Cypris Larvae Research Articles

On the structure of the antennular attachment organ of the cypris larva of Balanus balanoides (L.)

The third segment of the antennule of the cypris larva of Balanus balanoides is modified as an attachment organ with a disk by which the cyprid attaches to submerged surfaces. The attachment disk is covered with a felt of fine cuticular villi. Opening on to the disk are terminal branches of the cement duct, numerous glands and an array of sensory hairs. The sensory structures are arthropod scolopidia with the dendrites giving rise to cilia which, distally, change to distal sensory processes. It is suggested that the cuticular hairs situated in invaginations of the cuticle around the margin of the disk function as position receptors and that the two setae lying away from the cuticle of the segment are mechanoreceptors. Three of the scolopidia have structures suiting them for chemoreception; the distal sensory processes are exposed to the exterior at the tip of the hair. Two of these hairs are positioned at the margin and one at the centre of the disk. The fourth segment, which arises from the side of the attachment organ, is packed with sensory cell processes which are associated with setae arising at the distal end; its movements are controlled by a single muscle from the third segment. A suction mechanism of adhesion is precluded as there are no structures which could effect or release suction beneath the disk. The disk could act as an adhesive pad, with the cuticular villi increasing its surface area and the antennular glands possibly secreting a viscous substance. The presence of chemoreceptors on the attachment organ indicates that a chemosensory mechanism could operate during the gregarious behaviour of settling cyprids.

Settlement of barnacle larvae: surface structure of the antennular attachment disc by scanning electron microscopy

The surface morphology of the antennular attachment disc of the cypris larva of Balanus balanoides has been investigated by scanning electron microscopy, and its function is considered in the context of settlent behaviour. It is concluded that the attachment organ acts as an adhesive pad for temporary attachment while the larva explores the substratum. The surface of the disc is covered with villi, which could retain an adhesive substance thought to be produced by the antennular glands. The open-ended hair of the axial sense organ on the disc is shown.

HISTOLYSIS AND PHAGOCYTOSIS IN THE METAMORPHOSIS OF BALANUS BALANOIDES.

ALTHOUGH the morphological changes which occur during the metamorphosis of the cypris larva of cirripedes have been well described, very little is known of the histological changes that take place. The results described here form part of work undertaken to fill this gap in our knowledge of cirripede biology.

Characteristics of the heat balance of the northeastern part of the Atlantic Ocean in the summer of 1960 : Degtyarev G.M., Yu.A. Men'shov and B.E. Ye Alemesov 1962. Eng. Abstr.: Izv., Akad. Nauk, SSSR, Ser. Geofiz., (7): 965–970; Soc.-Bloc. Res. Geography. Astr. Space, 43: 3–4

Bacterial films on submerged substrata can affect settlement of marine invertebrate larvae. We examined the effects of three species of bacteria, Deleya marina (Cobet et al.; Baumann et al.), Alteromonas macleodii Baumann et al. and Pseudomonas fluorescens Migula, on the attachment of cypris larvae of the barnacle Balanus amphitrite Darwin in laboratory assays. Bacterial cells or culture supernatant containing extracellular materials were allowed to adsorb to replicate sterile polystyrene petri dishes or borosilicate glass vials, and B. amphitrite cyprids were introduced to filmed and unfilmed (control) containers. Cells and supernatant from both log- and stationary-phase bacterial cultures were used in assays, which were repeated using different batches of larvae. Attachment of cyprids to control and filmed containers was monitored for several days. Cells and supernatant from stationary-phase cultures of D. marina consistently retarded cyprid attachment compared to attachment onto control polystyrene petri dishes, but not glass vials. Assays using films derived from log-phase D. marina cultures, and all assays with both log- and stationary-phase A. macleodii and P. fluorescens films, yielded weak and inconsistent effects on cyprid attachment. Despite variability among assays, bacterial effects on larval attachment within a particular assay generally were consistent for the duration of the assay (up to a week). Settlement was independent of the number of cyprids introduced to a container, within the range employed in assays. However, attachment of cyprids to control containers varied significantly among batches of barnacle larvae. Variation in results among assays may be related to variability in larval behavior, possibly explainable by larval diet.

