A new freshwater crayfish species of Parastacus Huxley, 1879 (Malacostraca: Decapoda: Parastacidae) from southern Brazil

Abstract

The present paper describes a new species of freshwater crayfish of the genus Parastacus Huxley, 1879 from the municipality of Amaral Ferrador in the state of Rio Grande do Sul, southern Brazil, evaluates its conservation status according to the IUCN Red List Criteria (sub-criterion B1), and updates the identification key for the genus. Parastacus longidactylus sp. n. differs from all analyzed species by the large eyes, the prominent and wide rostral carinae, surpassing the rostral basis and extending to the proximal third of the postorbital carinae, postorbital carinae and rostral carinae prominent and with similar lengths, chelipeds carpus dorsomedial surface not divided longitudinally by groove and long dactylus, surpassing the fixed finger. The possible extent of occurrence was estimated to be 6,968 km² and the species was recorded in only one location in the Camaquã River basin. The main threats to the region are the replacement of native vegetation by crops and livestock, water pollution and soil erosion. However, because there is only one known location where Parastacus longidactylus sp. n. occurs we suggest classifying the species as Data Deficient.

Keywords: Conservation; crustaceans; Parastacoidea; Rio Grande do Sul; taxonomy

INTRODUCTION

Freshwater crayfish are conspicuous members of limnetic ecosystems around the world, except in continental Africa and Antarctica ( Crandall and Buhay, 2008; Rogers et al., 2020). In South America, 22 species are recorded in the genera Parastacus Huxley, 1879 (17 species), Samastacus Riek, 1971 (one species), and Virilastacus Hobbs, 1991 (four species) ( Huber et al., 2020; 2022; Ribeiro et al., 2020; Rudolph, 2015). The former genus is distributed along streams, wetlands, and swamp forests of Brazil, Uruguay, Argentina, and Chile ( Ribeiro et al., 2020; De los Rios-Escalante et al., 2022).

Eight new species of Parastacus were discovered and described from 2016 to 2022 ( Ribeiro et al., 2016; 2017; Huber et al., 2018; 2020; 2022) and its richness is still underestimated. The development of research concerning native South American crayfish is relevant. Firstly, due to the ancient origin of the group, around 85 Ma during the Cretaceous ( Toon et al., 2010) and additionally, the South American parastacids, especially Parastacus, exhibit peculiar biological characteristics, such as specialized burrowing behavior, intersexuality, and hermaphroditism ( Rudolph and Almeida, 2000; Ribeiro et al., 2020).

The state of knowledge of the group, despite the recent advances, is still quite precarious, which has implications for several issues, especially the conservation of the group. Thus, the aim of this paper is to describe a new species of Parastacus, endemic to the state of Rio Grande do Sul, southern Brazil, and to assess its conservation status based on the IUCN Red List Criteria. In addition, we update the identification key for the genus.

MATERIAL AND METHODS

The examined material was collected in the municipality of Amaral Ferrador, state of Rio Grande do Sul, southern Brazil. Specimens were illustrated with the aid of a stereomicroscope fitted with a camera lucida. Illustrations were improved with the aid of Nanking ink and tracing paper, then scanned and edited in Photoshop CS6. All measurements were performed with vernier calipers with 0.1 mm accuracy and a millimetric ocular lens on a stereomicroscope. Morphological descriptions follow Ribeiro et al. (2016) and setae classification follows Horn et al. (2008). Sex was identified based on the morphology of the gonopores, according to Rudolph (1997). The taxonomic classification follows Rogers et al. (2020) and the branchial count follows Huxley (1879). The type material is deposited in the Museu de Zoologia da Universidade de São Paulo (MZUSP), São Paulo, Brazil. Other material examined are deposited in the crustacean collections of the Museu Nacional/Universidade Federal do Rio de Janeiro, Rio de Janeiro (MNRJ) and Universidade Federal do Rio Grande do Sul, Porto Alegre (UFRGS).

The extinction risk for the new species was evaluated according to the B1 sub-criterion of the International Union for Conservation of Nature - IUCN ( IUCN 2019). For aquatic invertebrates, this sub-criterion takes into consideration the estimated Extent of Occurrence (EOO), calculated based on the hydrographic basins according to the Otto Bacias shape method (level 5) ( ANA, 2007) in QGIS 3.10.3 ( QGIS Development Team, 2021).

Abbreviations used are:

• AreL = Areola Length

• AreW = Areola Width

• ASL = Antennal Scale Length

• ASW = Antennal Scale Width

• CD = Carapace Depth

• CeL = Cephalon Length

• CL = Carapace Length

• CMW = Cornea Maximum Width

• CW = Carapace Width

• FW = Frontal Width

• OW = Orbital Width

• PL = Pleon Length

• POCL = Post Orbital Carina Length

• PW = Pleon Width

• RCL = Rostral Carina Length

• RDL/LDL = Right/Left Dactylus Length

• RL = Rostral Length

• RML/LML = Right/Left Merus Length

• RPrL/LPrL = Right/Left Propodus Length

• RPrT/LPrT = Right/Left Propodus Thickness

• RPrW/LPrW = Right/Left Propodus Width

• RW = Rostral Width

• S1 = Pleonal Somite 1

• S2 = Pleonal Somite 2

• SLP = Thoracic Sternite Lateral Processes

• TeL = Telson Length

• TeW = Telson Width

• TL = Total Length

The definition of each measurement can be found in Ribeiro et al. (2016). Additionally, in this contribution, we determine the proportions to classify the dactylus size (X = RDL/RPrL or/and X = LDL/LPrL): Long (X ≥ 65%), Medium (65% > X > 57%), and Short (57% ≥ X).

