The biology of a coelodendrid: a mesopelagic phaeodarian radiolarian
N. SWANBERG,* P. BENNETT,* J. L. LINDSEY* and O. R. ANDERSON*
(Received 17 May 1985; in revised form 5 July 1985; accepted 5 July 1985)
Abstraet--A coelodendrid phaeodarian with features diagnostic for several subfamilies is des- cribed from individual living specimens collected during mesopelagic submersible operations in the Bahamas. Scanning and transmission electron microscopy reveal features of the functional morphology of the organism which adapt it to its mesopelagic existence. There was no evidence of gelatinous material in the specimens examined, but these radiolaria maintained neutral buoyancy in vitro. There was an elaborate network of rhizopodial strands extending over the surfaces of the verticillate branches of the distal regions of the skeleton. These radiolaria readily accepted certain types of prey in the laboratory and remains of metazoan prey were found in recently collected organisms.
INTRODUCTION
PHAEODARIA are probably the least understood of the Radiolaria. Because their skeletons rarely persist in sediments (DuMITRICA, 1973; RESHETNJAK, 1971), they have not been studied extensively by micropaleontologists. Our divers working in tropical and temperate epipelagic waters of the Atlantic and Indian oceans have not encountered phaeodarian Radiolaria. Although Phaeodaria do occur in shallow waters, particularly in high latitudes (BJORKLUND, 1974; KLING, 1976; RESHETNJAK, 1966), those forms which are large enough to be studied by biologists are often most abundant below the euphotic z o n e (CAsEY et al., 1979; MORLEY and STEPIEN, 1984; SWANBERG and BJORKLUND, in press). Of the 43 species of coelodendrid and coelographid Radiolaria discussed by HAECKEL (1887), 14 were found at the surface near islands or other land masses and 26 were found below 1000 m. RESHETNJAK (1966) found coelodendrid Phaeodaria from 2000 m to the surface in the northwestern Pacific, the Sea of Okhotsk and the Bering Sea. Thus, although the features which distinguish these Phaeodaria from other Radiolaria are particularly interesting, their distribution has prevented widespread biological studies of living representatives. While participating in mesopelagic submersible operations in the Bahamas we were recently presented with a unique opportunity to directly observe, collect and study intact living specimens of a large phaeodarian, designated here as Coel6graphis sp.
PREVIOUS STUDIES
HAECKEL (1887) described two major families of closely related antler-like Phaeodaria; the Coelodendrida and Coelographida. These groups were characterized by their paired valves equipped with chambers called galea from which branched elaborate hollow tubes.
* Lamont-Doherty Geological Observatory of Columbia University, Palisades, NY 10964, U.S.A.
15
16 N. SWANBERG et al.
On the basis of their morphology he considered these two groups to be among the most complex of the Radiolaria or even of all protozoa.
The major features (Fig. 1) distinguishing the two families are the presence in the Coelographida of long paired styles (called contour spines by RESHETNJAK, 1966) extend- ing from the central skeletal mass, and a rhinocanna or nasal tube extending from the galea towards the phaeodial mass near the astropylum (the complex opening into the central capsule). The branching or anastomosing of the distal ends of the dichotomous brushes was the basis for Haeckel's subdivision of the Coelodendrida. Similarly, this and the relation- ship of the nasal tube or rhinocanna and the frenula (silica strands) extending to the various tubes were the bases for the subdivisions within the family Coelographida. RESHETNJAK (1966) removed the distinction between these two families, placing the Coelographida in the Coelodendrida, a decision adhered to by most subsequent researchers (e.g. CACHON and CACHON, 1985). The number of the styles, the structure of the galea and the dendritic or anastomosing character of the distal branches are still considered to be diagnostic traits, but the significance of the number of frenula has been dropped.
The Coelodendrida were originally described in HAECKEL'S (1862) monograph from preserved specimens. According to HAECKEL (1887) some of these were confused with
W
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Fig. 1. Schematic representation of the central skeletal mass of Coelographis sp. showing (a) astropyle, (c) central capsule, (f) frenule, (g) galea, (n) nucleus, (p) phaeodial mass, (r)
rhinocanna, (s) verticillate style, (v) valves, (w) vacuoles.
