BULLETIN OF MARINE SCIENCE, 33(3): 645-655, 1983

CIRRAL ACTIVITY AND FEEDING IN THE CORONULOID TESSEROPORA ROSEA (KRAUSS) AND TETRACLITELLA PURPURASCENS (WOOD) (TETRACLITIDAE)

D, T. Anderson and J. Buckle

ABSTRACT Adult T. rosea and T. purpurascens are extension-feeding planktivores, dependent on water currents to evoke extension of the eirral fan. T. rosea displays testing activity in still and slowly moving water and respiratory pumping beat in a moderate water current, but requires a fast current for cirral extension and feeding. T. purpurascens displays pumping beat in still and slowly moving water, and performs cirral extension in a moderate water current. Fast flow causes distortion of the cirral fan in T. purpurascens and often provokes cirral withdrawal. Juveniles of T. purpurascens show the same cirral responses as adults. Juveniles of T. rosea display pumping beat and normal beat in still, slowly moving and moderate water flow, but withdraw the cirri in response to fast flow. Transitional behavior is shown by T. rosea individuals of about 2 mm aperture length. The cirral responses to water flow in the two species are related to habitat. T. rosea inhabits wave washed rocks subject to fast water flow. T. purpurascensoccupies more sheltered habitats in which water flow is reduced. Juvenile T. rosea appear to feed when immersed and to survive fast flow by a protective withdrawal of the delicate cirri. The observation of cirral beating in a juvenile coronuloid adds to the number of cases of convergent evolution ofcirral beating among thoracican barnacles. It also raises the possibility that adult balanoids with cirral beating are a product of neotenic evolution.

Two species of tetraclitid feature prominently on the rock platforms of the open coast of New South Wales, dominating the rock faces between the mean high water level of the neap tides and a level about 0.5 m above mean low water neaps (Dakin et al., 1948; Dakin, 1953). One species, Tesseropora rosea (Krauss), occurs mostly on areas of rock exposed to direct sunlight and relatively strong wave action. The other species, Tetraclitella purpurascens (Wood), is found mainly in crevices and caves and under ledges, where there is considerable shade and reduced wave action. Denley and Underwood (1979) showed that each species settles in the area of the other, but does not survive. T. purpurascens is unable to withstand the physical stresses of high temperature and desiccation in sunny habitats. T. rosea survives in shaded areas provided that the water flow resulting from strong wave action is not reduced by the topography of the substratum, but is unable to survive in locations with a reduced water flow. The little that is known of feeding mechanisms in tetraclitid barnacles (Mori, 1958; 1961; Crisp and Southward, 1961; Southward and Crisp, 1965; Anderson, 1981) indicates that they are extension-feeding planktivores, dependent on an external water flow to evoke cirral extension. It is thus possible that the failure of T. rosea to survive in areas of reduced water flow is related to the pattern of cirral activity and feeding in this species. In T. purpurascens, in contrast, a pattern of cirral activity and feeding appropriate to the circumstances of reduced water flow might be expected. In the present investigation, we set out to determine experimentally the responses of the two species to external water currents of different velocities, to establish as far as possible the diet of the two species and to relate these observations to the distribution of the species on the shore. We included an examination of the cirral activities of juveniles as well as adults of

645 646 BULLETIN OF MARINE SCIENCE, VOL. 33, NO.3, 1983 the two species, since Denley and Underwood (1979) had emphasized the heavy mortality of newly settled juveniles within 2 months of experimental transfer to typical habitats of the other species.

METHODS

Adults and juveniles of both species attached to pieces of rock were collected from a numbcr of rock platforms in the vicinity of Sydney, N.S.W. (Harbord, Fairlight, Cape Banks). Juveniles were defined as individuals with an aperture length of less than 2 mm. The were held at 21·C in the laboratory and were used experimentally within 2 days of collection. Water currents were directed across the aperture using a small, immersible bilge pump controlled by a variable rheostat. The pump generated a jet of water at three rates of flow: slow (0.3-0.6 m ·sec-I), moderate (0.8-1.2 m ·sec-I) and fast (1.4-1.8 m·sec-I). These flow rates fall within the range of measured rates of water flow on rocky shores (Riedl, 1971; Koehl, 1977). Responses were observed visually and filmed using the methods of Anderson (1978). Films were subjected to frame by frame analysis. Mean times for rhythmic events were determined from 20 sequential repetitions of the event in each of 4 animals. Milk diluted with seawater was used to display water currents generated by the animals during cirral activity, following the method of Crisp and Southward (1956). The diet of adults of the two species were investigated by gut content analysis. 50 adults of each species were collected on the outgoing tide at Cape Banks, N.S. W., in March and August 1981. The animals were fixed in 7% formalin in seawater (v/v) at the time of collection. Stomach contents were later dissected out and analyzed, as a pooled sample for each species, for particle size distribution and qualitative composition.

