Article

 

Fine structure and taxonomy of two species of the marine diatom genus Climaconeis (Berkeleyaceae, Bacillariophyta): C. silvae sp. nov. and C. riddleae sp. nov. from the Caribbean Sea and Florida bay, USA

 

Ultraestructura y taxonomía de dos especies de diatomeas marinos Climaconeis (Berkeleyaceae, Bacillariophyta): C. silvae sp. nov. y C. riddleae sp. nov. del Mar Caribe y de la Bahía de Florida, USA

 

A. K. S. K. Prasad

 

Department of Biological Science. Florida State University. Tallahassee, FL 32306-1100 USA. Fax: 1 850 644 9829 E-mail: prasad@bio.fsu.edu

 

Recibido: 19 de julio de 2002.
Aceptado: 30 de enero de 2003.

 

Abstract

Two new species of marine biraphid diatoms of the genus Climaconeis, C. silvae, collected from several localities in Puerto Rico (Caribbean Sea), and C. riddleae, from two localities in Florida Bay, USA, are described by light and scanning electron microscopy. Climaconeis silvae is characterized by long arcuate cells (132-298 µm long and 5-10 µm wide) with extremely fine striae (28-35 in 10 µm), transapically elongated poroid areolae, biarcuate eccentric raphe, both polar and central raphe endings externally deflected toward the ventral side, 8-20 H-shaped plastids, and absence of central stauros and associated pores. Climaconeis riddleae is characterized by arcuate, asymmetrical cells, 4 plastids, valves measuring 82-182 µm long and 4-6 µm wide, transapical striae 24-27 in 10 µm, each stria composed of single row of squarish poroid areolae, and an almost central raphe. Climaconeis silvae and C. riddleae closely resemble only three other arcuate species, C. inflexa, C. ghurbensis and C. koenigii, in valve shape and in structure and arrangement of the striae but differ from them in stria density, number of plastids, valve dimensions, and some fine structural detail. They are compared with other members of the genus, including the generitype, C. lorenzii. A revised synoptic key to the 13 known species of Climaconeis is presented.

Key words: Biraphid diatoms, Climaconeis, C. silvae, C. riddleae, Florida Bay, Caribbean Sea, Berkeleyaceae, fine structure, taxonomy.

 

Resumen

Se describen dos nuevas especies para la ciencia de diatomeas birafidas, ambas del género Climaconeis; C. silvae, recolectada en varias localidades de Puerto Rico (Mar Caribe) y C. riddleae, proveniente de dos localidades de la bahía de Florida, USA. Las descripciones se basan en microscopía de luz y electrónica. Climaconeis silvae está caracterizada por células largas y arqueadas (132-298 µm longitud y 5-10 µm anchura) con estrías extremadamente finas (28-35 en 10 µm), areolas poroides elongadas transapicalmente, rafe eccéntrico biarqueado, los extremos polar y central del rafe curvados hacia el lado ventral, de 8 a 20 plastos en forma de H. Ausencia de estauro central y de poros asociados. Climaconeis riddleae se caracteriza por células asimétricas y curvadas con 4 plastos, valvas de 82-182 µm de longitud y 4-6 µm de ancho, estrías transapicales, 24-27 en 10 µm, cada estría compuesta por una sola hilera de aereolas cuadradas y poradas, rafe casi central. Climaconeis silvae y C. riddleae se parecen solamente a otras tres especies arquedas, C. inflexa, C. ghurbensis y C. koenigii, en la forma de la valva y en la estructura y arreglo de las estrías pero difieren en la densidad de estrías, número de plastos, dimensiones de la valva y en algunos detalles estructurales finos. Estas especies son comparadas con otros miembros del género, incluyendo al tipo genérico, C. lorenzii. Se anexó una clave sinóptica para las 13 especies conocidas de Climaconeis.

Palabras clave: Diatomeas birafidas, Climaconeis, C. silvae, C. riddleae, Florida Bay, Mar Caribe, Berkeleyaceae, ultraestructura, taxonomía.

