Clasper

bands in dorsiventral columns

Section RHIZOSOLENIA

lateral view

Rh. imbricata Rh. striata Rh. ostenfeldii Rh. fallax Rh. decipiens Rh. chunii Rh. sp.

lateral view ventral view bands in lateral columns band striation

Section IMBRICATAE

FIGURE 15 Schematic illustrations of Rhizosolenia spp. with terminology and type of striation for the section Imbricatae.

band

3a. Valves regular conical, process straight, generally with otaria

Rhizosolenia sensu stricto, p. 144

3 b. Valves irregular subconical, process claw like with no otaria

Pseudosolenia, p. 160

4a. Girdle composed of open (split) bands with ligulae and antiligulae

Guinardia, p. 160

4 b. Girdle composed of half bands Dactyliosolen, p. 165

Genus Rhizosolenia Brightwell 1858

Type: Rhizosolenia styliformis Brightwell. Valves conoidal; otaria and claspers usually present; apex characteristically terminated by one process which opens at the tip and communicates with the cell interior by a labiate structure. Areolae of copulae usually loculate (EM). For the complete diagnosis see Sundstrom (1986, p. 106).

The Rhizosolenia girdle is composed of numerous segments (bands, copulae) in two or several longditudinal columns. The outline of the copulae is scale like to trapezoid to rhomboidal to wing shaped, partly depending on the width of the cell and the number of columns. There is only one, seldom two (in the larger species), valvocopulae. The valvocopula is thus larger and differs in shape from the other copulae (e.g., R. acicularis, Plate 26).

Characters showing differences between species:

Segments (bands) in dorsiventral or lateral columns.

Number of columns of segments.

Shape of valve and process.

Otaria: position, extension, size, and shape.

Labiate structure visible or not with LM.

The genus is divided into two sections. A further grouping of the species may be based on the characters mentioned previously.

A. Section Rhizosolenia: Girdle segments (copulae, bands) in two dorsiventral columns or in several columns.

1. Two columns of segments; otaria, claspers, and labiate structure present (LM observations).

a. Otaria ending at base of process: R. styliformis and R. formosa (Table 32).

b. Otaria confined to valve proper, not extending to the base of the process: R. curvata and R. acicularis (Table 32).

c. Otaria along basal part of process: R. borealis (Table 32).

2. Two columns of segments, otaria and claspers present or absent; labiate structure (LM observations) present; dimorphism:

R. antennata, R. hebetata, R. polydactyla, and R. sima (Table 33).

R. acicularis

R. styliformis

R. formosa

PLATE 26 Rhizosolenia styliformis: epitheca in ventral and hypotheca in lateral view. Otaria and claspers evident on epitheca. Scale bar = 20 /¿m. Rhizosolenia acicularis: valve with valvoco-pula, ventral view. After Sundström (1986). Scale bar = 50 /urn. Rhizosolenia curvata: lateral view. From Hasle, 1968b. Scale bar = 50 /¿m. Rhizosolenia formosa: (a) ventral view; (b) lateral view. After Sundström (1986). Scale bar = 50 /am.

3. More than two columns of segments—labiate structure present (LM observations).

a. Otaria and claspers present: R. crassa, R. clevei, R. hyalina, R. castracanei, and R. debyana (Table 34).

b. Otaria and claspers lacking: R. temperei, R. acuminata, R. bergonii, and R. simplex (Table 34).

B. Section Imbricatae: Girdle segments (copulae, bands) in two lateral columns; otaria, claspers (LM), and labiate structure (EM) present: R. imbricata, R. ostenfeldii, R. fallax, R. striata, and R. decipiens (Table 35).

C. Incertae sedis (Rhizosolenia): R. setigera, R. pungens, and R. robusta. A. Section Rhizosolenia.

1. Two dorsiventral columns of segments; no dimorphism.

Rhizosolenia styliformis Brightwell (Plate 26, Table 32) Synonym: R. styliformis var. longispina Hustedt in A. Schmidt. References: Brightwell, 1858a, p. 94, Plate 5, Figs. 5a-5e; Schmidt, 1914, Plate 316, Figs. 5-7 and 12; Hustedt, 1930, p. 586, Fig. 334; Hasle, 1975, Figs. 1-3; Sundstrom, 1986, p. 15, Figs. 5 and 47-56. Otaria sometimes ending below the process base and sometimes extending a short distance along the basal part of the process.

Rhizosolenia formosa H. Peragallo (Plate 26, Table 32) Synonym: R. styliformis f. latissima "Brightwell" in H. Peragallo. References: Peragallo, 1888, p. 83, Plate 6, Fig. 43; Sundstrom, 1986, p. 33, Figs. 12, 13, 88-93, and 96-99.

TABLE 32 Morphometric Data of Rhizosolenia spp. with Two Columns of Segments and No Dimorphism

Species

Diameter (|im)

Length of Band areolae Valve process (|im) in 10 |xm areolae in 10 pm'

R. styliformis

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