The chemical basis of gregariousness in cirripedes

Surfaces on which the cypris larvae of barnacles do not settle readily were treated with aqueous extracts of whole barnacles. Cyprids then settled on the treated surfaces as readily as they do on surfaces bearing adult barnacles, thus simulating the gregarious response to their own species. It is inferred that a settling factor, present in barnacle tissues, was transferred to a neutral surface rendering it favourable for settlement. The settling factor was shown to be non-dialyzable and stable to boiling in aqueous solution. When attached to a surface, it resisted severe physical and chemical treatments. The settling factor evoked a greater response from cyprids of the species used in preparing the extract than from cyprids of other species. Extracts made from other cirripedes and from all other arthropods tested, promoted settlement, but were less effective than extracts made from the same species of cirripede. The settling factor was found to be located mainly in the integument of arthropods and was present in greater amount in newly moulted individuals. It is suggested that the settling factor to which the cyprid responds may be the arthropodins of its own species, and that arthropodins of related species evoke a similar response. No evidence was found for chemotaxis, the cyprids responding to the settling factor only after alighting on the treated surface. It is thought likely that cyprids, in common with the larvae of many other sedentary marine organisms, may not be capable of detecting or responding to such chemical releasers in the sea unless they are in contact with the surface on which the chemical is adsorbed or from which it is diffusing.

Mobility of Barnacles

IF a young barnacle is removed from a surface the remains of the antennal suckers, marking the point at which the individual cemented itself as a cypris larva, may sometimes be found near the centre of its base. It has generally been assumed that this point of basal attachment is fixed. The position selected by the barnacle, when a larva, would then always be included within the outline of its base, though not necessarily at the centre, for if growth were not radially symmetrical the original point of attachment might become eccentric.

The Orientation of Barnacles to Water Currents

Investigations have shown that barnacle larvae select suitable sites in relation to (a) depth (Hutchins 1952), (b) illumination (Pomerat & Reiner 1942, McDougall 1943, Gregg 1945, Weiss 1947, Barnes, Crisp & Powell 1951), (c) surface contour (Crisp & Barnes 1954), and texture (Moore & Kitching 1939, Pope 1945, Gregg 1948, Pyefinch 1948, 1950), (d) the presence of previously settled individuals of the same species (Knight-Jones & Stevenson 1950, Knight-Jones 1953), or of related species (Knight-Jones 1955) and (e) the velocity gradient of currents at the surface of the substratum (Crisp 1955). If the current flow relative to the substratum is too great, the cyprids fail to attach (Smith 1946, Korringa 1948). In addition to selecting a particular site, they orientate at settlement to surface contour and light (Barnes, Crisp & Powell 1951) and possibly also to water movement (Crisp 1955). Orientation along grooves (rugotropism) has been investigated by Crisp & Barnes (1954) who showed that it was a sensitive reaction invoked by contact with irregularities in the surface. Rugotropism was shown to override other orientation responses. In spite of statements to the contrary by Visscher (1928) the conclusion that cypris larvae orientate positively to light at settlement appears inescapable. Hiro (1939), McDougall (1943), and Pyefinch (1948) all recorded positive responses, and Barnes, Crisp & Powell (1951) showed a positive orientation to light in Balanus balanoides and B. crenatus while in Elminius modestus the proportion of individuals orientating towards the light could be correlated with the proportion of illumination falling in a given sector. They suggested that orientation to light might possibly have survival value since it would bring the eyes of the adult into the direct path of the incident light; nevertheless they thought it probable that this reaction might be non-functional, a continuation of the positive reaction to light shown throughout the planktonic phase. Knight-Jones & Crisp (1953) made observations of cypris larvae of B. balanoides during the setting process

