SPECIES starting with "a"

 

Achnanthes coarctata

  1. Valve margin biundulate
  2. Raphe valve with central fascia
  3. Areolae distinct
  4. Rapheless valve with eccentric axial area

Monoraphid - Valves have biundulate margins, with a central constriction. The raphe valve face has a broad, central fascia. The fascia maybe asymmetric. The rapheless valve has a narrow, eccentric axial area. Striae are uniseriate and distinctly punctate.


Achnanthes felinophila

  1. Valves triundulate
  2. Ends cuneate
  3. Proximal raphe ends deflected slightly
  4. Rapheless valve with eccentric axial area

Monoraphid - Valves are distinctly triundulate in large specimens, becoming less triundulate and more lanceolate in smaller valves. The valve ends are narrow and cuneate. The raphe valve has a narrow axial area and a rectangular central area, extending to the valve margin. The proximal raphe ends are slightly unilaterally deflected slightly. The rapheless valve has an eccentric axial area. Striae are punctate and radiate throughout the raphe valve. Striae on the rapheless valve are parallel in the center, becoming radiate and curved at the ends.


Achnanthes inflata

  1. Valve margin triundulate
  2. Raphe valve with central fascia
  3. Areolae distinct
  4. Rapheless valve with eccentric axial area

Monoraphid - Valves are broad, with triundulate margins. The raphe valve face has a broad, central fascia. The rapheless valve has a narrow, eccentric axial area that crosses one side of the central undulation. Areolae are uniseriate and distinctly punctate.


Achnanthes longboardia

  1. Valves lanceolate
  2. Raphe valve with laterally expanded central area
  3. Rapheless valve with eccentric axial area
  4. Ends broadly rounded

Monoraphid - Valves lanceolate, slightly swollen near the center, with broadly rounded ends. The raphe valve with a narrow axial area and wide central area, expanded laterally to the valve margins. The proximal raphe ends are slightly deflected in the same direction. The rapheless valve with an axial area positioned near the valve margin.


Achnanthes mauiensis

  1. Valves linear
  2. Center valve gibbous
  3. Raphe valve with broad central area
  4. Rapheless valve with eccentric axial area

Monoraphid - Valves are linear, with a gibbous center. The ends are narrow, rostrate ends and may be asymmetric to the apical axis. The raphe valve has a narrow axial area, with a central area expanded to the valve margins. The rapheless valve with the axial area positioned near valve margin. Striae are punctate.


Achnanthes tumescens

  1. Valves linear-lanceolate
  2. Central valve gibbous
  3. Raphe valve with nearly rectangular central area
  4. Rapheless valve with eccentric axial area

Monoraphid - Valves are linear-lanceolate, with a gibbous center and broadly rounded ends. The raphe valve has a nearly rectangular central area that extends to the valve margins. The axial on the rapheless valve is positioned near the valve margin.


Achnanthes undulorostrata

  1. Valves triundulate
  2. Ends broadly rounded
  3. Proximal ends slightly unilaterally deflected
  4. Rapheless valve with eccentric axial area

Monoraphid - Valves are triundulate with broadly rounded ends. The raphe valve has a nearly rectangular central area, extending to the valve margins. The proximal raphe ends are deflected slightly unilaterally deflected. The rapheless valve has an axial area positioned near the valve margin.


Achnanthidium alpestre

  1. Valves linear-lanceolate with blunt, subrostrate ends
  2. Stria density high, 25-32 at valve center

Monoraphid - Valves linear-lanceolate with subrostrate ends. The striae are parallel or very slightly radiate throughout both valves. The striae are very dense, up to 28-32 in 10 μm in the valve center. The axial area is narrow and only slightly widened in the valve center.


Achnanthidium atomus

  1. Raphe valve with strongly radiate striae
  2. Rapheless valve with more widely spaced, parallel striae
  3. Valves elliptical to linear-elliptical
  4. Areolae small, not visible in LM

Monoraphid - Valves are elliptical to linear-elliptical. The raphe valve is concave and the rapheless valve is convex. Terminal raphe fissures are absent. Striae are strongly radiate on the raphe valve and parallel on the rapheless valve. The raphe valve has a transverse fascia, while the rapheless valve lacks a central area. The axial area on both valves is narrow and linear.