RESULTS Cirral activity in the present study was found to fall mainly within the definitions of testing, pumping beat, normal beat and extension described for balanomorphs by Crisp and Southward (1961) and Anderson (1981).

Adults of T. rosea T. rosea, a typical tetraclitinid, has moderately long first and second maxi IIipeds, elongate antenniform third maxillipeds and three pairs of long posterior cirri (Pope, 1945). In still or slow flowing water, adult T. rosea exhibit only testing activity. The operculum is raised slightly at the carinal end and opened partially. Sometimes the body can be seen moving back and forth within the mantle cavity. Occasionally a single antenniform ramus ofa third maxilliped is protruded through the aperture. Testing activity begins almost immediately following immersion and usually precedes any other type ofcirral activity. Adult T. rosea kept out of water for some time also display testing activity in air. When the water flow across the is increased to moderate, the animal commences pumping beat. In this regular, rhythmic activity, the aperture is opened more widely and the cirri are protruded and withdrawn, remaining curled. The scuta 1 ends of the opercular valves are also raised and lowered in conjunction with the cirral protrusion and withdrawal of each beat. Rates of pumping beat ranged from 7 to 9 per 10 sec, with cirral protrusion taking longer (range of means 0.39-0.45 sec) than withdrawal (range of means 0.17-0.22 sec) on each beat. The interval between withdrawal and the next protrusion was 0.60-0.78 sec. Milk traces revealed that pumping beat in T. rosea is accompanied in the usual way by a flow of water through the mantle cavity (Fig. 1), drawn in at the rostral end on each upstroke (cirral protrusion and scutallift) and ejected as a jet at the carinal end on the following downstroke (cirral withdrawal and scutal depression). The length of the exhalant jet varies. In the example shown in Figure 1, an adult of 7-mm shell height and 5-mm aperture length, pumping at 9 beats per 10 sec, ejected a jet 14 mm above the orifice on each stroke. Jets up to 20 mm long were ANDERSON AND BUCKLE: ClRRAL ACTIVITY IN TETRACLlTlDS 647

1 2 '33' 2 lOmm 3 -~ jifJ /'445 ~

Moderate ~Xler~ > low

Figure 1. Production of a through-mantic current by T. rosea during pumping beat at 9 per 10 sec in response to a moderate external water flow. (a)-(c) represent three frames of a cinefilm at spaced intervals of 0.22 sec. The milk-laden plumes of water generated by three beats are shown. The times indicated for each plume represent the intervals following the cirral withdrawal that ejected each plume. In (a) the circal withdrawal of the third beat is about to occur. In (c) the first plume is dissipating, the second is drifting and the third is almost discharged. observed in other individuals. The successive jets are carried away on the water current flowing externally across the animal. The exhalant jet, and thus the water flow through the mantle cavity per beat, had a volume of about 0.16 ml in the above example. Water was thus flowing through the mantle cavity at a rate of about 0.5 I per h. When the external water flow is fast (> 1.4 m· sec-I), adult T. rosea react by prolonged cirral extension. The opercular valves are raised and opened and the long cirri are extended as an upright fan at the carinal end of the aperture. The long rami of the third maxillipeds flank the cirral fan. The first and second max- illipeds of each side emerge at the rostral end of the aperture and turn back against the opercular plates. In the extended position, the cirral fan may rotate up to 90° in either direction towards the impinging current. Cirral extension in response to fast water flow is a dynamic process in T. rosea. l At rates of flow approaching 1.8 m'sec , the cirri are held extended for periods of up to 4.5 sec (Fig. 2). During these periods, individual rami curl down towards the maxillipeds and are then raised again. Between successive periods of extension, however, the cirral fan is curled down and withdrawn as a whole into the mantle cavity, with the aperture remaining open. The timing of the events of this process is regular (mean withdrawal time 0.19 sec, interval in the withdrawn position 0.36 sec, extension 0.28 sec). Both the coiling of individual rami and the repeated withdrawal of the cirral net during cirral extension can be interpreted as food capture responses. When the external water flow is intermediate between moderate and fast, 1.2- 1.4 m· seC I, adult T. rosea display an intermediate level of activity best described as extension beat. At 1.2 m· sec-I, the operculum is held open and the cirri are uncurled to an upright position on each protrusion, but are not spread. The extended cirri are almost immediately withdrawn again, after remaining extended for about 0.15 sec (Fig. 2). The rate of beating during extension beat, 6.5 per 10 sec, is slower than in pumping beat. This is due to a slower cirral protrusion, with a mean duration of 0.5 sec. Cirral withdrawal (0.2 sec) and the interval before the next protrusion (0.73 sec) are similar to those of pumping beat. As the external 648 BULLETIN OF MARINE SCIENCE, VOL. 33, NO.3, 1983