SYSTEMATICS

I nfraorder Astacidea Latreille, 1802

Superfamily Parastacoidea Huxley, 1879

Family Parastacidae Huxley, 1879

Genus Parastacus Huxley, 1879

Parastacus longidactylus sp. nov.

( Figs. 1- 4)

Zoobank: urn: lsid:zoobank.org:act:EED4209E-8A29-4818-8137-98CBAC4805F7

Figure 1.
Parastacus longidactylus sp. n., holotype (MZUSP 45071) and female paratype (MZUSP 45072) . A, Habitus, dorsal view (holotype); B, cephalon, dorsal view (holotype); C, cephalon, lateral view (holotype); D, female abdominal somites, dorsal view (female paratype); E, male first, second and third abdominal pleura (holotype); F, female first, second and third abdominal pleura (female paratype); G, telson and uropods, dorsal view (holotype). Scale bars: A = 10 mm; B-F = 5 mm.

Figure 2.
Parastacus longidactylus sp. n., holotype (MZUSP 45071) and female paratype (MZUSP 45072). A, Epistome (holotype); B, thoracic sternites and gonopores (holotype); C, thoracomere 8, caudal view (holotype); D, antennal scale lateral view (female paratype); E, mandible (female paratype); F, third maxilliped, ventral view (female paratype); G, third maxilliped, dorsal view (female paratype); H, first pereiopod, lateral view (holotype); I, first pereiopod, dorsal view (holotype); J, second pereiopod, lateral view (holotype). Scale bars: B = 10 mm; H- J = 5 mm; A, F, G = 3.33 mm; E = 2.5 mm; C = 2 mm; D = 1.5 mm.

Figure 3.
Parastacus longidactylus sp. n., holotype (MZUSP 45071) in ethanol. A, Habitus, dorsal view; B, habitus, lateral view. Scale bar = 10 mm.

Figure 4.
Distribution of Parastacus longidactylus sp. n. in Amaral Ferrador, state of Rio Grande do Sul (RS), Brazil.

Type material. Holotype: adult male (MZUSP 45071), Brazil, Rio Grande do Sul, Amaral Ferrador, “Margem do Arroio Ladrão”, próximo da junção com o Rio Camaquã (30°52'46.6"S 52°14'33.0"W), VII/2015, coll. unidentified local residents, det. A.F. Huber. Paratypes: 1 female (MZUSP 45072), same data as holotype; 1 male (MZUSP 45073), Brazil, Rio Grande do Sul, Amaral Ferrador, 07/X/2013.