 

Introduction

In 1868 (see Mereschkowsky, 1901:415), Eulenstein proposed in an unpublished manuscript, the diatom genus Okedenia to accommodate an arcuate marine diatom with biarcuate raphe system, Amphipleura inflexa Brébisson ex Kützing (1849:88). De Toni (1891:229) validated the generic name with a Latin description and placed three species in the genus, including Okedenia inflexa (Brébisson) Eulenstein ex De Toni and two other questionable forms, O?. japonica (Suringar) De Toni and O?. cretae (Ehrenberg) De Toni. Mereschkowsky (1901:422) provided an emended description of the genus and included both arcuate, asymmetrical and straight, linear forms—a total of eight taxa, including two new species. He resurrected the genus Okedenia, solely on the basis of plastid morphology, a character that could not be used satisfactorily in the identification of the species in the genus.

Grunow (1862:421) described the genus Climaconeis to accommodate two straight, linear diatoms collected from marine localities off the Italian coast and from the Red Sea: C. lorenzii Grunow and C. frauenfeldii Grunow. Cox (1982) reviewed the nomenclatural and taxonomic history of the genus. In an extensive and thorough analysis of original as well as other authentic material, she found many structural similarities between Okedenia and Climaconeis and proposed to unite them under one genus, Climaconeis, which has nomenclatural priority over Okedenia. She also provided emended descriptions for the combined genus Climaconeis and its generitype, C. lorenzii. Cox (1982) included five linear, straight forms and a single arcuate, asymmetric diatom, C. inflexa (Brébisson) E. J. Cox. John (1991) described a new symmetrical, straight species, C. scopulorioides John from Australian waters. Prasad et al. (2000) added two new species, the arcuate C. koenigii Prasad and the straight, linear C. colemaniae Prasad, from several localities in Florida Bay, USA. Recently, Reid and Williams (2002) described two new species of the genus, the arcuate C. ghurbensis G. Reid and D.M. Williams and the straight, linear form C. coxii G. Reid and D. M. Williams collected from several localities in Abu Dhabi, the United Arab Emirates.

The present paper is the second of a series of contributions dealing with the previously recorded taxa ascribed to the genus Climaconeis as well as the interesting new members of the genus recognized from Florida's coastal waters and nearby localities. Climaconeis silvae sp. nov. is described from Puerto Rico, and C. riddleae sp. nov. from Florida marine habitats. Structural studies have been made by light microscopy (LM) and scanning electron microscopy (SEM). The morphology and taxonomy of the new species are discussed and compared with those of similar taxa. A revised synoptic key to the 11 known species is also presented.

 

Materials and methods

The material of C. silvae came from several periphyton collections from artificial substrates made during a 12-mo study of six different locations in Mayagüez, Puerto Rico, Caribbean Sea, in 1990-91. The material of C. riddleae came from coral-reef-associated sediment samples collected by K. A. Riddle from two different Florida Bay locations, Cotton Key (25°02'N, 80°37'W) and West Key (24°59'N, 80°38.9'W), in June 1993. Additional material was obtained from six other locations in Florida Bay, collected in October 1997, May 1998, and October 1998. (For further details, see Prasad et al. 2000, 2001). Samples were preserved in either seawater-based formalin or Lugol's solution. Material for light microscopy (LM) and scanning electron microscopy (SEM) was prepared as described by Prasad and Fryxell (1991) and Prasad et al. (1990). LM observations were carried out with a Nikon Labophot-II equipped with phase-contrast optics, Nikon Micropot-FX-35 and Leica-DMLB microscopes fitted with differential-interference-contrast (DIC) objectives, and a Leica MPS-60 35-mm camera. Acid-cleaned material of C. silvae and C. riddleae mounted on aluminum stubs was sputter-coated with gold-palladium and examined in a JEOL-840 scanning electron microscope using Polaroid 4"x5" film, operating at an accelerating voltage of 20 kV at the Florida State University's Biological Science Imaging Resource.

