Paraostenia voultensis Secrétan, 1985

Laville, Thomas, Forel, Marie-Béatrice & Charbonnier, Sylvain, 2023, Re-appraisal of thylacocephalans (Euarthropoda, Thylacocephala) from the Jurassic La Voulte-sur-Rhône Lagerstätte, European Journal of Taxonomy 898 (1), pp. 1-61 : 35-45

Paraostenia voultensis Secrétan, 1985

Figs 5D , 16–20

Paraostenia voultensis Secrétan, 1985: 388–389 , fig. 5c–h, l.

cf. Ostenia sp. – Secrétan & Riou 1983: 26–27, figs 1, 6–7.

Paraostenia voultensis – Rolfe 1985: fig. 4; 1992: fig. 1a. — Schram et al. 1999: 772, tab. 1. — Charbonnier 2009: 206, figs 233, 251, 339–340, tab. 14. — Charbonnier et al. 2010: 115, 121, fig. 5e, tabs 1–2; 2014: 375, tab. 1. — Schram 2014: 353, fig. 3d. — Ji et al. 2017: 174. — Ehiro et al. 2019: 330. — Rak et al. 2018: 268. — Braig et al. 2019: fig. 5.6, 5.31. — Van Roy et al. 2021: 1739. — Laville et al. 2021a: 310–311; 2021b: 92–94; 2021c: 305. — Schram & Koenemann 2022: fig. 41.4, tab. 41.2.

Original diagnosis ( Secrétan 1985)

As for genus.

Emended diagnosis

Paraostenia with a serrate dorsal margin and a dorso-lateral row of pores.

Material examined

Holotype FRANCE • La Boissine, La Voulte-sur-Rhône, Ardèche ; Callovian , Middle Jurassic ; morphotype 2; MNHN.F. R50977 .

Paratype FRANCE • 1 spec.; same collection data as for holotype; MNHN.F. R50979 .

Additional material

FRANCE • 73 specs; same collection data as for holotype; morphotype 2; MNHN.F. A29150 , A29231 , A29256 , A29300 A29320 to A29322 , A29326 , A29328 to A29338 , A29340 , A29341 , A29344 , A29346 , A29347 , A29351 , A29354 , A29355 , A29362 , A29369 , A29370 , A53132 , A53328 to A53330 , A53336 , A53340 , A84030 to A84038 A84041 , A84043 to A84058 , A84060 to A84063 , A84065 to A84071 , R50966 , R50978 • 4 specs; same collection data as for holotype; morphotype 2; MSNM i7597 , i18928 , i25037 , i25038 • 9 specs; same collection data as for holotype; morphotype 1; MNHN.F. A29339 , A29354 , A29357 , A29361 , A53131 , A84039 , A84040 , A84047 , A84055 , A84059 .

Measurements

See Table 2 .

Description

Shield morphology

Square-shaped to sub-trapezoidal shield in lateral view with an asymmetric anterior margin formed on a well-developed optic notch, a rounded or sharp antero-dorsal corner, a convex dorsal midline is slightly convex, with a large fin-like ( Fig. 18D–E ) or flat dorsal carina, a rounded postero-dorsal corner, a vertical or postero-ventrally tilted, concave posterior margin, a rounded postero-ventral corner and a ventral margin divided into a posterior half steeply descending antero-ventrally and a horizontal anterior one ( Figs 16 , 17A–D ). Rim of all free margin delimiting a marginal fold ( Fig. 16B, D ).

Shield macro-ornamentation

Presence of one straight and large medio-lateral carina, running along almost the entire length of the shield and divided into two parts by a longitudinal narrow furrow ( Figs 16A, C , 21A–B ). Presence of seven small serrations dorsally oriented on the anterior side of the dorsal carina and of seven serrations dorsally oriented, longer than the anterior ones on the posterior side ( Fig. 18D–E ).

At least 13 pores forming a sinuous row in the dorsal area of the shield, above the medio-lateral-carina ( Figs 16A, C , 18D–F ). Horseshoe-like ornamentation or field of punctuations covering the ventral area of the shield ( Fig. 19A, C, J ). Fields of punctuations also covering the surface of the dorsal area ( Fig. 19E–G ). Punctuations in the ventral area most probably correspond to degraded horseshoe-like ornamentation.

Presence of a hump either on the medio-ventral area of the shield or near the antero-ventral corner ( Figs 16A, C , 19H–J ).