w. (0) 2 4 6 8 10 12 14 16 18 20

E

w (b) 2 4 6 8 10 12 14 16 18 20

I I I I I I I I I 2 4 6 8 10 12 14 16 18 20

Time (s) Figure 2. Timing of cirral activity in T. rosea, based on cinematographic records. E, cirri extended; W, cirri withdrawn. (a) extension beat in response to an external water flow of 1.2 m·sec-I• The cirri are uncurled but not spread during each protrusion, and remain extended only briefly; (b) extension beat in response to an external water flow of 1.4 m· sec-I. The cirri are spread when extended, but are held in the extended position quite briefly on most occasions; (c) dynamic cirral extension in response to an external water flow of 1.8 m·sec-'. The cirri are held extended and spread for relative long periods, up to 4.5 sec.

water flow becomes faster, 1.4 m· sec-I, the pattern of extension beat changes (Fig. 2). The rate of beating remains about 6 per 10 sec, but cirral protrusion (0.28 sec) and withdrawal (0.19 sec) are speeded up to the levels of those observed in the extension response to fast water flow. The protruded cirri are also spread, but the duration of the extended phase is very variable (0-2.65 sec). The duration of the withdrawn phase between each beat also becomes irregular (0.1-1.0 sec). Extension beat appears to be a threshold activity in adult T. rosea, transitional between pumping beat and the dynamic cirral extension response of the species to fast water flow. ANDERSON AND BUCKLE: C1RRAL ACTIVITY IN TETRACLlTIDS 649

0·2 0·18 ~ 0·16 .s : } Adult 1 Qj 0'14 E i 0·12 : ~ Adult 3 '0 0'1 Qj : } Adult 4 E :> 0·08 ~ 0·06 0'04

0·02 : } Juvenile 1 ~ Juvenile 2 2 3 4 5 6 Aperture length (mm)

Figure 3. The relationship in T. rosea between size and the volume of water expelled from the mantle cavity during pumping beat. Each point represents a mean value for two plumes of water expelled on successive beats.

Food Capture in Adult T. rosea It is well known that the food intake of extension feeding barnacles is zooplank- ton, while balanomorphs with rhythmic feeding mechanisms augment their zoo- plankton intake with diatoms and other microplankton obtained by filter feeding (Crisp and Southward, 1961; Anderson, 1981). For coronuloids, direct observa- tion on food intake are limited to one species, squamosa, which con- sumes zooplankton (Barnes, 1959). In adult T. rosea, the largest proportion by far of the gut contents (85-90% of particles) comprised small , mainly copepods, and remains in the size range 0.5-1.00 mm. A number of cirripede nauplii 0.1-0.2 mm long were also present (10-15% of particles), together with a few diatoms and strands of filamentous algae. This analysis correlates well with the extension feeding response of T. rosea to fast water currents and indicates that pumping beat in adult T. rosea is a respiratory, not a filter feeding activity.

Juveniles of T. rosea Juveniles of T. rosea, in contrast to adults, never show testing activity. A more vigorous level of activity always follows immediately on opening the aperture, even in still water. Juveniles were observed to perform pumping beat in still and slow flowing water, at a faster rate than adults, ranging from 10.5 to 15 beats per 10 sec. In this activity, the time for cirral withdrawal (range of means 0.15-0.21 sec) and the interval between withdrawal and the next cirral protrusion (0.35- 0.61 sec) were not significantly different from those of adults (Mann-Whitney test, P < 0.05), but the time for cirral protrusion (0.21-0.22 sec) was significantly shorter. The slower rates of pumping beat in adult T. rosea as compared with juveniles, therefore, result mainly from a slowing of the cirral protrusion process in adults. At fast rates of beating, the interval in the withdrawn position also becomes brief in some juvenile individuals. A water flow through the mantle 650 BULLETIN OF MARINE SCIENCE, VOL. 33, NO.3. 1983

