Contributions to Zoology, 68 (4) 245-260 (2000)
SPB Academic Publishing bv, The Hague
Pyrgoma kuri Hoek, 1913: a case study in morphology and systematics of a
symbiotic coral barnacle (Cirripedia: Balanomorpha)
Arnold Ross & William+A. Newman
Scripps Institution of Oceanography, La Jolla, California 92093-0202, U.S.A
atrial Keywords: Pyrgomatidae, passageways, chemical mediation, parasitic dinoflagellates
“Whoever attempts to make outfrom external characters alone, Systematics 247 without the valves will almost Chemical mediation between barnacle and host 254 disarticulating ... certainly fall
into errors 259 many ...” Acknowledgements
Charles Darwin, 1854 References 259
Abstract Introduction
The of from the systematics pyrgomatids, stemming early 1800’s, During 1899 and 1900 H.M.S. “Siboga” explored has been based the number of traditionally on plates making up the waters of the Netherlands East Indies, or what the wall (six, four or one) and specializations in the opercular Indonesia. is now largely known as The “Siboga”, plates. A recent study ofthe related bryozobiines focused attention some 50 m in length, takes its name from a town on detailed structural modifications ofthe basis, which we now
on the west coast of Sumatra. find also applies to some highly derived pyrgomatids and an Although originally
archaeobalanine. Reexamination of the Indonesian coral barnacle designed to be a gun-boat it was retrofitted as a Pyrgoma kuri Hoek, 1913 has revealed previously unknown research vessel prior to completion. Under the lead-
morphological features, including separable opercular plates, a ership of Max Weber (Pieters & De Visser, 1993), and basis lined with ladder arch-like true tergal spur, a to the shipboard party collected samples at 323 sta- calcareous structures covering “atrial passageways”. Thus, the
tions, from shore to of 4400 m. A present study expands our knowledge of such specializations depths nearly
total of 114 and our understanding ofthe evolution and relationships ofthe species of barnacles were collected,
derived pyrgomatids as well as the archaeobalanines and 75 of which were new to science including an bryozobiines. The complex modifications ofthe basis found in unusualcoral-inhabiting pyrgomatid (Hoek, 1913). these three function for chemical groups evidently as an avenue The systematics of pyrgomatids traditionally has mediationofgrowth between the barnacle and its host. Although based been on the number of monophyly ofthe archaeobalanines and bryozobiines based on plates comprising
such structures is possible, there is no obvious connection bet- the wall (six, four or one) and on modifications of
ween them and the few derived in which these pyrgomatids the opercular plates (Leach, 1817, 1818; Gray, 1825;
features occur. There is apparently a propensity toward such Darwin, 1854; Hiro, 1931, 1935; Nilsson-Cantell, modifications in archaeobalanids resulting in parallel evolution 1938; Ross & Newman, 1973; Newman & Ladd, in association with different hosts corals distinctly (e.g., sponges, 1974; Galkin, Anderson, It was not and bryozoans). 1986; 1992). until recently that specializations involving (1) the
wall and feeding appendages (Ross & Newman,
Contents 1969, 1995), (2) the modified scuto-tergal flaps or
apertural frill (Anderson, 1992), and (3) the basis
Introduction 245 (Ren, 1986; Anderson, 1992) were noted and in
Material and methods 246 part utilized in classification (Anderson, 1992; Ross
of Terminology opercular plates 246 & Newman, 1995, 1996). 246 A. Ross & W.A. Newman - coral barnacle Pyrgoma kuri; a symbiotic
A study of distant relatives of the pyrgomatines, between archaeobalanines and bryozobiines, but
the bryozobiines, focused attention on detailed it appears to have evolved independently in pyrgo-
structural changes to the basis and wall (Ross & matines. However, the basis for the structure, chemi-
Newman, 1996). We now find such changes also cal mediation between the barnacle and its host, is
apply to some derived pyrgomatines and to an apparently well established in thearchaeobalanines
archaeobalanine. The present study not only ex- and their allies.
pands our knowledge of such changes in the ba-
sis, it also has a significant impact on our under-
standing of the evolution of the pyrgomatids and Materials and methods
their distant relatives among the archaeobalanids.
As in Bryozobia synaptos Ross & Newman, 1996, Armatobalanus terebratus (Darwin, 1854). - “Siboga” station
257, Duroa Strait, Kei Is, complex modifications of the basis, and to some (Kepulauan Kai); approx. 5°40’S, 52 Dec. 11, Zoologisch Museum Amster- the I32°44’E, m, 1899, extent wall, also likely involve chemical me- dam (ZMA) Cirr. 2038777. diation between it and its host. This has profound - Pyrgoma kuri Hoek, 1913. “Siboga” station 251, offKur as well as evolutionary systematic implications I., Moluccas, 5°28.4’S, 132°0.2’E, 204 m, Dec. 8, 1899, ZMA
because, while monophyly of these structures be- Cirr. 100.324. The wall and opercular plates described and
tween the archaeobalanines and bryozobiines is illustrated by Hoek (1913: 259, pi. 27, fig. I, wall of left speci-
men, see Fig. 1C (arrow) herein, and Hoek’s fig. 2, opercular possible, there is no obvious structural continuity plates) could not be located. The remaining complete, but between these structures in the foregoing and the originally undissected specimen, shown in apical view in Hoek
pyrgomatines. is described and illustrated herein, and it is designated the
Among the specimens collected by the “Siboga”, lectotype.