The biology of a coelodendrid 17
incomplete skeletons of some of the stylate Coeiographida. Complete specimens were obtained in later collections. In both groups HAECKEL (1887) described a "voluminous extracapsular jelly veil", enclosing the entire skeleton. There were no other observations of extracapsular cytoplasmic stucture. It is not entirely clear whether Haeckel saw these structures himself in preserved material or based his conclusions on information relayed from other collectors. HAECKER (1907) stated that the material he studied confirmed the same structures earlier described by Butscnu (1882), but it is apparent from his inferences about attitude in vivo that he never actually saw a living specimen. DOOEL (1951) ascribed the function of the complex skeletons in this group to support for this sarcodictyum or jelly veil. In this paper we present our data on the structure of the living specimens we examined. In some aspects this structure deviated widely from that described by earlier authors.
M A T E R I A L S AND M E T H O D S
Specimens of Coelographis sp. were observed and collected by the first author from the DSRV Sea Link during a joint cruise of the R.V. Sea Diver and R.V. Cape Florida in October to November of 1984. Dives were made at night to a depth of 600 to 700 m in the Tongue of the Ocean off Chubb Bay, Bahamas. Specimens were collected individually using the submarine's 10 1 detrital sampling devices (consisting of large diameter lucite tubes closed with hydraulically rotated end caps). Immediately on securing the submarine the specimens were removed from the detrital samplers to 500 or 1000 ml jars and transported in an ice chest to low temperature incubators in the laboratory on the Cape Florida.
The living specimens were promptly examined, photographed and recorded on video- tape under a Nikon Diaphot inverted microscope. Some specimens were held at 10°C for several days of observation before being fixed for electron microscopic study.
Specimens for transmission electron microscopy were fixed in accordance with our usual methods for solitary Radiolaria (ANI)ERSON, 1976), employing fixation in seawater- buffered glutaraldehyde, osmication in seawater buffered with cacodylate, dehydration in an acetone series and embedding in LX-112 medium. Epoxy blocks were sectioned to gold-silver thickness with a diamond knife in a Porter Blum MT-2 ultramicrotome and examined in a Philips EM 200 electron microscope at 60 kV. Specimens also were prepared for scanning electron microscopy. Whole specimens were fixed and stored in a 3'7o glutaraldehyde-seawater solution and later freeze-dried in the laboratory for SEM viewing of cytoplasmic structures. Other skeletons were cleaned of adhering cytoplasm and organic matter in a LFE low temperature asher (LTA302-4). SEM examination was done on a Cambridge STEREOSCAN 250 MK2 electron microscope; dispersive X-ray analysis was performed using a KEVEX attachment to the SEMI
R E S U L T S
General morphology
Individuals of Coelographis sp. (Fig. 2a) were clearly visible at a distance of several meters from the submarine's observation sphere. They were present throughout the cruise in moderate abundance. Four specimens of Coelographis sp. were seen on each of our three dives; observers studying other plankton groups usually reported several coelogra- phids on their dives. These were usually found in the depth range of 500 to 700 m; though
18 N. SWANBER6 et al,
one specimen was observed at 100 m. Viewed close to the window in the lights of the submarine, the Radiolaria appeared glisteningly white. When undisturbed by turbulence, the central capsule and central region of the skeleton was usually positioned uppermost with the long styles dangling down. The brush thicket or central part of the organism was about 4 mm in diameter. A single ashed skeleton weighed 195 I~g. The styles, each of which were 2 to 3 cm in length, appeared almost rigidly immobile, though occasional turbulence from the submarine revealed them to be quite flexible. The style surfaces were frequently covered with small white objects, visible but not identifiable from the submar- ine. Occasionally specimens were observed stuck together in the field. One such group of three individuals, which was collected and later examined in the laboratory, contained a rhizopodial linkage between the central capsules.
Seventeen specimens were studied carefully in the laboratory and later preserved or used for electron microscopy. When examined shortly after collection, many specimens were found to contain considerable detrital material (including at least one fecal pellet) and occasionally had dead metazoans adhering to their styles. In one instance a spathilla was covered with 4-~tm flagellates adhering to its rhizopodium. Specimens held in the laboratory almost always achieved neutral buoyancy, suspended in the midst of the j ar with their separate styles gracefully draping downward and away from the main skeletal mass. Collected specimens often had their styles crossed and stuck together. When zooplankton such as copepods were introduced to the Radiolaria, they were almost immediately stuck to the styles; one small salp, Cyclosalpa pinnata polae, from a surface collection remained stuck to a radiolarian for 24 h, after which the radiolarian's styles were partially embedded in the gelatinous mass of the salp. These radiolaria were the stickiest organisms we have seen in the plankton; their styles readily adhered to glass rods and dishes, metal spoons, and nearly every other solid object with which they came in contact.