E

w w

(0) 2 4 6 8 10 (b) 2 4 6 8 10 Time(s) Figure 4. Timing of normal beat in juvenile T. rosea based on cinematographic records. E, cirri extended; W, cirri withdrawn. (a) 11.5 beats per 10 sec; (b) 20 beats per 10 sec.

cavity results from pumping beat in juveniles in the same manner as in adults. The volume of water pumped on each beat is directly proportional to the size of the animal (Fig. 3). In still, slow flowing and medium flowing water, juveniles of T. rosea also display an activity never seen in adults-normal beat. This process has been reported hitherto as a cirral activity only in certain groups of balanoid balano- morphs (Crisp and Southward, 1961; Anderson, 1981). During each beat, the long cirri are extended fully and withdrawn, the aperture being closed between cach beat. A through-mantle current is generated in T. rosea juveniles during this activity, but at much lower volume than during pumping beat. In this respect, normal beat in T. rosea juveniles differs from that of balanoids, but in other respects it is typical. Rates of beat (Fig. 4) range from 11 to 20 per 10 sec. Cirral

Hls

(c)

lOmm Figure 5. Production of a through-mantle current by 1'. pllrpllrascens during pumping beat at 9 per 10 sec in still water. (a)-(c) represent three frames of a cinefilm at spaced intervals of 0.22 sec. The milk-laden plumes of water generated by three beats are shown. The times indicated for each plume represent the intervals following the cirral withdrawal that ejected each plume. In (a) the cirral pro- trusion of the third beat is about to occur. In (c) the first and second plumes linger above the animal as the third is discharged. ANDERSON AND BUCKLE: CIRRAL ACTIVITY IN TETRACLITIDS 651 protrusion (0.17-0.32 sec) is slower than withdrawal (0.13-0.19 sec). At slower rates of beating, the interval in the withdrawn position is similar to that of pumping beat. At faster rates, however, the interval between withdrawal and the next cirral protrusion becomes almost negligible (Fig. 4). This type of cirral activity ap- proaches the fast beat of some balanoids as defined by Crisp and Southward (1961), in which the extended long cirri beat back and forth outside the mantle cavity, but are not withdrawn between beats. No through-mantle current is pro- duced during fast beat in balanoids. When the external water current across a juvenile T. rosea is flowing at a fast rate, the young animal makes the opposite response to that of the adult of the species. The cirri are withdrawn and the operculum is closed. T. rosea juveniles must therefore feed primarily by normal cirral beat in slow to moderate water flow. Stomach contents were not analyzed, so the nature of the food particles captured by this action remains to be elucidated. Individuals of about 2 mm aperture length exhibit a transitional array of cirral activities. In still water and slow to moderate flow, normal beat continues, but fast water flow now evokes prolonged bouts of cirral extension, up to several seconds. During these periods, the extended cirral fan can be rotated up to 1800 to face the oncoming current, a level of rotational flexibility about twice that of adult T. rosea.

Adults and Juveniles of T. purpurascens T. purpurascens, a tetraclitellinid, differs from T. rosea in having a lower shell profile, a smaller aperture and three pairs of short maxillipeds in front of the three pairs of long posterior cirri (Pope, 1945). Unlike T. rosea, adults and juveniles of T. purpurascens both exhibit prolonged cirral extension as their major cirral activity. Furthermore, the response to external water currents is different. Adults and juveniles both commence pumping beat in still water, at rates of 6.5-9 and 10-13.5 beats per 10 sec respectively. These rates are similar to those observed in the pumping beat responses of adult and juvenile T. rosea to moderate water flow. The duration of the various components of the activity is also generally similar. In adult T. purpurascens, cirral protrusion (0.5-0.95 sec) is notably slower than withdrawal (0.16-0.22 sec) and the interval in the withdrawn position is 0.3-0.45 sec. The corresponding figures for juvenile T. purpurascens are 0.12-0.45 sec for cirral protrusion, 0.15-0.22 sec for withdrawal and 0.42-0.50 sec before the next protrusion. As in T. rosea, the faster rate of pumping beat in juveniles of T. pllrpllrascens results mainly from a faster rate of cirral protrusion on each beat. Pumping beat produces a water flow through the mantle cavity in T. purpur- ascens, as in T. rosea, following the same course (Fig. 5) but being ofIower relative volume. An 8-mm high individual of T. purpurascens, with an aperture length of 6 mm, beating at 9 per 10 sec, was estimated to pump 0.09 ml on each beat, generating a through-mantle flow of 0.3 I per h. Pumping beat is maintained in adult and juvenile T. purpurascens in slow water currents, but the application of a moderate external water flow immediately evokes prolonged cirral extension. Figure 6 shows a typical pattern. The cirral fan is withdrawn and re-extended at irregular intervals during the sequence, but the most striking feature is the length of time for which the cirri may be held in the extended position, up to 6 sec. Cirral protrusion and withdrawal rates are also relatively slow, 0.65 sec and 0.38 sec respectively (compare T. rosea, 0.28 sec and 0.19 sec). The duration of the withdrawn phase between successive extensions 652 BULLETIN OF MARINE SCIENCE, VOL. 33, NO.3. 1983

