Lathahypossia aculeata ( Busulini, Tessier & Visentin, 1984 )

Ossó, Àlex & Ng, Peter K. L., 2023, On the systematic placement of the fossil crab Lathahypossia aculeata (Busulini, Tessier & Visentin, 1984) (Crustacea: Decapoda: Brachyura), Zootaxa 5351 (2), pp. 265-275 : 268-271

Lathahypossia aculeata ( Busulini, Tessier & Visentin, 1984)

( Figs. 1–3 )

Titanocarcinus aff. Raulinianus.— Busulini et al. 1982: 82, fig. 3.

Titanocarcinus aculeatus Busulini, Tessier & Visentin, 1984: 107–114 , pl. 1 figs. 1–3, pl. 2 figs, 1, 2, pl. 3 figs. 1, 2.— De Angeli & Beschin 2001, fig. 36.— Beschin et al. 2002, text-fig. 15, pl. 4 fig. 3.— Karasawa & Schweitzer 2006: 53. Lathahypossia aculeata .— Schweitzer et al. 2007: 292, 293.—Beschin et al. 2012: 72, text-fig. 64, pl. 10 fig. 5.— Jagt et al.

2015: 898, fig. 71D.— De Angeli et al. 2019: 898.— Schweitzer et al. 2020: 2, fig. 1, 4.

Material examined. One complete carapace without pereopods: MSNVE-27378, L = 40.5; W = 54.5; FOW = 36.0; FW = 16.0/19.0; PM = 23.0. One specimen preserving partial sternopleonal features and chelipeds: MSNVE-27377, width from carpus to carpus = 67.5.

Diagnosis (emended). Carapace transversely ovate, wider than long, L/W ratio about 0.75; surface granulate, fairly vaulted longitudinally, regions well defined, spiny anterior half of outline; front bilobed, armed with acute spines; orbits ovate, complete, supraorbital margin spiny, with one closed medial fissure; anterolateral margins with 4 spiny lobes; posterior margin convex, posteriorly convergent; posterior margin straight, rimmed. Male thoracic sternum relatively broad, strongly vaulted longitudinally; sternopleonal cavity deep, exceeding midpoint of P1 coxa, reaching 2/3 of sternite 4, press-button on anterior margin of sternite 5. Pleon subtrapezoidal, somite 3 widest, somites 3–5 fused with subtle demarcations visible. Cheliped strongly spinous, heterochelous. Ambulatory legs slender, spiny.

Description. Carapace transversely ovate, wider than long, L/W ratio about 0.75, maximum width half carapace length, fairly vaulted longitudinally, slightly vaulted transversely; surface covered with scattered granules and setal pits. Regions swollen, well-defined by shallow, smooth grooves. Front bilobed, notched medially; each lobe, sinuous, with 3 acute spines internally and 1 acute spine at outer corner. Orbits transversely ovate, complete, slightly obliquely placed; supraorbital margin raised, spiny, with closed medial fissure; deep notch separating inner orbital spine from front; infraorbital margin spiny, dorsally visible; ocular peduncle short. Anterolateral margins gently convex, with 4 lobes or teeth: first lobe smaller, last lobe (epibranchial) largest, all armed with long, acute spines. Posterolateral margin slightly convex, with rounded edges, posteriorly convergent. Posterior margin straight in dorsal view, medially slightly concave in posterior view, with fine rim. Frontal region depressed, directed downwards. Epigastric lobes fairly swollen, stepped distally. Protogastric lobes slightly swollen, adjacent to epigastric lobes. Mesogastric region very slender anteriorly reaching middle of epigastric lobes, broadly subpentagonal posteriorly. Metagastric region weakly differentiated from mesogastric region. Urogastric region bounded laterally by branchiocardiac grooves, separated from meso-, metagastric lobes by cervical groove; adjacent and undifferentiated from cardiac regions, with 2 regions forming pentagon with the apex pointed downwards. Intestinal region short, smooth. Hepatic lobes swollen, demarcated by cervical and gastrohepatic grooves. Epibranchial region defined by 3 swollen lobes, separated by smooth grooves. Metabranchial region swollen, weakly defined. Metabranchial regions demarcated by 2 transverse swellings surrounding intestinal region. Suborbital region defined by smooth fringe between row of spines parallel to lateral and infraorbital margins. Subhepatic lobes swollen; with oblique shallow smooth grooves on ventral carapace surface. Pterygostomial regions subtrapezoidal, concave in upper and lower margins, finely granulated. Endostome broad, endostomial ridge weakly marked in lower part. Epistome widely subtriangular, edges ornate, with granules. Proepistome prominent, granulated. Basal antennular article subtrapezoidal, with granulated oblique ridge, folding transversely in antennular fossae. Basal antennal article spiny, obliquely placed.