Comparative material. Brazil, Rio Grande do Sul: Parastacus brasiliensis ( von Martens, 1869): 4 females and 1 male (UFRGS 2337), Mariana Pimentel, 09/X/1986, coll. N.F. Fontoura; 1 female (UFRGS 5757), Porto Alegre, morro Santana, 06/IV/2013, coll. K. M. Gomes; 1 male (UFRGS 5868), sítio do Mato, zona sul, Porto Alegre (30°07'04"S 51°08'47"W), 22/III/2014, coll. M. Pasolius; 2 juveniles and 3 males (UFRGS 5947), Porto Alegre, Parque Natural do Morro do Osso (30°07’07.7”S 51°14’15.1”W), 22/III/2014, coll. K.M. Gomes, F.B. Ribeiro, M.F. Pasolius; 2 juveniles and 3 males (UFRGS 5947), Porto Alegre, Parque Natural do Morro do Osso (30°07’07.7”S 51°14’15.1”W), 22/III/2014, coll. K.M. Gomes, F.B. Ribeiro, M.F. Pasolius; 1 male (UFRGS 6025), rua Dona Francisca, Lomba do Pinheiro, Porto Alegre (30°08'05.0''S 51°06'11.9''W), 26/IX/2014, coll. K.M. Gomes, D.C. Kenne. - Parastacus buckupi Huber, Ribeiro and Araujo, 2018: 1 male (UFRGS 3581), Maquiné, arroio Carvão, 25/X/2001, coll. F.S. Vilella; 1 female (UFRGS 3895), Maquiné, arroio Carvão, 25/X/2001, coll. F.S. Vilella. - Parastacus gomesae Huber, Araujo and Ribeiro, 2022 : 1 male (MNRJ 30203), São Jerônimo, Horto Florestal Quitéria, riacho de primeira ordem (30°29’05.8”S 52°04’09.9”W), 21/X/2020, colls. A.F. Huber, K.M. Gomes, F.B. Ribeiro; 1 female (MNRJ 30204), São Jerônimo, Horto Florestal Quitéria, riacho de primeira ordem (30°29’05.8”S 52°04’09.9”W), 21/X/2020, colls. A.F. Huber, K.M. Gomes, F.B. Ribeiro; 1 female (UFRGS 5339), São Jerônimo (30°29’05.0”S 52°04’11.0”W), VII/2011, colls. K.M. Gomes, C. Sokolowicz. - Parastacus guapo Huber, Araujo and Ribeiro, 2022: 1 male (MNRJ 30200), Pantano Grande, Horto Sanga das Pedras, zona alagada (30°13’28.4”S 52°24’44.1”W), 20/X/2020, colls. A.F. Huber; K.M. Gomes, F.B. Ribeiro; 1 female (MNRJ 30201), Pantano Grande, Horto Sanga das Pedras, zona alagada (30°13’28.4”S 52°24’44.1”W), 20/X/2020, colls. A.F. Huber; K.M. Gomes, F.B. Ribeiro; 1 male, 3 females, 2 juveniles (UFRGS 6932), Pantano Grande, Horto Sanga das Pedras, zona alagada (30°13’28.4”S 52°24’44.1”W), 20/x/2020, colls. A.F. Huber; K.M. Gomes, F.B. Ribeiro. - Parastacus macanudo Huber, Rockhill, Araujo and Ribeiro, 2020: 1 male (UFRGS 6672), São Leopoldo, Parque Imperatriz Leopoldina (29°45'40.7"S 51°07'47.6"W), 20/VII/2018, colls. A.F. Huber, F.B. Ribeiro; 1 male (MNRJ 29877), São Leopoldo, Parque Imperatriz Leopoldina (29°45'40.7"S 51°07'47.6"W), 20/VII/2018, colls. A.F. Huber, F.B. Ribeiro; 2 males (MNRJ 29877, MNRJ 29878), São Leopoldo, Parque Imperatriz Leopoldina (29°45'40.7"S 51°07'47.6"W), 20/VII/2018, colls. A.F. Huber, F.B. Ribeiro. - Parastacus promatensis Fontoura and Conter, 2008: 1 male (UFRGS 4153), São Francisco de Paula, riacho Garapiá, CPCN Pró-Mata (PUCRS), 09/VII/2005, coll. L.C.C. Daudt; 1 female (UFRGS 4157), São Francisco de Paula, riacho Garapiá, CPCN Pró-Mata (PUCRS), 15/I/2006, coll. L.C.C. Daudt; 1 male (UFRGS 4159), São Francisco de Paula, riacho Garapiá, CPCN Pró-Mata (PUCRS), 09/VII/2005, coll. L.C.C. Daudt; 1 male and 2 females (UFRGS 5949), São Francisco de Paula, riacho Garapiá, CPCN Pró-Mata (29°29'22.0''S 50°13'04.0''W), 2014.

Etymology. A combination of the Latin epithets “longus”, which alludes to a long size, and “dactylus”, which alludes to fingers. We suggest the common name “the long-finger crayfish” for this new species.

Diagnosis. Wide front with short triangular rostrum. Rostral apex shaped as inverted “U”, with straight, blunt spine. Suborbital angle 90°, unarmed. Rostral carinae prominent, wide, surpassing rostral basis, extending to proximal third of postorbital carinae. Postorbital carinae, rostral carinae prominent, with similar length. Cervical groove weakly V-shaped. Areola narrow. Telson subrectangular, longer than wide, with small blunt spines on lateral margins. Mandible with caudal molar process bicuspidate and incisor lobe with 10 teeth. S2 pleurae low and moderate with shallow groove parallel to margin. Chelipeds large and subequal, laterally flattened, with long dactylus surpassing fixed finger. Carpus with dorsomedial surface not divided longitudinally by groove.

Description of the holotype. Rostrum: triangular, wider than long (RL 84.9% of RW), short (11.6% of CL), reaching middle portion of second article of antennular peduncle ( Fig. 1A-C). Dorsum straight, apex inverted “U”-shaped, ending in straight blunt spine ( Fig. 1A-C). Few plumose setae on lateral margins. Carinae almost straight, prominent, wide, extending back to carapace, surpassing rostral basis, extending to proximal third of postorbital carinae; rostral carinae sides convergent and rostral carinae basis slightly convergent ( Fig. 1A-C).

Cephalon: Carapace lacking spines or tubercles. CeL 66.3% of CL. Eyes large (CMW 84.5% of OW); suborbital angle 90°, unarmed ( Fig. 1C). Front wide (FW 53.7% of CW). Postorbital carinae and rostral carinae prominent and similar in length (RCL 96.3% of POCL). Lateral cephalic edge with moderate setation ( Fig. 1A-C).

Thorax: carapace laterally compressed, deep, narrow (CD 42.4% of CL; CW 35.8% of CL). Cervical groove weakly V-shaped . Branchiocardiac grooves inconspicuous ( Fig. 1A). Areola narrow, 3.14( as long as wide (27.7% of CL) ( Fig. 1A).

Pleon: lacking spines or tubercles, short, wide (PL 72.9% of CL; PW 98.2% of CW), smooth, covered with small setae on pleural margins ( Fig. 1A). Pleural somites with rounded posterior margins. S1 pleurae with large distal lobe not overlapped by S2 pleurae. S2 pleurae low and moderate, with shallow groove parallel to margin ( Fig. 1D) .

