Ostenosculda teruzzii, Braig & Haug & Ahyong & Garassino & Schädel & Haug, 2023

Ostenosculda teruzzii n. gen., n. sp.

( Figs 1-7)

urn:lsid:zoobank.org:act:7C2C839B-81D7-4C97-9280-3DA3F62FB6BC

TYPE SPECIMENS AND ONLY MATERIAL. — Holotype. MSNM i13561 ( Figs 1; 2).

Paratype. MSNM i13562 ( Figs 3; 4).

DIAGNOSIS. — Compound eyes without apparent midband, on short peduncles. Short tapering rostrum. Shield rectangular in ventral and lateral view with postero-lateral corners elongated. Major raptorial appendages with thick ovate carpopropodi and spineless scythe-shaped dactyli. Eight circular insertion areas (foramina) of posterior four maxilliped pairs arranged evenly spaced in anterior-posterior axis. The first pair of insertion areas positioned further laterally, the following three pairs arranged successively medially in two anterior-posterior running, almost straight lines. Insertion area of each pleopod subdivided into three individual areas separated by bar-shaped sclerites.

DERIVATION OF NAME. — Named after Giorgio Teruzzi, Milano, in honour of his scientific work including fossils from Osteno.

TYPE LOCALITY. — Early Jurassic (Sinemurian), limestone quarry, Osteno, Lombardy, Italy ( Pinna 2000).

DESCRIPTION

Body apparently organised into six functional units ( Haug et al. 2012): 1) sensorial unit with ocular and post-ocular segments 1-2 (anterior head); 2) anterior food-processing unit with post-ocular segments 3-5 (posterior head); 3) posterior food-processing unit with post-ocular segments 6-10 (thoracic segments 1-5); 4) walking apparatus with post-ocular segments 11-13 (thoracic segments 6-8); 5) swimming and respiration unit with post-ocular segments 14-18 (anterior pleon); 6) tailfan with post-ocular segment 19 (pleomere 6) and telson (seeFig. 5 for comparison with extant mantis shrimp). The body length is 46.6 mm, from the tip of the rostrum to the end of the telson for the ventrally accessible specimen ( Fig. 2); for the laterally accessible one this measurement is difficult due to the spaces between the body segments.

The only clearly visible structure of the sensorial unit is one (presumably the left) large compound eye on a short peduncle, protruding near the anterior end of the shield. The cornea is shorter but wider than the stalk; an ommatidial midband is not determinable. Antennula and antenna are not preserved ( Fig. 4).

The only accessible feature of the food-processing unit (mandible, maxillula, maxilla) are the mandibles of the ventrally accessible specimen ( Fig. 2). They insert anterior to the major raptorial appendages, but more laterally to them on both sides, on the lateral edges of the body. The mandibles appear to be roughly triangular in ventral view, though their proximal parts at the lateral sides of the body are very round and their distal parts at the median areas of the body are very rough and serrated, indicating grinding/cutting structures. They measure 2.7 and 3.1 mm in length, left and right mandible respectively. The segments to which the appendages of the food-processing unit belong are indirectly observable as they dorsally form the prominent shield. The shield is about two times as long as wide, about 12 mm long and 6 mm wide in the ventrally accessible specimen ( Fig. 2), appearing subrectangular both in ventral and lateral view, covering the post-ocular segments 1-5 in ventral view and post-ocular segments 1-8 in lateral view. A short tapering rostrum bridging the gap between the eye peduncles is present at the anteromedial margin of the shield. The posterolateral corners of the shield are slightly produced posteriorly.