E

w

2 6 10 12 14 16 18 20 Time (5)

Figure 6. Timing of cirral extension in T. purpurascens in response to moderate water flow, 0.8-1.2 m'sec', based on cinematographic records. E, cirri extended; W, cirri withdrawn. The cirri are held extended and spread for periods up to 6 sec.

is variable, being either close to zero or moderately long, 0.5 sec. Thus in T. purpurascens, adults and juveniles make the cirral extension response to moderate external water currents and tend to hold the cirri extended for quite protracted periods. As in T. rosea, the cirral net may be rotated up to 900 in either direction towards the oncoming current. When the external water flow is increased to a fast rate, adult and juvenile T. purpurascens continue to exhibit the above pattern of cirral extension at first, but appear to have difficulty in holding the extended cirral fan in place. Withdrawal of the cirri and closure of the operculum soon follow.

Food Capture in T. purpurascens Stomach content analysis in adult T. purpurascens revealed a similar dietary intake to that of T. rosea. The material consisted mostly of small crustacean remains in the size range 0.5-1.00 mm, including many copepods, together with some cirripede nauplii 0.1-0.2 mm long. Very little fine particulate material was found in the gut.

DISCUSSION Adaptation to Habitat Adult T. rosea and T. purpurascens are thus extension-feeding planktivores dependent on water currents to evoke extension of the cirral net. Juvenile T. purpurascens respond to water currents in the same manner as the adult. Juvenile T. rosea, in contrast, display normal beat and rarely perform cirral extension until larger than 2-mm aperture length. The response of adult T. rosea to water flow correlates well with the evidence of Denley and Underwood (1979) that the species requires exposure to relatively strong wave action in order to survive. The extension-feeding response is made only to fast water flow. Moderate water flow evokes respiratory pumping beat. When the ambient water is still or slow flowing, adult T. rosea may open in a testing response but do not become active in either respiration or feeding. Denley and Underwood (1979) indicated that juveniles of T. rosea may survive ANDERSON AND BUCKLE: CIRRAL ACTIVITY IN TETRACLITIDS 653 up to 2 months after settlement in areas of reduced water flow. The cirral activities ofjuveniles appear to be related to this capability. T. roseajuveniles show pumping beat and normal beat in still, slow flowing and moderate flowing water. Normal beat is presumably a feeding activity. Cirral extension occurs occasionally in moderate flow, but the response to fast flowing water is cirral withdrawal and closure of the operculum. Two conclusions can be drawn from these observations. Firstly, normal beat in juveniles permits survival in areas of reduced water flow unsuitable for adults, but the transition to the adult mode of feeding is inimical to further survival in such areas. Secondly, juveniles settling in the normal wave- washed habitat of the species must also feed by normal beat. Their closure response to fast water flow is in complete contrast to the cirral extension response of older animals. It seems likely that the cirri of the young animals are too delicate to withstand strong currents. Normal beat in these juveniles appears to be an ad- aptation which permits juvenile T. rosea to feed while continuously immersed. Only when the animals are larger and the cirri more strongly developed does extension feeding in the wash of the waves take over. In terms of the habitat range and survival of T. rosea on the shore, these conclusions raise a puzzling question. Although the adult capacity for extension- feeding in strong water currents is clearly adaptive to exposed eulittoral rocky habitats, what features of the functional organization of adult T. rosea preclude extension-feeding in the circumstances of reduced water flow? There are numerous examples of extension-feeding barnacles which feed effectively in slow or moderate water flow, Tetraclitella purpurascens being one of the latter. T. purpurascens can also feed in fast water flow, though it does not live in exposed wave-washed habitats for other reasons (see below). There must therefore be a correlation in adult T. rosea between the ability to survive in exposed habitats, presumably based on the strength and organization of the wall and operculum, and the spe- cialized habit of feeding by cirral extension response in a fast-flowing current. On the shore, adult T. rosea extend their cirri only when the backwash of each wave surges over them. T. purpurascens, in sharp contrast to T. rosea, feeds by cirral extension as adults and