Terminology used is that of Anonymous (1975), Ross et al. (1979), Cox (1979a), and Cox and Ross (1981). Ross et al. (1979) defined an areola as a regular perforation through the basal siliceous layer and striae as rows of areolae, normally occluded by vela or cribra. Mann (1981) refined the terminology of pore occlusions and recommended that the delicate siliceous membrane across the entire pore be called a "hymen" (replacing the "rica" of Ross et al. 1979). Cox and Ross (1981; see also Cox 1999) introduced two terms to describe the structure of striae: "virgae" for the bars between the striae, to replace "interstriae" of Ross et al. (1979) and "costae," and "vimines" for the crossbars that separate areolae within a stria. They also suggested that striae with a single row of areolae be called uniseriate. In Cox (1977), Mann and Cox proposed the term "helictoglossae" for thickened internal polar raphe endings, replacing the "lipped endings" of Cox (1975) and "infundibulum" of Anonymous (1975).

 

Observations

Order: Naviculales Bessey 1907

Family: Berkeleyaceae D. G. Mann in Round et al. 1990.

Genus: Climaconeis Cleve 1862 emend Cox 1982.

Climaconeis silvae A.K.S.K. Prasad sp. nov. (Figs. 1-25 (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24)).

Description: Cellulae solitariae, marinae, epipelicae vel epiphyticae, cum 8-18(20) chloroplastes inter cytoplasma centralem et apices. Valvae biarcuatae vel leviter lunatae, angustatae, leviter asymmetricae secus axem apicalem, latiores et fere rectae ad centrum, gradatim decrescentes secus apicem; apices obtusi, rotundati, non-capitati. Longitudo valvae 132-298 µm, latitudo 5-10 µm; valvae latiores ad centrum, angustiores ad apices. Valvae, aspecto valvae, planae; limbus non profundum cum margine distincto et hyalino. Striae transapicales parallelae, 38-35 in 10 µm, leviter radiantes super polos, in latis oppositis sterni raphis numero plus minusve aequales. Striae uniseriatae, cum poroideis areolis rectangularibus et elongatis transapicaliter. Virgae variabiles latitudine; vimines breves. Striae in lato ventrali sterni raphis cum 9-12 areolis, in lato dorsali cum 3-6 areolis. In aream centralem, striae in lato dorsali raphi longiores (9-12 areolae), striae in lato ventrali raphi breviores (3-6 areolae). Areolae amplitudine variabiles; areolae prope sternum raphis aliquando majorem. Raphe-systema biarcuatum, proximum ad lato ventrali ad centrum, ad lato dorsali ad apicem. Area centralis 3.0-4.8 µm longitudine. Extrema raphis polaria centraliaque leviter ventraliter deflecta. Raphe internaliter et externaliter incrassatum ventraliter, externaliter non-uniformiter, internaliter uniformiter pro longitudine raphis. Externaliter extrema polaria raphis leviter plus expansum quam extrema centralia et deflecta ventraliter manifeste.

Holotype: Slide BM100979(PC91103) is deposited in the Natural History Museum (BM), London. It bears several specimens; a specimen can be located on the slide at England Finder (Graticules, Ltd., UK) coordinates N-47-1.

Isotypes: Slide PC91103 is deposited in the Academy of Natural Sciences of Philadelphia (ANSP), USA. The other iso-types are in the author's collection (PC, Prasad Collection): PC91102, PC91104, PC98085, PC98086, PC98087, and PC98088.

Type Locality: Mayagüez, Puerto Rico, Station D. Periphyton (artificial substrate). Collected on 6-18-1990. Temperature 28°C, salinity 35.2 parts per thousand.

Etymology: The species is named for Dr. Paul C. Silva, an eminent botanist, from University of California, Berkeley, California, USA, in recognition and appreciation of his outstanding contributions in phycology and botanical nomenclature.

