Elminius modestus cyprids settle readily in contact with adult barnacles in the field, and do not discriminate between conspecific and alien adults. This settlement strategy is contrasted with that previously shown to be employed by Balanus balanoides.

The growing interest in farming rainbow trout in the sea (MacLeod, 1977) or in brackish water (Tatum, 1973, 1976) is economically important because it involves the use of readily available sites and resources, and provides solutions to problems related to fresh water scarcity or its increased salinity (Al-Hamed, 1971; Al-Daham & Bhatti, 1977) in certain parts of the world.

INTRODUCTION

The small squid Alloteuthis, and the larger Loligo have elongate mantles chiefly made up of two distinct types of circular muscle fibres, partitioned by thin sheets of radial muscle fibres (Bone, Pulsford & Chubb, 1981).

Nerve terminals on both types of circular fibre and upon radial fibres contain 50 nm electron-lucent vesicles; preliminary pharmacological investigations (Bone & Howarth, 1980) indicate that L-glutamate is the excitatory transmitter at the terminals upon the circular fibres. In other cephalopods, such as Sepia, and the squids Lepidoteuthis and Taningia (Clarke & Maul, 1962; Clarke, 1967) there are in addition to the circular and radial fibres, layers of longitudinal muscle fibres in the mantle. Such longitudinal fibre layers are lacking over the greater part of the mantle in Alloteuthis and Loligo. In this note, we show that they are present only around the anterior margin of the mantle in these two squid, and that both these anterior longitudinal fibres and the radial fibres of the mantle are insensitive to L-glutamate, but contract in response to acetylcholine, as do the retractor muscles of the head and arms, and the siphon muscles.

INTRODUCTION

It has long been known that the ears of clupeoid fishes differ from most other fish in that they have a gas-containing bony bulla associated with each ear (for references to early work see Allen, Blaxter & Denton, 1976). The expansion and contraction, with changing pressure, of this gas causes liquid to flow in the ear and lateral line (Gray & Denton, 1979; Denton, Gray & Blaxter, 1979) thus causing displacements (Best & Gray, 1980) and excitation (Denton & Gray, 1980) of the utricular maculae; it also causes excitation of the lateral line neuromasts (unpublished). Only a small fraction of the alternating liquid flow from the bullae passes through the pars inferior of the labyrinth (Gray & Denton, 1979). Furthermore, in larvae, when the utricular structures can be seen to move vigorously with an alternating pressure the saccular otolith is not seen to move (Blaxter, Denton & Gray, 1981).

Henze (1911) was the first to discover large amounts of vanadium and sulphuric acid in the blood of certain species of tunicates. Webb (1939) established that both the sulphuric acid and the vanadium were present in blood in the same cell type, termed a vanadocyte. Since then much further work (reviewed by Goodbody, 1974) has been done on these highly unusual cells. Some species of tunicates accumulate other metals, including iron, titanium, niobium and tantalum (Carlisle, 1968) but the role(s) of these metals and indeed of vanadium itself remains unclear. The vanadium is present in vanadocytes in a reduced cationic form largely as vanadium(III) (Carlson, 1975; Tullius et al. 1980) which is complexed with a chromagen of as yet undefined structure and with sulphate as the counter anion (Bielig et al. 1966). The blood of Ascidia nigra is not capable of reversible oxygen binding (Macara, McLeod & Kustin, 1979), and there has been speculation that the reduced vanadium is involved in the synthesis of the tunic material (see Goodbody, 1974). The tunic of ascidians also contains cells rich in vanadium and sulphuric acid and roles for them in anti-fouling and anti-predation have been considered (Stoecker, 1980a, b).

The ormer, Haliotis tuberculata L. is a greatly prized species in the Channel Isles. Since the original survey of the ormer population of Guernsey and the subsequent tagging experiments (Forster, 1962, 1967), periodical short visits to the island have been made to investigate the stocks of ormers, especially in areas fished by divers; in 1968 and 1974 visits were also made to Jersey. These surveys were all made at the request of the local Sea Fisheries Committee. In this paper we seek to bring together those aspects of the results which are of scientific interest and to discuss the role of various factors which may have affected the ormer populations particularly that of changes in temperature over the last hundred years. The reproductive biology of this species has recently been reported on by Hayashi (1980).

INTRODUCTION

The food and feeding habits of rays (genus Raja) have received more attention than other aspects of their biology. Being nocturnal feeders (Bigelow & Schroeder, 1953), they have been thought to locate food by smell rather than by sight (Steven, 1930, 1947). More recently, the ability of the electric receptors to detect even weak action potentials has been linked with food foraging (Kalmijn, 1966). Wilson (1953) observed that the behaviour of Raja while apprehending prey was similar to that of Torpedo spp. The functional advantages of a ventral mouth as an adaptation to bottom feeding have been stressed by Alexander (1970).