Achnanthidium deflexum

  1. Striae parallel throughout both valves
  2. Areolae within a stria usually visible
  3. Short marginal striae present in the central part of raphe valve

Monoraphid - The raphe valve is concave and the rapheless valve convex. Valves are linear-elliptical or elliptical with subrostrate ends. The striae are parallel throughout both valves. The striae are uniseriate and areolae are usually discernible. There are often very short striae present at the margin of both valves. The axial area is narrow and only slightly widened in the valve center.


Achnanthidium druartii

  1. Valves linear-lanceolate to lanceolate with subrostrate ends
  2. Striae very slightly radiate on both valves
  3. Stria density differs markedly between center valve and ends

Monoraphid - Valves are linear-lanceolate to lanceolate with subrostrate ends, 4.1-5.3 μm wide. The raphe valve has a linear axial area, which widens slightly in the middle portion of the valve. The rapheless valve has a narrow, linear axial area widening slightly in the middle. Striae are very slightly radiate throughout both valves, 15-20 in 10 µm in the center valve, 40-50 in 10 µm at the ends of the raphe valve, 25-35 in 10 µm at the ends of the rapheless valve. Very short marginal striae are are often present in the middle portion of the valve.


Achnanthidium duthiei

Achnanthes duthiei

  1. Valves linear to linear-lanceolate
  2. Valve ends broadly capitate
  3. Striae parallel or slightly radiate throughout both valves

Monoraphid - Valves linear to linear-lanceolate with broadly capitate ends.The striae are parallel or very slightly radiate throughout both valves. Striae density on both valves is 14-22 in 10 µm in the middle and 28-34 in 10 µm at the apices.


Achnanthidium eutrophilum

Achnanthes eutrophila

  1. Striae radiate throughout both valves
  2. Valve rhombic

Monoraphid - Frustule monoraphid, raphe valve concave and rapheless valve convex. Valves rhombic-elliptical to rhombic-lanceolate. Striae radiate throughout both valves, uniseriate. Two or three striae in the middle of the raphe valve are more distant from one another than other striae. Axial area narrow, only slightly widened at valve center.


Achnanthidium exiguum

  1. Valves with capitate to subrostrate apices
  2. Raphe valve with stauros
  3. Rapheless valve with small transversely rectangular central area
  4. Striae more dense on raphe valve than on rapheless valve
  5. Terminal raphe ends curved to opposite sides

Monoraphid - Valves are linear-elliptical to elliptical-lanceolate with narrowly capitate to subrostrate apices, 4.5-6.2 µm wide, 5-17 µm long. The raphe valve has a stauros. The rapheless valve has a small, transapically rectangular central area. The raphe is straight, but deflected to opposite sides near the apices with terminal raphe fissures strongly curved to opposite sides. The central external raphe ends appear to be expanded. The striae are radiate on both valves, but almost parallel at the apices. Raphe valve has 24-34 striae in 10 µm in mid-valve, up to 40-45 in 10 µm at apices; rapheless valve has 20-25 striae in 10 µm in mid-valve, up to...


Achnanthidium gracillimum

Achnanthes alteragracillima

  1. Valve ends narrowly rostrate to subcapitate
  2. Central area absent on both valves
  3. Striae parallel or slightly radiate throught both valves
  4. Striae 21-25 in 10 μm at valve center, 36-45 in 10 μm at valve apices

Monoraphid - Valves linear-lanceolate with narrowly rostrate or subcapitate ends. The axial area is narrow and only slightly widened in the valve center. The central area is absent. The striae are parallel or slightly radiate throughout both valves, 21-25 in 10 μm in the center valve, 36-45 in 10 μm at the valve apices.


Achnanthidium kranzii

  1. Valves linear-lanceolate to linear-elliptical
  2. Striae radiate in the center, parallel at the ends
  3. Raphe valve with large rectangular central area
  4. Rapheless valve with apically elliptical or rhomboid central area
  5. Terminal raphe fissures curved to one side

Monoraphid - Valves are linear-lanceolate to linear-elliptical with slightly drawn-out ends, 2.8-3.8 µm wide, 8-18 µm long. The raphe valve has a large rectangular central area that often extends to valve margins. The rapheless valve has an apically elongated elliptical or rhomboid central area. Terminal raphe fissures are sharply curved to the same side. Striae are uniseriate, moderately radiate in the middle part of both valves, becoming parallel at the apices, 24-30 in 10 µm in the central valve, up to 40 in 10 µm at the apices.


