Alan N. Hodgson

A comparison of the structure of the spermatozoa and spermatogenesis of 16 species of patellid limpet (Mollusca: Gastropoda: Archaeogastropoda)

Light and transmission electron microscopy of the spermatozoa and spermatogenesis of 16 species (in three genera, Patella, Helcion, Cellana) of patellid limpet have shown that head lengths of the sperm range from 3 to 13 μm, and each species has a sperm with a unique morphology, indicating that the spermatozoa can be used as a taxonomic character. Although spermatozoon structure is species specific, five types can be recognized, based on the size, shape, and structure of the nucleus and acrosome. The occurrence of five morphological types of sperm, one of which (Cellana capensis) is particularly different from other patellids, suggests that the taxonomy of the family Patellidae be re‐examined. The morphological changes that occur during spermatogenesis are very similar in all species, although two patterns of chromatin condensation are found. Those species with sperm that have short squat nuclei (length:breadth < 3.5:1) have a granular pattern of condensation. Species with sperm that have more elongate nuclei (length:breadth > 5:1) have an initial granular phase followed by the formation of chromatin fibrils. These fibrils become organized along the long axis of the elongating nucleus. The absence of a manchette suggests that nuclear elongation is brought about from within the nucleus.

Distribution and abundance of the macrobenthic fauna of the kariega estuary

The Kariega estuary is an open estuary which is about 18 km in length. The freshwater inflow into the estuary is very sporadic and consequently the water is often hypersaline at the head. Quantitative and qualitative sampling has been undertaken to describe the distribution and abundance of the macrobenthos along the estuary. Of the 107 species that have been recorded, 80% can be classified as euryhaline. One of the possible reasons for the high species diversity, when compared to other eastern Cape estuaries, is the growth of Zostera capensis along the entire length of the estuary. The major contributors to the macrobenthic biomass are the crustaceans, Cleistostoma edwardsii, C. algoense, Upogebia africana, Sesarma catenata and Uca urvillei and the bivalve Solen cylindraceus. The latter is particularly abundant in the middle reaches of the estuary where it can reach densities of 400 m-2. Its successful colonization is attributed to food availability and stable physical conditions within the estuary which...

The fine structure of the sperm and spermatid differentiation in the brown mussel Perna perna

The mature sperm of Perna perna is 50-55 µm long and comprises three regions: a head, a mid-piece and a tail. The head incorporates a round electron-dense nucleus and an elongated cone-shaped acrosoma The mid-piece consists of a ring of five mitochondria, in the centre of which is the distal centriole from which the tail arises. The early spermatid is characterized by a large nucleus and perinuclear cytoplasm containing numerous mitochondria and proacro- somal vesicles. By mid-spermiogenesis the nuclear chromatin begins to condense, the proacrosomal vesicles coalesce to form the acrosome and the mitochondria are reduced to five in number. At this stage the tail first appears. During late spermiogenesis the acrosome elongates and in- vaginates on its adnuclear surface. The structure of the sperm of P. pema is therefore similar to that of other mytilaceans, thus supporting the contention that sperm ultrastructure could be used in studies on bivalve phylogeny

Paraspermatogenesis in gastropod molluscs

Summary Dimorphic, and sometimes polymorphic, spermatozoa are a feature of many caenogastropod and some archaeogastropod (s.l.) taxa. The two types of sperm, named euspermatozoa (fertilizing) and paraspermatozoa (non-fertilizing) by Healy and Jamieson (1981), are produced simultaneously in the same testicular acini. Paraspermatozoa develop from spermatogonia which are similar in structure to those producing euspermatozoa. Formation of parasperm from paraspermatocytes proceeds by atypical meiotic divisions. Despite the variability in the structure of parasperm of prosobranchs, the morphological changes which occur during paraspermatogenesis are remarkably similar between taxa. Multiple flagella develop from numerous basal bodies which in turn originate from two parent and their satellite centrioles (procentrioles). In parasperm which loose all the chromatin (apyrene sperm), the nucleus initially fragments into a number of vesicles. The chromatin in the vesicles gradually degenerates, the remaining material...

