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). Downloaded from Brill.com10/11/2021 01:57:26AM via free access 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” Downloaded from Brill.com10/11/2021 01:57:26AM via free access 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