juveniles in response to moderate water flow, and exhibits respiratory pump- ing beat in still and slow-moving water. In terms of habitat occupancy, the adults and juveniles of T. purpurascens are adapted to feeding in locations in which the water flow is reduced to some extent, though they need more than still or slow- flowing water to evoke the feeding response. The feeding mechanism ofthe species thus allows the occupation of crevices, caves and overhangs unsuitable for T. rosea. The failure to survive on exposed surfaces is not due to an incapacity for feeding in such places. Cirral extension also occurs in response to fast water flow, although T. purpurascens is less strongly built than T. rosea and the cirral net tends to be distorted by strong currents. An inability to withstand high temper- atures and desiccation as juveniles appear to be the arbiter of the exclusion of T. purpurascens from exposed habitats in which T. rosea thrives (Denley and Un- derwood, 1979). At the same time, the same question presented by T. rosea can be asked of T. purpurascens. Why is the species unable to extend its cirri and feed when immersed in still or slow-flowing water? This characteristic inability is convergently common to many intertidal barnacles of wave-washed rocky shores (Crisp and Southward, 1961; Foster, 1978; Anderson, 1981; 1983). Perhaps, as in T. rosea, the ana- tomical and behavioral requirements of protection during emersion impose con- straints on the operation of the feeding mechanism, such that strong stimulation is then required to evoke cirral extension. Present understanding of the functional 654 BULLETIN OF MARINE SCIENCE. VOL. 33. NO.3. 1983

morphology and physiology of balanomorph barnacles is insufficient to evaluate this proposition.

Cirral Activity The occurrence of pumping beat and cirral extension as the two major types of cirral activity in T. rosea and T. purpurascens fulfils the expectations for coronuloid and tetraclitid cirral activity based on earlier comparative analyses of cirral activity in balanomorphs (Crisp and Southward, 1961; Anderson, 1981). Pumping beat had not previously been recorded as a major activity among co- ronuloids, although it is well known among balanoids. The pattern and timing of respiratory pumping beat and the volume of water passing through the mantle cavity in T. rosea and T. purpurascens fall within the range established for other balanomorphs. The cirral extension activity of T. purpurascens is of a relatively primitive type, resembling that of chthamaloid balanomorphs. Cirral extension in T. rosea is a more dynamic process, with a rhythmic component approaching the cirral beating of balanoids. The periods of continuous extension are quite short and the cirri are withdrawn and re-extended rapidly at frequent intervals. A striking contrast obtains with the catophragmid Catomerus polymerus which lives intermingled with T. rosea on the same rock platforms. C. polymerus also manifests cirral extension in response to fast water flow, but acts much more slowly, in the manner of a scalpellid, and holds the cirri extended for much longer periods (Anderson, 1983). The occurrence of a pattern of normal cirral beating in juvenile T. rosea is unexpected. This activity is similar to normal beat in balanoids, although at faster rates it comes closer to the fast beat of certain balanoids (Crisp and Southward, 1961). Lewis (1981) gave the first description for of cirral activity in a juvenile different from that of the adult. Her example was the lepadomorph Pollicipes polymerus, in which the adult feeds by cirral extension in response to water currents but the juveniles display rhythmic cirral beating in still water. The pattern of cirral activity in juvenile P. polymerus is one in which the cirri are held extended on each beat, and are immediately extended again after withdrawal (Lewis, pers. comm.). This pattern is also known for adults of other lepadomorphs (Anderson, 1980a) and a verrucomorph (V. stroemia, Anderson, 1980b), but is the opposite of the pattern of rhythmic cirral activity in balanoids (Anderson, 1981). T. rosea, the first balanomorph example in which the juvenile displays cirral beating and the adult shows cirral extension, conforms to the balanoid pattern of cirral beat. The occurrence of cirral beating in a tetraclitid gives further support to the contention of Anderson (1981) that rhythmic cirral beating has evolved indepen- dently several times in balanomorphs, as well as in other thoracicans. Another question is also raised. Since cirral beating in T. rosea is an adaptive feature of juvenile animals, are balanoid adults that show cirral beating an outcome of neotenic evolution?