those taken off Kur Island in the Banda Sea in- Hoek encountered problems prying off the first specimen,
having broken the tipofthe steel tool he was using which remains cluded two pyrgomatid barnacles attached to the embedded in the coral. Therefore, we used a small hand-held, same solitary, ahermatypic, caryophyllid coral. electric-driven diamond-coated wheel to remove the remaining These obligate symbionts were described as Pyr- specimen from the host coral. The cut was placed so as to leave
kuri Hoek (1913), and none has been found of goma by a small portion the basis intact on the coral (Fig, 3C). The
soft then removed below. since. parts and opercular plates were from
The wall and the coral were soaked overnight in a 5.25% solution As part of our ongoing studies of pyrgomatids, ofsodium hypochlorite (commercial bleach), and the opercular P. we decided to reexamine kuri. Among the fea- immersed plates were for about 30 minutes to remove adhering tures especially in need of reevaluation was the tissues. Contrary to expectations the scuta and terga disassociated both the presence of sutures on surfaces of oper- in the then transferred the process. They were to water, remaining
which cular plates, were purportedly “calcified” adhering cuticle removed with a fine-tippedartist’s brush, rinsed
several times in together and therefore inseparable. We also wanted tap water, and air dried.
The opercular plates, wall with the principal ofthe ba- evaluate the which part to various parameters of tergum, : sis, and the coral were mounted on aluminum stubs with dou- is similar to that of Pyrgoma cancellatum Leach, ble-sided tape, sputter coated with gold-palladium,viewed and 1818 several related and species. then in photographed a Cambridge S360 scanning electron
In addition, our dissection of the lectotype re- microscope operatingat 3 to 10 kV. The specimens of. A. terebra-
vealed previously unappreciated features similar tus were similarly prepared and photographed. Procedures for the preparation of soft are detailed in to structures described earlier in bryozobiines (Ross parts Newman & Ross (1971: 17). We elected to mount the mouth & Newman, 1996), and mentioned briefly in pass- parts and cirri on a single glass slide using glycerin jelly. The Ren Anderson and ing by (1986), (1992) Ogawa muscles and of the and opercular remaining portion prosoma ct al. it (1998) in other species. Furthermore, was thorax are stored in 80% ethanol. necessary to restudy the archaeobalanid.Armatoba- lanus terebratus (Darwin, 1854) also collected by the “Siboga” off the Kei Islands, because Darwin Terminology of opercular plates
(1854) and Hoek (1913) had noted that the basis in this species has tissue-covered perforations. This The terminology employed in the past for describing the
of the the lead different unusual feature could be indicative of monophyly relationship scutum to tergum can to the interpretations. Therefore, we suggest avoiding terms “fused” Contributions to Zoology, 68 (4) - 2000 247
and “concrescent” when the applied to opercularplates. Instead, transversely elongate, adductor ledge large, extend- the following criteria and terms, to describe their relationships ing below true basal margin, rostral tooth present; are recommended: tergum with true spur. Separate. - Movably articulated together and readily disarticulated Type species: Pyrgoma cancellatum Leach, 1818, manually, but commonly treated with bleach before attempting
their separation to avoid breakage. by original monotypy; Recent, Shirahama, Honshu
Cemented. - bound cement that is Immovably together by a I., Japan, 33°39’N, 135°22’E; on Turbinaria
or immersion in bleach before partly wholly destroyed by contorta Bernard.
separation occurs.
- Calcified. Secondary deposition ofcalcareous material on the
Remarks. - Pyrgoma is related to Hiroa Ross & internal surface therebyobliterating the suture, not separable in
bleach. Newman, 1973, and to a new genus from Taiwan
- Fully calcified. No evidence ofanexternal or internal suture (Ross & Newman, 1999). Hiroa has separate wall between plates, not separable. that it from the new and plates distinguish genus, When the opercular plates are articulated they are either from and Pyrgoma, separate opercular plates similar the separated by integument, or the suture may simply be filled to those of Pyrgoma which distinguish it from the with organic cement. The absence ofa suture line on the interior
ofthe indicates new genus. What allies these genera is the trans- plates they are calcified together. We know of no example where a suture line is visible internally but not versely elongate scutum having a large adductor externally. ledge and a prominent rostral tooth (lacking in
The use of commercial bleach in the above definitions,which and the Hiroa), tergum having a true spur (“...a has replaced potassium hydroxide (= caustic potash, Darwin, projection...on the basal margin” Darwin, 1854; 1854: 3) stems from its common use in removing tissue adhering 52). to the calcareous parts of barnacles (Newman & Ross, 1971;
Anderson, 1992; Ross & Newman, 1995; Ogawa et ah, 1998).
When used with discretion it has little obvious effects or no on
the parts themselves. Pyrgoma kuri Hoek, 1913
(Figs. 1-5)
Systematics Pyrgoma kuri Hoek, 1913: 259; Hire, 1931: 155; Hire, 1935
25; Nilsson-Cantell, 1938: 70 (relationships).