Examination of living specimens in the light microscope revealed a network of rhizopodial strands ramifying over the surfaces of the styles and extending to most of the terminal brushes. Individual rhizopodia did not always follow a continuous skeletal pathway, particularly near the brushes, but instead traversed more direct routes across open spaces. Movement of particles was visible along these rhizopodia. The rhizopodial abundance was higher within the central skeletal mass where various branches converged. Very large particles could be seen moving about in this area. A thin membrane-like structure, suspended like a tent from the medullary layer of branching skeletal material (Fig. 2b, c), appeared to enclose much of the cytoplasmic material inside the skeleton. A similar structure was depicted, but not commented upon by RESHETNJAK (1966). There was no evidence of any gelatinous material or 'sarcodictyum' to be found anywhere in the living specimens of any of these Radiolaria.
Skeletal fine structure
Cleaned skeletons viewed under the light and scanning electron microscopes revealed morphology much like that described by HAECKEL (1887) for the family Coelographidae, but with features of both of its subfamilies. In our specimens (Fig. 2d, e) the values were absent or incomplete, presumably having collapsed or dissolved during handling. Their remnants were extremely delicate in appearance. The galea, which were roughly triangu- lar in shape, had only three primary tubes emerging (Fig. 1). The rhinocanna was not pronounced, but broad and short. The paired frenula were neither as symmetrical nor as clearly defined as are those depicted in HAECKEL'S (1887) plates, but were irregular and
Fig. 2. (a) A living specimen of Coelographis sp. suspended in the water column in an aquarium aboard ship shows the commonest attitude encountered in nature. The central capsule lies at the center of the lattice mantle from which protrude the elongate styles. Scale = 10 mm. (b) A light micrograph of a portion of a living specimen shows the central capsule (c) and a tent-like membranous structure (m) suspended from the inside of the lattice mantle. The style (s) is visible emerging from the lattice. Scale = 400 ~tm. (c) A scanning electron micrograph of a freeze-dried specimen shows an overview of the lattice mantle with the underlying organic membrane (m). Scale = 1 mm. (d) Light micrograph of a dead specimen showing the paired galea (g) from which the primary tubes emerge. The valves are absent or invisible. Scale = 4(~1 pm. (e) A scanning electron micrograph shows the detailed structure of the galea, and emerging primary tubes (t). Scale = 200 Ixm. (f) A light micrograph shows the suture line (arrows) between the two halves of the lattice mantle. Scale = 400 lam. (g) The two anchor types are shown in a scanning electron micrograph. That with the concave inner surface is found on the shorter anchor threads; the longer, flatter one behind it is found on the elongate thread found on each pencil. Scale = 10 lam. (h) The conical plug visible in this scanning electron micrograph is repair to a broken tube. Scale = 10 lain.
Fig. 3. (a) A centrally located nucleus (N) delimited by a typical eucaryotic membranous envelope is further enclosed by a vacuolar space (arrow) and surrounded by a vacuolar membrane that is confluent with the nuclear envelope (asterisk) at sporadic locations. A thin envelope of cytoplasm in continuity with the perinuclear vacuolated cytoplasm surrounds the nuclear region. Scale - 2 p.m. (b) Large masses of condensed chromatin occur within the nucleoplasm. Scale - 1 p.m. (c) Masses of highly vacuolated cytoplasm in the central region of the intracapsular cyto- plasm, and (d) more dense peripheral cytoplasm containing occ~tsional intracapsular digestive vacuoles (arrow) are loosely organized within the intracapsular space. Scales - 2 p.m. Occasional bands of flattened membranous saccules (e) sometimes arranged in a circular profile surrounding masses of cytoplasm are probably part of the complex, cytopharyngeal (astropylar) membranous system used to ingest food. Scale = 2 jam. (f) Masses of parallel electron-dense spindle-form bodies occur throughout the intracapsular cytoplasm. Scale - | p.m. (g) A non-living, organic capsular wall (arrow) surrounds the intracapsular cytoplasm and appears to lack perforations
except the large parapylea and astropylum in the oral region. Scale - 1 p_m.