Achnanthidium kriegeri

  1. Striae parallel throughout both valves.
  2. Striae composed of two rows of areolae.
  3. Striae interrupted in the central part of both valves, forming an asymmetric central area.

Monoraphid - Achnanthidium kriegeri has a convex raphe valve and concave rapheless valve. The valve margin is linear or linear-elliptical with rounded, slightly drawn-out, or slightly capitate ends. The striae are parallel throughout both valves. The striae consist of two rows of areolae, with exceptions. At the valve margins there may be one row of areolae. At the sternum and distal ends, there may be three rows of areolae. An asymmetrical central area is present on both valves.


Achnanthidium latecephalum

  1. Valve ends broadly rostrate or subcapitate
  2. Central area absent on both valves
  3. Striae parallel or slightly radiate throughout both valves

Monoraphid - Valves linear-lanceolate with broadly rostrate or subcapitate ends. The axial area is narrow and only slightly widened at the valve center. A central area is absent. The striae are parallel or slightly radiate throughout both valves, 20-26 in 10 μm in the center valve.


Achnanthidium minutissimum

  1. Striae radiate throughout both valves
  2. Areolae typically not visible in LM
  3. Valves linear-lanceolate

Monoraphid - Raphe valve concave, rapheless valve convex. Valves linear-lanceolate, with subrostrate or subcapitate ends. Striae radiate throughout both valves, uniseriate. Areolae usually not discernible under LM. Axial area narrow, only slightly widened in the valve center. Centermost striae of raphe valve often more widely spaced than in the rest of the valve, considered to be a ‘fascia’.


Achnanthidium pyrenaicum

  1. Terminal raphe ends curved to the same side of the valve
  2. Striae mostly parallel, may be slightly radiate in the valve center and slightly convergent at the ends
  3. Fascia usually present on raphe valve

Monoraphid - Valves are linear-lanceolate with slightly drawn-out ends, often slightly asymmetrical about median transapical plane. The raphe valve is concave and rapheless valve is convex. The terminal raphe fissures are curved to the same side of the valve. Striae are parallel throughout both valves, or slightly radiate in the middle and slightly convergent at the ends. The striae are uniseriate with 2-4 areolae per stria. A fascia, or subfascia, is usually present on the raphe valve.


Achnanthidium reimeri

  1. Valves with subrostrate or subcapitate apices
  2. Valve width 3.5-5.5 µm
  3. Central area rhomboid in rapheless valve
  4. Central area rectangular or transversely elliptical in raphe valve

Monoraphid - Valves are linear-elliptical or linear-lanceolate with subrostrate or subcapitate ends. The striae are uniseriate. The striae are radiate in the center of the valves and parallel near the ends. The central area is rhomboid in the rapheless valve and rectangular or transversely elliptical in the raphe valve. The valve width is 3.5-5.5 µm.


Achnanthidium rivulare

  1. Striae parallel throughout both valves, slightly radiate at the apices of rapheless valve
  2. Striae parallel or slightly convergent at the apices of the raphe valve
  3. Areolae usually not visible with LM
  4. Valves lack short marginal striae in the central valve

Monoraphid - Raphe valve concave and rapheless valve convex. Valves linear-elliptical. The striae are parallel throughout most part of both valves. The striae are uniseriate and areolae are usually not discernible under LM. The axial area is narrow and only slightly widened in the valve center. The raphe has terminal fissures curved to one side.


Actinella punctata

  1. Valves asymmetric to transapical axis
  2. Raphe highly reduced
  3. Raphe positioned on valve mantle

Eunotioid - Actinella punctata is heteropolar. The raphe is very short and positioned mostly on the valve mantle, rather than the valve face.


Amphipleura pellucida

  1. Median rib narrow
  2. Raphe branch length nearly constant across specimens from large to small
  3. Transapical striae extremely fine

Symmetrical biraphid - The median rib in A. pellucida is narrow and does not vary in width across its length. Comparing specimens from large to small in size shows that the length of the raphe branch increases only slightly with valve length. The transapical striae are extremely fine and difficult to resolve under the LM.


