C. G. Alexander

Reproductive behaviour of the caprellid amphipod, Caprella Scaura Typica, Mayer 1890

Caprella scaura typica is common in communities of fouling animals in tropical waters. Courtship and mating involve exploration of the female by the male using antennae and maxillipeds followed by moulting of the female and copulation. During courtship and mating, males are very aggressive and will fight off all other animals. There were significantly more deaths from intraspecific fighting between males when sexually receptive females were present. Soon after a successful mating, the female also becomes very aggressive and resists further attempts at mating. The young hatch 4 days after the eggs are deposited in the brood pouch but remain there for up to 12 hours while their locomotory movements become fully coordinated. The young may be assisted from the pouch by the mother and will initially cling to her body. They scrape epiphytes from her body for food and she will periodically groom them. After a week the young are actively removed by the mother to fend for themselves.

Aggressive behaviour of Caprella Scaura Typica Mayer, 1890. (Crustacea: Amphipoda)

In amphipods, the majority of aggressive encounters occur during mating periods when mate selection and guarding takes place (Caine, 1991; Dick and Elwood, 1996; Lewbel, 1978; Lim and Alexander, 1986). There are many examples in the Crustacea of appendages modified for use as weapons for example the Chelae of the Decapoda are enlarged to varying degrees for use in threat display or combat and in the Stomatopoda, the second maxillipeds have been modified into raptorial appendages are used to strike prey. In the Amphipoda, the second gnathopod is enlarge and used in aggression and prey capture (Caine, 1991; Lewbel, 1978; Lim and Alexander 1986).

The mechanism of food ingestion by the banana prawn, Penaeus merguiensis

Food passed by the chelate pereiopods to the mouthparts of Penaeus merguiensis de Man is propelled dorsally to the mouth through a pre‐oral cavity made up of the setal fringes of the first two pairs of maxillipeds and the two pairs of maxillae. The setal fringes interdigitate and move with a ratchet action. Food is sheared off and crushed by the mandibles, pushed into the oesophagus by the setae on the labrum and prevented from escaping from the mouth by the paragnaths and labrum. In addition to setae, the endopods of the second maxillipeds and the paragnaths have glands the pores of which open on to their surfaces. Non food items are expelled by downward directed movements of the appendages forming the pre‐oral cavity.

Studies on the composition and enzyme content of the crystalline style of Telescopium telescopium (L.) (Gastropoda)

Abstract 1. 1. Preliminary investigations have been carried out on the chemical composition of the crystalline style of T. telescopium . 2. 2. Polyacrylamide gradient gel electrophoresis of crystalline style extracts can be used to distinguish between molluscs of the family Potamididae. 3. 3. No difference in structural protein composition was detected along the length of the style but laminarinase and β-glucosidase appear to be secreted into the proximal end of the style only. 4. 4. Laminarinase, fucoidanase, amylase, cellulase, xylanase, β-glucosidase and β-galactosidase activities were found in style extracts. These were further fractionated by ion-exchange chromatography. 5. 5. The level of enzyme activity in the style is correlated with the tidal cycle.

Effect of Feeding on the Structure of the Digestive Gland of the Tropical Sepioid Idiosepius Pygmaeus

The digestive gland of the tropical sepioid Idiosepius pygmaeus (Steenstrup) (Cephalopoda: Idiosepiidae) is characterized by a single cell type which secretes proteinaceous spherical bodies, the secretory spheres. Changes in the structure of the gland with feeding were investigated through a field sampling programme and a laboratory feeding experiment. Specimens were collected in the field on three consecutive days. There was a significant increase in the number of spheres during the day. A laboratory-based night trial showed that numbers of secretory spheres remained high during the night. After feeding there was a rapid and marked increase in the number of secretory spheres, suggesting that upon registering a stimulus the digestive gland secretes large amounts of enzymes. The process is rapid with an increase in the number of secretory spheres detected 30 minutes after feeding. The major peak in numbers of spheres occurred one hour after feeding. A second peak occurred 16 hours after feeding, suggesting that there may be two phases to the digestive cycle. This study examined natural and experimental patterns in the digestive gland and estimated the time involved in the digestive activity of I. pygmaeus.