Ischium of third maxilliped with convex inner margin, with 2 longitudinal sulci, 1 medial and second parallel to inner margin, lined by setal pits, inner margin subtruncate, lined by setal pits; merus subtrapezoidal; exopod almost straight, half width of ischium.

Male thoracic sternum relatively broad, strongly vaulted longitudinally. Sternites 1 and 2 form a triangular structure with margins lined by fine granules; sternite 3 surface medially concave, distal margin granulated; sternite 4 subtrapezoidal in shape, surface medially concave, divided by sternopleonal cavity, broadly vaulted laterally, lateral edges granulated. Sternites 5–7 subtrapezoidal, sternite 5 longer, sternite 7 shorter; sternite 8 not visible when pleon closed. Episternites 4–7 posteriorly directed, sutures not visible. Suture 1/2 distinct; suture 2/3 complete; suture 3/4 only visible laterally; sutures 4/5, 5/6 and 6/7, laterally complete. Sternopleonal cavity deep, narrow, reaching beyond gynglyme for P1, reaching two–thirds of sternite 4 to become deeper, margins ornate, lined with granules. Press button on anterior margin of sternite 5, adjacent to suture 4/5.

Male pleon relatively narrow, slightly vaulted ventrally; somites subrectangular, transversely elongate; somites 1 and 2 shorter; somites 3–5 subequal in length, fused, with demarcations shallow but visible, somite 3 widest; somite 6 slightly longer than somite 5, with sockets in inner distal corner to receive tubercle of press-button of male pleonal-locking mechanism; telson subtriangular elongate with rounded tip.

Chelipeds strongly spinous, heterochelous, palm robust, armed with rows of acute spines on outer and upper margins; dactylus about one–third length of propodus, with black tips.

Ambulatory legs slender, margins weakly spinose.

Remarks. As for the genus.

Figures

FIGURE 1. A, B, Lathahypossia aculeata (Busulini, Tessier & Visentin, 1984), holotype, MSNVE-25083, from the Middle Eocene of the Cava Main, Arzignano (northeast Italy). A, dorsal view; B, frontal view. Scale bar = 10 mm (pictures by G. Tessier).

FIGURE 2. A–F, Lathahypossia aculeata (Busulini, Tessier & Visentin, 1984), from the Middle Eocene of the Cava Main, Arzignano (northeast Italy). A–E, male, MSNVE-27378: A, dorsal view; B, ventral view; C, frontal view, D, posterior view; E, right lateral view. F, male, MSNVE-27377, ventral view. Abbreviations, s: pleonal somites; st: thoracic sternites; t: telson. Scale bar = 10 mm.

FIGURE 3. A–G, Lathahypossia aculeata (Busulini, Tessier & Visentin, 1984), from the Middle Eocene of the Cava Main, Arzignano (NE Italy). A, B, D–F, male, MSNVE-27378: A, view of sub-cephalic region; B, view of endostomial region; D, detail of pleon; E–G, detail and close-up of ‘press-button’, male pleonal locking mechanism. C, male, MSNVE-27377, detail of anterior part of sternum. Abbreviations, aa: basal antennular article; ab: basal antennal article; en: endostome; ep; epistome; er: endostomial ridge; ex: exopod of third maxilliped; is: ischium of third maxilliped; mxp3: third maxilliped; P1: first pereopod; pb: ‘press-button’; s: pleonal somites; st: thoracic sternites. Scale bar = 10 mm.