Cells are solitary, free living, marine, epipelic (Fig. 1) or epiphytic on macroalgae, each with variable number of plastids, between 8 and 18 (rarely 20), depending on the cell size, distributed along the cell from the central cytoplasm to the cell apices (Figs. 4-8). The valves are arcuate or slightly lunate, narrow, slightly asymmetrical along the apical axis, wider and almost straight at the center and gradually narrowing and curving along the obtuse apices (Figs. 2-9), which are rounded and not capitate (Figs. 12, 14). They measure 132-298 µm long in apical axis and are 5-10 µm wide; wider at the center and narrower at the apices. The valve face is flat, and the mantle is shallow and has a distinct hyaline rim (Figs. 18, 19). The transapical striae, 28-35 in 10 µm, are parallel (Figs. 18-23) throughout, except at the apices, where they become slightly radiating over the poles (Figs. 18, 19, 24, 25). The density of the striae is almost uniform on both sides of the raphe sternum. They are uniseriate (Figs. 18-23); each consists of rectangular poroid areolae, which are transapically elongated throughout except at the poles, where they are apically slightly radiating (Figs. 18, 19, 22-25). The virgae ("inter-striae") are of variable width, and the vimines (cross bars) separating the areolae are short. Because of the off-center (eccentric) location of the raphe, striae are longer on the ventral side of the raphe sternum (9-12 areolae; Figs. 18, 19, 22, 23) than on the dorsal side (3-6 areolae). In the central area, where the raphe is close to the ventral (concave) side, striae are longer on the dorsal (primary) side (9-12 areolae) of the raphe than on the ventral side (3-6 areolae). The areolae within each stria are variable in size; those adjacent to the raphe sternum are at times larger (Figs. 18, 19, 20, 21) than elsewhere, as in other species of the genus examined by SEM. The raphe system, like the valves, is biarcuate (Figs. 11, 13, 15, 16); unlike those of other arcuate species of the genus, it is not central but eccentric, much closer to the ventral (concave) side of the valve (Figs. 11, 13, 15, 16), gradually running closer to the dorsal (convex) side near the apices (Figs. 10, 12-14, 17). The length of the central area between the two central raphe endings is 3.0-4.8 µm. Both at the center (Fig. 20) and at the poles (Figs. 18, 19), the external raphe fissures are deflected in the same direction, i.e. slightly toward the ventral (secondary) side. The raphe is not flush with the valve surface; both externally (Figs. 18, 19) and internally (Figs. 22, 23), additional thickening occurs on only one (i.e. the ventral) side of the raphe sternum. The raphe sternum is additionally thickened on the exterior, not uniformly but at intervals, whereas, internally, the additional thickening appears to be uniform throughout the length of the raphe. The additional thickening seems more evident on the secondary side of the raphe sternum. Externally, the polar raphe endings are more expanded than the central raphe endings, and the curvature toward the ventral side is evident. Internally, variation is apparent within the same valve; it is either straight (Fig. 25) or slightly deflected. The internal raphe fissures terminate at the poles into uniformly thickened, raised helictoglossae (Figs. 22, 23, 24, 25) but not at the central raphe endings (Fig. 22). The axial areas and the terminal fissures are refractive. There is no hyaline area between the helictoglossae and the polar mantles (Figs. 24, 25); the row of slits on the polar mantle usually seen in other species is also absent. Girdle bands are open, each bearing two rows of poroid areolae.

Remarks: Climaconeis silvae was first noticed in epiphytic collections from station BRA, DPA in March-May 1990 but found growing on artificial substrates in large numbers at Station C and Station D, Puerto Rico, and in surface sediment samples in June 1990. The diatom species that were dominant in the samples include Toxarium undulatum Bailey, Toxarium kennedyarum Grunow, Ardissonia fulgens var. mediterranea Grunow, and Licmophora remulus Grunow. The subdominants were L. flabellata (Carmichael) Agardh, Climacosphenia moniligera Ehrenberg, and Haslea sp. As far as I know, C. silvae is the first arcuate member of the genus ever recorded and only the second species of the genus for Puerto Rico and for the entire Caribbean (see Navarro and Hernández-Becerril 1997); C. lorenzii (as Navicula scopulorum Brébisson) was known to be widely distributed from San Juan Bay, Puerto Rico (Hagelstein 1939).