Amphora copulata

  1. Dorsal fascia distinct
  2. Ventral striae uninterrupted
  3. Raphe arched
  4. Proximal raphe ends dorsally deflected
  5. Dorsal striae interrupted by intercostal ribs

Asymmetrical biraphid - Valves semi-lanceolate to semi-elliptical. Raphe positioned near the ventral margin, arched, with proximal and distal ends dorsally deflected. Dorsal and ventral fascia present, dorsal fascia typically ‘closed’ by a row of short axial striae, ventral fascia extending to valve margin. Dorsal striae interrupted by intercostal ribs, ventral striae composed of a single row of areolae.


Amphora minutissima

  1. Ventral margin tumid
  2. Raphe biarcuate
  3. Ventral fascia wider than dorsal fascia

Asymmetrical biraphid - Valves semi-elliptical with a smoothly arched dorsal margin, and tumid ventral margin. Raphe is biarcuate with proximal ends deflected dorsally. Dorsal fascia distinct and square shaped. The ventral fascia is distinct and wide.


Amphora ovalis

Navicula amphora

  1. Dorsal fascia absent
  2. Proximal raphe ends dorsally deflected
  3. Raphe ledge distinct
  4. Dorsal striae interrupted by intercostal ribs
  5. Ventral striae uninterrupted

Asymmetrical biraphid - Valves semi-elliptical with smoothly arched dorsal margin and slightly concave ventral margin. An uninterrupted raphe ledge is present. The raphe ledge is visible extending the length of the cell, covering the dorsal and ventral striae near the axial area. Raphe arched with proximal and distal ends dorsally deflected. Striae interrupted dorsally by intercostal ribs, composed ventrally of a single row of areolae. Dorsal fascia absent, ventral fascia present and extending to the valve margin.


Amphora pediculus

Amphora ovalis var. pediculus

  1. Raphe straight
  2. Distinctly punctate dorsal striae
  3. Straight to slightly concave ventral margin
  4. Small size

Asymmetrical biraphid - Valves moderately dorsiventral, semi-elliptical to semi-circular. Ventral margin straight to slightly concave. Raphe straight, with proximal raphe ends straight. Dorsal and ventral fascia distinct and extending to valve margins. Dorsal striae distinctly punctate, ventral striae composed of a single row of areolae.


Aneumastus minor

Navicula tuscula f. minor
Aneumastus tusculus f. minor
Aneumastus tuscula f. minor

  1. Valves elliptic to broadly lanceolate
  2. Apices acute, with blunt ends

Symmetrical biraphid - Aneumastus minor has small elliptic, to broadly lanceolate, valves. Valve length is less than 35 µm. Apices are acute with either unprotracted or weakly protracted blunt ends.


Aneumastus pseudotusculus

Mastogloia pseudotuscula

  1. Striae 12-16 in 10 µm
  2. Apices protracted
  3. Areolae evenly arranged

Symmetrical biraphid - Valves are lanceolate with protracted apices. The axial area is relatively straight, expanded in the center to form an unequal, irregular rectangular central area. Areolae are small, evenly arranged and nearly square, to dash-like.


Aneumastus rostratus

  1. Striae 11-12 in 10 µm
  2. Apices rostrate
  3. Areolae irregularly spaced

Symmetrical biraphid - Aneumastus rostratus has lanceolate to elliptic-lanceolate valves with rostrate apices. Striae are 11-12 in 10 µm and composed of irregularly spaced areolae. The raphe is weakly lateral.


Aneumastus tusculus

  1. Striae 11-12 in 10 µm
  2. Apices subcapitate
  3. Areolae irregularly spaced and dash-like
  4. Areolae 8-10 in 10 µm

Symmetrical biraphid - Aneumastus tusculus has wide linear-elliptic valves with abruptly protracted subcapitate apices. Striae number 11-12 in 10 µm and areolae number 8-10 in 10 µm. The areolae are irregularly spaced and dash-like, loosely arranged in wavy longitudinal rows.


Aulacoseira alpigena

  1. Ratio of mantle height to valve diameter < 1
  2. Rows of mantle areolae curve to the right
  3. Valve face flat
  4. Valve face with marginal areolae
  5. Spines located at the end of each pervalvar costa

Centric - Valves are 4-15 µm in diameter, mantle height is 4-7 µm. The ratio of the mantle height to valve diameter is less than 1. The rows of mantle areolae are curved to the right. The valve face is flat with one row of marginal areolae. Spines are positioned at the end of each pervalvar costa.