Nobia Family Pyrgomatidae Gray, 1825 kuri; Ross & Newman, 1973: 155 (opercular plates); Newman & Ross, 1976: 58 (references); Ogawa & Matsuzaki, Subfamily Pyrgomatinae Gray, 1825 1992: 95 (host coral). (nom. transl. Ross & Newman, 1973 [ex Pyrgomati- Paranobia kuri; Galkin, 1986: 1293 dae Gray, 1825])
Tribe Pyrgomatini Gray, 1825 Supplementary description (lectotype). - Wall and (nom. transl. Ross & Newman, 1995 [ex Pyrgomati- opercular plates white in preserved specimen; wall nae Gray, 1825]) dome-shaped, with periphery growing vertically
rather than obliquely from the basis (Fig. 2E); Genus Pyrgoma Leach, 1817 surface ornamented with 24 low, broadradial ridges
in various stages of overgrowth by the coral (Fig. Pyrgoma Leach, 1817: 67; Leach, 1818: 171; Darwin, 1854: 2F); orifice ovate, rostro-carinal diameter less than 354 (synonymy); Ross & Newman, 1973: 156 (synonymy, 1/3 that of wall; internal surface of wall included species); Newman & Ross, 1976: 58. smooth; sheath less than Paranobia Galkin, 1986: 1293; Newman, 1996; 503, 1/2 height of wall at rostral end,
basal margin slightly sinuous, adpressed except for
Definition (emended). - Wall low conical to flat, lateral and rostral areas where there are low ridges
solid, fully calcified (no sutures present); sheath (Fig. 3A). Basis moderately deep, enlarging to maximum diameter ladder arch- 3B: - adpressed; transverse, calcareous, to in distinct steps (Figs. nos. 1
like structures internally bridging gap between 3; C); external ribs corresponding with those on
longitudinal ribs of basis terminating at suture wall (Fig. 2E); internal longitudinal ribs with median between wall and basis; opercular plates separate sulcus to receive radial septa of wall, adjacent ribs
cemented but ladder-like or not calcified together; scutum bridged by transverse calcareous con- 248 A. Ross & W.A. Newman - Pyrgoma kuri.' a symbiotic coral barnacle
nections (Fig. 3B, C), becoming arches as basis
develops (Fig. 4B).
Scutum transversely elongate (Fig. 2A), with
large, depending adductor ledge; apical angle 58°;
growth ridges simple; occludent margin toothed,
slightly convex; tergal margin straight, less than
1/2 length of occludent margin, ratio of occludent
to tergal margin 2.29 : 1; basal margin sinuous,
longer than tergal margin; articular furrow narrow,
shallow; adductor ledge depending, basal margin
not paralleling true basal margin; rostral tooth long,
bluntly rounded, slight irregular ridges on upper
surface for insertion of lateral depressor muscle;
adductor muscle depression large, ovate, deep,
medial (Fig. 2C). Tergum higher than wide (Fig.
2B), height to width ratio 1.78 : 1, apical angle
external 90°; longitudinal furrow open; growth
of ridges furrow reflected on internal surface (Fig.
distal end of articular 2D); spur truncated; ridge
cuneiform; muscle crests with subsidiary ridges,
separated from spur by shallow depression (Fig.
2D).
Labrum with one tooth on each side of notch; a
single row of numerous stiff setae along apical
margin (Fig. 5A). Palps ovate, medially proximate;
apical margin with short slender setae; setae of distal
margin longer, slender; posterior face and basal
margin covered by exceedingly long, slender se-
tae. Mandible with 4 teeth and straight molariform
lower angle (Fig. 5B); teeth 2-3 bicuspid; apical
Fig. I. Pyrgoma kuri Hoek, from Hoek, 1913, pi. 27, figs. 1-2 margin with slender widely spaced setae; basal (slightly reduced). A, internal view of left opercularplates. The margin with closely spaced long, slender setae; serratebasal margin ofthe adductor ledge is likely due to breakage short, stout spines covering lateral face; left man- (cf. Fig. 2A). B, external view of right opercular plates. C, dible with malformed tooth 4 in situ. due constraints and artiitic apical tooth, barnacles Apparently to space simple
Hoek oriented the coral Maxilla I with license, upside down, as shown here. or bicuspid (Fig. 5C). single, long,
The rostro-carinal axis of both barnacles is with the aligned stout, bifid spine above subapical notch (Figs. 5E, long axis ofthe coral, with the carina in the lectotype orientated F); 4-5 short slender spines in notch; medial clus- towards the expanding calyx. The specimen on the left (arrow), ter bearing 6 long, stout spines; basal cluster with in side view, is the one dissected by Hoek, but it apparently has 7 shorter, slender spines; apical and basal been lost. The other, the lectotype (ZMA Cirr. 100.324),is shown margins slender in Figs. 2-5. clothed with setae; lateral face armed with
Fig. 2. Scanning electron micrographs of Pyrgoma kuri Hoek (lectotype, ZMA Cirr. 100.324). A, external view of right scutum. Note the continuous smooth ofthe external of the furrow. margin adductor ledge. B, view right tergumshowing open spur C, internal view of left scutum. D, internal view ofleft tergum. Note the crests do not extend beyond the basal margin (cf. Fig. 1A, B). E, lateral view ofright side ofwall and apical portion ofthe basis, carinal end at right. Note narrow seam between wall and basis and the continuity ofthe atrial with the ofthe wall. Both wall and basis covered coral passages spaces between septa are by overgrowths, F, apical view ofwall. Note of between ribs the coral. The of orifice partial to complete roofing over spaces by perpendicular surface the appears uniformly worn resulting from cirral rasping, which also produced the notch in the carinal end ofthe wall. - Contributions to Zoology, 68 (4) 2000 249 - 250 A. Ross & W.A. Newman Pyrgoma kuri; a symbiotic coral barnacle