The biology of a coelodendrid 21
extended only partly towards the primary tubes emerging from the galea: There were only four verticillate styles, two emerging from each valve. Haeckel, who considered this a generic trait, described three style pairs in the genus Coelographis as the minimum for the family. The hollow tubes were dichotomously branched and appeared to form a fork thicket, although the distal ramules of the brushes and stylar branches ended in an anastomosing network or lattice-mantle. This mantle was bivalved with a clearly identifi- able suture line (Fig. 2f).
The branching styles were hollow at least as distally as their anchor thread spathillae. The spathillae (Fig. 2g) appeared to be slightly more complex than those depicted by Haeckel. The lateral anchor pencils had numerous spiraling anchor threads branching dendritically from the base of the pencil. Most of these were the same approximate length, but most pencils had one prominent long thread. The spathilla on this long thread was narrower, more elongate and less concave (Fig. 2g) than on the majority of the threads. The trailing edge of each anchor thread spiral was abundantly supplied with a regular array of proximally directed spines (Fig. 2g). One broken style segment had been partially repaired; a cone of siliceous material was deposited at the proximal end of the hollow tube (Fig. 2h).
Examination of our freeze-dried specimens confirmed the presence of rhizopodial strands along the style surfaces. These extend out to and in some cases over the ancho~ pencil spathillae; sometimes in a helical pattern complementary to that of the anchor pencil threads. Underlying the mantle, the tent-like membranous structure was also visible as a partially collapsed organic film. X-ray dispersive analysis revealed no clear evidence of silica in this membrane.
Cytoplasmic fine structure
Some of the major fine structural features of the central capsule are discussed to illustrate the characteristic cytoplasmic organization of this species and its ultrastructural features in common with other phaeodaria. The nucleus (Fig. 3a, b), containing large masses of condensed chromatin, occupied a central position in the intracapsular cytoplasm and was enclosed by a typical eucaryotic double membranous envelope. This membrane was surrounded by a vacuolar membrane at approximately 1 to 2 lam from the nuclear envelope. The vacuolar membrane was closely appressed to the nuclear envelope at restricted locations (asterisk, Fig. 3a). A thin layer of cytoplasm enclosed the perinuclear vacuolar space (arrow, Fig. 3a) and was continuous with the highly vacuolated cytoplasm (Fig. 3c, d) surrounding the nuclear region. The degree of vacuolization varied among specimens, apparently in relation to the physiological state of the organism, and perhaps the amount of food consumed. In one of the specimens observed, the perinuclear cytoplasm was so highly vacuolated that it appeared to be composed of thin strands radiating from the perinuclear cytoplasmic layer.
At more distal regions of the intracapsular cytoplasm, the vacuoles tended to be smaller and some were filled with partially digested organic matter which was probably part of the food drawn into the central capsule through the large cytoplasmic strands forming a cytopharynx or astropylum that communicates to the extracapsular space (e.g. CACHON and CACHON, 1973). The intracapsular cytoplasm was rich in mitochondria, single- membrane bound bodies resembling peroxisomes, and endoplasmic reticulum. Unlike polycystine radiolaria which possess a rich deposit of Golgi bodies dispersed throughout the intracapsular cytoplasm (ANDERSON, 1976, 1983), few typical Golgi bodies have been
22 N. SWANBERG et al.
observed in these large Phaeodaria. Localized regions of flattened membranous saccules (Fig. 3e), presumably associated with the complex infolded membranous system of the astropylum (CACHON and CACHON, 1973), occurred in the distal part of the cytoplasm at some distance from the nucleus. Cytoplasmic electron-dense fibers (Fig. 30 were sparsely distributed near the nucleus, but were more abundant near the capsular wall surrounding the intracapsulum. The function of such fibers is not known, although CACHON and CACHON (1973) hypothesized that similar fibers might be trichocyst-like structures based on their resemblance to ejectosomes in Paramecium sp. and some Heliozoa. As an alternate hypothesis we suggest they may be intracapsular stores of a sticky mucus secreted on the surface of the rhizopodia, thus accounting for the remarkably adhesive quality of the extracapsular cytoplasm.
The capsular wall was an organic deposit (arrow, Fig. 3g) surrounding the intracapsular cytoplasm and was lined on the proximal surface by a distinct plasma membrane. The distal side was surrounded by a thin membranous sheath closely applied to the surface which appeared to be a plasma membrane, but it was so closely appressed to the wall that it was difficult to resolve its fine structure. Numerous rhizopodia, and inter-connected vacuo- lated masses of cytoplasm surrounded the capsular wall and extended outward into the pericapsular space.