ACKNOWLEDGMENTS

This investigation was supported by research grants from The University of Sydney and the Aus- tralian Research Grants Committee. We are grateful to Mrs. J. T. Anderson for technical assistance.

LITERATURE CITED

Anderson, D. T. 1978. Cirral activity and feeding in the coral-inhabiting barnacle Boscia anglicum (Cirripedia). J. Mar. BioI. Ass. U.K. 58: 607-626. ANDERSON AND BUCKLE: CIRRAL ACTIVITY IN TETRACUTIDS 655

1980a. Cirral activity and feeding in the lepadomorph barnacle Lepas peclinata Spengler (Cirripedia). Proc. Linn. Soc. N.S.W. 104: 147-159. ---. 1980b. Cirral activity and feeding in the verrucomorph barnacles Verruca reCla Aurivillius and Verruca Slroemia (0. F. Muller) (Cirripedia). J. Mar. BioI. Ass. U.K. 60: 349-366. ---. 1981. Cirral activity and feeding in the barnacle Balanus perforatus Bruguiere (Balanidae), with comments on the evolution of feeding mechanisms in the thoracican cirripedes. Phil. Trans. R. Soc. Lond. B. 291: 411-449. ---. 1983. Catomerus polymerus and the evolution of the balanomorph form in barnacles (Cirripe- dia). Mem. Aust. Mus. 18: 7-20. Barnes, H. S. 1959. Stomach contents and microfeeding of some common cirripedes. Can. J. Zool. 37: 231-236. Crisp, D. J. and A. J. Southward. 1956. Demonstration of small scale water currents by means of milk. Nature, Lond. 178: 1076. --- and ---. 1961. Different types of cirral activity in barnacles. Phil. Trans. R. Soc. Lond. B. 243: 271-308. Dakin, W. J. 1953. Australian sea shores. Angus and Robcrtson, Sydney. 378 pp. --, r. Bennett and E. C. Pope. 1948. A study of certain aspects of the ecology of the intertidal zone of the New South Wales coast. Aust. J. Sci. Res. B. I: 176-230. Denley, E. 1. and A. 1. Underwood. 1979. Experiments on factors influencing settlement, survival and growth of two species of barnacles in New South Wales. J. Exp. Mar. BioI. Ecol. 36: 269- 294. Foster, B. A. 1978. The marine fauna of New Zealand: barnacles (Cirripedia, Thoracica). Mem. N.Z. Oceanogr. Inst. 69: 1-60. Koehl, M. A. R. 1977. Effects of sea anemones on the flow forces they encounter. J. Exp. BioI. 69: 87-105. Lewis, C. A 1981. Juvenile to adult shift in feeding strategies in the pedunculate barnacle Pollicipes polymerus (Sowerby) (Cirripedia, Lepadomorpha). Crustacean a 41: 14-20. Mori, S. 1958. Rhythmic activity of the seaside barnacle, Tetraclita squamosa japonica Pilsbry. Mem. Coil. Sci. Kyoto Univ. B. 25: 23-30. ---. 1961. Rhythmic activity of the seaside barnacle, Tetraclita squamosa japonica Pilsbry, in winter. Publ. Seto Mar. BioI. Lab. 9: 373-378. Pope, E. C. 1945. A simplified key to the sessile barnacles found on the rocks, boats, wharf piles and other installations in Port Jackson and adjacent waters. Rec. Aust. Mus. 21: 351-372. Riedl, R. 1. 1971. Water movement. Pages 1085-1088 and 1124-1156 in O. Kinne, ed. Marine ecology. Vol. I, Pt. 2. Wiley-Interscience, London. Southward, A. J. and D. J. Crisp. 1965. Activity rhythms of barnacles in relation to respiration and feeding. 1. Mar. BioI. Ass. U.K. 45: 161-185.

DATE ACCEPTED: January 6, 1983.

ADDRESS: Zoology Building. A08. School of Biological Sciences. The University of Sydney. Sydney. N.S. W. 2006. Australia.