Fig. 3. Scanning electron micrographs of Pyrgoma kuri Hock (leototype, ZMA Cirr. 100.324). A, internal view ofwall and sheath,
carinal end at left. At the rostral end (right), there are diverging raised areas between which there is a sulcus to accommodate the
curvature ofthe scuta. The raised lateral to the left ofthe mid ofthe orifice accommodate the inflected of areas, slightly point portion - Contributions to Zoology, 68 (4) 2000 251
slender spines. Maxilla II tall, bilobed (Fig. 5D); Weltner, here assigned species rank, P. projectum basal lobe shorter and with fewer setae than apical Nilsson-Cantell, and Nobia sinica Ren, suggests lobe; anterior border of apical lobe bearing mod- all of these also should be included in Pyrgoma. erately long setae. Pyrgoma kuri differs from P. projectum in hav-
I than few Posterior ramus of cirrus less 1/2 length ing only a tergal crests and these extend to or of anterior ramus (Fig. 5G); basal segments of barely beyond the basal margin (cf. Figs. IB, 2B).
wider than The for cirri I-Ill identical in these anterior ramus high, rapidly tapering counts are spe-
11 to higher than wide. Cirrus about 2/3 length of cies, but there are differences in the others and in cirrus I and 3/4 length of cirrus III (Fig. 5H); rami the opercular plates and trophi. Although Nilsson- subequal, articles slightly wider than high. Rami Cantell (1938: 71) stated they may be one and the
them of cirrus III subequal; anterodistal margins bear- same species, we consider to be distinct.
The muscle P. sinica ing a few ctenoid scales and short, acicular spines. tergal crests of are more
Cirrus IV with subequal rami; somewhat shorter numerous and extend well beyond the basal mar- and with fewer articles than cirri V and VI. Cirrus gin, more so than in P. projectum. These crests
4 in P. VI having equal rami; setation ctenopod, pairs are lacking cancellatum and P. japonica. The
2 3 P. (Fig. 5J); 1 or short slender setae at base of tergum in cancellatum is dwarfed by compari- apical pairs of setae; 2-3 short to long setae at son with the scutum; its apical portion is the smallest
about the it the posterodistal angle, longest seta 2/3 length of species, and has narrowest spur which, of article; ratio of anterodistal setae to width of like, the apical portion, becomes progressively wider article 5.1 Basi-dorsal of intromittant in P. P. and P. ; 1. point organ P.japonica, kuri, projectum, lastly
Intromittant The rostral tooth of the is far large, triangular, apex acute (Fig. 5K). sinica. scutum by
of cirrus and slender in organ about 3 times length VI; setae in 4 longer more P. sinica, becoming
distal end in clusters. broader and shorter in fol- longitudinal rows; setae at progressively P. kuri,
= = anterior lowed and Cirral counts follow (a ramus; p pos- by P. cancellatum, P.japonica, P. pro-
terior = ramus; xx damaged ramus); jectum.
I II III IV V VI Wall orientation. - Although the two specimens
21/xx right (a/p) 15/7 8/7 9/7 17/19 xx/23 of P. kuri settled approximately 90° apart (Fig. 1C) left (a/p) 14/5 7/6 10/8 16/19 21/23 23/23 and perpendicular to the major axis of the coral
(Fig. 1C) neither appears to have settled on the
Lectotype not brooding eggs. rim ofthe coral as is commonly the case in Mega-
- in Remarks. Cirral counts for the first three cirri trema anglicum (Sowerby; see Ross & Newman,
the specimen that Hoek dissected (11/6, 8/7 and 1973: fig. 1). The original orientation of the host
those of the coral is 9/8) are similar to those above, but unknown, but both barnacles likely had a last three (16-17, 18-19 and 20-21) have fewer preferred orientation on its surface. The polarity
segments than those of the lectotype. Hoek stated of the rostro-carinal axis of the specimen Hoek
the removed could be it there were two teeth on each side of labral cleft not determined, although was
in the specimen he dissected, but we found only aligned with the long axis of the coral. However,
it one in the lectotype. was likely as in the lectotype, which similarly
Ross & Newman (1973) and subsequent work- aligned, had the carina oriented toward the rim of
considered cancellatum to be the sole the coral. ers P. rep-
resentative of Pyrgoma. Our evaluation herein of
P. kuri, as well as P. cancellation var. japonica Parasites. - Between the setae at the juncture of
the scutum. B, enlarged view ofbasis of specimen removedby Hoek. After initialformation the basis expanded laterally to essentially
maximum diameter in three steps (1-3). In certain areas the initialatrial openings are simply ovate (cf. Fig. 6C). C, enlarged view of
basis of lectotype. The spaces between the uniform ladder-likerungs have been filledsecondarily by calcareous material presumably
of coral tissue from how the atrial arches confluent upon withdrawal the beneath. Note passages beneath the atrial are with comparable
in the skeleton ofthe coral passages (cf. Fig. 4B). - 252 A. Ross & W.A. Newman Pyrgoma kuri; a symbiotic coral barnacle - Contributions to Zoology, 68 (4) 2000 253
Fig. 5. Trophi and cirral appendages of Pyrgoma kuri Hoek (lectotype, ZMA Cirr. 100.324). A, labrum and right palp. There is only
mandible. left mandible one tooth on the left side. B, right C, with “abnormal” bicuspid apical tooth. D, maxilla II. E, enlarged view
ofcutting edge of maxilla 1. F, maxillaI. G, cirrus I. H, cirrus II. I, cirrus HI. J, intermediate article of cirrus VI. K, basidorsal point
of below cirri I-III the cirral the anterior intromittent organ. Fractions are counts, with ramus preceding the posterior.
