ASYNCHRONOUS CALCIFICATION IN JUVENILE MEGALOSPHERES: AN ONTOGENETIC WINDOW INTO THE LIFE CYCLE AND POLYMORPHISM OF PENEROPLIS MARTIN R. LANGER 1,3 ,WALID A. MAKLED 1 ,STEPHANIE J. PIETSCH 2 AND ANNA WEINMANN 1 ABSTRACT Fully calcified megalospheric juveniles were found to be closely packed within a brood chamber of the larger symbiont-bearing foraminifer Peneroplis sp. (d’Orbigny) from Chuuk Island (Micronesia). The juveniles exhibit a notable variation in size of the proloculi and various forms of test deformations. Both the size variation of the megalo- spheric proloculi and the test deformations are indicative of asynchronous calcification and are a potential source of natural polymorphism in Peneroplis. The results of this study have implications for the interpretation of abnormal shell forms as bioindicators and place constraints on the classic definition of three size classes in Peneroplis. INTRODUCTION Our modern understanding of the life cycle of benthic foraminifera has largely been influenced by the ground- breaking studies of Winter (1907) on Peneroplis pertusus from the Mediterranean Sea. Winter postulated a classic dimorphic life cycle with an alternation of sexual and asexual generations and meticulously illustrated every stage by hand drawings. In the Winter model, the sexual generation produces microspheric diploid agamonts, which in turn lead to megalospheric haploid gamonts by multiple fission (asexual reproduction). Later, the general life-cycle model was modified to include a third asexual generation, the schizont, positioned between the agamontic and the gamontic generations (Rhumbler, 1909; Ro ¨ ttger and others, 1990; Lee and others, 1991; Goldstein, 1999). The modification from the dimorphic to the paratrimorphic life-cycle model was believed to be valid for all larger symbiont-bearing foraminifera (Leutenegger, 1977). In 1993, using light and transmission electron microscopy, Faber and Lee observed that both agamonts and schizonts of Peneroplis pertusus released megalospheric juveniles and, thus, suggested that a paratrimorphic life cycle seems to be applicable to this taxon as well. Their observations were documented by light and high-resolution transmission electron microscopy. While examining benthic foraminifera for biogeographic studies from the Chuuk Island atoll system (Micronesia; Fig. 1), we discovered an adult specimen of Peneroplis sp. in the reproductive stage ready to release juveniles. The adult specimen contained numerous calcified megalospheric juveniles that were seen through the broken apertural face of the parental shell. We examined the parental test in detail and the megalospheric juveniles by high-resolution, scan- ning electron microscopy (SEM). Our observations can be integrated into the life-cycle models of Winter (1907) and Faber and Lee (1993), and they provide new insights into the reproductive biology of the larger symbiont-bearing foraminifer Peneroplis. MATERIALS AND METHODS The sediment sample containing Peneroplis specimens was collected in April 2006 within the Chuuk Lagoon atoll system south of Uman Island (Fig. 1). The Chuuk system is part of the Caroline Island group and a member of the Federated States of Micronesia. The atoll consists of 11 major islands and many smaller islets within a 64-km-wide lagoon surrounded by a protective reef. The sample site is located near the shipwreck of the WW II freighter, the Sankisan Maru, about 500 m off the southern end of Uman Island at a depth of 30 m (7u009–7u219N, 151u859 E; Fig. 1). Sedimentary sample material was collected by scuba diving, dried, and later transported to the laboratory in Bonn, Germany. The juvenile-bearing parental test of Peneroplis sp. was picked from the dried sediment sample material without prior washing. The test was inspected by light microscopy and carefully mounted on stubs for SEM examination. For full documentation, the adult specimen was SEM-photomicrographed at different high-resolution levels and from various observational angles. The parental test was carefully opened up with a picking needle to isolate the juveniles chamber by chamber. All juveniles present within the brood chamber were counted. During the course of investigation, a few megalospheres detached from the SEM stub and could not be measured. RESULTS High-resolution SEM of Peneroplis sp. showed the parental test to contain densely packed juveniles within the largest chamber (Pl. 1, Figs. 1 and 3–5). The juveniles were visible through the partly opened apertural face of the test wall. The opening of the apertural face was not inflicted by the examiners and took place prior to our examination. The rupture on the apertural face of the pre-opened chamber showed sharp, tooth-like, and somewhat irregular breakage fissures in addition to sub-rounded and rather smooth edges (Pl. 1, Figs. 3–5). The parental test was characterized by planispirally arranged, involute chambers, 10 to 11 of which were visible from the exterior (Pl. 1, Fig. 1). Close examination of the test revealed residues and suture lines of another two chambers that had already broken off the test (Pl. 1, Fig. 1; reconstructed Pl. 1, Fig. 2). The largest chamber, which contained the juveniles, thus represents the third-to-last Journal of Foraminiferal Research fora-39-01-03.3d 24/11/08 16:38:22 8 1 Steinman Institut fu ¨ r Geologie, Mineralogie und Pala ¨ ontologie, Rheinische Friedrich Wilhelms Universita ¨t, Nussallee 8, 53115 Bonn, Germany. 2 Zoologisches Forschungsmuseum Alexander Koenig, Museums- meile Bonn, Adenauerallee 160, 53113 Bonn, Germany. 3 Correspondence author. E-mail: martin.langer@uni-bonn.de Journal of Foraminiferal Research, v. 39, no. 1, p. 000–000, January 2009 0