Consumption and apparent dry matter digestibility of six intertidal macroalgae by Turbo sarmaticus (Mollusca: Vetigastropoda: Turbinidae)

Laboratory experiments on feeding of Turbo sarmaticus have shown that this gastropod mollusc is capable of consuming and digesting algae from the Rhodophyta (Gelidium pristoides and Corallina spp.), Chlorophyta (Ulva rigida and Codium extricatum) and Phaeophyta (Ecklonia radiata and Iyengaria stellata). The consumption rates of animals feeding on these different algae at 20°C ranged from 1.45 to 9.5% body weight per day (juveniles) and 1.06 to 6.08% body weight per day (adults). Juvenile T. sarmaticus had significantly (P<0.05) higher consumption rates (1.6–2.8 times higher) for each algal species (except E. radiata) than adults. In both juveniles and adults, consumption rates of three species of algae (G. pristoides, U. rigida and Corallina spp.) were 1.5 to 5.8 times higher at 20°C and 25°C than at 15°C. The apparent dry matter digestibility for the different algae at 20°C ranged from 9.1 to 74.8% (juveniles) and 7.3 to 77.1% (adults). Juvenile T. sarmaticus had significantly (P<0.01) higher apparent dry matter digestibility values (12–24% higher) for each algal species, except G. pristoides where there was no significant difference (P=0.444). In both juvenile and adult T. sarmaticus, algal digestibility was not affected by temperature. Monthly comparisons of the energetic value and nutritional content (protein, soluble carbohydrate and lipid) of the algae indicated that, with the exception of U. rigida and C. extricatum, there was little seasonal variation.

Comparative spermatology of 11 species of Polyplacophora (Mollusca) from the suborders Lepidopleurina, Chitonina and Acanthochitonina

Transmission electron microscopy of the spermatozoa and spermatogenesis of 11 species (in three suborders Chitonina, Acanthochitonina, Lepidopleurina) of chiton has shown that each species has a sperm with a unique morphology indicating that spermatozoa can be used as a taxonomic character. Although structure is species-specific, similarities between species within suborders and subfamilies can be recognized. The spermatozoa of species from the suborders Chitonina and Acanthochitonina have a head comprising nuclear material only, the anterior portion of which is in the form of a long thin (approximately 80 nm diameter) filament. In many species the centrioles and mitochondria of the mid-piece are lateral in position, the mitochondria often being sited anteriorly alongside the nucleus. By contrast, Leptochiton asellus, a member of the more ancient suborder Lepidopleurina, has a sperm with a head comprising a nucleus and an acrosome. The mid-piece is also more conventional in structure with a ring of five or six spherical mitochondria (sited behind the nucleus) that surround the centrioles. The presence of the acrosome in L. asellus suggests that in the more recent chitons the acrosome has been secondarily lost. It is proposed that loss of the acrosome is correlated to a modification in egg-coat thickness. A preliminary examination of the structure of the eggs of three species has shown that those of L. asellus are surrounded by a very thick chorion (14-30 μm) whereas in Acanthochitona crinitus and Dinoplax gigas there are regions of the chorion that are less than 2 μm thick. The morphological changes that occur during spermatogenesis are very similar in the Chitonina and Acanthochitonina. During spermiogenesis the nucleus elongates to develop a long anterior filament. Chromatin condensation within the nucleus involves the formation of fibrils that become orientated along its long axis. Closely associated with the elongating nucleus is a manchette. In L. asellus a spherical proacrosomal vesicle appears in the spermatocytes. This vesicle becomes compressed as it matures and simultaneously it migrates to the presumptive anterior end of the spermatid where it invaginates and elongates. Although the pattern of chromatin condensation in the nucleus is similar to that described above, a manchette has not been observed.