Fig. 4. Scanning electron micrographs ofPyrgoma kuri Hoek (lectotype, ZMA Cirr. 100.324). A, external view of seam between wall
and basis. Note the and the horizontal of of the basis that will be the open suture narrow zone vertical growth likely overgrown by
coral. internal lower ofthe basis removed, the arch-like roof of the atrial well their B, view, portion showing passages as as relationship
in the wall and coral skeleton. view ofthe left shown to passages C, enlarged side in B. Both margins ofthe sulcus between the arches
are dentate, and a depression above the uppermost denticle prevents the wall from being driven downward. 254 A. Ross & W.A. Newman - Pyrgoma kuri; a symbiotic coral barnacle
the protopod and rami of cirrus II and III and else- ordinately long. According to Crisp (1954: 476)
where on the other cirri there are numerous small, length “...is a function of the size of the individual.”
unicellar from 2.75 found the number of annula- ovate, organisms ranging pm Barnes (1992: 486)
x 1.63 3.75 x 2.0 x 1.67 but pm to pm pm (=3.22 pm tions to vary between species, not with “...the
= pm, n 11). They have been identified as a para- size ofanimal within a species once it has reached
sitic dinoflagellate possibly related to Ellobiopsis the size of maturity.” The number of annulations
which known because the chattoni Caullcry, is to parasitize gives no indication of length length
copepods (Wickstead, 1963; Timofeev, 1997; R. of each annulation varies. There are about 232
This is the first known annulations in with A. Lewin, pers. comm.). P. kuri, the number changing
occurrence of this type of parasite on a barnacle. from 18/mm proximally to 25/mm distally. Also,
the diameter of the annulations diminishes gradu-
- Malformation of trophi. The right mandible in ally from base to tip where they are about one-
the lectotype (Fig. 5B) is considered normal whereas half the size, as in Balanusbalanus Linnaeus (Klepal
the bifid tooth the left “mal- apical on appears et al, 1972).
formed.” The absence of on the The the of the in a subsidiary cusp setae along length penis occur
third tooth is not viewed as abnormal because not four distinct rows but they do not occur in pairs or
uncommonly the mouth appendages are bilaterally multiples as in B. balanus (Klepal et al., 1972).
in asymmetrical this regard. Nilsson-Cantell (1938: Also, some annulations are apparently devoid of
72) also commented on the asymmetry of the setae.
mandibles in P. projectum. The penis is generally capable of considerable
Hoek (1913: 260) found two large apical teeth extension, some three to four times its resting length
on maxilla I whereas the right maxilla of the lec- (Klepal et al., 1972: 246). If the resting length of
11 totype is distally bifid (Fig. 5E). The other max- mm in the lectotype were increased by a factor
illa was lost. Apparently these appendages were of three, it would have been sufficient to reach the damaged early in life, and surprisingly, they did other individual on the coral.
not fully regenerate during subsequent molts.
Cirral damage. - The distal portions of the right Chemical mediation between barnacle and host
posterior ramus of cirrus V as well as the anterior
VI miss- ramus of cirrus are missing. Damaged or Two avenues for chemical mediation between coral
ing appendages are often found in barnacles liv- barnacles and their hosts have been recognized.
ing in shallow waters and the intertidal zone where The first is associated with the suture between the
1854: visual predators are common (Darwin, 158; wall and basis (Fig. 4A; Moyse, 1971: 137; Ross have Barnes, 1992: 516). Although we not observed) & Newman, 1973: 143). The second is the apertural similar mishaps in other pyrgomatids, it is not likely frill (Anderson, 1992: 305), an elaboration of the
in hand. In the the unique to the specimen present case scuto-tergal flaps that guard aperture between it is the barnacle lost the of these probable tips the opercular plates. The uniquely pigmented scuto-
to rather than to the coral. appendages a predator tergal flaps in pyrgomatines (Anderson, 1992) may
also contain structures believed to have a chemosen-
Intromittent - The intromittent is in- function & organ. organ sory (Foster Nott, 1969).
