Catenatus argentinus, Carrera & Voldman & Mango & Nestell, 2021

Carrera, Marcelo G., Voldman, Gustavo G., Mango, Matias J. & Nestell, Galina P., 2021, Ordovician enigmatic sclerite-type elements from western Argentina: possible oldest axial components of alcyonacean octocorals, Acta Palaeontologica Polonica 66 (3), pp. 535-544 : 538-539

Catenatus argentinus sp. nov.

Fig. 3.

2009 Lavella ? sp.; Nestell et al. 2009: 332, pl. 1: 6, pl. 4: 2; misidentified as a foraminifer.

2009 Amphitremoida sp. 2 ; Nestell et al. 2009: 332, pl. 1: 7; misidentified as a foraminifer.

2011 Amphitremoida longa Nestell and Tolmacheva ; Nestell et al. 2011: 604, fig. 3 (3); misidentified as a foraminifer.

2013 Lavella ? sp.; Mestre et al. 2013: fig. 2 (3); misidentified as a foraminifer.

ZooBank LSID: urn:lsid:zoobank.org:act:CAE9314D-7B79-42F8-AC

A-ADB671A33FF9

Etymology: After Argentina, the country where the type material was collected.

Type material: Holotype: two connected, spindle shaped sclerite-type elements CEGH-UNC 27465 . Paratypes: a set of 17 loose or connected spindle shape sclerites-type elements, CEGH-UNC 27454–27464 , CEGH-UNC 27466–27472 from the type ocality and horizon .

Type locality: Los Gatos creek section, western flank of the Cerro Viejo, Huaco area, San Juan Province, Argentina .

Type horizon: Top of the San Juan Formation at the Los Gatos Creek section ( Paroistodus horridus Subzone of the Lenodus variabilis Zone (lower Darriwilian; Mango and Albanesi 2018)

Material.—202 sclerite-type elements of which 37 were photographed in SEM and 17 illustrated (CEGH-UNC 27454– 27495). 32 elements are from sample FSJ 3 o hardground, 19 from sample U+20, 41 from sample RIN 34, 85 from sample LG42, and 25 from sample TFSJ QA.

Description.—The sclerite-type element association consists of a possibly connected association of spindle-shaped elements, ornamented with regularly distributed granular or tubercles (Fig. 3). In our collection, few connected forms were found (Fig. 3I, K 1, L, M 1). The spindles range from slightly fusiform elongated, rod-like forms to oval or strongly ellipsoidal. The elongated forms range 1–1.8 mm long and 0.2 mm wide, whereas the more inflated spindle forms are 1 mm long to 0.3 mm wide.

The surface of most spindle elements is covered or ornamented by small granules or rounded to oval tubercles (Fig. 3A 2, O 2, P 2), some of them terminating with a tip (Fig. 3H 1, M 1, M 2). Some broken elements show a solid inner structure, which appears porous and homogeneous in thin section ( Fig. 2C–E ).

Some elements have rounded terminations whereas others show small expansions of the tips. These expansions are frequently found connecting the elements (“neck” connection), forming a linear continuous structure. Small longitudinally aligned corrugations or ridges can be seen at neck or tip junctions (Fig. 3I, K, L, M).

Some sclerite-type elements have two articulation tips (thus they possibly occur in the middle of some linear construction) and some only at one tip, the other one being rounded, suggesting that it was the final (apical) element in the linear structure. There is one form that apparently shows two rounded terminations (Fig. 3H), and if it is the case (excluding physical abrasion of the tips) it can be considered as a typical isolated sclerite commonly found in alcyonacean octocorals.

Remarks.—The studied forms, based on their shape, resemble the Silurian genus Atractosella from the island of Gotland ( Bengtson 1981), and they could be included in the same spindle morphotype. However, different morphologies in Atractosella , such as bifurcated or branched spindle forms, are absent in our material, and in contrast, the commonly occurring fused sclerite-type elements in the Argentinean forms are absent in the Silurian Atractosella .

Reich (2002) also reported simple sclerites, which are referred to Atractosella , from glacial erratic Silurian age boulders of Northern Germany. These forms are simple elongated spindles ornamented with crowded small granules, the same type of fine ornamentation as observed in Atractosella and in our sclerite-type elements. However, the Silurian sclerites represent only one of the morphotypes found in Atractosella , whereas the bifurcated or branched forms are absent. The connecting neck, commonly found in the Argentinean material, is also absent among the sclerites of Atractosella described by Reich (2002).

The Silurian Termieralcyon Fernández-Martínez, Coronado, Rodríguez, Tourneur, and Badpa, 2019, an encrusting form attached to a syringoporoid coral described by Coronado et al. (2015) and Fernández-Martínez et al. (2019), has sclerites with slightly pointed and serrated ends that are clearly different and not comparable with the Argentinean forms.

Stratigraphic and geographic range.—Lower to Middle Ordovician (Floian–Darriwilian), San Juan Formation, San Juan Province, Argentina .

Figures

Fig 2. Alcyonacean octocoral Catenatus argentinus gen. et sp. nov. sclerite-type elements from the Middle Ordovician (Darriwilian), Lenodus variabilis– Yangtzeplacognathus crassus zones, San Juan Formation, San Juan Province, Argentina and its chemical composition by surface EDX analysis. A. Siliceous sclerite-type element, CEGH-UNC 27474, sample LG42 (unpolished sample). B. Phosphatic sclerite-type, CEGH-UNC 27475, sample RIN34. C. Partially broken element showing a solid inner structure, CEGH-UNC 27471, sample LG42. D, E. Thin sections of isolated elements of Catenatus argentinus gen. et sp. nov., showing the internal homogeneous structure, CEGH-UNC 27472, sample LG42 (D), and CEGH-UNC 27473, sample FSJ 3º hardground (E). Scale bars 100 μm.