Parastacidae Huxley, 1879

Ribeiro, Felipe Bezerra & Araujo, Paula Beatriz, 2024, Taxonomic review of the genus Parastacus Huxley, 1879 (Decapoda: Astacidea: Parastacidae) with description of five new species, Zootaxa 5455 (1), pp. 1-84 : 9-10

Family Parastacidae Huxley, 1879

Genus Parastacus Huxley, 1879

Astacus .—­ Poeppig, 1835:314.

Parastacus Huxley, 1879: 759 , 771.

Type species. Astacus pilimanus by subsequent designation ( Faxon, 1898: 683): Astacus pilimanus von Martens, 1859: 15 . Gender: masculine.

Diagnosis.

Moderate body size (up to 15 cm of total length). Deep carapace, narrow or wide, lacking spines and tubercles; rostrum mainly triangular, but spatulate in P. brasiliensis and quadrate in P. bah sp. nov. and P. nicoleti ; postorbital carinae ranging from obsolete to well developed; cervical groove V or U–shaped, deeply impressed; branchiocardic grooves inconspicuous or conspicuous with anterolateral part often hardly distinguishable and very close to cervical groove, both usually merging dorsolaterally. Pleon lacking tubercles or spines; first pleonal pleura partly overlapped by that of second; posterior margin of second pleonal pleura rounded, except in P. varicosus . Telson subtriangular or subrectangular, entirely or weakly calcified with dorsomedian longitudinal groove (sometimes inconspicuous) and with blunt or sharp lateral spines. Epistome with anteromedian lobe pentagonal, hexagonal or septagonal shape. Antennal scale lateral margin straight to curved with a terminal strong spine. Third maxilliped with mesial half of ventral surface of ischium bearing setiferous punctuations, but P. varicosus and P. saffordi present a line of sharp and blunt spines in the middle part, respectively; setae coverture sparse or dense; flagellum of exopodite reaching, or slightly overreaching, basal part of merus. Caudal molar process of mandible unicuspidate, bicuspidate or tricuspidate; incisor lobe with eight to ten teeth, usually the third is the largest. Chelipeds carpus can be divided by a groove impression; propodus dorsal region with squamose or verrucous tubercles that can form well-defined rows, ventral region with two rows of tubercles that can reach or surpass the beginning of the fixed finger; dactylus moving subvertically. Male genitalia consisting of a fixed and slightly elevated ventromesial ridge bearing a small noncalcified papilla; male cuticle partition (sensu Morgan, 1986) present; all members with supernumerary gonopores in both sexes (permanent intersexuality). Branchial count 20 + epr + r, or 20 + ep + r (podobranchs on segments VIII–XIII; anterior arthrobranchs on VIII–XIII; posterior arthrobranchs on IX–XIII, that on 13 rudimentary pleurobranchs on XI–XIV; and epipodite on VII bearing few branchial filaments). SLP8 with a deep median suture or widely separated.

Remarks. The first diagnosis for Parastacus was proposed by Huxley (1879).He created this genus and the family Parastacidae to group Southern hemisphere crayfish based mainly on the branchial structure. The author proposed that the podobranchiae are devoid of more than a rudiment of a lamina and that the stem may be alate. In addition, podobranchiae of the first maxilliped has the form of an epipodite, but it can bear branchial filaments. Subsequent diagnosis for Parastacus were provided by Faxon (1898) and Riek (1971). Hobbs (1991) further improved upon the diagnosis of Parastacus and discussed the mandible morphology of South American Parastacidae and included the mandible as a character in the genera diagnosis. However, the drawing that illustrates the mandible of P. varicosus is apparently wrong, since both species present the caudal molar process bicuspidate and not quadricuspidate as pointed out by Hobbs’ illustration. Parastacus is morphologically similar to the Australian genera Engaeus Erichson, 1846 and Engaewa Riek, 1967 in having the dactyls of chelipeds subvertically moving and the male genitalia consisting of a small papilla. Parastacus is a unique genus with all individuals of the species with supernumerary gonopores (intersexuality). This phenomenon was already recorded in some populations of the South American species S. spinifrons ( Rudolph 2002) , V. araucanius ( Rudolph & Rivas 1988; Martínez et al. 1994) and the Australian genera Engaewa , Engaeus , Euastacus Clark, 1936 and Cherax Erichson, 1846 ( Horwitz 1988; Honan & Mitchell 1995; Sagi et al. 1996; Horwitz & Adams 2000; Vazquez & López-Greco 2007).

Distribution. Brazil (states of Rio Grande do Sul and Santa Catarina), Uruguay, Argentina, and Chile ( Buckup and Rossi, 1980; 1991; Rudolph, 2010; Ribeiro et al. 2020).