Tailfan: telson more calcified in proximal portion than in distal margin, subrectangular, longer than wide (TeW 80.2% of TeL) , with small blunt spines on lateral margins; rounded distal margin with abundant long plumose setae and short simple setae. Dorsal surface with tufts of short setae and inconspicuous dorso-median longitudinal groove ( Fig. 1A, E). Uropod protopod bilobed, with rounded and unarmed margins; proximal lobe largest. Exopod lateral margin unarmed, mid-dorsal carinae few prominent, ending in a sharp spine. Transverse suture (diaeresis) straight, with 8 dorsolateral spines (outer) and 8 dorsolateral spines (inner) on right exopod, and 7 dorsolateral spines (outer) and 8 dorsolateral spines (inner) on left exopod. Endopod, mid-dorsal carina weakly projecting, unarmed; lateral margin with 1 sharp spine at level of exopod transverse suture ( Fig. 1E).

Epistome: anterolateral section with 4 marginal tubercles on both sides; anterior most tubercle biggest. Posterolateral section with simple setae and with deep lateral grooves converging to basis of anteromedian lobe. Median section with longitudinal groove. Anteromedian lobe irregularly septagonal, 1.04( as long as wide; apex acute, wide, with some small serrated setae, surpassing median part of antepenultimate article of antennal peduncle; apex concave, basis with shallow groove ( Fig. 2A) .

Thoracic sternites: SLP4 smallest and very close to each other, median keel present and not inflated; SLP5 small and close to each other, median keel present and not inflated; SLP6 larger than SLP4; SLP5 and SLP8 with concave surface, median keel inflated; SLP7 largest, with surface concave, median keel inflated, bullar lobes absent; SLP8 small, median keel absent, vertical arms of paired sternopleural bridges close to each other, bullar lobes not visible ( Fig. 2B, D).

Antennule: internal ventral border of basal article with sharp spine in middle portion ( Fig. 2A).

Antenna: reaching posterior margin of carapace when extended back. Antennal scale widest at distal to mid-length, reaching middle of third antennal article, ASW 36.6% of ASL ( Fig. 2A, C), lateral margin straight, distal spine well developed. Coxa with weakly prominent carina above nephropore. Basis unarmed ( Fig. 2A).

Mandible: cephalic molar process molariform, caudal molar process bicuspidate with 1 cephalodistal cusp and 1 distoproximal cusp. Incisor lobe with 10 teeth; third tooth from anterior margin being largest ( Fig. 2E).

Third maxilliped: ischium, ventral surface covered by tufts of composite setae with some sparse long and simple setae ( Fig. 2F); dorsal surface with few setiferous punctations on inner margin and dorsal surface and 2 short, serrated setae on proximal portion ( Fig. 2G); ‘crista dentata’ bearing 23 teeth on both right and left ischia ( Fig. 2F, G). Merus, dorsal surface glabrous in proximal and middle portions, anterior outer margin portion with few long, serrated setae. Merus ventral surface sparsely covered by some long simple setae in median and outer regions ( Fig. 2F); exopod longer than ischium, with flagellum surpassing proximal margin of merus and with tufts of long and composite setae in last and first articles ( Fig. 2F, G).

First pair of pereiopods (chelipeds): large and subequal, laterally flattened (RPrT 25.3% of RPrL; LPrT 23.9% of LPrL) (Figs. 1A; 2I). Ischium ventral surface with 6 and 4 tubercles in right and left, respectively. Merus: right merus (RML) 60.2% of propodus length (RPrL); left merus (LML) 59.4% of propodus length (LPrL); ventral surface with 2 longitudinal series of tubercles: inner series with 17 tubercles, outer 11, plus 15 mesial tubercles irregularly distributed on right merus; inner series with 11 tubercles, outer 12, plus 14 mesial tubercles irregularly distributed on left merus. Dorsal and midventral spines absent. Carpus with dorsomedial surface not divided longitudinally by groove (Figs. 1A; 2I). Internal dorsolateral margin with row of tubercles, increasing in size distally; inner surface with 20 small mesial tubercles. Carpal spine absent ( Fig. 2I). Propodus width (RPrW and LPrW) 46.3% of length in right cheliped and 45.5% in left cheliped. Dorsal surface of palm with irregularly distributed rows of squamous tubercles ( Fig. 2H, I). Inner margin without tubercles. Ventral surface bearing 2 rows of squamous tubercles, surpassing the proximal part of fixed finger ( Fig. 2H). Dactylus: articulating sub-vertically, right dactylus long (RDL) 69.4% of propodus length (RPrL), left dactylus long (LDL) 71.2% of left propodus (LPrL); dorsal surface with few squamous tubercles more concentrated in proximal portion ( Fig. 2H). Cutting edge of fingers visible. Fixed finger with 10 teeth, fifth tooth largest in right cheliped. Dactyli with 12 teeth, third tooth largest in both chelipeds ( Fig. 2H, I); right fixed finger with 11 teeth, left fixed finger with 9 teeth; fifth tooth largest. Second pair of pereiopods: dorsal surface of dactylus and propodus with tufts of long and simple setae. Dorsal and ventral surface of carpus with few sparse, simple and long setae in ( Fig. 2J).

Gonopores: presence of both genital apertures on coxae of third and fifth pairs of pereiopods. Female gonopores semi-ellipsoidal (maximum diameter 1.35 mm) with well-calcified membrane. Male gonopores rounded, opening onto apical end of small, fixed, calcified and truncated phallic papilla, close to inner border of ventral surface of coxae of fifth pair of pereiopods. Male cuticle partition present ( Fig. 2B).

