Luticola hamiltonii

Identification

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Description

Valves outline is elliptic-lanceolate in large specimens and more elliptical in smaller specimens. Apices are narrowly round in large specimens becoming broadly rounded in small specimens. Valve faces are flat and may be exceptionally maculose (covered with shallow surficial depressions).

Areolae are punctate to slightly elongate along the transapical axis. Areolae bordering axial area are aligned, but other areaolae are scattered.

Striae are radiate across the valve face, becoming more pronounced toward the apices. The central area is not easily distinguished, because it is ornamented with scattered areolae and irregular depressions. There is an internal thickening of silica across the central area. The stigma is difficult to distinguish from the scattered areola, but may become apparent in deep planes of focus.

Proximal raphe ends deflect away from the stigma before curving back toward the transapical axis. This is easily distinguished on large specimens but becomes difficult to resolve in small specimens. Distal raphe ends are sickle shaped, first curving away from the stigma before reversing course as it wraps onto the mantle.

Raphe branches are straight in most specimens, though in some specimens the raphe curves slightly away from the stigma. The axial area is hyaline and tapers as it approaches the apices, becoming closest to the raphe on the side of the valve bearing the stigma.

Under SEM it can be resolved that the stigma is a slit externally and opens as a semicircle on the inside (Levkov et al. 2013)

The specimens observed in Colorado are slightly wider (< 1 µm) than those observed by Levkov et al. (2013). This difference appears to be an acceptable level of morphological variability within geographically isolated populations.

The identity of the widely reported Luticola mutica is rather uncertain. Further work is needed to determine the type of L. mutica and how L. hamiltonii compares.

Autecology

Specimens presented here were collected from a high alpine wetland (~10,000 ft a.s.l.) where water was seeping out of a hillside and trickling into a small pool. This taxon was a minor member of a community dominated by Meridion anceps. This community included large taxa in the genera Neidium and Pinnularia, as well as a population of Iconella delicatissima.

Size Range, µm3

101-1000
Motility

Moderately motile
Attachment

Prostrate
Habitat

Moist habitats Benthic
Colony

Solitary
Occurrence

Rare
Waterbody

Inland Wetlands
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Credit: Lane Allen

Close up of some periphyton covered bryophytes that were sampled.

Credit: Lane Allen

This is the wetland where the specimens were collected, on the north shore of Joe Wright Reservoir.

Original Description

67. Luticola hamiltonii sp. nov. (Figs 42: 1-12; 43: 1-8)

Frustules rectangular in girdle view. Valve mantle with single row of elliptic areolae. Each girdle band with single row of small, round poroids. Valves elleptic-lanceolate in larger specimens and elliptic in smaller specimens, with broadly rounded to truncate and not protracted valve apices. Valve length 18-43 µm, valve width 8.5-13.5 µm. Axial area linear throughout. Central area on both valve margins bordered by 3-5 isolated round areolae. Central area ornamented with several scattered areolae and shallow, irregular depressions. Internally, central nodule strongly thickened forming stauros. Single isolated, slit-like stigma present in central area, located close to valve margin. Internally, stigma with prominent semi-lunate opening covered with large, tongue-like occlusion. Raphe branches straight to slightly curved. In some specimens raphe branches bordered by narrow ridges. Proximal raphe endings prolonged, hook shaped, or just doubly curved, deflected to side opposite to stigma. Distal raphe fissures hooked, first deflected towards the same side as proximal raphe endings and then hooked towards the opposite side, continuing onto the valve mantle, terminating shortly before valve edge. Internal raphe slit simple. Proximal raphe endings weakly deflected towards stigma, while distally, raphe branches terminating with small helictoglossae. Transapical striae composed of 3-4 round or elongated areolae. External foramina of areolae recessed, giving uneven appearance of valve face. Internally, areolae, occluded by hymenes, forming continuous strip across valve. Transapical striae in LM punctate, radiate throughout, 12-15 in 10 µm. Marginal channel, located on valve face/mantle junction, narrow, indistinct and occluded with hymenes.

Holotype (designated here): Slide BRM 101/96. Holotype specimen is represented by Fig. 42: 6. Finder no. 379.3.

Isotype Slide BRM 101/95.

Type locality Yellowstone Park, Moorerde, USA. Leg. J. D. Möller.

Etymology: The species is named in honor of Paul Hamilton, Canadian Museum of Nature, Ottowa, Canada, for his contribution to diatom research.

Distribution Observed from several samples from Yellowstone Park

Main differential characters: Valve outline and size, shape of the valve apices.

Similar species: Luticola pseudocharcotii sp. nov., L. plausibiloides Metzeltin, Lange-Bertalot & García-Rodríguez and L. modica Li, Metzeltin & Levkov sp. nov.

Remarks: Luticola hamiltonii resembles Luticola pseudocharcotii with respect to valve outline and the stria density, however, the latter taxon has higher number of areolae per stria (6-7 areolae per stria). Luticola plausibiloides (Figs 117: 1-11) can be differentiated by the shape of the valve apices and by being consistently wider than L. hamiltonii for any given valve length. Larger Valves of L. modica (Figs 41: 6-11) have a slight constriction at the valve apices, a narrower central area and a different shape and position of the stigma.