Fig. 6. Scanning electron micrographs ofthe gregarious “coraf’-dwelling Armatobalanusterebratus (Darwin), “Siboga” station 257,
Kei Is. (ZMA Cirr. 2038777).A, lateral view ofwall and basis. Note the projecting buttresses or “holdfasts” on the basis that anchor the barnacle to the substratum or to adjacent barnacles, the shell of one ofwhich can be seen in the lower left. B, enlarged view of external surface of between wall and basis and the atrial in the basis. Note the in the base seam perforations or passageways slight gap ofthe radius (arrow) between the rostrum (R) and the carinal latus (CL 1 ) reminiscent of the first whorl of atrial openings found in the archaeobalanidBryozobia (Ross & Newman, 1996), C, enlarged view ofinternal surface ofwall and basis. Note the sulci, into which the radial septa ofthe wall fit, have been filledsecondarily by the barnacle (cf. Fig, 3B, C, in which the sulci have been filled in older
ofthe parts basis, and Fig. 4B, in which the sulci are still open). Contributions to Zoology, 68 (4) - 2000 255 A. W.A. Newman - 256 Ross & Pyrgoma kuri.- a symbiotic coral barnacle
Atria, only recently described(Ross & Newman, these structures begin ontogenetically, as in P. kuri,
1996), are another avenue for mediation. These are as simple ladder-like, tissue-covered perforations,
become arches relatively simple to complex passageways formed but subsequent rungs (Figs. 3B, C,
the by the barnacle between its basis and host’s 4B, C). These cover the coral tissue-fdled passage- skeleton. In A. terebratus atria appear in the sim- ways radiating from essentially the center of the plest form known, as a single or double row of basis to the seam between the wall and basis and
1854: membrane-covered perforations (Darwin, terminating between the external radial ribs on the
286) radiating from the center of the cup-shaped wall. The coral tissue filling these passages con- basis (Fig. 6C). Darwin (1854: 285) noted that A. tinues up between the radial ribs on the wall and terebratus was attached to a lamelliferous coral terminates shortly before reaching the orifice of and therefore it might be tempting to speculate the the barnacle (Figs. 4, 2E, F).
Another perforations were to facilitate mediation between cirriped having similar passageways is the barnacle and the coral. However, the barnacle the archaeobalanid Bryozobia synaptos Ross & and coral were simply skeletons when Darwin Newman, which lives on bryozoans. Openings for described whether the coral their atrial become into them, so or not was passageways incorporated
it the living when the barnacle grew on is unknown. wall during ontogeny, but otherwise their struc-
Living specimens ofA. terebratus were collected ture is comparable to that of Pyrgoma. They start by the “Siboga” and described by Hoek (1913: 207). out as simple perforations through the calcareous
the Although attached to a coral skeleton, Hoek noted basis, as in A. terebratus (Fig. 6B, C), but lad- that these der-like similar arch- gregarious specimens were overgrown rungs subsequently change to
We have in P. Some by a “sponge-like organism.” studied this like structures, as kuri (Fig. 4B, C). of
is in in material, and it definitely a yellow sponge that the latter open the radii whereas others open
between the where become elevated invades the atrial passages and the space parietes they ultimately the calcareous substrate and the barnacle as well above the substratum with growth (Ross & Newman, as between barnacles when one has partially over- 1996).
another. it if chemical Ren did not comment on the function or grown Therefore, appears, (1986)
the and of the he mentioned mediation occurs, it is between sponge significance structures briefly
which it did et al. Anderson’s barnacle rather than the coral upon hap- nor Ogawa (1998). However,
be had Darwin of hav- pens to growing. Parenthetically, (1992; 337) study P. cancellata, a species
“... small cirral seen this material he may have been compelled ing a reduced orifice and a relatively to have ranked [terebratus] in ...Acasta.” However, net, led him to suggest these structures “...raise
the reduced external true Acasta not only settle directly on sponges, rather possibility that a feeding
indi- in than on solid calcareous substrates, but also mechanism is compensated some species by
of the coral viduals are not known to attach to each other. Thu,s uptake dissolved nutrients from host”, terebratus is retained in Armatobalanus. but no evidence of nutrient transfer was found in
What aboutbarnacles that are obligate symbionts a distantly related form (Cook et al., 1990). In the of corals? Ren (1986: 157) noted one of the fea- Hoekiini there is not only an extreme reduction of
P. sinica the of the but also elaboration of tures characterizing was presence thoracopods, an poten-
“...narrow and an unusual basis having radial grooves tial absorptive surfaces thereforenutrient trans- between thick ribs, which are imperfectly calci- fer in these seems likely (Ross & Newman, 1969, fied and sculptured with rows of slightly curved 1995). However, at the same time there are other transverse ridges, and covered with brownish interactions between barnacle and host related to membrane.” Anderson (1992: 305) commented on coordinating rates of growth. a similar structure in specimens referred to P. Pyrgomatids only settle on and penetrate the soft cancellatum, noting the presence of passages that tissue of actively growing surfaces of the host coral.
