Chaetoceros coloradensis Li & Kociolek, 2016

Li, Jing, Kociolek, J. Patrick & Gao, Yahui, 2016, Chaetoceros coloradensis sp. nov. (Bacillariophyta, Chaetocerotaceae), a new inland species from Little Gaynor Lake, Colorado, North America, Phytotaxa 255 (3), pp. 199-213 : 202-205

Chaetoceros coloradensis Li & Kociolek , sp. nov. ( Figs 2–5 , 9–17 , 27–35 )

Cells solitary, rectangular in girdle view, one chloroplast per valve, Cells 3.0–9.5 μm in the apical axis, 2.4–8.1 μm in the transapical axis, and 2.0–9.0 μm in the pervalvar axis. Valves elliptical, sometimes nearly circular, lacking processes. Valve surface flat. An anastomosing pattern of siliceous ribs on valve face. Girdle bands delicate, weak costae on the bands. Setae thin, hollow, not fused, and closed at the end. Spiral rows of rectangular pores and tiny spines on setae. Pores smaller at the base of setae. Setae offset 30 to 45° between setae on opposite valves. Resting spores heavily silicified, smooth on the surface. Primary valve convex. Secondary valve with variable morphology, usually with a chimney-like protrusion, sometimes with almost the same apical length as the primary valve. Puncta randomly distributed on the mantle of the secondary valve. A siliceous annulus is present on the mantle of secondary valve.

Type: — UNITED STATES. Colorado: Boulder County, Little Gaynor Lake (40.12° N, 105.12° W), May 3 rd 2012. (holotype: COLO!, individual on slide JPK 9560, Kociolek Collection, here illustrated as Fig. 4 . Isotype: AU!, slide MMDL 120503).

Etymology: —Named for the state where the species was collected.

Observations: —Over 100 vegetative cells have been measured. Frustules are solitary, delicate, containing only one chloroplast ( Figs 2–3 ). The cells are rectangular in girdle view ( Figs 3–5 ), sometimes nearly square ( Fig. 3 ). Valve surfaces are flat ( Figs 3–5 ), an anastomosing pattern of narrow ribs can be found on the valve face ( Fig. 9 ). No processes are present on the valve ( Fig. 9 ). Cells are 3.0–9.5 μm in the apical axis, 2.4–8.1 μm in the transapical axis, and 2.0–9.0 μm in the pervalvar axis. Very weak siliceous costae are ornamented on girdle bands ( Fig. 10 ). Setae are thin, 3–4 times longer than apical axis. Setae on opposite valves have different orientation, with a 30–45° difference between these on opposite valves ( Fig. 2 ). Spiral rows of rectangular pores, spiral rows of minute spines on setae ( Fig. 13 ), and the pores, are smaller at the base of the setae ( Fig. 11 ). Setae are closed at the end tip ( Fig. 12 ).

Nearly 300 resting spores have been measured. Resting spores are smooth, and form inside of vegetative cells ( Fig. 5 ). Apical length of primary valve is 2.4–13.8 μm, width of the primary valve is 2.6–10.0 μm, height of primary valve is 3.6–6.2 μm. Length of secondary valve is 1.0–6.0 μm. Spore height ranges from 4.8 to 11.0 μm. The shape of resting spores is highly variable ( Figs 27–35 ). The primary valve is convex, sometimes concave at the center ( Fig. 28 ). The secondary valve sometimes has a chimney-like protrusion ( Fig. 15 ). The secondary valve is not always substantially narrow when compared with the apical length of the primary valve ( Figs 16 , 27, 33 ). In addition, the secondary valve can be narrow and long ( Fig. 34 ). The margin of the secondary valve is flat ( Fig. 29 ) or concave ( Fig. 30 ). Additionally, the secondary valve can be trapezoidal ( Fig. 29 ) or inverted trapezoidal ( Figs 28, 32 ) in shape. The secondary valve mantle might be elongated ( Figs 17 , 33, 35 ), or even be separated from the primary valve ( Fig. 32 ). The primary and secondary valves can also be similar to one another ( Fig. 31 ). There is a siliceous annulus at the margin of the secondary valve mantle ( Fig. 15 ). Puncta are randomly distributed on the secondary valve mantle ( Figs 15 , 27 ).

Phylogenetic analyses: —The ML and MrB for LSU have the same topologies ( Fig. 24 ). In these trees, all solitary Chaetoceros species, including C. coloradensis , fall into clade V with high support (96% ML/100% MrB). Within the clade V, C. coloradensis clusters with C. muelleri (strain GSL5) and C. gracilis F. Schütt (1895: 42) with high support (100% ML/ 100% MrB); while inside the small clade formed by these three species, C. muelleri clusters with C. gracilis and forms a smaller clade (ML 80%/99% MrB), which suggests that C. muelleri is more closely related to C. gracilis in the LSU analysis.

