Synura morusimila W. Pang & Q. Wang 2013, sp. nov.

Synura morusimila W. Pang & Q. Wang, sp. nov. (Figs. 2–16)

Colony rectangular, large; cell ovate, two types of scales: caudal scale ovate to obovate, 1.6–2.9 × 3.0– 3.5 µm, spineless, small pores on the base plate, upturned edge supported by radial ribs; body scale, oval, ovate or obovate, 2.1–2.6 × 2.8–3.6 µm, spine-bearing, with teeth on the top, ridges or an irregular reticulum radiating from the base of the spine to the plate, small pores on the center to the back of the base plate. Stomatocyst of smooth surface, ovate, 14.0–15.7 × 19.5–22.1 µm, with a low conical collar and a regular pore.

Type:–– CHINA. Inner Mongolia: Genhe, Yuelian, 23 July 2006, coll. Quanxi Wang & Wanting Pang, 063376 (holotype: SEM stub 063376 and permanent light microscopic slide 063376, Shanghai Normal University, Shanghai, China).

Colonies (Figs. 2–4) rectangular, 63.6–68.2 × 109.1–186.4 µ m. Cells ovate (Figs. 5–6), 16.5–17.7 × 22.9–24.7µm with pale chloroplasts. The stomatocyst (Figs. 7–10), Stomatocyst 55, Pang, W & Q. Wang, is large and ovate, 14.0–15.7 × 19.5–22.1 µm, smooth. It is relatively flat or depressed at anterior extremity and round at posterior extremity. There is a low conical collar (basal diameter 1.5–2.2 µm; apical diameter 1.2–1.4 µm; height 0.13–0.24 µm) surrounding the regular pore (diameter 0.9–1.1 µm). From broken specimens it can be observed that the body is 0.65–0.86 µm thick, but it is thinner near the collar (thickness ca. 0.4 µm).

The scales consist of two distinct types (Figs. 11–12). The body scales (Figs. 13–17) are oval, ovate or obovate, 2.1–2.6 × 2.8–3.6 µm. The spine is cylindrical, 1.1–1.8 µm long, terminating in 10–14 teeth. The base of the spine is covered with ridges or irregular reticulum, radiated to the plate. The upturned edge is broad, inside it is supported by struts. The base plate in the center to back of the scale is provided with small pores. The spineless caudal scales (Fig. 18) are ovate to obovate, 1.6–2.9 × 3.0– 3.5 µm. The upturned edge is supported by radial ribs. The base plate in the back of the scale is provided with small pores.

Synura morusimila sp. nov. is most closely related to species in the section Synura (Balonov & Kuzmin 1974: 1677) based on distal spines of the body scales and spineless caudal scales. It is distinguished from other Synura taxa by the cylindrical spine on the body scale and the irregular reticulum on the base of the spine.

The colony and cell descriptions of S. morusimila are based on the LM observation of the cells with stomatocysts forming in them. However, the colony shape of S. morusimila might be similar to S. spinosa (Kristiansen & Preisig 2007) where the colony is often elongated.

Our new species shares many morphological features of the scales with S. uvella (Kristiansen & Preisig 2007). In TEM, differences between the two species are evident, including the distal part of the scale, the shape of the spine and density of the pores in the centre of the scale. The scale of S. uvella has a conical spine while the spine on the scale of S. morusimila is cylindrical. A meshwork covers the distal part of the scale in S. uvella, while there is an irregular reticulum seen in S. morusimila. In the case of S. uvella, more densely arranged pores are on the center of the scale.

Compared to the fossil Synura species, S. recurvata Siver & Wolfe (2005: 303), the spine apex of S. morusimila is round and ornamented randomly with teeth. The spine apex of S. recurvata is flat and lined with a ring of teeth which most often are bent slightly backwards.

The stomatocyst of S. morusimila is similar to Stomatocyst 302, Gilbert & Smol (Gilbert et al. 1997) which is produced by S. splendida (Bourrelly 1957), but in the latter the collar is larger, and its body is ornamented with five or six smooth, flat, elevated plateaux. It is also similar to the cyst of S. uvella (Bourrelly 1957) which was described with a line drawing based on LM.

Synura species have diverse ecologies; some species are widespread, others are extremely rare and confined to special habitats (Kristiansen 1975). The colony and stomatocyst of S. morusimila were abundant in the samples collected from bogs with Sphagnum and Carex. Scales and stomatocysts were found from the Yuelian, Alongshan and Amuer localities, but colonies were only observed from Yuelian, where they were in deep forest showing little trace of human habitation. These observations might suggest that S. morusimila might prefer peat bogs with low temperature, low pH and scarce human disturbance.

Distribution and ecology:–– Synura morusimila was found in bogs in Yuelian, Alongshan and Amuer with pH lower than 7, water temperature 10–15 ºC (summarized in Table 1).

Etymology:— The species name is derived from the shape of the colony with stomatocysts as in the fruit of the mulberry.