Eoserratosagitta serrata, Doguzhaeva & Mutvei & Mapes, 2002

Doguzhaeva, Larisa A., Mutvei, Harry & Mapes, Royal H., 2002, Chaetognath grasping spines from the Upper Mississippian of Arkansas (USA), Acta Palaeontologica Polonica 47 (3), pp. 421-430 : 428

Eoserratosagitta serrata sp. nov.

Figs. 1A–C , 2A–C, 3A–D, 4A, B .

Holotype: OUZC 4002 /A, ( Fig. 2A, B) . Paratypes ( OUZC 4002 /B, C, D; Fig. 4 ) .

Type locality: Cove Creek locality (See Mapes 1979, locality M−22) in northern Arkansas ( USA).

Type horizon: Middle Chesterian (Namurian Aequivalent), Upper Mississippian (Lower Serpukhovian). The phosphate concretion that contains the specimens is estimated to have come 1 to 3 m above the base of the formation in a black platy shale exposed in the banks and in the bed of Cove Creek.

Derivation of name: From the Latin serra, meaning saw, based on the saw−like inner edge of the spine bearing numerous denticles.

Diagnosis.—Small horny spines (approximate length 0.4– 0.5 mm and width 0.05–0.06 mm); gently curved; central cavity long; with convex side rounded and concave side acute; five to six longitudinal bands on each lateral side; concave side serrated, with more than 20 straight, conical hollow denticles, inclined towards the pointed tip; distal portion (1/3 to 2/5 of total length) not serrated. The ratio between length of denticle and width of spine 2/5 (proximally) to 1/2 (distally). Denticles closely spaced, being in contact with each other in their proximal parts. Shape of denticles bullet−like: proximal portion, 2/3 of their length, cylindrical, and remaining distal portion conical, strongly pointed; ratio between maximum diameter and length 1/3–1/4.

Figures

Fig. 1. Eoserratosagitta serrata gen. et sp. nov., Cove Creek (Arkansas, USA), Middle Chesterian (Namurian Aequivalent). A. Aconcretion fragment showing part of the accumulation of spines (s), scale bar 0.1 mm. B. A fragment of the middle part of a spine showing the concretion filled central cavity (cc), a row of bullet−like, hollow (now concretion−filled) denticles (d) on the concave side (to the left), and five longitudinal bands (b) separated by fine ribs (r) on the outer surface of the spine wall, scale bar 0.1 mm. C. Close−up of B showing fiber (f) impressions, scale bar 0.01 mm. All SEM micrographs.

Fig. 4. Eoserratosagitta serrata gen. et sp. nov., Cove Creek (Arkansas, USA), Middle Chesterian (Namurian A equivalent). A. Three relatively complete paratypes (OUZC 4002/B, C, D from top to bottom, respectively) with nearly identical basic morphology including bands (b) and bulletlike denticles (d), scale bar 1.0 mm. B. Enlargement of the lower right segment of paratype OUZC 4002/B showing the phosphate replaced, fibrous ultrastructure of the spine wall, scale bar 0.1 mm. All SEM micrographs.