Climaconeis silvae is characterized by its long, narrow arcuate cells, with 8-20 plastids, fine uniseriate striae of poroid areolae that are transapically elongated, eccentric raphe sternum (closer to the valve margin rather than central), and deflection of both the external polar raphe fissures and central raphe fissures toward the same side of the valve. It differs sufficiently from the generitype, C. lorenzii, in being arcuate with a biarcuate raphe system, instead of straight, linear valves; in lacking craticular bars on the girdle; in having much finer (denser) striae (28-35 rather than 21 in 10 µm); and in having fewer plastids (8-20 rather than 70). Climaconeis silvae differs sufficiently from all the four arcuate species of the genus known thus far, C. ghurbensis (Reid and Williams 2002), C. inflexa, C. koenigii (Prasad et al. 2000), and C. riddleae Prasad (this paper), in the number of plastids, density of striae, and valve measurements. Climaconeis ghurbensis shows greater resemblance to C. silvae in shape but differs in having a valve length of 120-160 µm, a width of 4-5 µm and in the presence of numerous plastids (Reid and Williams 2002). C. silvae resembles C. riddleae in many ways but can be distinguished from it by plastid number, valve dimensions, and most importantly, the eccentric raphe system, which runs closer to the valve margin, and the parallel uniseriate striae composed of transapically elongated poroid areolae rather than squarish areolae. Virgae and vimines are all of uniform thickness and length in C. riddleae, whereas in C. silvae, virgae are of variable width, and the vimines (crossbars) separating the areolae are shorter than those in C. riddleae and variable in length. Comparisons with the other members of the genus are presented in Table 1. The valves of Climaconeis silvae have a structure similar to that of C. inflexa (syn. Okedenia inflexa (Brébisson) Eulenstein) and a species that Cox (1979a) had indicated as corresponding to Okedenia scopulorum sensu Mereschkowsky (1902) (see Cox 1979a figs. 30, 31, 1979b).

Climaconeis riddleae A.K.S.K. Prasad sp. nov. (Figs 26-41 (27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40)).

Description: Cellulae solitariae, marinae, cum sedimento e corallio consociatae, cum (2)4 chloroplastes in ambabus lateribus cytoplasmatis centralis. Valvae arcuatae; 82-182 µm longitudino, 4-6 µm latitudino. Valvae ad centrum latiores, gradatim decrescentes secus apicem; apices obtusi, rotundati. Valva c. 4.0 µm in latitudine minima. Pagina valvae plana; limbus-humile cum margine distincto et hyalino, praecipue ad polos. Striae transapicales parallelae, 24-27 in 10 µm, aliquando leviter radiantes super polos. Striae uniseriatae, cum poroideis areolis quadrangularibus vel sub-rectangularibus in latis oppositis sterni raphis numero plus minusve aequales. Areolae aliquot striarum leviter elongatae, praecipue ad polos. Raphe-systema biarcuatum, fere centrale. Area centralis 3.0-3.5 µm longitudine. Extrema raphis polaria centraliaque leviter ventraliter deflecta. Internaliter extrema centralia raphis habitu recta. Helictoglossae uniformiter incrassatae elevataeque ad polaria sed non ad centralia extrema raphis. Raphe internaliter et externaliter incrassatum ventraliter, externaliter non-uniformiter, internaliter uniformiter pro longitudine raphis. Area hyalina inter helictoglossa et pallia polaria deest; pallium polare sine rimis. Taeniae cingulares apertae, cum 2 seriebus areolarum poroidearum variabilium. Internaliter extrema polaria raphis leviter deflecta vel recta. Helictoglossae uniformiter incrassatae elevataeque ad polaria sed non ad centralia extrema raphis. Areae axiales et rimae terminales refractivae. Area hyalina inter helictoglossa et pallia polaria deest; pallium polare sine rimis. Taeniae cingulares apertae, cum 2+ seriebus areolarum poroidium.

Holotype: Slide BM100980(PC93441) is deposited in the Natural History Museum, London, UK. A number of specimens are present on the slide. One specimen is marked on the slide, at England Finder coordinates M-33.

Isotypes: Slide PC 93443 is deposited in the Academy of Natural Sciences (ANSP), and a specimen can be located on the slide between England Finder coordinates K-42-2 and K43-1. The other isotype slides, PC93439, PC93440, PC93442, and PC93444, are in the Prasad Collection.

Type Locality: Captain's Key, Florida Bay, USA. Epipelon. Collected on 8-3-1993 by Kimberley A. Riddle. Temperature and salinity data are not available.

Etymology: The species is named for Kimberly A. Riddle, of Florida State University's Department of Biological Science Imaging Resource.