Sensory structures

Rounded, stalked, compound eyes protruding from the optic notch and occupying most of it ( Figs 16 , 18B–C ). Eyes formed of hexagonal ommatidia (w = ~80 µm; l = ~80 µm; about 236 per mm²; Fig. 17F ).

Cephalic appendages

Antenniform structure only perceptible by the muscle fibres protruding from the optic notch and decreasing in diameter distally ( Fig. 17E ).

Raptorial appendages

Presence of three pairs of slender raptorial appendages recognised by the preservation of the muscles,

protruding from the ventral margin, posterior to the presumed cephalic appendages. Raptorial appendages consisting of two parts: a proximal postero-ventrally oriented and a distal one, antero-ventrally oriented. Articulation between both parts forming an elbow.

First pair of raptorial appendages ( Figs 16 , 19A, C ), the shortest, consisting of a proximal part with two podomeres: podomere 1 being 3.7 times as long as wide; podomere 2 being 4.7 times as long as wide and being longer than podomere 1. Distal part of the appendages formed by three podomeres: podomeres 3 being 4.4 times as long as wide; podomere 4 being 4.8 times as long as wide; podomere 5, the most distal one, being 3.1 times as long as wide.

Second pair of raptorial appendages consisting of a proximal part with two rectangular podomeres ( Fig. 18M, O ): podomere 1 not being well preserved; podomere 2 being 6.1 times as long as wide. Distal part of the appendage consisting of three podomeres: podomere 3 being 5.6 times as long as wide and bearing one spine on its medial side; podomere 4 being 5.2 times as long as wide and bearing three spines on its medial side; podomere 5 being 2.8 times as long as wide and ending distally in a cluster of three long spines.

Third pair of raptorial appendages, the longest, consisting of a proximal part formed by two podomeres, podomere 2 being 5.9 times as long as wide ( Fig. 18I–K ). Distal part consisting of three podomere: podomere 3 being 4.4 times as long as wide, bearing two spines on the distal part of its medial side; podomere 4 being 6.4 times as long as wide and bearing nine spines on its medial side, with the first four arranged in pairs; podomere 5 being 4.3 times as long as wide and ending distally with a cluster of three long spines.

Oval structure

Oval structure protruding from the ventral margin, behind the last pair of raptorial appendages ( Fig. 18G– H ). Structure associated with a lamellar structure in one specimen ( Fig. 17G ).

Posterior trunk

Nine rectangular pleural parts of trunk segments protruding from the posterior part of the ventral margin ( Figs 16B, D, G , 20 ). In some specimens, pleural part increasing in size until tp 6, then decreasing until tp 9 ( Fig. 16B, D, G ). In other specimens, pleural parts decreasing in size posteriorly with last one (tp 9) thinner than the rest ( Fig. 17H ). Proximally, they have a postero-dorsal orientation while they are curved downward distally. Trunk ending in a square segment, i.e., the telson, bearing a rounded structure ( Fig. 17I–J ). Field of setae visible on the telson.

Posterior trunk appendages

Nine pairs of appendages attached to the pleural part of the posterior trunk ( Fig. 20F–H ). Appendages oriented postero-dorsally and proximally consisting of a curved square-shaped plate ( Fig. 20H ) and ending distally in a styliform part ( Fig. 20I–J ). Last pair of appendages with a rounded distal plate.

Gills

Eight arcuate, lamellar gills preserved below the medio-lateral carina ( Fig. 19A–B ).

Remarks

Paraostenia voultensis displays an important variability for some features. For instance, some specimens have a trapezoidal shield with a vertical posterior margin and a horseshoe-like ornamentation ( Figs 17– 20 ), while others have a square-shaped shield with a postero-ventrally tilted posterior margin and no ornamentation ( Fig. 16 ). Moreover, it seems there is a slight difference in total length ( Fig. 21A ): the histogram shows a bimodal distribution that might indicate the presence of two different morphotypes.

Morphometry

In order to characterise the variability of Paraostenia voultensis and to confirm the presence of two morphotypes, we ran various morphometric and statistical analyses. In this section, we consider separately both P. voultensis putative morphotypes in order to test for their differences. Morphotype 1 corresponds to the small specimens with a square-shaped shield, a postero-ventrally tilted posterior margin, and no ornamentation. Morphotype 2 corresponds to bigger specimens having a square-shaped shield with a postero-ventrally tilted posterior margin and no ornamentation.