Day (1880–1884) recorded that rays ate molluscs, crustaceans and fish. That the young of Raja clavata, R. montagui (as R. maculata), R. naevus and R. brachyura feed on crustaceans was observed by Clark (1922). Steven (1930, 1932, 1947) confirmed this in a wider age sample of the same species, adding that juveniles which ate amphipods and crangonids later changed to Upogebia, Portunus and Corystes cassivelaunus, whereas the adults were highly piscivorous and sometimes cannibalistic. Both Clark and Steven obtained their fish close to Plymouth. Lazzareto (1964) and du Buit (1969), largely corroborating the above, included polychaetes in the list of food items but specified no differentiation according to size.

Holden & Tucker (1974), recording only presence or absence of food items, studied R. clavata, R. brachyura, R. montagui and R. naevus from a much wider area.

In cartilaginous fish, holocephalians and elasmobranchs, the endolymphatic system of the inner ear generally communicates with the exterior via the endolymphatic ducts. The openings of the ducts on the dorsal side of the head were known already by eighteenth-century anatomists (Retzius, 1881). In certain elasmobranchs mineral particles from the environment pass into the inner ear through the ducts. Stewart (1906) described presence of sand grains in the membranous labyrinth of the shark, Squatina. Nishio (1926) found black volcanic particles of varying sizes in the endolymphatic duct, the sacculus and the lagena of Squatina angelus and the ray, Torpedo ocellata, from the gulf of Naples.

I have studied the inner ear of two species of electric rays, Torpedo nobiliana and T. marmorata. Considerable amounts of fine sand grains are found in the endolymphatic system of both species. The mineral particles are kept together by a gelatinous material or occur free in the endolymph. The size of the sand particles varies between 10 and 400μm. The grains are white or transparent, yellow, brownish or black. Mineralogical analysis with a polarizing microscope reveals that 85–90% of the particles consist of quartz, 5–10% of calcium carbonate and less than 5% of an unidentified opaque mineral, possibly corroded felspar. The grains are irregular with rounded or sharp edges. They differ in appearance from the round or lens-shaped concentrically layered aragonite octoconia found in the labyrinth of most elasmobranchs (Retzius, 1881; Nishio, 1926). The present findings seem to be consistent with the results by Stewart (1906) and Nishio (1926) suggesting that certain psammophilous elasmobranchs lack the ability to produce calcium carbonate otoliths and compensate for this by uptake of sand grains through their endolymphatic ducts.

Harpacticoid copepods (Crustacea) comprise an important taxon of the sedimentdwelling meiofauna, generally being numerically inferior to only the Nematoda (Hulings & Gray, 1971). This paper reports those species comprising the fauna of the sediments of the River Ythan estuary, particularly the intertidal sediments, and describes some of the properties of the meiobenthic copepod community structure.

Protandric hermaphroditism, the sequential change from male to female, has been reported in several superfamilies of prosobranch gastropods including the Fissurellacea, Patellacea, Calyptraeacea, and Eulimacea (Webber, 1977). It is most common in members of the Calyptraeacea and the Patellacea. In the Calyptraeacea changes in sex are readily followed by observing copulative structures (Coe, 1944). Because patellacean limpets are predominantly broadcast spawners with external fertilization, external characters that can be used to determine the sex of individuals are rare. Hence, previous to this report the occurrence of protandry in most patellacean limpets has been based primarily on sexual dimorphism in size; the smaller size classes being made up of male individuals and the larger size classes of female individuals (Willcox, 1898; Orton, 1920, 1928; Orton, Southward & Dodd, 1956; Dodd, 1956; Branch, 1974). However, given this type of data it is often difficult to assess whether the observed sexual dimorphism is indicative of protandry or merely a result of differential growth and/or survival. The presence of simultaneous hermaphrodites in the intermediate size classes, as evidence of protandry is of limited value because simultaneous hermaphrodites occur sporadically in patellaceans that do not show a sexual dimorphism in size (Dodd, 1956; Branch, 1974). The only unambiguous way of proving the existance of protandry in patellacean limpets is the direct monitoring of gonadal changes in individuals through time. We report here the first direct observations of protandric hermaphroditism in a patellacean limpet.

Lottia gigantea Sowerby, 1834 is a large (100 + mm), territorial, intertidal limpet that ranges from northern California to central Baja California, Mexico (Stimson, 1970).

Many pinnipeds travel long distances between breeding and feeding grounds in some cases showing remarkable homing abilities (James & Dykes, 1978). Very little is known about the methods they use to plot their course but if they were aware of their rate of movement, this ability could conceivably assist them. The following procedure which was undertaken with a captive male harbour seal (Phoca vitulina Linnaeus) demonstrated that the animal was able to determine his swimming speed.

The seal was first trained to swim at any speed through ten hoops 48 cm in diameter submerged at equal intervals around the periphery of an 8 m oval tank filled with sea water to a depth of 1.2 m. Each trial consisted of one circuit of the tank, and always began at the same hoop. A screen preventing the seal from going through this start hoop was removed to indicate the onset of each trial. The seal was then trained to swim the 17 m course maintaining a speed of 6 km/h. The experimenter observed from a bridge suspended over the tank, and measured the animal's speed by listening to a series of tones. These tones were audible only to the experimenter and were timed such that if the seal were swimming at 6 km/h, he would reach each hoop at the same moment the experimenter heard the tone. A buzzer was sounded whenever the animal swam at less than the required speed, and a whistle was blown if he were moving too quickly.