Aulacoseira ambigua

Melosira ambigua

  1. Ratio of mantle height to valve diameter > 1
  2. Rows of mantle areolae curved to right
  3. Ringleiste hollow
  4. Separation valve with short, pointed spines
  5. Spines originate from every pervalvar costa

Centric - Valves are 3-12 µm in diameter, with a mantle height of 5-15 µm. The ratio of the mantle height to valve diameter is greater than 1. The spiral rows of mantle areolae are curved to the right (dextrorse) and number 17-22 in 10 µm. Spines are located at the end of each pervalvar costa. Linking spines are short, triangular or bifurcated. Separation spines are small and pointed. In some separation valves, rows of areolae coalesce near the valve face, giving the appearance of spines originating from two pervalvar costae. The ringleiste is hollow, described by some authors as a ‘U-shaped sulcus’.


Aulacoseira canadensis

  1. Ratio of mantle height to valve diameter >1
  2. Rows of mantle areolae straight
  3. Mantle areolae large and square or oblong
  4. Spines of one size

Centric - Valves are 5-16 µm in diameter, with a mantle height of 13-22 µm. Mantle areolae are large and square or oblong in shape and arranged in straight rows. Spines of one size.


Aulacoseira crassipunctata

  1. Ratio of mantle height to valve diameter > 1
  2. Rows of areolae on mantle straight
  3. Mantle areolae round, widely separated
  4. Valve face strongly convex or concave
  5. Ringleiste bell-shaped in cross-section

Centric - Valves are 4-12 µm in diameter, with a mantle height of 9-18 µm. The ratio of the mantle height to valve diameter is greater than 1. The valve face is strongly concave or convex. Rows of areolae on the mantle are straight, 5.5-9 in 10 µm, with 5-10 round areolae in 10 µm. The collum is approximately 1/3-1/4 of the mantle height. The valve face is covered by areolae. The ringleiste is broad, shallow.


Aulacoseira granulata

Melosira granulata

  1. Ratio of mantle height to valve diameter > 0.8.
  2. Separation valves often with 1-2 very long spines
  3. Mantle areolae square
  4. Straight rows of mantle areolae on separation valves
  5. Rows of mantle areolae in linking valves curved slightly to right

Centric - Valves are 4-17 µm in diameter, with a mantle height of 4-20 µm. The ratio of the mantle height to valve diameter is usually greater than 0.8 but lower than 5. The mantle areolae are square. The rows of areolae on the mantle are curved to the right (dextrorse), but often are almost straight and parallel to pervalvar axis in separation valves, 8-18 rows in 10 µm. The short linking spines are located at the end of each pervalvar costa. Separation spines originate from two pervalvar costae. Most separation spines are 2-6 µm long, but a few, usually 1-2 spines per valve, are very long, almost equal in length to the valve mantle. The...


Aulacoseira granulata var. angustissima

Melosira granulata subsp. angustissima

  1. Ratio of mantle height to valve diameter > 3.2
  2. Valve diameter 2.5-4 μm
  3. Separation valves with 1-2 very long spines
  4. Rows of mantle areolae in separation valves straight, or slightly curved to right
  5. Rows of mantle areolae in linking valves curved to right

Centric - Valves are 2.5-4 µm in diameter, with a mantle height of 8-20 µm. The ratio of the mantle height to valve diameter is greater than 3.2.The rows of mantle areolae are curved to the right (dextrorse), but often are almost straight and parallel to pervalvar axis in separation valves. The rows of mantle areolae number 10-20 in 10 µm. Linking spines are located at the end of each pervalvar costa. The linking spines are short and bifurcated. Separation spines originate from two pervalvar costae. Most separation spines are 2-6 µm long and broadly triangular, but 1 or 2 spines per valve are very long, almost equal in length to the height of the...


Aulacoseira herzogii

  1. Ratio of mantle height to valve diameter >= 1
  2. Valves with 2(4) long spines
  3. Mantle areolae hardly visible in LM
  4. Rows of mantle areolae straight
  5. Ringleiste shallow

Centric - Valves are 3-7 µm in diameter and have a mantle height between 7-14 µm. The ratio of mantle height to valve diameter is either equal to, or greater than, 1. The straight rows of mantle areolae are often not resolvable in the light microscope and number 30-32 per 10 µm. These small areolae, if visible in LM, appear circular, 27-37 per 10 µm along the pervalvar row. On the valve mantle, two diametrically opposed grooves containing no areolae extend the entire length of the valve and two large, pointed separation spines diametrically opposed on the valve face extend in the plane of the mantle onto grooves of the neighboring valves. The...