Descriptive statistics

The measurements made on Paraostenia voultensis allow us to test the homogeneity of the sample. With the exception of the length of the shield (Ls), histograms appear normally distributed for all measurements ( Fig. 21A ). According to the results of the Shapiro-Wilk test (W> 0.95; p> 0.13), all measurements probably follow a normal law.

Simple allometry

For Paraostenia voultensis ( Fig. 21 ; Table 3 ), a strong and significant correlation has been found for morphotype 2 (R² = 0.892, p-value <0.05) while it is non-significant for morphotype 1 (R² = 0.605, p-value = 0.222). The slope (likelihood ratio statistic equal to 0.4298, p-value = 0.5121) and the elevation (Wald statistic equal to 0.7178, p-value = 0.39687) are equal between the allometric line of both morphotypes. This indicates that there is no difference in static allometry of both morphotypes and that they are located on a similar allometric line.

For all other species, a strong and significant positive correlation has been found between shield length and shield height (R²> 0.86, p-value <0.02; Table 3 ).

Complex allometry

The first two principal components account for 89.0% of the variance ( Fig. 22A ). PC1 accounts mostly for variation in height and angle measurements while PC2 accounts mostly for variation in shield length (Supp. file 3). Size measurements appear to be correlated between them ( Fig. 22B ), but not with angles measurements, which also appear correlated between them.

Clustering analysis ( Paraostenia voultensis )

Based on the VAT, the dataset presents a good clustering tendency that is not confirmed by the Hopkins statistic (0.57), which indicates a low clustering tendency. An optimal number of three clusters for the K-Means analysis was determined. Results of the prediction are presented in Figure 22 . Cluster 1 corresponds to specimens identified as morphotype 1 while specimens identified as morphotype 2 are split between clusters 2 and 3.

Figures

Fig. 5. Scatter plots of length of the shield against maximal height of the shield. A. Kilianicaris lerichei Van Straelen, 1923. B. Ostenocaris ribeti (Secrétan, 1985) comb. nov. C. Paraclausocaris harpa gen. et sp. nov. D. Paraostenia voultensis Secrétan, 1985. Abbreviations: Hmax = maximal shield height; Ls = length of the shield.

Fig. 16. Juvenile of Paraostenia voultensis Secrétan, 1985 (morphotype 1). A–C. Specimen MNHN.F.A84040. A. General view. C. Drawing. B–D. Specimen MNHN.F.A29357. B. General view. D. Drawing. E. Specimen MNHN.F.A29354. F. Specimen MNHN.F.A84039. G. Specimen MNHN.F.A29261. Abbreviations: ce = compound eye; dc = dorsal carina; dm = dorsal midline; hu = hump; mlc = medio-lateral carina; on = optic notch; p 1–5 = podomeres of raptorial appendages; pm = posterior margin; po = pore; ra2–3 = raptorial appendages; sp = spines; tp1–7 = pleural part of posterior trunk segments; vlg = ventro-lateral groove; vm = ventral margin. Scale bars = 5 mm. Photos: T. Laville.

Fig. 17. Adult of Paraostenia voultensis Secrétan, 1985 (morphotype 2; MNHN.F.A29300). A, C–H, J. Counter-part.A. General view.C. General view (colour-marked).D. Drawing.E. Close-up of cephalic appendage (colour-marked). F. Close-up of compound eye. G. Close-up of oval structure. H. Close-up of posterior trunk.J. Close-up of telson.B, I. Part. B. General view. I. Close-up of telson. Abbreviations: ca = cephalic appendage; ce = compound eye; cs = circular structure; dc = dorsal carina; dm = dorsal midline; g = gills; mlc = medio-lateral carina; on = optic notch; os = oval structure; pm = posterior margin; po = pore; ra2–3 = raptorial appendages; t = trunk; tls = telson; ta1–7 = posterior trunk appendages; tta = terminal trunk appendages. Scale bars: A–D = 10 mm; E, G–H = 5 mm; F = 500 µm; I–J = 1 mm. Photos: T. Laville.

Fig. 18. Adults of Paraostenia voultensis Secrétan, 1985 (morphotype 2). A–C. Specimen MNHN.F.A29347. A. General view (counter-part). B. General view (part). C. Close-up of compound eye with stalk (counter-part).D–F. Specimen MNHN.F.A29341. D. General view. E. Close-up of dorsal carina. F. Close-up of pores. G–H. Specimen MNHN.F.A29329. G. General view. H. Close-up of oval structure. I. General view of MNHN.F.A53329. J–K. Specimen MNHN.F.A29351. J. General view. K. Close-up of raptorial appendages. L, P. Specimen MNHN.F.A29256. L. General view (part). P. General view (counter-part). M, O. Specimen MNHN.F.A29325. M. General view. P. Close-up of raptorial appendages. Scale bars: A–B, D, G, I–J, L–M, P = 10 mm; C, H, K, O = 5 mm; E–F = 1 mm. Photos: A–B, M: L. Cazes; C–L, O–P: T. Laville.