Branchial count: 20 + epr + r. Branchial arrangement follows the same described by Hobbs (1991) with epipod of first maxilliped with rudimentary podobranchial filaments.

Measurements: holotype male, CL 31.8 mm and TL 61.1 mm. In the type series, CL ranges from 27.8 to 31.8 mm (mean = 29.8 mm). FW/CW: 0.43 ± 0.12 (min: 0.29; max: 0.53). RL/RW: 0.82 ± 0.06 (min: 0.76; max: 0.87). CMW/OW: 0.75 ± 0.08 (min: 0.70; max: 0.85). Postorbital carina longer than the rostral carina in all specimens analyzed. CW/PW: 1.05 ± 0.05 (min: 1.02; max: 1.09). AreW/RW: 0.71 ± 0.11 (min: 0.64; max: 0.79) ( Tab. 1).

Table 1.
Measurements (mm) of the type series of Parastacus longidactylus sp. n.. For abbreviations, see Material and Methods.

	Holotype male	Paratype female	Paratype male
	(MZUSP 45071)	(MZUSP 45072)	(MZUSP 45073)
TL	61.10	55.90	-
CL	31.80	27.80	-
CW	11.40	12.05	13.20
CD	13.50	14.00	16.80
CeL	21.10	18.30	22.90
RL	3.70	3.10	3.20
RW	4.40	3.55	4.20
RCL	7.80	4.60	6.40
CMW	1.26	1.30	1.25
OW	1.49	1.85	1.74
POCL	8.10	5.90	8.20
FW	6.12	3.55	5.70
ASL	4.40	3.33	3.55
ASW	1.60	1.25	1.70
AreL	8.80	7.90	-
AreW	2.80	2.80	-
LPrT	5.30	2.20	4.10
LPrL	22.20	9.10	19.20
LPrW	10.10	3.10	8.90
LDL	15.80	6.20	14.10
LML	13.20	6.70	13.80
RPrT	5.80	5.20	8.00
RPrL	22.90	-	25.10
RPrW	10.60	9.00	12.00
RDL	15.90	12.10	15.70
RML	13.80	10.90	13.70
PL	23.20	21.10	-
PW	11.20	11.05	-
TeL	9.10	8.70	10.40
TeW	7.30	6.80	8.20

Color of living specimens. Data not available.

Variations in type-series. All paratypes exhibit both masculine and feminine gonopores in the same individual. Male paratypes also exhibit semi-ellipsoidal female gonopores (average maximum diameter 1.36 mm) covered by a calcified membrane. Male gonopores are very similar in all male paratypes. The number of teeth in the ‘crista dentata’ ranges from 20 to 25 in the left ischium and from 19 to 26 in the right ischium of the third maxilliped in the paratypes.

Distribution. Parastacus longidactylus sp. n. appears to have a limited distribution, being registered so far only from the municipality of Amaral Ferrador, state of Rio Grande do Sul, southern Brazil ( Fig. 4).

Habitat and Ecology. Parastacus longidactylus sp. n. was collected in the “Ladrão” creek near to the junction with the Camaquã River, in the Camaquã hydrographic basin, in the state of Rio Grande do Sul ( Fig. 4). It is also part of the physiographic region of Serra do Sudeste region, bordering the Encosta do Sudeste region ( IBGE 2004a; 2004b; UFRGS-IB-Centro de Ecologia, 2016).

Vegetation. The type locality of this species is in the Pampa biome. Types of vegetation in the area are Submontane Semideciduous Seasonal Forest, and Alluvial Semideciduous Seasonal Forest, commonly called gallery forest, or riparian forest, in the lower part, flat and prone to flooding in the rainy season ( Beier et al., 2018; Rambo, 2015; SEMA, 2023).

Soil. The soil is classified as Dystrophic Red-Yellow Argisols ( Santos et al., 2011). This soil usually occurs in areas of undulating relief, yet they may also be present in less steep areas. It has a characteristic yellowish-red color, which is related to higher levels of hematite and goethite iron oxides ( Santos et al., 2023). Moreover, they are considered deep soils, with high drainage capacity, low fertility, nutrient limitations, strong acidity, and high susceptibility to degradation and erosion ( Santos et al., 2011; 2023; Streck et al., 2002; 2008).

Burrowing behavior and burrow structure. Data not available.

Conservation status. Data Deficient. The extent of occurrence (EOO) was estimated as comprising approximately 6,968 km² (B1) ( Fig. 4). Considering the data concerning the Camaquã River Hydrographic Basin, this species can only be classified under subitem b(iii): continuing decline observed in quality of habitat ( IUCN, 2019). Taking this into account, we classified this species as DATA DEFICIENT (DD).

DISCUSSION

Morphology

Parastacus longidactylus sp. n. differs from P. brasiliensis, P. buckupi, P. guapo, P. gomesae, P. macanudo, and P. promatensis by the large eyes, rostral carina surpassing rostral basis and extending almost to the middle of postorbital carinae, cheliped palm dorsal surface with irregularly distributed verrucose tubercules, long dactylus, and blunt telson lateral spines ( Figs. 1A-C, G; 2H, I; Tab. 2).