Aulacoseira humilis

Aulacoseira distans var. humilis

  1. Small valve size
  2. Valve face concave or convex
  3. Long, thin spines at the end of each costa
  4. Extremely fine areolae in double rows
  5. Valve face with large areolae

Centric - Valves are 5-9 µm in diameter and have a mantle height of 2-5 µm. The valve face is strongly convex or concave and covered with large areolae. The striae are straight, composed of two rows of fine areolae, terminate in a single large areola, and are situated between raised costae. There is a long, thin spine at the end of each costa.


Aulacoseira italica

Melosira italica

  1. Rows of mantle areolae inclined to the left, or almost straight
  2. Linking spines large and broadly spatulate
  3. Mantle areolae "slit-shaped"
  4. Valve diameter 4-24 µm, mantle height 9-20 µm
  5. Ringleiste shallow, broad

Centric - The rows of slit-shaped mantle areolae are curved to the left or almost straight (parallel to pervalvar axis). The linking spines are large and spatulate, or anvil-shaped. The valve diameter is 4-24 µm and the mantle height is 9-20 µm. The ringleiste is thick and shallow.


Aulacoseira lirata

Melosira lirata
Melosira distans f. lirata
Aulacoseira distans var. lirata

  1. Ratio of mantle height to valve diameter close to 1
  2. Rows of mantle areolae straight or slightly curved to the right
  3. Valve face flat
  4. Valve face with marginal areolae
  5. Spines located at the end of each pervalvar costa

Centric - Valves 6-23 µm in diameter, with a mantle height of 5-14 µm. The ratio of the mantle height to valve diameter is close to 1. Rows of coarse round or elliptical pervalvar areolae are straight and parallel to the pervalvar axis or slightly curved to the right, 7-13 in 10 µm. The areolae closest to the collum are often the largest. The valve face is flat, unornamented except for one row of marginal areolae. Spines are located at the end of each pervalvar costa. Spines are branching at the end.


Aulacoseira muzzanensis

Aulacoseira granulata var. muzzanensis

  1. Ratio of mantle height to valve diameter < 1.2
  2. Separation spines long, few
  3. Mantle areolae appear square or oval
  4. Rows of mantle areolae in separation valves straight or curved to right
  5. Rows of mantle areolae often appear biseriate

Centric - Valves are 9-24 µm in diameter, with a mantle height of 5-13 µm. The ratio of the mantle height to valve diameter is 0.4-1.2. The mantle areolae are square, but sometimes appear as oval in LM. The rows of are almost straight and parallel to pervalvar axis in separation valves, but often curved to the right in linking valves, 7-15 in 10 µm. Areolae in separation valves are often coarse and disorganized. The straight rows of areolae often appear as biseriate in LM. Linking spines are located at the end of each pervalvar costa. They are short, triangular or bifurcated. Separation spines originate from two pervalvar costae. Most separation...


Aulacoseira nivalis

Aulacoseira  distans var. nivalis
Melosira  distans var. nivalis

  1. Ratio of mantle height to valve diameter < 1
  2. Rows of mantle areolae straight, inclined to the right
  3. Valve face flat
  4. Valve face with large areolae
  5. Spines located at the end of each pervalvar costa

Centric - Valves are 6-18 µm in diameter, mantle height is 2.5-6 µm. The ratio of the mantle height to valve diameter is less than 1. Rows of pervalvar areolae are straight, slightly inclined to the right, 12-16 in 10 µm, with 2-6 elongated areolae in each row. The valve face is flat, covered by large areolae. The spines originate from every costa. The ringleiste is very shallow. One rimoportula is present on the mantle, near the ringleiste.


