Hartnollius nobilii ( Perger & Wall, 2014 ), 2025

Paula, Danièle Guinot, Rodríguez, Paula A., Atzimba, Moreno I. & Toledano-Carrasco, Atzimba, 2025, The charismatic Gecarcinus ruricola (Linnaeus, 1758), type species of Gecarcinus Leach, 1814, with a neotype designation and genetic data, and new generic assignment, Hartnollius n. gen., for the three remaining species of the genus (Crustacea, Brachyura, Gecarcinidae), Zoosystema 47 (16), pp. 261-314 : 296-299

Hartnollius nobilii ( Perger & Wall, 2014) n. comb.

( Fig. 15 ; Table 1 )

Gecarcinus ruricola – Nobili 1901: 46 (nec Cancer ruricola Linnaeus, 1758 ).

Gecarcinus (Gecarcinus) lateralis quadratus – Türkay 1970: 338. — Prahl 1981: 207: fig. 56.1. — Prahl & Manjarrés 1984a: 155, 166, figs 3, 5.3 (nec Gecarcinus quadratus Saussure, 1853 ).

Gecarcinus lateralis – Türkay 1987: 147, fig. 7 (nec Gecarcinus lateralis Fréminville in Guérin, 1832).

Gecarcinus nobilii Perger & Wall, 2014: 97 , fig. 2C-E, 3, 4A-G, 5D. — Toledano-Carrasco 2019: 3, 11, 15. — N. K. Ng et al. 2019: 100 , fig. 2G. — Toledano-Carrasco et al. 2021: 215, 216, 229, 231.

TYPE MATERIAL. — Paratype. Ecuador • ♀ 36.6 × 44.3 mm, in ethanol; St Helena, Festa coll. Original label: “ Gecarcinus Festae Nob. (cotype), Nobili 1901, Muséum Paris”, Perger & Wall, 2014 det. Gecarcinus nobilii ; MNHN-IU-2014-11211 (= MNHN-B 12314).

TYPE LOCALITY. — Punta Galera, Ecuador (see Perger & Wall 2014).

DIAGNOSIS

Carapace

Carapace transversely ovate, broader than long, widest in anterior half, relatively flat, with hepatic, subhepatic and branchial regions moderately inflated; widest part of carapace being in line with antero-lateral angles of mesogastric region. Frontal width distinctly wider than distance between the mesial ends of suborbital cristae. Dorsal surface with weakly developed grooves, i.e, cervical, median (or urogastric) and longitudinal mesogastric grooves. Striae along lateral sides of carapace. Front short, broad, moderately produced and deflexed, widening very little below, its inferior margin being slightly arcuate. Mesial lobe of infraorbital margin just joining carapace front edge and completely exposed. Supraorbital margin gently sinuous, with small granules, confluent with anterolateral margin; exorbital tooth weakly developed, tip not over-reaching orbit. Orbital and anterolateral margins marked by row of small granules in males as in females. Anterolateral margins entire, not as rounded, joining exorbital angle, with more or less marked junction.

Cephalic structures

Antennules very small, folded obliquely. Antennae completely exposed. Eyestalks relatively short, curved.

Proepistome, epistome and pterygostome

Proepistome covered by subfrontal plate. Epistome rather developed, with one median crest and a lateral crest on each side. Suborbital, subhepatic and pterygostomial regions sparsely granular laterally.

Mxp3

Mxp3 rather small, not concealing epistome, leaving between them a narrow rhomboid gap, in longitudinal position. Ischium and merus subequal, with their articulation only slightly oblique; ischium without longitudinal groove (only a small trace); anterior margin of merus without distinct emargination, nearly straight, but may be with a slight notch; meri of both sides not joining medially; palp inserted below merus with only distal portion of last mobile article exposed. Exopod of mxp3 as narrow plate, completely concealed by fringe of thick setae, apex not reaching ischium-merus articulation; without flagellum.

Chelipeds

Male chelipeds subequal, widely gaping; heterochely and heterodonty usually not or only slightly marked; occlusal margins of fingers with small, spaced teeth on both sides; in the rare cases of greatly uneven chelipeds (heterochely), a more pronounced gap and pronounced heterodonty. Merus with only small granules on inner lower margin; carpus with denticles on inner upper margin. Female chelipeds subequal or nearly so, moderately gaping, therefore sexual dimorphism moderate.

Ambulatory legs

P3 moderately spiny. Propodus with unequally developed lateral carinae bearing four rows of weakly developed spines. Dactylus with four rows of small equal spines.

Sterno-pleonal cavity and pleon

Sterno-pleonal cavity completely glabrous, short, ending far from sternal suture 2/3, with marked ridge around telson. Male pleon moderately long, bell-shaped; with all somites free plus telson; lateral margins with fringe of setae; somite 6 with convex lateral margins, forming lateral shoulder; telson campanulate, narrower than somite 6, with lateral margins slightly marked, tip rounded, relatively narrow.