Table 2.
Main characters distinguishing Parastacus longidactylus sp. n. from other species of Parastacus cited in the Remarks. Asterisk ( *) indicates variations in species of comparative material. For abbreviations, see Material and Methods.

Characters		P. brasiliensis	P. buckupi	P. gomesae	P. guapo	P. longidactylus sp. n.	P. macanudo	P. promatensis
Rostrum
	Shape	Triangular or spatulated	Triangular	Triangular	Triangular	Triangular	Triangular	Subtriangular
	Apex	Rounded, ending in an upward spine	Rounded, ending in an upward spine	Rounded and smooth*	Rounded, ending in an upward spine	Rounded, ending in a straight blunt spine	Rounded, ending in a tiny straight blunt spine*	Acute, ending in a short and depressed spine.
	Dorsal Surface	Concave	Straight	Straight with a slightly concave in the anterior portion	Straight	Straight	Straight	Flat
	Eyes	Small	Small	Small*	Small	Large	Small	Small
	Rostral carina	Surpassing the rostral basis	Surpassing the rostral basis	Surpassing the rostral basis	Surpassing the rostral basis	Surpassing rostral basis and extending almost to the middle of postorbital carinae	Surpassing the rostral basis	Surpassing the rostral basis
Suborbital angle		=90°	=90°	>90° *	>90°*	=90°	>90°	=90°
Postorbital carina		Weakly prominent	Weakly prominent	Prominent in anterior and middle portions	Prominent in anterior and middle portions	Prominent	Weakly prominent	Prominent
Cervical groove		Weakly V-shaped	Weakly V-shaped	Weakly V-shaped	Weakly V-shaped	Weakly V-shaped	Weakly V-shaped	U-shaped
Epistome
	Anteromedian lobe	Pentagonal	Pentagonal	Septagonal	Pentagonal	Septagonal	Pentagonal	Pentagonal
Mandible
	Incisor process	Nine teeth (the third tooth from the anterior margin is the largest)	Ten teeth (the fourth tooth from the anterior margin is the largest)	Seven teeth (the second tooth from the anterior margin is the largest)	Nine teeth (the third tooth from the anterior margin is the largest)*	Ten teeth (the third tooth from the anterior margin is the largest)	Nine teeth (the second tooth from the anterior margin is the largest)	Nine teeth (the third tooth from the anterior margin is the largest)
	Caudal molar process	Bicuspidate	Unicuspidate	Bicuspidate	Bicuspidate	Bicuspidate	Bicuspidate	Bicuspidate
Chelipeds
	Carpal spine	Absent	Absent	Absent	Present	Absent	Present	Absent
	Size and shape	Large and flattened	Large and globose	Large and flattened	Large and flattened	Large and flattened	Large and flattened	Large and flattened
	Palm dorsal surface	2-3 rows of verrucose tubercles irregularly distributed	2 rows of verrucose tubercles irregularly distributed	3-4 rows of verrucose tubercles irregularly distributed	2-3 rows of verrucose tubercles irregularly distributed	Verrucose tubercles irregularly distributed	Single row of verrucose tubercles irregularly distributed	3-4 rows of verrucose tubercles irregularly distributed
	Palm internal surface	Smooth	Smooth	Few small tubercles	Sparse tubercles more concentrated in the low portion and close to the insertion of dactylus	Smooth	Smooth	Tubercles in medial portion
	Dactylus Size	Medium	Medium	Short	Medium	Long	Medium	Medium
Areola		Wide	Narrow	Narrow	Narrow*	Narrow	Narrow	Narrow
Pleon
	Shape	Long and wide	Short and wide	Short and wide*	Short and wide*	Short and wide	Long and wide	Long and wide
Telson
	Shape	Subrectangular	Subrectangular	Subrectangular	Subrectangular	Subrectangular	Subrectangular	Subrectangular
	Lateral spines	Large and sharp	Small and sharp	Small and sharp	Large and sharp	Small and blunt	Large and sharp	Large and sharp
References		Buckup and Rossi (1980); Miranda et al. (2018); Ribeiro et al. (2020).	Huber et al. (2018); Ribeiro et al. (2020).	Huber et al. (2022).	Huber et al. (2022).	Present paper.	Huber et al. (2020); Ribeiro et al. (2020).	Fontoura and Conter (2008); Miranda et al. (2018); Ribeiro et al. (2020).

The present new species is morphologically similar to P. brasiliensis in regard to the general shape of rostrum and shape of the telson (sub-rectangular) ( Fig. 1A-C, G; Tab. 2) . It differs from P. brasiliensis in the straight rostral surface, prominent postorbital carinae, hexagonal anteromedian lobe of the epistome, mandible incisor process with ten teeth, narrow areola, and short pleon ( Figs. 1A-C; 2A, E; Tab. 2).

It is also morphologically similar to P. buckupi in the general shape of the rostrum, and in the shape of the telson (subrectangular) ( Fig. 1A-C, G; Tab. 2) ; it differs from P. buckupi in the straight and blunt rostral spine, prominent postorbital carinae, hexagonal anteromedian lobe of the epistome, bicuspidate mandible caudal molar process, and flattened chelipeds ( Figs. 1A-C; 2A, E, I; Tab. 2).