The Behaviour of Barnacle Cyprids in Relation to Water Movement Over A Surface

ABSTRACT The velocity gradient of the fluid close to the solid boundary is the most appropriate description of the conditions of water flow which affect the attachment of the larvae of sessile forms to solid objects. The nominal speed of the water movement past the object is of importance only in so far as it influences the velocity gradient in the boundary layer. Experiments in glass tubes on cypris larvae of Elminius modestus and Balanus balanoides show that moderate velocity gradients exceeding 500 sec.-1 sweep the cyprids past the surface before they can attach. For large objects exposed to turbulent flow, the critical velocity gradient corresponds very approximately to a flow of 1-2 knots. Attachment under conditions of water flow is accompanied by negative rheotaxy, and can occur equally in the light and in the dark. Maximum attachment occurs at or below velocity gradients just great enough for the cyprid to be able to maintain position by swimming along the surface against the current. Once the cyprid has attached it cannot be pulled off the surface even by gradients greatly in excess of those which prevent attachment. Cyprids can migrate in all directions when exposed to moderate gradients, but they do so only with difficulty when the velocity gradient is high, particularly if the water is flowing in the same direction as that in which the cyprids are walking. The direction in which the cyprid migrates is altered only momentarily by changes in the direction of the current, the animal actively resisting the redistribution of forces acting on it. No direct evidence is given in this paper on the influence of water currents on fixation, but a critical comparison with other published work suggests that fixation can occur in places where the velocity gradients are greater than those which limit attachment, provided the cypris is able to migrate there after attachment. Moderate velocity gradients have little effect on the orientation at metamorphosis. Individuals tend to settle with the anterior end pointing downstream rather than in any other position. This orientation is the opposite from that which would be expected if the cyprid were passively orientated by the water current, but is likely to make subsequent feeding more efficient. The ability to attach under conditions of water flow, and the tendency not to attach under stagnant conditions, may have an important influence on the animals’ distribution and survival. Solid particles in suspension may profoundly influence the behaviour, hence the results given in this paper may not be relevant to conditions where scouring takes place.

Observations on the Orientation of Some Species of Barnacles

There are in the literature a number of conflicting statements regarding the effect of various stimuli on the cypris stage of barnacle larvae, before and at the time of metamorphosis, and little experimental work has been done to elucidate the type of reactions involved. Visscher (1928), working with Balanus amphitrite, B. improvisus and Chthamalus fragilis, stated that during the earlier part of their free-swimming stage the cypris larvae were positively phototropic, but later the reaction to light became erratic, and at the time of attachment was decidedly negatively phototropic. He further stated that in a settlement experiment they orientated with the anterior end (i.e. with the paired eyes) away from the light source. However, MacDougall (I943) working with two of the above species (Balanus improvisus and Chthamalus fragilis) and also Balanus eburneus, and Pyefinch (I948) working with B. balanoides and B. crenatus, both state that the cypris larvae retain their positive reaction to light up to the time of settlement. There also appears to be some disagreement regarding the orientation at, and subsequent to, metamorphosis of several species of barnacles. Moore (1935), in considering B. balanoides, has suggested that if a barnacle is settling in a current, then at the time of settlement it is likely to be orientated with the current. A general orientation at right angles to the current was supposed to be due to rotation after settlement. This rotation was considered to be a response to the orientation of the beating cirri in relation to the current; it was suggested that feeding would be more effective with the animal orientated across the current.

Change of Orientation of a Barnacle after Metamorphosis

IT is known that immediately after settlement, the cypris larvae of the acorn barnacle can move about for a short time before they metamorphose; and that they tend to collect in cracks along which their long axis is usually orientated. I am not aware, however, of any record of a change of orientation occurring once the larva has metamorphosed.

The Fixation of the Cypris Larva of Sacculina carcini (Thompson) upon its Host, Carcinus mænas

ABSTRACT The fixation of the Cypris larva of Sacculina has hitherto been successfully observed only by Delage (1), and since a considerable degree of doubt has been thrown on his account it may be of interest to record that I have been able this autumn, at Plymouth, to rear the larvæ and observe all the stages of fixation upon their host. My inability to obtain the Cypris larvæ of any of the Rhizocephala at Naples had left a gap in my observations, which I am now in a position to fill, and thus I am able to present a complete account of the life-history of Sacculina from my own observations (2).