The cells are solitary, marine, associated with coral reef sediments, each with 4 (rarely 2) plastids distributed on both sides of the central cytoplasm (Fig. 26). The valves are arcuate, measuring 82-182 mm in length and 4-6 mm in width. They are wider in the center and gradually become narrower toward the poles, which are obtuse with rounded ends (Figs. 26-30, 32-34 (33)). The narrowest part of the valve is c. 4.0 mm wide. The valve face is flat and the valve mantle shallow, with a distinct hyaline rim, especially evident on the polar mantles (Figs. 36, 37). The transapical striae are parallel almost throughout the valve except at the extremities of the valve, where they may be slightly radiating and sometimes appear almost parallel like rest of the valve face (Figs. 36,37, 40, 41), 24-27 striae in 10 mm. They are uniseriate, composed of squarish or subrectangular poroid areolae (not transapically elongated as in C. silvae). Some striae show areolae that are slightly apically elongated, especially at the apices. The number of areolae per stria is mostly uniform on each side of the raphe sternum; striae are shorter, consisting of only 6 areolae, on the primary side of the raphe sternum, except at the apices, where 4-5 areolae are seen, whereas longer striae, each consisting of 7-8 areolae, are seen on the secondary side of the raphe sternum, except at the poles, where they have fewer areolae (5-7). The virgae ("interstriae") and the vimines (cross bars) are of equal thickness; the vimines separating the uniform areolae are all of the same length. In the wider central area, each stria is composed of 7-10 areolae (Fig. 38). The areolae adjacent to the raphe sternum are of the same size as elsewhere (Figs. 38, 39) or slightly larger than those on the rest of the valve (Fig. 41). The raphe system is biarcuate as in other arcuate species and is almost central (Fig. 33). The central area between the two central raphe endings is 3.0-3.5 mm in length (Fig. 38). The polar and central raphe endings on the exterior are dot-like (Figs. 28, 33, 36, 38). The polar raphe endings are slightly deflected in the same direction, toward the secondary side (Figs. 36, 37). Internally, thick, raised helictoglossae (Figs. 40, 41) occur at the poles but not at the central raphe endings (Fig. 38). The central raphe endings appear to be straight internally (Fig. 38). Externally, the raphe sternum is not flush with the valve surface on the ventral side but irregularly thickened at intervals (Fig. 35, 36. 37); internally the additional thickening on the ventral side of raphe sternum is uniform (Figs. 38-41) throughout. At the apices, there is no hyaline area between the polar mantle and helictoglossa. No distinct row of slits on the polar mantle, as seen in other species of the genus (C. koenigii, C. stromatolitis), was observed. Girdle bands are open, each bearing two rows of poroid areolae of variable size.

Remarks: Climaconeis riddleae was seen in sediment samples retrieved from the coral reef surface at Captain Key and West Key in Florida Bay, USA. It was common but not abundant at the sites indicated. The more abundant diatoms were Rhabdonema adriaticum Kützing. and Synedra bacillaris (Grunow) Hustedt. Other diatoms present were straight and linear forms, Climaconeis scopulorioides Hustedt (1961) and C. colemaniae. Climaconeis riddleae is characterized by arcuate, asymmetrical cells, 4 plastids, valves measuring 82-182 µm long and 4-6 µm wide, transapical striae 24-27 in 10 µm, each stria composed of a single row of squarish poroid areolae, and an almost central raphe. The only report of the occurrence of Climaconeis species from Florida Bay is that of Prasad et al. (2000), and C. riddleae can be easily differentiated from the previously known species from Florida Bay, such as C. lorenzii, C. colemaniae, and C. koenigii, as follows: C. riddleae differs from the generitype, C. lorenzii, in having arcuate (rather than straight, linear) cells, only 8-20 plastids (rather than 70), finer striae, and no craticular bars. It differs from C. koenigii in valve length, plastid number, and density of striae. C. riddleae bears greater resemblance to C. ghurbensis (Reid and Williams 2002) in shape, length, and width but differs sufficiently in having coarser striae of 24-27 striae in 10 µm, squarish poroid areolae and much fewer number of plastids (only four) per cell. Climaconeis riddleae differs from C. colemaniae in having arcuate, asymmetrical valves rather than straight, linear valves and in the lack of pores associated with the central area.