Fig. 19. Adults of Paraostenia voultensis Secrétan, 1985 (morphotype 2). A–C. Specimen MNHN.F.A29321. A. General view (part). B. General view (counter-part). C. Drawing (part). D. Specimen MNHN.F.A29275, general view. E–F. Specimen MNHN.F.A84058. E. General view. F. Close-up of dorsalarea with ornamentation.G. Specimen MSNM i25038, general view.H–J. Specimen MNHN.F.A84036. H. General view. I. General view. J. Close-up of ventral area with ornamentation. Abbreviations: ce = compound eye; cs = circular structure; dc = dorsal carina; dm = dorsal midline; on = optic notch; os = oval structure; p2–4 = podomeres of raptorial appendages; pm = posterior margin; pu = punctuations; ra 1–3 = raptorial appendages; ta 1–7 = posterior trunk appendages; tls = telson; tp 2–8 = pleural part of posterior trunk segments; tta = terminal trunk appendages; vm = ventral margin. Scale bars: A–E, G–I = 10 mm; F = 1 mm; J = 5 mm. Photos: A–B, D: L. Cazes; E–F, H–J: T. Laville; G: S. Charbonnier.

Fig. 20. Adults of Paraostenia voultensis Secrétan, 1985 (morphotype 2). A–C. Specimen MNHN.F.A29320. A. General view. B. Drawing. C. Close-up of posterior trunk. D. Specimen MNHN.F.A84038, general view. E. Specimen MNHN.F.A29332, general view. F–H. Specimen MNHN.F.A29330. F. General view. G. Close-up of posterior trunk. H. Drawing of posterior trunk. I–J. Specimen MNHN.F.A29337. I. General view. J. Close-up of posterior trunk. Abbreviations: ce = compound eye; cs = circular structure; dc = dorsal carina; dm = dorsal midline; mlc = medio-lateral carina; on = optic notch; os = oval structure; p 2 = podomere 2 of raptorial appendages; pm = posterior margin; po = pore; pu = punctuations; ra 1–3 = raptorial appendages; ta 1–7 = posterior trunk appendages; tls = telson; tp2–8 = pleural part of posterior trunk segments; tta = terminal trunk appendages; vlg = ventro-lateral groove. Scale bars: A–B, D–E, I = 10 mm; C, F, J = 5 mm; G–H = 1 mm. Photos: T. Laville.

Fig. 21. Frequency distribution and simple allometry of shield measurements for Paraostenia voultensis Secrétan, 1985. A. Histograms of shield measurements. B. Standardised major axis (no groups). C. Standardised major axis (morphotypes 1 and 2). D. Residuals vs fitted data plot. E. Q-Q plot. Abbreviations: Aad = antero-dorsal angle; Aav = antero-ventral angle; Apd = postero-dorsal angle; Apv = postero-ventral angle; Ha = anterior height; Hmax = maximal shield height; Hp = posterior height; Ls = shield length; SMA = standardised major axis.

Fig. 22. Complex allometry for Paraostenia voultensis Secrétan, 1985 (morphospace). A. Principal component analysis projection of morphospace on principal components 1 and 2. B. Correlation circle of variables for principal components 1 and 2. Abbreviations: Aad = antero-dorsal angle; Aav = anteroventral angle; Apd = postero-dorsal angle; Apv = postero-ventral angle; Ha = anterior height; Hmax = maximal shield height; Hp = posterior height; Ls = shield length.

Tables

Table 3. Coefficients of standardised major axis analyses and dependence parameters.

	Kilianicaris lerichei	Ostenocaris ribeti	Paraclausocaris harpa gen. et sp. nov.	Paraostenia voultensis General morphotype 1 morphotype 2
elevation	0.027	-0.267	-0.096	-0.115	-0.117	-0.0574
slope	0.827	0.986	0.9	0.943	0.88	0.88
R 2	0.93	0.973	0.894	0.923	0.605	0.892
p-Value	2.75e- 05	0.0134	0.0547	4.21e- 17 0.222		4.06e- 13