Langeites Kielan-Jaworowska, 1966

Gao, Danxia, Shen, Cen, Huang, Liebin, Chen, Liurunxuan, Zhang, Shitao, Tian, Yimin & Li, Yujing, 2025, New scolecodonts (polychaeta, annelida) from the Late Silurian of Yunnan, South China, Swiss Journal of Palaeontology (22) 144 (1), pp. 1-14 : 8-9

Genus Langeites Kielan-Jaworowska, 1966

Type species Langeites glaber Kielan-Jaworowska, 1966

Langeites aff. glaber .

( Fig. 3A–H ).

Material. YLSS 01, right MI ( Fig. 3A–B, G ); YLSS 11, right MII ( Fig. 3C, D, H ); YLSS 21, right MIV ( Fig. 3E ); YLSS 22, left MIV ( Fig. 3F ).

Description. Eulabidognatha-type apparatus consisting of right MI, right MII, left MIV and right MIV are known; carriers and precise relationships of elements in apparatus are unknown.

Right MI, dorsal side: Length 2.4 mm, width about 1/5 of the length. Te inner and outer margins are almost parallel, but the jaw tapers anteriorly with a well-developed, dorsolaterally directed, slender fang. Te inner margin is slightly curved and only a few sub-distal denticles spread along from the posterior most of the arch to the middle part ( Fig. 3G ). Subsequently, the inner margin to the undenticulated ridge has no denticles. Te basal furrow is short and shallow oriented parallel to outer margin of basal portion.

Ventral side: Tere is no discernible difference between the inner and outer margins. A very short distinct spur exists on the posterior outer part, but is not visible in dorsal view. Te ventral side features nine sub-distal denticles along the inner margin. Te crescent-shaped myocoele opening is narrow, slightly enclosed, representing about one-quarter of its jaw length. Te opening is surrounded by a narrow rim.

Right MII, dorsal side: Length 3.96 mm, width about half of the length. Two very large pre-cuspidal denticles of almost equal size are followed by a large, triangular, and slanting cusp, which in turn is followed by about 13 intermediate denticles. Te shank is moderately to fairly short with a blunt angle. Te ramus is needle-shaped, long, and narrow.

Ventral side: Te crescent-shaped myocoele opening is wide, slightly enclosed, representing about half of the jaw length. Te opening is surrounded by a narrow ligament rim ( Fig. 3H ).

Right MIV, ventral side: Length 0.7 mm, and width half of the length. Comb-like jaw with a slightly curled inner margin. It bears 11 densely spaced denticles along the inner margin, with the size gradually decreasing from the anterior to the posterior. Te myocoele opening is open and extends from the posteriormost to anteriormost, occupying the whole jaw length.

Left MIV, ventral side: Length about 0.5 mm, width half of the length. Incomplete jaw with the open myocoele opening occupying the whole jaw length. Almost a mirror image of the ventral side of the right MIV, except that 8 densely spaced denticles along the inner margin.

Comparisons. Both of the MI and MII of Langeites aff. glaber are similar to those of L. glaber , particularly in the MII. However, the MI of L. aff. glaber bears a small and dorsolaterally directed fang. MIV of L. glaber are absent. Compared with L. siciliensis ( Corradini & Olivieri, 1974) , the right MIV of L. aff. glaber has a different shape, denticles, and myocoele opening. Te right MIV of L. siciliensis is quadrangular with 6–10 tapering denticles, while that of L. aff. glaber is comb-like with 11 short and blunt denticles. Te myocoele opening of L. aff. glaber is wide open from the posteriormost to anteriormost, while that of L. siciliensis closes at the anterior and posterior edges.

Remarks. Te right MI, right MII, and MIV of L. aff. glaber are well-preserved, particularly the MIV, which has received little attention in previous studies. Here, we infer the location of the two MIV based on the size relationships and MIV of L. siciliensis ( Corradini & Olivieri, 1974) . Te MI and MII are the most informative elements in revealing the similarities and differences between extinct and extant maxillae ( Bergman, 1989; Paxton & Eriksson, 2012). Although the MI and MII of L. aff. glaber are similar to those of L. glaber , there are still differences in the denticulation, inner margin, and bending direction.

Stratigraphic Occurrence. Dadukou section, Yiliang County, Yunnan Province, China; Late Ludlow to Early Pridoli, Miaogao Formation.

Langeites sp.

( Fig. 3I–N ).

Material. YLSS 02, right MI ( Fig. 3I, J, M, N ); YLSS 12, right MII ( Fig. 3 K ); YLSS 13, left MII ( Fig. 3L ).

Description. Eulabidognatha-type apparatus, consisting of right MI, right MII, and left MII, are documented; the carriers and precise relationships of elements in apparatus remain unknown.