Evidence for filter‐feeding by the wood‐boring isopod, Sphaeroma terebrans (Crustacea: Peracarida)

The morphology of the mouthparts and proventriculus of the wood-boring isopod Sphaeroma terebrans has been described, with particular reference to its possible filter-feeding abilities. Scanning electron microscopy revealed that while the mandibles might be designed to scrape pieces of wood from the cavity wall during boring, the rest of the mouthparts are better suited for microphagous feeding. Video observations of the mouthparts demonstrated the ability of S. terebrans to filter out particulate material from the water column, by means of the filtering setae on the first three pairs of pereiopods. The morphology of the gut was found to be largely similar to that of terrestrial herbivorous isopods; primary and secondary filter apparatuses were present, but the masticatory apparatus present in terrestrial herbivores was missing. The morphology of both the gut and mouthparts provides additional support for the assumption that wood is an unlikely food source for S. terebrans.

Habitat partitioning by two wood-boring invertebrates in a mangrove system in tropical Australia

Driftwood was collected from Stuart Creek, North Queensland, to examine the relationship between the wood-boring isopod, Sphaeroma terebrans (Isopoda: Sphaeromatidae), and the wood-boring mollusc, Bankia australis (Bivalvia: Teredinidae). Broadly non-overlapping distributions in individual pieces of driftwood were found for S. terebrans and molluscan wood-borers at the study site.

The Paragnaths of Some Intertidal Crustaceans

The paragnaths are soft outgrowths of the crustacean exoskeleton lying close to the mandibles on the aboral side. They are sometimes termed the metastoma, for instance in Pike (1947) in Galathea squamifera Leach, or the hypopharynx by Wagele (1987) in the isopod Antarcturus Schultz. It should be noted however that Manton (1964) stated that the crustacean paragnath was not the same structure as the insect hypopharynx.

The distribution of two species of alpheid shrimp, Alpheus edwardsii and A. Lobidens , on a tropical beach

Alpheus edwardsii Audouin and Alpheus lobidens de Man (Crustacea: Decapoda: Alpheidae) are two intertidal snapping shrimp that burrow in association with rocks. They are morphologically similar and are often found in the same intertidal zone. The competitive exclusion theory states that two co-existing species must partition resources. The partitioning of food items as a resource appears unlikely, as gut content analyses revealed that the two species have similar diets and the relationship of shrimp condition and shrimp density indicates that food supply was not in limited supply. Instead the two species partition the resources of space within the intertidal zone, and shelter. The two species were found to exist largely in isolation from each other. Alpheus edwardsii occurred across much of the intertidal zone. Within this range A. edwardsii were most abundant in substrata with a low proportion ( A. lobidens allows this species the potential to occupy a wide range of substratum types; however, they were found only in muddy substrata with substantial surface rock cover at tidal elevations of 1.18m above datum or below. The restriction of A. lobidens to this region of the intertidal zone is probably related, in part, to their physiological requirements. In regions of co-occurrence, A. lobidens were significantly smaller than A. edwardsii , and utilized smaller rocks as shelters, thus avoiding direct interspecific competition for this resource. The absence of large A. lobidens from these areas may reflect their ability to procure shelter in competition with A. edwardsii , as behavioural experiments conducted in this study found that A. edwardsii were the dominant competitors for this resource.

Diatoms on the cirri of tropical barnacles

Two species of large extension feeding barnacles are abundant on exposed tropical rocky shores of northern Australia. The cirri of many specimens carry varying numbers of a commensal diatom in some cases with as many as 2000 individuals on a single cirrus. The araphid diatom resembles the genus, Lichmophora within the family Fragilariaceae although no description has yet been published. Species of Lichmophora are common benthic diatoms in these waters as an epiphyte on macroalgae and common primary fouling diatoms on test panels. The diatom reported here has not been found on any substratum other than the barnacles Tetraclita squamosa and Australobalanus imperator, very rarely on Balanus amphitrite. Analysis of the diatom distribution on the cirri shows significantly higher numbers on the posterior captorial cirri. The effect of commensal diatoms on the feeding efficiency of the barnacles is discussed.