Palaeocambarus Taylor, Schram & Shen 1999
Creators: name: Audo, Denis
name: Kawai, Tadashi
name: Letenneur, Charlène
name: Huang, Diying
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Cambaridae
Palaeocambarus

description: Genus Palaeocambarus Taylor, Schram & Shen, 1999
Palaeocambarus Taylor, Schram & Shen, 1999: 122-130, figs 2, 4-6. — Type species: Astacus licenti Van Straelen, 1928b, by monotypy.
Cricoidoscelosus Taylor, Schram & Shen, 1999: 130-135, figs 3, 7, 8, n. syn. — Type species: Cricoidoscelosus aethus Taylor, Schram & Shen, 1999.
ORIGINAL DIAGNOSIS (Taylor et al. 1999). — “Entire dorsal surface of cuticle covered with fine granulations. Rostrum with basal lateral spines. Elongate, bladelike scaphocerite. Chela of first pereiopod long and narrow with extensive pitting and spination. No hooks visible on ischia. Pleura large and rounded on abdominal segments 2-5, 2nd pleuron being largest. Pleopods elongate and blade like, with no specialization on first. Telson subrectangular with pair of large lateral spines and rounded distal margin.” (Taylor et al. 1999).
EMENDED DIAGNOSIS (present work). — Pyriform cephalothoracic shield, longer than wide; rostrum in two parts, proximal part wide, less than half total rostrum length, tapering distally, flanked by a pair of lateral spine at the tip of supra-orbital carina, acumen (distal part) blade-like; deep-curved cervical groove, crossing median-line; subdorsal carina extending into the rostrum and on the cephalic region; postorbital carina double: dorsal part near subdorsal carina, formed of two spines aligned horizontally, each extending posteriorly in a short carina; ventral part formed of at least four spines posterior to the ocular incision; postrostral carina on median dorsal line, formed of at least four spines on the anterior half of the cephalic region, posterior to the rostrum; epistome with a wide cephalic lobe forming three spines anteriorly, no spine on the rest of epistome; telson with diaeresis and rigid distal portion; pleopods 1-2 forming copulatory gonopods in males; uropodal exopodite with a diaeresis and rigid distal portion.
COMMENTS
Taylor et al. (1999) described a new species, genus and family of crayfish from the Jehol biota. Following their revision, the two species they considered valid in Jehol biota therefore belonged to two distinct genera (Palaeocambarus and Cricoidoscelosus Taylor et al. 1999) and two distinct families (Cambaridae and Cricoidoscelosidae respectively).Concerning Cricoidoscelosidae, we herein consider that diagnostic characters used in the erection of this family are not sufficient to distinguish a new family: some of them are common to all crayfishes, such as the bladelike scaphocerite, well-developed first chelae and large rostrum with large lateral spines (observed in several species of Cambaridae, Astacidae, Cambaroides and Parastacidae) or the gonopores on the coxa (not sternite) of females (plesiomorphic condition, occurring in most decapods). The first pleopod being styliform in males (first gonopod) is an important diagnostic character, but only excludes Parastacidae from consideration. Rounded pleurae, as observed in Shen et al. (2001), were not observed in all specimens: our observations led us to believe this is only a preservation artefact, due to flattening of the specimens. More importantly perhaps, the namesake character for Cricoidoscelosidae, the pleopods formed of numerous rings (multiarticulated – Fig. 1A, B) is also visible in other crayfishes such as Cambaroides (Fig. 1C) and even fossil Austropotamobius Skorikov, 1907 (Fig. 1D). In fact, the presence of multiarticulated pleopods in other decapods, such as dendrobranchiate shrimps (Fig. 1E) and in polychelidans (Fig. 1F) suggests that multiarticulated pleopods are in fact a plesiomorphic character state for decapod crustaceans. It is worth mentioning that fossilization appears to make pleopod annulations more visible (Fig. 1A, B, D, E) than in specimens preserved in alcohol (Fig. 1C, F). We were not able to observe the variations noted by Taylor et al. (1999) or Shen et al. (2001): our observations suggest that the variations may be due to variation in preservation, or angle at which these structures are flattened.
