Estoniaster maennili, Blake & Rozhnov, 2007
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publication ID |
https://doi.org/ 10.5281/zenodo.13741483 |
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persistent identifier |
https://treatment.plazi.org/id/FB2787BC-5B56-FFE6-95E0-E02CFA8AFB05 |
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treatment provided by |
Felipe |
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scientific name |
Estoniaster maennili |
| status |
sp. nov. |
Estoniaster maennili sp. nov.
Fig. 2 View Fig .
Derivation of the name: The name in honor of the memory of the Estonian paleontologist and student of echinoderms, Ralf M. Maennil, 1924–1990.
Type material: Holotype PIN 4125/766; paratypes PIN 4125/767 and PIN 4125/768.
Type locality: Collected in the working Vasalemma Quarry , a limestone quarry about 1 km southeast of the railway station of the village of Vasalemma , near the town of Keila, near Tallinn, northern Estonia .
Type horizon: Upper Ordovician (Caradocian, upper part of the Didymograptus multidens Zone ) .
Material.— Holotype PIN 4125/766, a relatively complete specimen consisting of the disk and the proximal intervals of all arms. The abactinal skeleton is partially recrystallized and form of many ossicles is unclear. Because PIN 4125/766 is relatively complete, paratypes PIN 4125/767 and PIN 4125/768 appear derived from one or two additional individuals.
Diagnosis.— Estoniaster differs from other representatives of the family in the presence of a large, domed madreporite near the body margin; presence of two well−defined marginal series in which the superomarginals are fusiform and at least some bear a single enlarged accessory; inferomarginals lack enlarged spines.
Discussion.—Abactinal ossicles are small in palasteriscids and prone to alteration; nevertheless those of Estoniaster are most like those of new genus A (Blake in press) in being relatively short, robust, with a broad base; those of Lanthanaster are delicate with a broad base. Abactinals of Platanaster are slender with a small base; those of Palasteriscus are more robust than those of Platanaster but more delicate than those of Estoniaster ; data are very limited for both new genus B (Blake in press) and U. kinahani but those of both appear not to be clearly paxilliform, those of the former perhaps somewhat flattened and the latter more robust. Estoniaster differs from Lanthanaster , Platanaster , and Palasteriscus in the presence of two well−defined series of marginal ossicles. The fusiform, accessory−bearing superomarginals are unlike the more paxilliform superomarginals of new genus A (Blake in press) and Uranaster kinihani , the superomarginal series not well defined in U. kinihani . The madreporite is ventral in Palasteriscus and perhaps Lanthanaster but not recognized in new genus A (Blake in press) and U. kinahani . Disk form suggests Estoniaster has at most few actinal ossicles, unlike new genus A (Blake in press) and Uranaster kinihani . Adambulacrals are nearly equidimensional in Estoniaster and U. kinahani but appear a little wider than long in Lanthanaster and new genus B (Blake in press) and they are very wide in the other three genera. The ventral mouth frame expression of only new genus B (Blake in press) includes shovel−like mouth angle ossicles partially enclosed by proximal adambulacrals. Estoniaster appears similar to Lanthanaster and U. kinihani in body whereas arms are broad in Platanaster and Jurgiaster and columnar in Palasteriscus . New genus B (Blake in press) has long, tapered arms.
Description; form.—Five−armed palasteriscid; disk, although collapsed, appears small but larger than juncture of arms; presence of adambulacrals with overlapping marginals indicate absence of actinals at approximate midarm position; incomplete longest preserved arm (PIN 4125/766) approx. 18 mm. Abactinal abundance suggests some arching of profile in life.
Abactinals.—Abactinals ( Fig. 2A View Fig 5 –A View Fig 7) small, robust, paxilliform, appearing to vary somewhat in size and form locally. Bases enlarged, faceted; column robust, crown more or less expanded. Abactinals probably aligned in series inclined to the arm axis. Primary circlet, carinals not recognized.
Madreporite.—Madreporite ( Fig. 2A View Fig 1 View Fig , A 5 View Fig , A 6 View Fig ) dorsal, near marginal frame; ovate, long axis apparently radially oriented; madreporite 3.75 mm long, reconstructed width approx. 3 mm; surface sharply domed, grooving radiating from central area.
Marginal identification.—Marginals are poorly exposed, and the two marginal series (supero− and inferomarginal) are not exposed together. Inferomarginals are recognized based on similarities in form and position to those of other platyasteriscids. Enlarged fusiform dorsal ossicles (PIN 4125/766) are superomarginals ( Fig. 2A 2 View Fig , A 5 View Fig , also C 1), these separated from the disk margin by smaller paxilliform ossicles, which are therefore intermarginals ( Fig. 2C View Fig 1 View Fig ). In PIN 4125/768, the arm edge is preserved and positioning suggests ossicles of all three series.
