Bysmatrum caponii (Horiguchi and Pienaar) Faust and Steidinger, 1998
Species Overview:
Bysmatrum caponii is an armoured, marine, benthic dinoflagellate species. It was discovered in tidal pools in southern California, Pacific Ocean.
Taxonomic Description:
Unique to the Bysmatrum genus is the recessed chamber-like apical pore complex (APC) containing a large apical pore plate (Po) with a central raised dome, and an elongated canal plate (X plate). The most striking feature of this genus is the separation of intercalary plates 2a and 3a by apical plate 3' (Horiguchi and Pienaar, 1988b, Faust and Steidinger, 1998).
Cells of Bysmatrum caponii are conical and almost pentagonal (Figs. 1,2). The longitudinal axis is slightly oblique, inclined ventrally. The epitheca is conical (Figs. 2,4). The hypotheca is slightly smaller than the epitheca with a rounded antapex (Fig. 1) which can appear obliquely flattened (Fig. 2). Often, a short posterior projection on the right side of the hypotheca has been observed (Fig. 2). Smaller projections are rarely observed on the left posterior end. Cell length and width are almost equal ranging from 20 to 34 µm; dorso-ventral depth is less than the cell width (Steidinger and Balech, 1977, Horiguchi and Pienaar, 1988a, Faust and Steidinger, 1998).
The thecal surface is covered in a reticulate pattern that gives the appearance of longitudinal striae (Figs. 1-4) (Steidinger and Balech, 1977, Horiguchi and Pienaar, 1988a, Faust and Steidinger, 1998).
Thecal Plate Description:
The plate formula of B. caponii is: Po, X, 4', 3a, 7'', 6C, 4S, 5''', 2''''. The APC is polygonal and prominent with raised edges formed from overlapping neighboring apical plates (Figs. 3,5). The X plate, situated between the Po and plate 1', is small and rectangular or triangular (Figs. 3,5). Apical plate 1' is pentagonal and reaches the cingulum (Fig. 1). Characteristic of this genus, the intercalary plates 2a and 3a are separated by apical plate 3' (Figs. 4,5) (Horiguchi and Pienaar, 1988a, Faust and Steidinger, 1998).
The cingulum is well excavated and displaced nearly 1 time its width (Figs. 1,2). It consists of six plates, including a transitional plate, and is longitudinally striated. The sulcus, made up of four plates, is narrow anteriorly and widens posteriorly towards the left (Figs. 1,2). It does not reach the antapex (Horiguchi and Pienaar, 1988a).
Morphology and Structure:
Cells of Bysmatrum caponii are photosynthetic with many radially arranged chloroplasts. The elongated nucleus is in the epitheca (Steidinger and Balech, 1977). This species also has an eyespot (Horiguchi and Pienaar, 1988b).
Reproduction:
B. caponii reproduces asexually by binary fission.
Species Comparison:
Bysmatrum caponii is similar to three species: Bysmatrum arenicola, B. subsalsum and Peridinium sociale. These species share several thecal plate arrangement characteristics, most notably the lack of contact between plates 2a and 3a, as well as a pentagonal and asymmetric 1' apical plate and a chamber-like APC (Steidinger and Balech, 1977, Horiguchi and Pienaar, 1988a, Faust and Steidinger, 1998).
Bysmatrum arenicola, also a tide pool species, differs from B. caponii by several features: a. cell shape nearly ellipsoidal; b. larger average cell size; c. prominent dorso-ventral compression; d. lack of thecal plate striations; e. presence of numerous minute, wart-like projections on thecal surface; f. lack of antapical spines; and g. lack of an eyespot (Horiguchi and Pienaar, 1988b).
Bysmatrum subsalsum and B. caponii share a number of features: a. round to convex shape with an oblique axis; b. presence of a pusule and stigma; c. radiating chloroplasts; d. elongated nucleus; and e. reticulate thecal pattern that gives the appearance of longitudinal striae (Steidinger and Balech, 1977, Horiguchi and Chihara, 1983).
B. subsalsum, however, differs from B. caponii by several features: a. larger average cell size; b. position of nucleus; c. lack of antapical spines; and d. different habitats (Horiguchi and Pienaar, 1988a).
B. caponii resembles Peridinium sociale by several features: a. angular apical pore plate; b. possession of antapical spines; c. shape and arrangement of the chloroplasts; d. and possession of an eye spot (Horiguchi and Pienaar, 1988a).
P. sociale, however, differs from B. caponii by several features: a. significantly larger size (45-60 µm); b. greater displacement of the cingulum; c. clearly reticulated thecal plates, d. position of the nucleus; and e. different habitat (Horiguchi and Pienaar, 1988a).