Once attached their live for are “...tubular, thin-walled and uncalcified except to skeleton, they may for calcified several 1973: transverse ring thickenings. Narrow years (Ross & Newman, 142; Newman gutters separate the tubular ribs.” We have found & Ladd, 1974). Should the rate of growth of the Contributions to Zoology, 68 (4) - 2000 257
host exceed the then and in that barnacle overgrowth similar some respects to in explaining the entombment of the barnacle follows. Conversely, situation in Bryozobia, and a similar scenario could
barnacle in more rapid growth by the would result probably be applied to the situation involving A. its protruding well above the corallum, thereby terebratus namely inducing the host to satisfy the , becoming more exposed to predation and fouling. needs of the barnacle.
there selection Thus, has likely been ample pres- Although it seems quite likely there has been sure for chemical mediation of growth rates in the morphological and genetic continuity between barnacle and the coral. complex atrial structures in archaeobalanids, such
Available evidence indicates have A. and there is obvi- pyrgomatines as terebratus Bryozobia, no
& an armatobalanid ancestry (Ross Newman, 1973; ous continuity with the pyrgomatids because atria
& Healy Anderson, 1990; Anderson, 1992). Pyr- are only evident in a few derived forms, and thus goma is clearly a derived genus far removed from the development of atria in pyrgomatids could be the ancestral armatobalanids and early pyrgomatids. convergent. However, there is a less complex struc-
The decided absence of atrial perforations or pas- ture anticipating atria in both archaeobalanids and
in that sageways early pyrgomatids was initially puz- early pyrgomatids effectively bridge this gap.
To zling to us. Why these atrial passages should re- fully understand the situation, we first need to
innovation chemical mediation appear as a parallel may relate to the look at examples where be-
habits of the host the barnacle growth corals, i. e., slow growing tween and its host is either negligible and/or rapidly spreading corals that do not sub- or absent.
thicken their skeleton tend leave the In the archaeo- stantially to conopeans, among 6-plated
the with barnacle behind, or do not thicken enough to keep balanids, relationship the gorgonian hosts the basis of the barnacle covered. Therefore, these is apparently largely physical. Species such as
be for passageways may an avenue mediating the Conopea galeata (Linnaeus) generally become localized growth of the coral skeleton. established by settling where the axial skeleton of
The foundation for this hypothesis follows; the host has been exposed by damage (Gomez,
kuri on a horn coral. The As the barnacle it Pyrgoma grows solitary 1973). grows can force its way corallite of such corals enlarges disproportionately between the axial skeleton and undamaged spicule- with little if skeleton is added tissues of the host. The host also growth, whereby any bearing overgrows to the older portions. Furthermore, soft tissue of the enlarging shell of the barnacle commonly form-
tends the oldest the coral to withdraw from parts. ing functional polyps on its surface, and therefore
Consequently, when P. kuri settles on the column the gorgonian is treating the shell of the barnacle of such it a coral, may not only loose the protec- as self. Apparently the tissue of the gorgonian is tion of the coral skeleton it as grows, but coral stretched rather than broken along the wall-basis tissue withdraw from it well. It may as apparently and radial sutures of the barnacle during diamet- overcomes these problems, without giving up this ric growth. Furthermore, host tissue is prevented
coral with otherwise open niche, by inducing the to treat from interfering the orifice and aperture largely
its exoskeleton as coral rather than barnacle. Thus, by the mechanical activities of the opercular plates
of coral and we see a thick layer skeleton surrounding the cirri, which are armed with hooks as in
P. kuri as it above the surface of armatobalanids in If there is grows general general. any chemi-
How Most the coral. might this be accomplished? cal mediation at all, where it occurs is not obvious
between likely by chemical mediation barnacle and because the radial sutures as well as that between
coral tissues the membranesassociated with the wall and basis the through boat-shaped are among tight- the in the atrial in the basis openings passageways est fitting seen in balanomorphs.
would be of the barnacle. This the reverse of the Megabalanines are 6-plated, generally free-liv- process taking place at the suture between the wall ing, albeit opportunistic balanids, but M. stultus and the basis of such barnacles where coral skel- (Darwin, 1854: SIO C-9722) and M. ajax (Dar- eton production is inhibited from sealing the suture win, 1854; SIO C-9944) of the tropical West At- with skeletal material This scenario is Indo-West (Fig. 4A). lantic and Pacific, respectively, are - 258 A. Ross & W.A. Newman Pyrgoma kuri; a symbiotic coral barnacle
associated with the fire coral Millepora (cf. Ross, come intobroad contact with the coral, there seems
the be ofcoral skeleton the 1999). These are quickly overgrown by coral, to no breakage along open
but continue wall-basis This a lack of calcifi- to grow diametrically by breaking suture. suggests
rather than inhibiting growth of the coral skeleton cation there and hence chemical mediation. When
covering the wall-basis and radial sutures. In both growth of the barnacle apparently slows, this su-
thin species, skeletal tissue is deposited within the ori- ture becomes a mere line similar to that seen
the these barnacles able in fice and on scuta, yet are conopeans, and we have observed similar se-
to maintain an operable operculum also likely nescent conditions in pyrgomatids. Therefore, the
in entirely by mechanical means. system ofgrowth seen this species is essentially
the in Similarly, 6-plated Hexacreusia durhami the same as that found early 4-plated pyrgomatids
(Zullo, 1961), living on Porites in the Gulf of (Ross & Newman, 1973).