Right MI, dorsal side: Length about 1.55 mm, width about 0.35 mm. Due to the damage of the anterior-most part, the length/width ratio is uncertain. Te inner and outer margins are near-parallel. Te inner margin is covered with 18 knob-like sub-terminal, densely spaced denticles, occupying about half of the well-preserved jaw length. Te denticles are almost equal in size except for the posteriormost ones, which increase in size ( Fig. 3M ). Te undenticulated ridge is almost straight, with a length of approximately 0.23 mm ( Fig. 3N ). Te basal angle is approximately 18° and the basal furrow is narrow and deep.

Ventral side: Te ovoid-shaped myocoele opening is wide and slightly enclosed, representing about half of the jaw length. Te opening is surrounded by a narrow rim

( Fig. 3I ).

Right MII, ventral side: Conical element with a length of 0.8 mm and width of more than half the length. One pre-cuspidal denticle is followed by a large, tall triangular cusp ( Fig. 3K ). Te three sloped-backward intermediate denticles are small and sub-triangular. Te six post-cuspidal denticles are sharp and triangular. Te shank end is broken. Te crescent-shaped myocele opening is relatively narrow, slightly enclosed, representing about 0.6 of the jaw length. Te needle-shaped ramus is medium length and narrow with a posteriorly oriented, pointed extremity.

Left MII, dorsal side: Length about 0.73 mm, width half of the length. Almost a mirror image of the ventral side of the right MII, except that the element has a double equal-sized cusp and eight small post-cuspidal denticles along the inner margin ( Fig. 3L ). Te shank is narrow and bluntly ended.

Comparison. Although the right MI is poorly preserved on the fang, the basal portion and the denticles on the inner margin are well preserved. Te MI of Langeites sp. are similar to those depicted for L. aff. glaber and L. glaber in shape, but differ in denticulation and size. L. sp. is much smaller than others and is distinguished from L. aff. glaber and L. glaber by the densely spaced denticles along the inner margin.

Stratigraphic Occurrence. Dadukou section, Yiliang County, Yunnan Province, China; Late Ludlow to Early Pridoli, Miaogao Formation.

Family Polychaetaspidae Kielan-Jaworowska, 1966 .

Genus Oenonites Hinde,1879 .

Type species Oenonites curvidens Hinde,1879 .

Oenonites spp.

( Fig. 3O–S ).

Material. YLSS 23– YLSS 24, left MI ( Fig. 3O, P ); YLSS 25– YLSS 27, incomplete MI ( Fig. 3Q–S , Tables S25–S27).

Description. Labidognatha-type apparatus, only consisting of MI, are documented. Two of the MIs are well-preserved and are assigned to the left MI based on the direction of the fang ( Fig. 3O, P ). Tese MIs vary in size and display ventral and dorsal features, respectively.

Left MI, dorsal side ( Fig. 3O ): Narrow and elongate jaw. Length about 1.39 mm, width slightly less than 1/3 of the length. Greatest width at mid-length. Outer margin slightly concave to straight. At about mid-length, there is a well-pronounced ramus which points slightly posterodextrally. Posterior of the ramus, the outer face tapers strongly and becomes hidden by the posteriormost denticles. Te anteriormost denticle is developed as a large, long, and hooked fang. A series of 16–18 small, tightly packed, and slanted denticles decrease in size posteriorly, approximately the 7–11th denticles are slightly larger than the surrounding ones. Anterior of the cove, inner face very narrow. Te inner margin follows the dentary in the anterior part of the jaw, but at approximately mid-length, it turns right and then posteriorly.

Left MI, ventral side ( Fig. 3P ): Myocoele opening extends for more than 0.9 of the jaw length. Te anteriormost denticle is developed as a large, long, and hooked fang. A series of more than 10 small, tightly packed, and slanted denticles decrease in size posteriorly, approximately the 2nd–4th denticles are slightly larger than the surrounding ones. Te myocoele opening exhibits a long and narrow ligament rim.

Remarks. Despite the determination at the species level being impossible because of the state of preservation, all of them are assigned to Oenonites based on the preserved fang, the triangular denticles and the inner and outer faces, with at least two species present. Te two left MIs differ in denticulation and size. Posterior of the cove, the outer face of one incomplete MI ( Fig. 3R ) exhibits greater width compared to others than others ( Fig. 3O, Q ). Tus, the specimens were assigned to Oenonites spp.

Stratigraphic Occurrence. Dadukou section, Yiliang County, Yunnan Province, China; Late Ludlow to Early Pridoli, Miaogao Formation.

Figures

Fig. 3 (See legend on previous page.)