D I S C U S S I O N
The fine structure of the cytoplasm clarifies some of the earlier light microscopic observations (e.g. HAECKEL, 1887, plate 127) which showed the nucleus surrounded by a wide double membrane. The perinuclear space separating the nuclear envelope and the surrounding vacuolar membrane accounts for the wide double membrane figured by these earlier authors. The function of the vacuolar space is unknown, although it appears to contain finely fibrillar material. The condensed chromosomes are clearly similar to those observed in Aulacantha (CACHON et al., 1973), but we find no evidence of microtubules suggesting karyokinesis. Hence we conclude that the cell was not undergoing mitosis at the time of fixation. The presence of digestive vacuoles within the specialized vacuolar regions of the intracapsulum differs from the arrangement in the polycystine Radiolaria where all digestive activity is restricted to the extracapsular cytoplasm. This is further evidence that the Phaeodaria are very different from polycystine Radiolaria and adds strength to the arguments for a taxonomic separation of the Phaeodaria from the Polycystina (LEvINE et al., 1980; MERINFELD, 1978). Furthermore, no evidence of thin slits penetrating the capsular wall in the Polycystina was observed in these Phaeodaria. We have observed, however, very fine, membranous intrusions extending from the intracapsular cytoplasm across the capsular wall, but not transversing it completely. These were much more closely spaced than most slits observed in polycystine Radiolaria. Further work is clearly needed to determine the role of the density stained intracytoplasmic fibers and to examine the feeding mechanisms and kind of food consumed by these large deep-dwelling Phaeodaria.
Although the ultrastructure was in accordance with the light microscope observations, certain features of the skeletal morphology of this radiolarian conflicted sharply with earlier descriptions and with existing taxonomic schemes (HAECKEL, 1887; RESHETNJAK, 1966). Most important among these was the possession of paired frontal tubes with frenula and the anastomosing lattice mantle. The extensive branching of the proximal hollow tubes produced a complex 'fork thicket' structure underlying the anastomosing lattice-mantle
The biology of a coelodendrid 23
which is not typical for the Coeloplegmida. None of Haeckel's or Reshetnjak's genera possess only two pair of styles.
Numerous authors (BuTsCHU, 1882; DOGEL, 1951; DOGEL and RESHETNJAK, 1952; HAECKEL, 1887; HAECKER, 1907; RESHEXNJAK, 1966) have referred to or illustrated an extensive and dense gelatinous sarcodictyum surrounding the skeletal material. All of our specimens were individually collected and promptly examined and recorded on film and videotape while they were alive and in nearly perfect condition. They survived, captured prey and maintained neutral buoyancy in the water for days after collection; yet none of these specimens had any obvious gelatinous structure. We have no satisfactory explana- tion for this; there is absolutely no doubt that our material was non-gelatinous. It is conceivable that this species is an exception and the other species in this family could have a gelatinous architecture, but we do not find this a satisfactory explanation because the general morphology differs only in minor details. It would be difficult to hypothesize a consistent function for the skeleton if two such radically different morphologies were supported by the same type of structure. The possession of gelatin could be influenced by the developmental or nutritional stages of the organism, but if that were the case one would expect to find a mix of such stages in any given population. Our experience with gelatinous Spumellaria has shown that preserved material is generally unsuitable as an indicator of the condition of the living organism, but usually one errs in the direction of underestimation of gelatinous structures. It is possible that other gelatinous material in a net collection could become so entangled with the complex spines that it could appear to be part of the organism. Once made, such an error could have been perpetuated in the literature. Few of the authors cited above actually claim to have seen the whole organism or its soft tissues; none claim to have seen it alive. Because of the indisputable nature of our data, we suggest that our predecessors may have erred on this feature.
Gelatinous material in Radiolaria is usually hypothesized to serve either a buoyancy or a structural role. Its absence in an organism of these dimensions raises the question of how neutral buoyancy is achieved. Haeckel stated that the hollow tubes of the Coeloplegmidae were filled with gelatin (we found no indication of this). Haeckel did not hypothesize a function for such a gelatin; clearly its function could not be supportive. If the gelatin were buoyant or if the tubes were filled with some buoyant fluid then one might hypothesize that the skeleton would provide at least some of its own buoyancy; however a few calculations show that it would not be sufficient to support the skeleton. The mass of an entire skeleton was 200 ~tg, equivalent to ca. 0.1 mm 3 biogenic silica (TAKAHASHI and HONJO, 1983). Based on a few measurements of cross sections of broken segments of the skeleton, the ratio of solid material to hollow space ranges approximately from 1 : 1 to 3 : 1, depending on the overall diameter of the section. The hypothetical fluid would thus have a volume of 0.03 to 0.1 mm 3 and to support the entire skeleton of'200 ~tg it would have to have a density o f -2 (impossible) to 0.06 g c m -3.