The long-finger crayfish is morphologically similar to P. gomesae in the general shape of the rostrum, and in the shape of the telson (subrectangular) ( Fig. 1A-C, G; Tab. 2) ; it differs from P. gomesae in the straight and blunt rostral spine, straight rostral surface, suborbital angle = 90°, prominent postorbital carina, mandible incisor process with ten teeth (the third tooth from the anterior margin is the largest), and smooth cheliped palm internal surface ( Figs. 1A-C; 2E; Tab. 2).

Parastacus longidactylus sp. n. is morphologically similar to P. guapo in the general shape of the rostrum, and in the shape of the telson (subrectangular) ( Fig. 1A-C, G; Tab. 2) ; it differs from P. guapo in the straight and blunt rostral spine, suborbital angle = 90°, prominent postorbital carina, hexagonal anteromedian lobe of the epistome, mandible incisor process with ten teeth, absent carpal spine, and smooth cheliped palm internal surface ( Figs. 1A-C; 2A, E, H, I; Tab. 2).

Additionally, P. longidactylus sp. n. is morphologically similar to P. macanudo in the general shape of the rostrum, and in the shape of the telson (subrectangular) ( Fig. 1A-C, G; Tab. 2) ; it differs from P. macanudo in the suborbital angle = 90°, prominent postorbital carina, hexagonal anteromedian lobe of the epistome, mandible incisor process with ten teeth (the third tooth from the anterior margin is the largest), absent carpal spine and short pleon ( Figs. 1A, C; 2A, E, I; Tab. 2).

Finally, P. longidactylus sp. n. is morphologically similar to P. promatensis in the general shape of the rostrum, and in the shape of the telson (subrectangular) ( Fig. 1A-C, G; Tab. 2) ; it differs from P. promatensis in the rounded rostrum apex (ending in a straight blunt spine), straight rostrum dorsal surface, cervical groove weakly V-shaped, hexagonal anteromedian lobe of the epistome, mandible incisor process with ten teeth, smooth cheliped palm internal surface, and short pleon ( Figs. 1A-C; 2A, E; Tab. 2).

Conservation status

Assessing the conservation status of a newly described species can be problematic due to the lack of knowledge of the general biology, population demographics, and distribution ( Boos et al., 2019). This situation is common with aquatic invertebrate fauna since their conservation status is usually rated using criterion B from IUCN. This criterion takes into consideration the decline in the habitat quality, the geographic distribution of the species and the fragmentation of its population ( Cumberlidge et al., 2009; 2017; Ribeiro et al., 2016; 2017; Santos et al., 2017; Huber et al., 2018; 2020; 2022; Miranda et al. 2018; IUCN, 2019). In this contribution, to estimate the distribution of P. longidactylus sp. n., we calculated its EOO. According to the IUCN (2019), an EOO between 5,000 and 20,000 km², added to at least two conditions or subitems of this criterion, categorizes a species as Vulnerable (VU). However, Parastacus longidactylus sp. n. can only have subitem b(iii) apply, related to the observed decline in the quality of habitat due to local threats, which is the case in the Camaquã River Hydrographic Basin (CRHB) region ( Fig. 4).

The CRHB has been suffering modification of its natural characteristics due to human occupation and activities, such as the replacement of native vegetation by crops and livestock, water pollution (disposal of agricultural pesticides and organic material, domestic sewage, and solid waste) and soil erosion ( Lima and Silva, 2013; SEMA, 2015; Lense et al., 2022). The main crops in the CRHB are rice plantations and forestry of Eucalyptus spp, “Acácia Negra” ( Acacia mearnsii) and pine ( Pinus elliottii), which are considered invasive species and can affect the surrounding natural environments ( Beier et al., 2018; SEMA, 2015). These crops represent a serious risk to the natural environment since usually they are irrigated using channels from natural water bodies, which causes a reduction in the volume of these natural water bodies, contamination by pesticides, soil compaction, fragmentation, and erosion ( SEMA, 2015; Lense et al., 2022). Furthermore, the region also suffers from deforestation and fragmentation of riparian forests, which increases erosion of the banks, while also causing significant loss of forested soil and increased siltation of the water bodies ( De Marchi, 2006; Borges-Martins et al., 2007; Didoné et al., 2014; Chen et al., 2019).

In conclusion, even with literature data for the CRHB region and the estimated EOO of P. longidactylus sp. n., it is still difficult to infer how limited and fragmented the distribution and population of this species are. Based on that, we suggest that P. longidactylus sp. n. should be categorized as Data Deficient (DD) for now. However, we reinforce the necessity of exploring the CRHB area to check for new records of this species, and evaluate its real distribution, habitat conservation, and population connectivity.

Updated key to genus Parastacus.

The following key is modified from Huber et al. (2022), with the addition of Parastacus longidactylus sp. n.