Ultrastructure of the spermatozoa of five species of South African bivalves (Mollusca), and an examination of early spermatogenesis

Transmission electron microscopy of the spermatozoa of five species from three families of bivalves has shown that each species has a sperm with unique morphology. However, the morphology of the acrosomes of each species is typical of the subclass of bivalve to which they belong. An examination of spermatogenesis in the five species, along with a re‐examination of material from six other species of bivalves, has revealed that pre‐spermiogenic cells possess flagella. In addition, acrosome formation begins in the spermatocytes with the formation of proacrosomal vesicles in the Golgi body. During spermiogenesis the proacrosomal vesicles coalesce at the presumptive posterior of the spermatid, with a larger vesicle produced by the Golgi body. The single acrosomal vesicle eventually migrates to the anterior of the spermatid where it assumes its mature form.

Structure of the sperm of some South African archaeogastropods (Mollusca) from the superfamilies Haliotoidea, Fissurelloidea and Trochoidea

The structure of the spermatozoa of 11 species from five families of archaeogastropod (Haliotidae, Fissurellidae, Trochidae, Turbinidae, Phasianellidae) has been examined using transmission electron microscopy. All sperm are of the primitive, or ect-aquasperm type and each species has a sperm head (nucleus and acrosome) with unique morphology. Furthermore, the results from the present study together with those published in the literature reveal that, although there are a few exceptions, the size (length to breadth ratio) and spape of the nucleus and acrosome of sperm of species within each family are similar. It is therefore possible to identify members of a family and differentiate between families using sperm morphology. The intrafamilial similarities and interfamilial differences in sperm structure indicate that a spermiocladistic study of the suborder Vetigastropoda could provide interesting insights into the phylogenetic relationships of this group.

Phylogenetic trends and variation in the ultrastructure of the spermatozoa of sympatric species of South African patellid limpets (Archaeogastropoda, Mollusca)

Summary Phylogenetic parsimony analysis of sperm ultrastructure allows recognition in South African patellid limpets of four monophyletic groups: the argenvillei group (3 species); the aphanes group (2 species); the concolor group (6 species) and a more heterogeneous cochlear group (3 Patella species and dubiously associated with these, species of the genera Helcion, Nocella and Celiano). Of 5 pairs of spermatological sister-species, each species is extensively sympatric with its sister-species. Sperm of such sympatric species may be morphologically almost identical or may show structural differences which would be expected to block hybridization. Where, as in the argenvillei and aphanes groups, the sperm within each group are structurally similar, it is likely that immunological and biochemical rather than structural features of the gametes act as species barriers preventing hybridization. Where contrasting morphological specializations of the sperm of sister-species are demonstrated, these are considere...

The exploitation of Upogebia africana (Crustacea: Thalassinidae) for bait in the Knysna Estuary

The activities of people collecting Upogebia africana for bait at six popular collecting sites in the Knysna Estuary were monitored from February 1995 until April 1996. Three groups of bait harvesters were identified on the basis of their source of income: subsistence fishers who rely on bait collecting and fishing for their income; supplementary fishers who catch fish to supplement their income; leisure anglers who draw no income from fishing. Two groups of collectors were identified based on methods of collecting bait and fishing: leisure anglers who collect bait using a prawn pusher or pump and fish using a rod and tackle; non-leisure fishers who collect using tin cans and fish with hand or planted lines. The average harvest of bait per collecting trip by leisure anglers was 59 mud prawns, whereas non-leisure fishers took 101 animals, twice the legal limit. The numbers of bait collectors present per mud bank were found to be highest on public holidays ([xbar] = 43.5) and higher during the summer holidays ([xbar] = 16.5) than during the spring/summer ([xbar] = 8.6) and autumn/winter ([xbar] = 4.6) periods. Most collectors spent 11–30 minutes on the mud banks. It was estimated that 1.86 x 106 U. africana or about 740 kg (dry mass) was removed by bait collectors annually from the six bait-collecting sites studied. This represented about 8.5% of the mud prawn stocks at these sites and about 0.9% of the entire estuary stock. 85% of the mud prawns taken as bait was removed by 77% of the bait collectors who were the non-leisure fishers.