For SSU, the ML and MrB analyses also have the same topologies ( Fig. 25 ). However, members of the section Simplicia do not fall into a single clade in the SSU analyses, indicating that the section Simplicia is not monophyletic. Although most Simplicia taxa are in clade IV (62% ML/87% MrB), two strains of C. muelleri , two strains of C. calcitrans f. pumilus Takano (1968: 3) and two strains of C. calcitrans ( Paulsen 1905: 6) Takano (1968: 1) fall outside of this clade. These two strains of C. muelleri form clade I with C. decipiens ( Cleve 1873: 11) and C. cf. lorenzianus Grunow (1863: 157) with high support (100% ML/100% MrB). The four strains of C. calcitrans and C. calcitrans f. pumilus form clade II with high support (100% ML/100% MrB). Chaetoceros coloradensis falls into clade IV and forms a sister clade with the strain of C. muelleri collected from Great Salt Lake, but the support is low (60% ML/63% MrB).

The ML and MrB analyses generated the same topologies for the phylogenetic tree of LSU+SSU ( Fig. 26 ). Solitary Chaetoceros species fall into clade V with high support (98% ML/100% MrB). Chaetoceros coloradensis forms a small clade with C. muelleri (strain GSL5) and C. gracilis with high support (100% ML & MrB). Inside this small clade, C. coloradensis forms a clade with C. muelleri (strain GSL5) (88% ML and 100% MrB).

The analyses of LSU, SSU and LSU+SSU provide high support that the position of C. coloradensis is close to C. muelleri (strain GSL5) isolated from Great Salt Lake. The molecular analyses also indicate C. coloradensis is one member of the clade composed by solitary Chaetoceros taxa.

Figures

FIGURE 24. PhyML tree for LSU analysis. Bootstrap support from maximum likelihood and Mr Bayes. “–“ indicates support values less than 50%.

FIGURE 25. PhyML tree for SSU analysis. Bootstrap support from maximum likelihood and Mr Bayes. “–“ indicates support values less than 50%.

FIGURE 26. PhyML tree for LSU+SSU analysis. Bootstrap support from maximum likelihood and Mr Bayes. First sequence number shows LSU sequences, second sequence number shows SSU sequences.

FIGURES 2–8. LM micrographs of C. coloradensis sp. nov. and C. muelleri.S 2–3. Images of C. coloradensis (Strain LGL4) from wild live samples collected on April 27th, 2014. 2. Single cell in valve view.Arrow indicating angles between straight setae on opposite valve of C. coloradensis in valve view. 3. Frustules in girdle view. One chloroplast in single vegetative cell. 4–5. Images of C. coloradensis from slide JPK9560. 4. Holotype. Frustules in girdle view. Arrow shows primary valve of the resting spore forming inside a vegetative cell. 5. Frustules in girdle view. Resting spore already formed inside a vegetative cell (arrow). 6–8. Images of wild live C. muelleri (Strain GSL5) collected on May 14th, 2014. Scale bars = 5 μm. 6. Frustules in girdle view.Arrow indicates resting spore formed inside of C. muelleri in girdle view. 7. Frustules in valve view.Arrow shows nearly parallel curved setae on opposite valve of C. muelleri in valve view. 8. Colony in girdle view, process between sibling cells (arrow).

FIGURES 9–13. SEM micrographs of C. coloradensis. Cleaned sample of JPK 9560. Vegetative cells. 9–12. TEM. 9. Anastomosing pattern of the valve and processes lacking. Scale bar = 2 μm. 10. Parallel costae on girdle band. Scale bar = 2 μm.11. Small pores at base of the setae (arrow). Scale bar = 2 μm. 12. Closed end tip of the setae (arrow). Scale bar = 2 μm. 13. SEM. Arrow indicating spiral rows of rectangular pores and minute spines on the setae and the closed end of the setae. Scale bar =1 μm.

FIGURES 14–17. SEM. Resting spores of Chaetoceros coloradensis.14. Primary valve of resting spore. Arrow indicates arched primary valve of resting spores. Scale bar = 1 μm. 15. Secondary valve of resting spore. Siliceous annulus and randomly distributed puncta on secondary valve of resting spores (arrow). Scale bar =1 μm. 16. Resting spore. Short secondary valve of resting spores (arrow). Scale bar = 1 μm. 17. Resting spores. Elongated secondary valve of the resting spores (arrow). Scale bar = 1 μm.

FIGURES 27–35. Variable resting spores of Chaetoceros coloradensis (from slides in JPK collection from sample 9560). LM photos. Scale bars = 5 μm. 27. Arrow indicates short and robust secondary valve and puncta on the mantle of secondary valve of resting spore. 28. Central concave primary valve and inverted trapezoidal secondary valve of a resting spore (arrow). 29. Flat secondary valve margin on the left, convex secondary valve margin on the right and trapezoidal secondary valve of resting spore (arrow). 30. Arrow showing the margin of a concave secondary valve of a resting spore. 31. Arrow exhibiting primary valve similar to secondary valve of a resting spore. 32. Arrow showing separated primary valve and inverted trapezoidal secondary valve of a resting spore. 33. Narrow and long secondary valve of a resting spore. 34. Elongated mantle of secondary valve and short secondary valve of a resting spore. 35. Elongated mantle of secondary valve and bullet-like secondary valve of a resting spore.