California (Ross, 1962), repeatedly breaks its way From the foregoing, while evidence for chemi-
it and in cal mediation is universal in bar- as grows diametrically upward keeping not symbiotic
with of the host where it it is involved in pace growth (SIO C-5885). How- nacles, occurs prevent-
in the the rim of of the wall-basis host ever, contrast to megabalanines, ing overgrowth suture by
the orifice and opercular plates are devoidof coral. skeleton, and it is apparently developed to vary-
in In fact, the coral simply extends to the orifice where ing degrees a numberof armatobalanids associ-
ated it ends in a clean line, suggestive of cirral rasping with corals. Chemical mediation also takes
rather than mediation via an apertural frill or the place at the orifice, where it prevents interference
chemical erosion by the latter. Evidence that Hexa- by the coral with the activities of the operculum
creusia apparently relies on mechanical breakage and hence with feeding and other activities of the
rather than chemical mediation at the wall-basis barnacle (Anderson, 1992). However, the primary
suture is a situation we have not observed in site remains the suture between the wall and basis
pyrgomatids, and thus there is no justification for where, while preventing deposition of skeletal the assumption (Zullo, in litt. in Newman, 1996) material, soft tissue of the coral is free to deposit
Hexacreusia is more appropriately placed in the skeletal material on either side of the suture (Fig. pyrgomatids than in the armatobalanines. 2E).
A better model of the ancestral armatobalanine In most moderately fast-growing corals tissue
Armatobalanus leading to the pyrgomatids is circe is relatively superficial, so the open wall-basis suture
(Kolosvary) dwelling on the branching coral apparently provides ample surface area through
Stylophora danae Milne-Edwards & Haime from which to chemically inhibit coral skeleton while
the Indies settles the side soft tissue the East (SIO C-6013). It on allowing to overgrow suture. But of a branch, and develops a largely free-standing, what about when on slowly growing corals? The deeply cup-shaped basis capped by a diametrically \ barnacle can outpace its hosts growth and thus growing, 6-plated, conical wall. The whole bar- become exposed. Or conversely, on corals that tend nacle extends outward at an angle from the coral, to withdraw tissue from the older parts of the skel- and during its growth soft coral tissue covers it, eton, the barnacle can be left without the advan-
subsequently secreting a thin layer ofprickly coral tages of having living coral tissue depositing skeletal
skeleton. The side of the barnacle closest to the material around it. In such cases it would be ad- coral acquires a thicker layer of skeletal material vantageous to induce the host into favoring the
the it than elsewhere, especially the portion of wall barnacle as though were an actively growing area where the coral establishes corallites encircling the of the coral, and this could require a more exten- orifice. The generally thin skeletal covering on the sive contact zone for chemical mediation such as rest of the wall forms curiously elevated ridges that provided by an atrial system. The same can associated with the breakage plane along the carinal be said for barnacles like A. terebratus stimulat- side of each and these divide around it the suture, ridges may ing sponge growth through exten- corallites that straddle them. However, until the sive surfaces in the basis and comparable scenarios skeleton the on wall has thickened sufficiently to apply to bryozobiines as well as certain pyrgo- Contributions to Zoology, 68 (4) - 2000 259
matids. In fact, derived forms ofPyrgoma, including ofTritonia festiva (Stearns) with comments onother tritoniids (Mollusca; Opisthobranchia). Veliger 16: 163-165. P. kuri and P. cancellatum are associated with either Healy JM, Anderson DT. 1990. Sperm ultrastructure and its the slower slower-growing corals, or growing por- phylogenetic significance. Rec. Australian Mus. 42: 1-26. tions of them. Hire F. 1931. Notes on some new Cirripedia from Japan, Mem.
It is important to note that atria in the basis are College Sci., Kyoto Imp. Univ. (B) 7: 143-158.
Hiro F. 1935. A of built study cirripeds associated with corals occur- simply as periodic replications of the gap along ring in Tanabe Bay. Rec. Works Japan 7: 1-28. i. oceanogr. the wall-basis suture, e., there is in essence a Hoek PPC. 1913. The Cirripedia ofthe Siboga-Expedition. B. continuity of atrial structures between all three Cirripedia Sessilia. Siboga Expect. 31b: 129-275.
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of the J. Biol. Ecol. 10: gest the appearance of the complex manifestations histology cirripede penis. exp. mar.
243-265, of this junction in pyrgomatids remained latent until Leach WE. 1817. Distribution systematique de la classe des rather need arose in derived forms, than that atria Cirripedes. J. Phys. Chim. D’Hist. nat. 85: 67-69. in were either lost or nonexistent early forms. Leach WE. 1818. Cirripedes. In: Supplementto the fourth and
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late Ellobiopsis chattoni (Protozoa: Mastigophora) on the Received: 10 May 1999