Female pleon subcircular; telson forming isosceles triangle, narrower than posterior margin of somite 6, lateral margins straight, smooth.

Thoracic sternum, locking pleonal structures and setal tufts Thoracic sternum wide, slightly narrowing at level of somite 5; sternite 1 as small triangular tooth, not separated by suture from sternite 2, not recessed; sternite 2 semi-ovate, with slightly convex margins; suture 2/3 present, practically straight or barely concave and only forming an obtuse angle; suture 3/4 absent, without lateral trace; sternites 3 + 4 completely fused, with obliquely directed margins slightly convex at junction of mxp3, almost straight or gently concave at level of articulation of P1; sutures 4/5 to 7/8 interrupted; sternites 5-7 similarly shaped, sutures well defined; suture 7/8 rather short; sternite 8 not developed medially, totally hidden when pleon is folded; posterior emargination reaching sternite 7.

Male gonopore and penis

Male gonopore and penis at level of suture 7/8 emerging rather far from P5 coxo-sternal condyle.

G1

See Perger & Wall (2014: 101, fig. 2D-E).

Vulvae

Protruding, oriented nearly horizontally, normally occluded by rigid calcified immobile operculum.

COLOUR

Red and white forms in males and females. Light lateral margin on dorsal carapace present, contrasting to dark median pattern, same colour as lateral carapace; some white forms with orange tinge; no orange patch at anterolateral carapace border and at posterior lateral urogastric groove; mesial lobe of infraorbital margin mostly grey; ventro-lateral carapace homogeneously red or white; cheliped palm uniformly red or white (see Perger & Wall 2014: 97, figs 3 with faded colour, 4A-H, 5D, table 2).

REMARKS

The MNHN paratype was collected by Enrico Festa probably during his 1895-1898 trip to Ecuador (Viaggio del Dr. Enrico Festa nella Republica dell’Ecuador et regioni vicine), then studied by Nobili, who initially considered it new and dedicated it to Festa under the name “ Gecarcinus festae ” without definitively establishing it. In fact, Nobili never published a description of Gecarcinus festae , which is therefore a nomen nudum. In 1901, Nobili described Sesarma festae and Uca festae , and, in the same article, he referred specimens collected in Ecuador to Gecarcinus ruricola , a species restricted to the western Atlantic islands ( Perger & Wall 2014). The MNHN specimen examined by Nobili and selected as the paratype of the new species Gecarcinus nobiili , dedicated to Nobili by Perger & Wall (2014), is shown in their fig. 3D-F and is deposited at the MNHN ( Fig. 15 ). The holotype is preserved at the LACM (see Perger & Wall 2014: 97; N. K. Ng et al. 2019: 99).

GEOGRAPHICAL DISTRIBUTION

Ecuador, Colombia and Peru. The specimens of Gecarcinus (Gecarcinus) quadratus from Peru previously reported by Türkay (1970: 338) may belong to Hartnollius nobilii n. comb. (see Perger & Wall 2014). The Gecarcinus ruricola of Cano (1889: 101, 227) from Ecuador must be also assigned to H. nobilii n. comb.

PALAEONTOLOGICAL DATA

Palaeontological analyses can be informative in assessing the continuity of phenotypes over time and geographical areas, but they are limited by the availability of fossils. Practically nothing is known about fossil or subfossil records from Gecarcinus . Fossil crab chelae attributed to Gecarcinus cf. ruricola reported by Donovan & Dixon (1998: 825) from the Pleistocene of Jamaica were later recognised as belonging to a species of Sesarma Say, 1817 (see Luque 2017; Luque et al. 2017). The Late Holocene remains of Gecarcinus sp. reported from Antigua by Pregill et al. (1988) would be conspecific with Hartnollius lateralis n. comb. (Luque 2017: fig. 1H-J, table 1, as Gecarcinus lateralis ). A Gecarcinus sp. from the late Pleistocene of Bermuda (Crystal Cave) is reported by Luque (2017: table 1). A total of 1400 identifiable Holocene remains of the two co-occurring species G. ruricola and G. lateralis have been found through field surveys along the northern coast of San Salvador Island and in the Bahamas, with various levels of disarticulation suggesting a low preservation potential ( Locatelli 2013: 867, figs 2-7, table 1). Schweitzer et al. (2023: 2) report G. ruricola from the Holocene in the Caribbean Sea and Mexico. According to Schweitzer et al. (2023) records are very few in gecarcinids. According a molecular phylogeny of Thoracotremata by Tsang et al. (2022: 5), the family Gecarcinidae (with also the Sesarmidae ) originated along with the warm climates during the Late Paleocene and Early Eocene (c. 60-50 MYA).