The posterior food-processing unit is mainly represented through the major raptorial appendage (maxilliped 2). The exact number of appendage elements of these is not observable. Only the two most distal elements are recognizable: the thick and bulky, in lateral view oval-shaped carpopropodus (propodus of other authors), and the long and spineless scythe-shaped dactylus ( Fig. 4). The dactylus is arcuate, at least three-fourths as long as the carpopropodus, evenly tapering to a spiniform tip; the outer margin is smooth, lacking a proximal notch or swelling. The carpopropodus is twice as long as high, about 8.9 mm long in the ventrally accessible specimen and about 4.3 mm wide in the laterally accessible specimen, and is deepest at the midlength. Other appendages are not fully preserved, but two additional dactyli are visible between the posterior portion of the maxillipeds 2; these small dactyli are about one fourth of the length of the dactyli of maxilliped 2 ( Fig. 2) and possibly belong to maxillipeds 3 or 4. In lateral view, darkened areas are visible ventral to the shield, which may represent proximal maxilliped elements stacked dorsoventrally on top of each other ( Fig. 4: mx?). Furthermore, the insertions of the posterior four maxillipeds (appendages of post-ocular segments 7-10) are clearly recognizable. These are evenly arranged in anterior-posterior axis, slightly decreasing in size from anterior to posterior. The first pair of insertion areas is positioned further laterally, the following three pairs are arranged successively medially in an almost straight line. The most anterior pair of insertions belongs presumably to the major raptorial appendages (maxilliped 2) since the bulging cuticle rings surrounding the insertions are thicker than those of the more posterior maxillipeds and the diameter is significantly larger ( Fig. 2). The next posterior insertion is smaller, but slightly larger in diameter and with a thicker bulging ring than the next two insertions. The last segment of this tagma has a distinct short dorsal sclerotisation (tergite) and a longer (anterior-posterior axis) ventral sclerotisation (sternite).

The thoracic segments 6-8, which form the walking apparatus, are clearly recognizable. Each segment seems to have an oval cross-section and is about four times as high as long ( Fig. 4). Each segment has two cuticle plates, a dorsal tergite and a ventral sternite; in lateral view, the tergite occupies two-thirds of the segment height, the sternite only one-third, possibly as a result of compressional displacement ( Fig. 4). While the tergites are continuous and broad rectangular-shaped cuticle plates, the sternites are interspersed with softer structures. Most anteriorly on each sternite, and probably marking its anterior edge, is a continuous crescent-like shaped sclerotised bar stretching over the full width of the segment and continuing in posterior direction (after a kink with roughly 90°) at both of its ends to the posterior end of the segment. Posterior to this bar, the seventh thoracic segment shows structures of hardened cuticle. These form two broadly connected ovate forms around the possible insertion areas of the walking appendages. Posterior to the sclerotised bar of the eighth thoracic segment is a broad rectangular cuticle plate with small anterior spines pointing laterally. Posterior to this is a structure mirrored on an anterior-posterior running middle line of the segment. The structure consists of a walking-stick-shaped cuticle bar (curved end pointing medially) above a rough triangle pointing posterior and has its anterior corners elongated laterally. These triangles reach into the gap between the eighth thoracic and the first pleon segment ( Fig. 2).

The anterior pleon consists of a narrow anterior segment, followed by four broader segments, each two times higher than long ( Fig. 4). Dorsally, the tergite of each of the five segments is a broad continuous plate covering the whole segment ( Fig. 2). The sternites show multiple structures and soft spots that are best described by the letter “W”, but with the three anterior tips being connected and by overall broader lines. This leads to two triangular gaps, which form the insertion areas (foramina) of the pleopods. Within these gaps, there are two cuticle bars, one running from the middle of the lateral side towards the midline and bending posterior after two thirds of the way, and one running from posterior towards the spot where the first line starts to bend. This pattern continues with slight variation for the other four sternites.

The tailfan is formed by the telson and the appendages (uropods) of pleomere 6, which is slightly narrower compared to the other pleon segments. Pleomere 6 again consists of a continuous broad cuticular plate that is the tergite, but in contrast to further anterior sternites, the sternite of pleomere 6 is broad and almost continuous, only with spaces postero-laterally for the uropods. The uropods (at least the parts that are preserved) are bent in ventral view and curved around the lateral edges of the telson ( Fig. 2). The telson is flatter than the body segments and flattens out even further towards its posterior end ( Fig. 4). It is about 6.9 mm wide in the ventrally accessible specimen and about 5.2 mm long in the laterally accessible specimen, yet it is neither in lateral nor in ventral view fully preserved, therefore we could draw no further information from it. Telson spines are not preserved.