 

Discussion

The systematics of Climaconeis has been controversial. Mereschkowsky (1901:422) considered plastid morphology in his redefined genus, Okedenia, to be "so peculiar and so different from all other naviculoid diatoms" that it seemed necessary for him to accord a familial status for the genus Okedenia, so he established the family Okedeniaceae Mereschkowsky (Mereschkowsky 1901:422; 1903:30, "Okedenieae"). Cox (1982), following Mereschkowsky, despite "noncorrelation of aspects of the raphe system and areola arrangement," considered plastid features an important criterion in placing both symmetrical and asymmetrical forms in Climaconeis but chose to assign the genus to the family Naviculaceae Kützing (1844). The Naviculaceae, according to Hendey (1937; 1964), is restricted to biraphid diatom cells having bilateral symmetry on both apical and transapical axes. Thus, the position of Climaconeis in part (with asymmetrical, arcuate forms) is problematic or anomalous within the Naviculaceae. Valve symmetry (asymmetrical, arcuate forms) was probably the major criterion used by Eulenstein (see Mereschkowsky 1901) in establishing the genus Okedenia. Hendey (1964:58), relying on symmetry, placed Okedenia in the Cymbellaceae Greville 1833 ("Tribe xxv. Cymbelleae"), a family created to accommodate biraphid diatoms, whose valves are symmetrical on the transapical axis but asymmetrical on the apical axis. Mann in Round et al. (1990:659) established a separate family, Berkeleyaceae D. G. Mann, with Berkeleya Greville as the generitype, to accommodate Berkeleya, Parlibellus E. J. Cox (Cox 1988), and Stenoneis Cleve (all consisting of symmetrical forms) and Climaconeis, a genus of both asymmetrical and symmetrical forms. Round and Crawford (1989) recognized two genera in the Berkeleyaceae, Berkeleya and Climaconeis. Round et al. (1990) added Parlibellus and Stenoneis to the family. All four genera of the family occur in brackish and marine habitats. Mann's familial description (in Round et al. 1990), while retaining traditional elements like valve symmetry, also included nontraditional characters like habitat, plastid number and arrangement, fine structure of the raphe system, and girdle elements. The Berkeleyaceae is one example of their new system of classification, in which genera of different symmetries are placed together in the same family. The implication here is that shape and form have been subject to convergent and parallel evolution (Cox 1979a, Medlin 1991, Mann 1994). Members of the Berkeleyaceae are generally symmetrical along all major planes, but a few asymmetrical, arcuate forms are also known. Cleve (1896:99) argued that more or less asymmetrical forms occur that are so closely related to symmetrical ones that it would be artificial to separate them. For example, Amphora clevei Grunow is closely related to the genus Trachyneis Cleve; Amphora elegans is allied to the section Navicula orthostichae (see Cleve 1896 for more examples). In addition, Ross (1963a, b) described an unusual species with an amphoroid symmetry in Capartogramma Kufferath, as C. amphoroides Ross, even though other members of the genus have typical naviculoid symmetry, as in Climaconeis. Likewise, Lyrella amphoroides D. G. Mann and Stickle (Mann and Stickle 1997) is yet another unusual species; it has a dorsiventral frustule similar to that of Amphora but possesses valve, raphe, and plastid characteristics that show unambiguously that it belongs in Lyrella, where the majority of species are symmetrical across all major planes (naviculoid symmetry).

Despite leveling criticism over the use of symmetry in the generic and familial classification as proposed by Hendey (1937, 1964), Cox (1979a) clearly recognized its significance in the identification of species, as in Climaconeis. She argued that, for the classification to reflect evolutionary change, the two different types of plastid morphology (number and arrangement) must be recognized as the basis for separating Berkeleya and Climaconeis at the generic level. In view of the increasing evidence (Prasad et al. 2000, the present study) for greater diversity in asymmetrical forms (three additional species, viz. C. koenigii, C. silvae, and C. riddleae), it seems reasonable, for the present, to support the placement of Climaconeis in the Berkeleyaceae.