Aulacoseira nivaloides

Aulacoseira distans var. nivaloides
Melosira distans var. nivaloides

  1. Ratio of mantle height to valve diameter < 1
  2. Rows of mantle areolae straight, inclined to the right
  3. Valve face convex or concave
  4. Valve face covered by areolae
  5. Spines originate from every second or third costa

Centric - Valves are 4-11 µm in diameter, with a mantle height of 4-7 µm. The ratio of the mantle height to valve diameter is close to 1. The valve face is convex or concave, covered by areolae. Rows of pervalvar areolae are straight or slightly inclined to the right, 14-22 in 10 µm, with 13-21 areolae in 10 μm. The height of the collum is approximately 1/3 of the mantle height. The pointed spines originate from every second or third costa. The ringleiste is very shallow.


Aulacoseira nygaardii

  1. Ratio of mantle height to valve diameter close to or < 1
  2. Rows of mantle areolae straight
  3. Valve face appears slightly convex
  4. Valve face with short radial striae at the periphery
  5. Spines originate from every second or third costa

Centric - Valves are 5-11 µm in diameter, with a mantle height of 4-19 µm. The ratio of the mantle height to valve diameter is close to 1. The valve face appears slightly convex in LM. Rows of pervalvar areolae are straight, 22-31 in 10 µm, with 30-42 areolae in 10 μm. The valve face is plain with short radial striae at the periphery. The spines are anchor-shaped, narrow, and originate from every second or third costa. The ringleiste is shallow and bell-shaped in cross-section.


Aulacoseira pusilla

  1. Ratio of mantle height to valve diameter close to 1 or < 1
  2. Rows of areolae on mantle curve to the right
  3. Valve face flat or slightly convex
  4. Valve face with small scattered areolae
  5. Spines originate from two or three pervalvar costae

Centric - Valves are 4.5-7.5 µm in diameter, with a mantle height of 2.2-4.5 µm. The ratio of the mantle height to valve diameter is close to or slightly less than 1. Valve face is flat or very slightly convex with small scattered areolae. Rows of pervalvar areolae are curved to the right, 24-26 in 10 µm. Spines originate from two or three pervalvar costae. Ringleiste is solid, shelf-like.


Aulacoseira subarctica

Aulacoseira  italica subsp. subarctica

  1. Ratio of mantle height to valve diameter >= 1
  2. Rows of areolae on mantle curve to the right
  3. Spines originate from two or three pervalvar costae
  4. All spines pointed, long and robust
  5. Valve face flat

Centric - Valves are 3-14 µm in diameter, with a mantle height of 2.5-14 µm. The ratio of the mantle height to valve diameter is equal or greater than 1. The mantle has straight sides and the valve face is flat. Rows of pervalvar areolae are curved to the right (dextrorse). there are 15-22 rows in 10 µm. The spines are robust, pointed and originate from two or three pervalvar costae. Unlike most other Aulacoseira species, A. subarctica does not have differentiated linking and separation valves; all valves have the spines of the same type. The ringleiste is solid, shelf-like.


Aulacoseira tenella

Melosira distans var. tenella
Aulacoseira distans var. tenella

  1. Ratio of mantle height to valve diameter < 1
  2. Rows of mantle areolae straight, inclined to the right
  3. 2-3 areolae in each row of mantle areolae
  4. Valve face with small areolae
  5. Spines very short

Centric - Valves are 5-8.5 µm in diameter, with a mantle height of 1.8-2.6 µm. The ratio of the mantle height to valve diameter is less than 1. The valve face is flat. Rows of pervalvar areolae are straight, slightly inclined to the right, and 21-25 in 10 µm, with 2-3 areolae in each row. The height of the collum is approximately 1/2 of the mantle height. The valve face is covered by small areolae. The spines are very short and triangular. The ringleiste is very shallow.


Aulacoseira valida

Melosira valida

  1. Ratio of mantle height to valve diameter 0.8-1.5
  2. Rows of mantle areolae curve to the right
  3. Mantle areolae become smaller from valve face to collum
  4. Spines large, spatula-shaped
  5. Spines originate from two pervalvar costae

Centric - Valves have thick walls and are 10-16 µm in diameter, with a mantle height of 7-16 µm. The ratio of the mantle height to valve diameter is 0.8-1.5. The valve face is slightly convex, covered by small areolae. Pervalvar rows of areolae are strongly curved to the right (dextrorse), 12-17 in 10 µm. There are 11-17 areolae in 10 µm along the pervalvar row. The mantle areolae are larger at the valve face and gradually become smaller toward the collum. The spines are large, spatula-shaped and originate from two pervalvar costae.