Marginal description.—Superomarginals fusiform, elongate parallel to arm axis. Length at midarm approx. 1.5 mm, width approx. 1.0 mm. Exposed surface pustulate, arched; enlarged spines present. Lateral (i.e., adradial, abradial) margins irregularly faceted for contact with intermarginals, abactinals; distal termini sunken for articular tissues. One superomarginal preserved adjacent to madreporite appears enlarged, curvature suggests it abutted madreporite in life.
Inferomarginals ( Fig. 2B 2 View Fig , B 3 View Fig ) tabulate, thickened. IMs from approximately midarm position at least 2.75 mm in breadth, overlapped by adambulacrals; length approximately 1.5 mm. Ventral surfaces weakly arched; adradial portion of ventral face notched for overlapping adambulacrals. Abradial ossicular edge rounded; abradial portion of ossicle exposed dorsally, pustulate. Adradial portion of dorsal surface flattened where marginals abut intermarginals. Side faces ridged for intermarginal articulation. Abradial edge of ossicles pustulate but enlarged spine bases not present.
Intermarginals.—Intermarginals ( Fig. 2C View Fig 1 View Fig , below ambulacrals) similar to abactinals; rows few distally on arms.
Actinals.—No actinals identified; size of collapsed specimen suggests disk small and therefore at most only few actinals. Adambulacrals.—Adambulacrals and ambulacrals paired; adambulacral width at marginals approx. 2 mm, length approx. 1.5 mm. Adambulacrals ( Fig. 2B View Fig 1 View Fig , B 3 View Fig , C 2 View Fig ) rectangular, wider than long, arched, pustulate, enlarged spine bases not recognized. Adambulacral nose prominent, near−medial; ossicular curvature and ambulacral form suggest presence of skeletal gap. Abradial end of ossicle broadly rounded; ventral surface weakly arched. Dorsal surface ( Fig. 2B View Fig 1 View Fig ) smooth, transverse profile concave. Ambulacrals.—Ambulacrals ( Fig. 2A View Fig 1 View Fig , A 3 View Fig , A 4 View Fig , A7, B1, C1)
rectangular, slightly wider than long. Cross−furrow articular structures gracile; ambulacral channel broad, concave, radial canal not distinct. Transverse ridge robust, T−shaped, breached by well−developed distal groove for transverse water canal; abradial end of ridge weakly flared for contact with adambulacrals; ambulacral abutting or only weakly overlapping adambulacral ( Fig. 2B View Fig 1 View Fig ). Podial basin broad, approximately shared between successive ambulacrals. Dorsal ambulacral outline problematic: re−entrant in few ossicles suggests podial passageway ( Fig. 2B View Fig 1, C 1 View Fig ). Abradial end of ambulacral appears straight thus allowing space for skeletal gap adjacent to adambulacral nose, this edge only weakly recurved to partially enclose podial basin. Contact between successive ambulacrals with abactinal edge of more proximal ambulacral weakly overlapping more distal ambulacral; contact weakly sinuous. Articular structures consisting of marginal ridge and central depression ( Fig. 2A View Fig 4 View Fig ). Dorsal surface weakly undulating, adradial end of ossicle weakly raised, surface arched medially; abradial edge upright.
Mouth frame.—Mouth frame region obscured by debris.
Discussion.—The adambulacral and ambulacral series are displaced relative to one another in Fig. 2B View Fig 1 View Fig , thereby superficially appearing offset rather than paired. The left arrow in the figure identifies the articular nose of the adambulacral, and the adjacent ambulacral has been partially pushed between the successive adambulacrals; its adambulacral articular facet now lies adjacent to the next adambulacral to the right. The prominent nose is also visible in Fig. 2C 2 View Fig . Ambulacral−adambulacral positioning is not well exposed in the present specimen, but it is both well preserved and well exposed in specimens of the very similar new genus A (Blake in press).
A re−entrant present in the dorsal outline of a few ambulacrals ( Fig. 2B View Fig 1, C 1 View Fig ) suggests a podial pore similar to those suggested in a Devonian specimen of Promopalaeaster ? ( Haude 1995). Exposure for both Haude’s and the present specimen is poor. If the gaps indeed are podial in both the new species and in the Promopalaeaster ? of Haude (1995) then transfer of ampullae to the arm interior occurred in at least two asteroid lineages. Further, podial pore presence between only some ossicles indicates that transfer did not occur in a single evolutionary step in either lineage. Finally, available specimens are sufficient to demonstrate transfer of only a few ampullae, not of all, as found in post−Paleozoic asteroids.
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