GENETICS

An alignment of 658 base pairs (364 conserved, 139 parsimony-informative and 173 variable) was used for the COI gene and 559 bp (292 conserved, 70 parsimony-informative and 120 variable) for the 16S gene, resulting in a concatenated matrix of 1217 bp ( Table 2 ). Since the trees generated using Bayesian Inference and Maximum Likelihood displayed the same topology, only the BI tree is shown, with the BI and ML support values.

The concatenated tree recovers the two major groups of gecarcinids proposed by Guinot et al. (2018), based on the consistency of morphological, larval and genetic data. On the one hand, the clade of crabs with less terrestrial habits (highlighted in purple) formed by the genera Cardisoma Latreille, 1828 , Discoplax A. Milne-Edwards, 1867 , and Tuerkayana Guinot, N. K. Ng & Rodríguez Moreno, 2018 . On the other hand, the clade of gecarcinids with markedly terrestrial habits (highlighted in red) that includes the genera Gecarcinus , Johngarthia Türkay, 1970 and Hartnollius n. gen. ( Fig. 16 ). Focusing on crabs highly adapted to terrestrial life, which are central to this study, Gecarcinus is identified as the probable sister taxon to Hartnollius n. gen. while in the less terrestrial clade, Discoplax and Tuerkayana form sister groups, collectively maintaining a close evolutionary relationship with Cardisoma ( Fig. 16 ).

Individuals of Gecarcinus ruricola from Cuba (ZMHK65343) and Guadeloupe (MNHN-IU-2024-7258 and MNHN-IU-2024-4640), which morphologically show some differences (position of merus mxp 3 in relation to frontal margin, and position of extremity of sterno-pleonal cavity in relation to thoracic sternal suture 2/3), are nested in the same clade with a high branch support ( Fig. 16 ), highlighting that Gecarcinus ruricola is a species with some morphological variability across its distribution range.

Pairwise nucleotide divergences for COI with K2P distance ( Table 3 ) indicate a high divergence between Gecarcinus and Hartnollius n. gen. (on average 9.56 with H. lateralis n. comb. and 11.14 with H. quadratus n. comb.), values comparable with the divergence between species of different genera such as those of Hartnollius n. gen. and Johngarthia lagostoma (10.62 with H. lateralis n. comb. and 11.40 with H. quadratus n. comb.) and Discoplax longipes with Tuerkayana latens (12.67 %). Notably, the genetic distance between Gecarcinus and Johngarthia is lower than that between Gecarcinus and Hartnollius n. gen. (see Table 3 ), as previously highlighted by Toledano-Carrasco et al. (2021). All these findings further support the validity of the new genus.

The average interspecific divergence between Hartnollius lateralis n. comb. and H. quadratus n. comb. (5.56%) closely matches the 6.1% previously reported by Toledano-Carrasco et al. (2021).

Genetic divergence between the two individuals of Gecarcinus ruricola (MNHN-IU-2024-7258 and MNHN-IU-2024-4640) from Guadeloupe and the individual from Cuba (ZMHK65343) is extremely low, almost zero (0.37%).

The genetic distances between individuals of the two subclades of Gecarcinidae are remarkably high, ranging from 17.44% between Cardisoma guanhumi and Johngarthia lagostoma to 20.58% average between Discoplax longipes and Gecarcinus ruricola reflecting the high divergence between the two groups.

Figures

FIG. 15. — Hartnollius nobilii (Perger & Wall, 2014) n. comb., paratype, ♀ 36.6 × 44.3 mm, Ecuador, MNHN-IU-2014-11211 (= MNHN-B12314): A, dorsal view; B, ventral view; C, front, orbit, and mesial lobe of infraorbital margin; D, front, proepistome (hidden), antenna (exposed), mesial lobe of infraorbital margin, and mxp3; E, thoracic sternum, female pleon and vulvae; F, left cheliped, internal view; G, chelipeds, external view; H, right P3; I, left P4. Scale bar: 10 mm. Credits: MNHN-Rodríguez Moreno.

FIG. 16. — Bayesian inference phylogenetic tree of Gecarcinidae based on the concatenation of mitochondrial COI and 16S rRNA gene fragments.Numbers at nodes are support values for BI (posterior probability) and ML (Ultrafast bootstrap). The clade of crabs with less terrestrial habits (Cardisoma Latreille, 1828, Discoplax A.Milne-Edwards,1867,and Tuerkayana Guinot,N. K. Ng & Rodríguez Moreno, 2018) are highlighted in purple,whereas the clade with markedly terrestrial habits (Gecarcinus Leach, 1814, Hartnollius n. gen. and Johngarthia Türkay, 1970) are highlighted in red. Ocypode rotundata Miers, 1882 was included as outgroup.