From our assessment, the epistome of Palaeastacus (Fig.2 A-C) is similar to that of Cambaroides (Fig. 2D, see also Kawai et al. (2003) for illustrations of epistomes in several Cambaroides): there is no spine on the epistome except for that of the cephalic lobe (Fig. 2A, C; contrary to Astacidae, which have spines; see Fig. 2E), a wide cephalic lobe (about 30% of the total width, contrary to North American Cambaridae (Fig. 2F) and Pacifastacus, in which the cephalic lobe is narrower than 30% of total width; see NIGP-Shen-12, NIGP-Shen26, NIGP-Shen-38), and there is a cephalic median central projection on the cephalic lobe (Fig. 2C, as in Cambaroides Fig. 2D). Beside the rostrum, the presence of a telson diaeresis (articulation), two pairs of gonopods, the probable presence of ischial hooks (on the holotype of C. aethus, NIGP-126337, Figs 3 A-3D, possibly on specimen NIGP-Shen-22, Fig. 3 E-F, although our evidence is ambiguous due to preservation, ischial hooks may be present on specimens and NIGPAS-Shen-3, 5, 14, 32), all are similar to Cambaroides. We note that it is not unexpected that Taylor et al. (1999) and Shen et al. (2001) could miss this structure: it is only present in males of Cambaroides and Cambaridae, is rather small and placed on the inner margin of the ischium of periopods 2-4 (often only on two pairs: Fig. 4A, compare with Fig. 4B), so is rarely noticeable in fossils, and is even difficult to see on radiographic images of extant specimens. Examination of the neotype NIGP-126342 shows that the sternite between pereiopods 4-5 (Fig. 4C, D) does not form an annulus ventralis with a hemicircular fold like that of Cambarus. It resembles, however, the smaller annulus ventralis found in Cambaroides. For these reasons, we propose an assignment to Cambaroididae Villalobos, 1955. This placement is in line with the geographic origin of Palaeocambarus, indeed, Cambaroididae are only known to occur in East Asia (eastern China and Russia, North and South Korea, Japan, Mongolia: Kawai et al. 2003, 2016). Ďuriš & Petrusek (2015) and Schram & Koenemann (2022) also suggested a possibly close relationship between Palaeocambarus and modern East-Asian crayfishes.
For all these reasons, we consider Palaeocambarus Taylor, Schram & Shen, 1999 and Cricoidoscelosus Taylor, Schram & Shen, 1999 to be synonyms. Since these two genera were simultaneously published, we consider Palaeocambarus as the senior name, under the first reviser principle (ICZN 1999: art. 24.2): we believe this choice is more appropriate as the name Cricoidoscelosus refers to the annular pleopods, a character we do not consider as diagnostic, and also, Palaeocambarus appears before Cricoidoscelosus in the text, in Taylor et al. (1999).
Although Taylor et al. (1999) assigned Palaeocambarus to Cambaridae, and we assign it to Cambaroididae, these assignments are not so different, indeed, Taylor et al. (1999) considered Cambaroides as a Cambaridae. So, in this regard, we agree withTaylor et al. (1999) that Palaeocambarus belongs to the same family as modern-days East Asian crayfishes.
Another consequence of this synonymy and new familial assignment is the synonymy of Cricoidoscelosidae Taylor, Schram & Shen, 1999 to Cambaroididae Villalobos, 1955. Schram & Koenemann (2022) suggested that Cricoidoscelosidae may have precedence over Cambaroididae. We consider that Cambaroididae have precedence over Cricoidoscelosidae as this family was published as a subfamily earlier than Cricoidoscelosidae. Also, the name Cricoidoscelosidae refers to a character of taphonomic significance, which has little to contribute to the classification of crayfishes.
description: Published as part of Audo, Denis, Kawai, Tadashi, Letenneur, Charlène & Huang, Diying, 2023, Crayfishes from the Jehol biota, pp. 689-719 in Geodiversitas 45 (24) on pages 692-694, DOI: 10.5252/geodiversitas2023v45a24, http://zenodo.org/record/10376394