A somewhat more attractive alternative is that the large membranous structure (Fig. lb, c) underlying the lattice mantle might enclose a buoyant fluid. This structure occupies a roughly spherical space of ca. 4 mm diameter. The volume of this space, less the volume of the central capsule, is ca. 33 mm 3. To offset 200 ~tg of skeletal mass with this volume, a fluid would have to have a density of ca. 1.022 g cm -3. This is within the range of many biological fluids and the hypothesis is consistent with the observation that in s i tu the organism is normally suspended in the water with the central part of its cell uppermost and its styles dangling downwards.
24 N. SWANBERG et al.
The distribution and activity of the rhizopodia, the ready adherence of prey organisms to the styies, and the stylar connections to the phaeodial mass are all compelling arguments that the primary function of the styles is feeding. A similar strategy of substantially increasing the feeding surface area by the elongation of structural elements is employed in some gelatinous groups (SWANBERC et al., 1985). The use of the finely branching skeleton instead of a gelatinous sheath to increase surface area may confer an advantage in that it allows the predator to present larger feeding surfaces in a wide variety of size scales at low metabolic cost. The size and robust structure of the styles and the large number of their anchor threads allow them to snare large metazoan prey, such as copepods or even gelatinous organisms of a cm or more in size. The large surface area presented by the thousands of tiny separate spathillae also allows the organisms to capture microscopic prey. In freshly collected specimens we found both metazoan prey entangled in the styles and microflagellates affixed to their spathillae. In the mesopelagic environment, which we believe to be sparse in plankton abundance, the ability to utilize prey of a wide size range would be highly desirable.
The Coelodendridae display considerable variation on the compact basic form of Coelodendrum. Three separate features are still used to subdivide the group; these are the form of the galea including the presence of a rhinocanna, the absence or number of stylar protrusions of skeleton or cytoplasm, and the extent of anastomosis of the distal segments of the hollow tubes. Without some knowledge of the function of these features and their development or the evolutionary patterns within the group, the choice of diagnostic features is purely arbitrary and must be based on the intuition of the systematist. The organism described in this paper has features which are diagnostic for both of the major subdivisions of the Coelodendridae: an extremely reduced rhinocanna, fewer than the minimum number of verticillate styles, and both dichotomously branching and anastomos- ing distal hollow tubes. This suggests to us that the subdivisions of this group are artificial. Accordingly, even though our specimens do not actually 'fit' into any existing genus, we have refrained from erecting a new genus.
One can easily imagine that the Coelographidae might have developed styles which facilitated capture of large prey. It is much harder however to establish a sound hypothesis which can explain how two separate coelodendrid subgroups are naturally divided by identical sets of morphological criteria. Haeckel's use of anastomosing skeletal elements in a suite of identical subfamilial traits in two separate families constitutes an unnatural and non-heirarchical systematic division. Actually it is very difficult to account for the predictable regularity attributed to many other groups of Radiolaria as well. In fact one of the most intriguing features of radiolarian systematics is the precise iteration of the characters used to distinguish between lower groupings. This has been recognized in specific cases by most modern authors, but we believe it to be a significant and general problem in radiolarian sytematics. While such order may be intellectually appealing, it defies our understanding of the evolutionary processes which generate the diversity we see. We submit that in the absence of a thorough understanding of their biology we have often accepted easy but arbitrary and inappropriate criteria for classifying the Radiolaria.
Acknowledgements--We thank G. R. Harbision for enabling the participation by the first author on the DSRV Sea Link cruise and we thank the crew of the R.V. Sea Diver for their efficient and highly professional efforts. This is L-DGO Contribution 3888 and DSMC Contribution 06. This work was supported by NSF OCE 84-08137 and by an L-DGO Seed Money Grant to N. Swanberg. Figure 2a courtesy of L. P. Madin.
The biology of a coelodendrid 25
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