1 Telson with lateral spines ………………………………………………………………………………….………...…………………….. 2

1’ Telson without lateral spines, maxilliped III exopod flagellum surpassing ischium distal margin …… Parastacus nicoleti ( Philippi, 1882)

2(1) Postorbital carina proximal edge ending in a strong spine; uropod protopod proximal lobe bearing a spine; areola delimited by carinae …………………………………………….…………………………………………………………….………………………….……………… 3

2’ Postorbital carina proximal edge not ending in spine; uropod protopod lobe lacking spine; areola not delimited by carinae …………… 4

3(2) Cheliped merus, carpus, and propodus medially with tufts of long setae; maxilliped III ischium ventral margin with longitudinal spine row ……..……..……..……..……..……..……..……..……..……..……..……..……..……..……….. Parastacus varicosus Faxon, 1898

3’ Cheliped merus, carpus, and propodus medially glabrous; maxilliped III ischium ventral margin with longitudinal tubercle row ……………………………………………………………………………………………………………... Parastacus saffordi Faxon, 1898

4(2’) Telson distal margin rounded …………………………………..……………………………………………………………………….. 5

4’ Telson distal margin acute ……...……...……...……...……...……...……...……... Parastacus buckupi Huber, Ribeiro and Araujo, 2018

5(4) Cheliped carpus distally glabrous …………………...……...……...……...……...……...……...……………...………………………. 6

5’ Cheliped carpus distally with tufts of long and simple setae ………………... Parastacus pilicarpus Huber, Ribeiro and Araujo, 2018

6(5) Epistome anteromedian lobe hexagonal or pentagonal…………………...……...……...……...……...……...……......……………….. 7

6’ Epistome anteromedial lobe septagonal …………………………...……...……...……...……...……...……...….…………………….. 8

7(6) Cheliped dactyl and pollex cutting edges covered by long setal tufts …………...……...……...……...……...……...……...………..… 9

7’ Cheliped dactyl and pollex cutting edges visible ………………...……...……...……...……...……...……...………………………... 10

8(6’) Dactylus long ………………..………………...……...………...……...……...……...……...…………. Parastacus longidactylus sp. n.

8’ Dactylus short …………...……...……...……...……...……...……...…………… Parastacus gomesae Huber, Araujo and Ribeiro, 2022

9(7) Postorbital carinae prominent …………...……...……...……...……...……...……...……… Parastacus pilimanus ( von Martens, 1869)

9’ Postorbital carinae obsolete …………...……...……...……...……...……...……...…… Parastacus laevigatus Buckup and Rossi, 1980

10(7’) Chelipeds with globose palm ………………...……...……...………...……...……...……...………………...………………………... 11

10’ Chelipeds with flattened palm ………………...……...……...……...……...……...……...……...……………………………………. 13

11(10) Cervical groove U-shaped ………………………..…………… Parastacus caeruleodactylus Ribeiro and Araujo in Ribeiro et al., 2016

11’ Cervical groove V-shaped ………………………………..……...……...……...……...……...……...……...………………………… 12

12(11’) Rostral carinae reaching postorbital carinae proximal edge ……………………………… Parastacus defossus Faxon, 1898

12’ Rostral carinae surpassing postorbital carinae proximal edge ……………………………………… Parastacus pugnax ( Poeppig, 1835)

13(10’) Telson subrectangular ……………………...……...……...……...……...……...……...……………………………………………... 14

13’ Telson subtriangular ………………… …………………………….. Parastacus fluviatilis Ribeiro and Buckup in Ribeiro et al., 2016

14(13) Cheliped palm dorsal surface with tubercles irregularly distributed …………...……...……...……...……...……...……...………….. 15

14’ Cheliped palm dorsal surface with three well-defined tubercle rows ………………. Parastacus tuerkayi Ribeiro, Huber and Araujo in Ribeiro et al., 2017

15(14) Cheliped ventral surface bearing one row of squamose tubercles ………………...……...……...……...……...……...……...……….. 17

15’ Cheliped ventral surface bearing two rows of squamose tubercles ………………...……...……...……...……...……...……...……… 16

16(15’) Postorbital carinae prominent in anterior and middle portions ………………….. Parastacus guapo Huber, Araujo and Ribeiro, 2022

16’ Postorbital carinae weakly prominent ……………………………… Parastacus macanudo Huber, Rockhill, Araujo and Ribeiro, 2020

17(15) Cheliped palm medial margin tuberculate, cervical groove U-shaped ……………. Parastacus promatensis Fontoura and Conter, 2008

17’ Cheliped palm medial margin smooth; groove weakly V-shaped ………………….......… Parastacus brasiliensis ( von Martens, 1869)

ACKNOWLEDGMENTS

We thank the anonymous reviewers for their suggestions.

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• 1
  Zoobank: http://zoobank.org/urn:lsid:zoobank.org:pub:D73CB1C7-AB83-4D4B-B654-AAB1A8E67888
• Consent for publication
  All authors declare that they have reviewed the content of the manuscript and gave their consent to submit the document.
• Data availability
  All study data are included in the article.
• Funding and grant disclosures
  The Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) provided a Master’s scholarship to A.F. Huber and a postdoctoral fellowship to F.B. Ribeiro (PNPD nr 88887.470134/2019-00).
• Study permits
  All sampled specimens were collected according to Brazilian laws (SISBIO license number 45759-5).

Edited by

• Editor-in-chief:
  Christopher Tudge

• Associate Editor:
  Sandro Santos

Data availability

All study data are included in the article.

Publication Dates

• Publication in this collection
  19 Jan 2024
• Date of issue
  2024

History

• Received
  12 Jan 2023
• Accepted
  01 Aug 2023