and one female specimen of Argulus personatus
Cunnington, 1913, were collected from Bathybates ferox Boulenger, 1898,
from Lake Tanganyika in northern Zambia. Results from light and scanning
electron microscopy (SEM) examinations documented a thickening of cuticle
located on the dorsal surface between the last thoracic segment and
abdomen, which was rectangular in shape; the pre-oral spine and the
proboscis ornamented with simple scales; a set of 3 large simple setae on the
distal end of the basal plate; the dorsal distal end of second podomere of the
maxillae ornamented with scales resembling those of a fish; the second and
third podomeres of maxillae ornamented with two types of pectinate scales
(with fine bristle-like ends and scales with large pointed ends); the ventral
distal end of third and fourth maxillary podomeres bearing large teardropshaped
scales; a pair of tubular structures present adjacent to the anterior
projection; a peg on the fourth pairs of legs of males bearing shallow grooves
running irregularly across surface; and an accessory cushion bearing minuteprojections. These characters found in A. personatus were addressed in a
redescription.
The digestive system of Argulus japonicus metanauplii is described following
reconstruction from serial sections. The similarities between the larval and
adult digestive system are described. Both digestive systems consist of an
oesophagus, oesophageal funnel, anterior midgut, midgut enteral diverticula,
posterior midgut and a hindgut. Histologically, the foregut of both the adult and
larva consist of cuboidal epithelium and both the adult and larval hindguts are
composed of columnar epithelium. Despite the similarities between the adults
and larvae some differences exist. Differences include that the epithelium
lining of the midgut of newly hatched larvae contain yolk. The midgut
diverticula are less ramified than in the adult. The posterior midgut is lined
with large swollen cuboidal epithelium with large vacuoles and a ciliated
border whereas the adult posterior midgut is lined by large papilliform cells.
Argulus japonicus larvae only survive a day after hatching without nutrition
from a host and once the first stage larvae start to feed on host tissue they
feed mainly on epithelial cells and mucus. There was no blood observed in the
lumen of the digestive system. It is concluded from the study that much work
remains concerning the taxonomy of African species. Many of the species
remains inadequately described and new identification keys must be created.
New environmentally safe treatments should be a focus of future
development. Also, many physiological aspects of the argulid digestive
system remain unknown and provide another focus of future research.
Prof. A. Avenant- Oldewage