At the time of redefinition, Cox (1982) conceived the genus with six species, including five straight, linear species and one arcuate species. She considered two other marine, arcuate species, Okedenia ponticola Mereschkowsky and O. granulata Mereschkowsky to be questionable forms for want of critical examination. Recent studies have also demonstrated the occurrence of further diversity in the genus; symmetrical forms, such as C. stromatolitis (John 1991), C. colemaniae (Prasad et al. 2000) and C. coxii (Reid and Williams 2002) and arcuate asymmetrical forms like C. koenigii (Prasad et al. 2000) and C. ghurbensis (Reid and Williams 2002) have been described from several marine localities. With the discovery of two additional arcuate species, presented here, the genus now includes 13 species, five arcuate, asymmetrical forms and eight linear, straight, symmetrical forms. The linear, straight forms are C. colemaniae, C. coxii, C. delicatula (Cleve) E. J. Cox, C. fasciculata (Grunow ex Cleve) E. J. Cox, C. lorenzii Grunow, C. scalaris (Brébisson) E. J. Cox, and C. scopulorioides Hustedt, and C. stromatolitis; the arcuate, asymmetrical forms are C. ghurbensis, C. inflexa (Brébisson ex Kützing) E. J. Cox, C. koenigii, C. riddleae, and C. silvae. The emergence of two cell-symmetry subgroups within Climaconeis is becoming increasingly evident. Further it is also possible to resurrect Okedenia as a generic name for the arcuate taxa forming a natural group (Prasad et al. 2000; Reid and Williams 2002).

Climaconeis, with its long, narrow, linear, straight or curved, lunate asymmetric valves; straight and biarcuate raphe system; uniseriate striae of poroid areolae; and internal thickenings of raphe sterna, is clearly a member of the Berkeleyaceae (Cox 1982, Round and Crawford 1989, Round et al. 1990). Prasad et al. (2000) provided a discussion of generic characters of Cliamconeis. One important character that distinguished the other members of that family is plastid morphology, not a sufficient reason to separate it from the remaining three genera of the family at a higher level than genus. Reid and Williams (2002) also briefly discussed the usefulness of plastid morphology in differentiating Climaconeis from Berkeleya. Both subgroups of species within Climaconeis include both species with numerous plastids that are evenly distributed on either side of the central cytoplasm (C. koenigii, 48-72; C. coxii, 20-26; C. lorenzii, 20 or more) and species with few plastids (C. inflexa, 2; C. stromatolitis, 2).

Cox (1977) and Mann (1982) demonstrated the usefulness of raphe fissure endings in assessing relationships. In C. silvae and C. riddleae, the central and polar external raphe fissure endings curve in the same direction, reminiscent of the Type I of Cox (1977), seen in Berkeleya rutilans (Trentepohl) Grunow (Cox 1977, fig. 5). The internal polar raphe fissure endings in C. silvae and C. riddleae terminate in thickened helictoglossae, very much like those of C. koenigii (Prasad et al. 2000, figs 13, 14; compare with Figs 24, 25 of C. silvae and Figs 40, 41 of C. riddleae), and the external polar endings in C. silvae and C. riddleae are also similar to those of C. koenigii (Prasad et al. 2000, figs 3, 6, 7, 8; for C. silvae, see Figs 10, 12, 18, 19 in this paper, and for C. riddleae, see Figs 29, 33, 36, 37), although external central raphe fissure endings are also curved in the same direction in C. silvae (Fig. 20) and C. riddleae (Fig. 13), rather than being straight as in C. koenigii (Prasad et al. 2000, figs 5, 9).

 

 

Acknowledgements

Paul Silva was ungrudging in his help to others and there are many besides me who are indebted for his lucid explanation and simple solution for many of the complex issues of botanical nomenclature, that beset us in our profession. He has been my teacher and friend, professionally as well as personally for more than two decades. His help and encouragement throughout the years will always be remembered.

I am grateful to E. J. Cox of the Natural History Museum, London (UK), for her insightful comments (in 1990-1991) and her helpful discussion at the International Phycological Congress at Duke University in August 1991 on C. silvae. I am thankful to Kimberley Riddle for the Florida Bay collections; to R. L. Moe for providing Latin diagnoses for the new taxa; to the curators at the Natural History Museum, London (UK), for arranging the loan of the type material of Amphipleura inflexa from the Kützing Collection; to Anne B. Thistle for expert editing; and to Charles Badland and K. A. Riddle for preparing digitized images. I thank Dr. Francisco F. Pedroche for his patience and understanding as an editor.

 

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