Research Article |
Corresponding author: William Santana ( willsantana@gmail.com ) Academic editor: Sammy De Grave
© 2020 Jessica Colavite, Amanda M. Windsor, William Santana.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Colavite J, Windsor AM, Santana W (2020) A new genus for Pericera septemspinosa Stimpson, 1871 and Pericera heptacantha Bell, 1836 (Crustacea, Brachyura, Majoidea), based on morphology and molecular data. Zoosystematics and Evolution 96(1): 205-216. https://doi.org/10.3897/zse.96.50360
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A new genus of majoid spider crab, Pohleus gen. nov. is established for Pericera septemspinosa Stimpson, 1871 and Pericera heptacantha Bell, 1836, based on morphology and molecular data from the partial sequences of the 12S and 16S mitochondrial genes and the 18S small subunit rRNA nuclear locus. The species are re-described and illustrated, based on material from several localities of the western Atlantic and eastern Pacific oceans. The carapace, antennal and pterygostomial spines, male thoracic sternum and first gonopods are distinctive characters, distinguishing Pohleus gen. nov. from species assigned to Macrocoeloma Miers, 1879, where P. septemspinosus and P. heptacanthus are currently included.
Epialtidae, Pisidae, western Atlantic, eastern Pacific, Macrocoeloma heptacanthum, Macrocoeloma septemspinosum
Macrocoeloma heptacanthum (Bell, 1836) and M. septemspinosum (Stimpson, 1871) were originally described as Pericera Latreille, 1825 and transferred by
Pohleus gen. nov., is proposed herein to receive Pericera heptacantha and P. septemspinosa and a lectotype and a neotype are designated for each species, respectively. The species are re-described, illustrated and the morphological differences between them are detailed below. A phylogenetic framework for Pohleus gen. nov. and allied genera is proposed, based on partial sequences of the 12S and 16S mitochondrial genes and the 18S small subunit rRNA nuclear locus.
Specimens examined are deposited in the collections of the Coleção de Invertebrados Aquáticos do Sul da Bahia, Universidade Estadual de Santa Cruz, Brazil (CIASB/
Abbreviations used are: cl, carapace length (along the dorsal midline, from the base of the rostral sinus to the posterior margin of the carapace); cw, carapace width (taken at the widest point including lateral spines); P2–P5, pereopods 2 to 5 (P1 is the cheliped); G1, first gonopod; G2, second gonopod; ovig., ovigerous; juv., juvenile; RV, research vessel; exped., expedition; stn, station; leg., collector or collected by; det., determined by.
Total genomic DNA was extracted from muscle tissue using either the Qiagen DNeasy Blood and Tissue extraction kit or Omega Bio-tek EZNA Tissue DNA Kit. Partial sequences of the 12S, 16S mitochondrial genes were amplified with the following primers, respectively: 12SF (
Sequences, generated for this study, were combined with other sequences available from GenBank and previously unpublished sequences generated by AMW, in order to place the target taxa within the context of the superfamily Majoidea. Locality information and GenBank accession numbers for taxa included in the molecular analyses are provided in Suppl. material
The ongoing revision and phylogenetic study of Macrocoeloma by the authors (unpubl. data), based on both morphological and molecular data, revealed this genus to be a paraphyletic group. Pohleus gen. nov. therefore, needs to be established to accommodate P. septemspinosus gen. nov. et comb. nov. and P. heptacanthus gen. nov. et comb. nov.
Molecular phylogenetic tree represented as maximum likelihood topology of two mitochondrial and one nuclear loci (12S, 16S and 18S) to place Pohleus septemspinosus (Stimpson, 1871) gen. nov. et comb. nov. based on six close genera. Nodal support values represent the frequencies observed, using 1000 bootstrap pseudo-replicates. Values below 50% are not represented.
All three genes (12S, 16S and 18S) were successfully amplified and sequenced only for Pohleus septemspinosus gen. nov. et comb. nov. The final alignment for this combined analysis of nuclear and mitochondrial genes included a total of 2659 bp (1868 bp 18S, 417 bp 16S and 372 bp 12S). The data were not saturated, considering the R2 value for transitions R² (s) = 0.8665 and R² (v) = 0.9856 transversions, demonstrating that the sequences are appropriate for phylogenetic studies at this level.
Pohleus septemspinosus gen. nov. et comb. nov. has a high support value (84%) as sister to a clade containing Thersandrus compressus and Macrocoeloma spp. Thersandrus, presently assigned to the subfamily Majinae sensu
Pericera septemspinosa Stimpson, 1871, by present designation.
Pohleus septemspinosus (Stimpson, 1871) gen. nov. et comb. nov. and Pohleus heptacanthus (Bell, 1836) gen. nov. et comb. nov.
Carapace subglobose, covered by short velvet pubescence interspaced by dense rows of long, hooked and simple setae in all carapace regions. Carapace armed with strong spines, including seven sharp spines on posterior half: one short mesial metagastric, four long, strong, conical lateral spines (two in each branchial region) aligned with one cardiac spine and one intestinal spine; lateral spines longest, slightly directed upwards. Pterygostomial region with strong spines visible in dorsal view. Rostrum bifurcated, base elongated, fused, diverging abruptly forming a Y-shape, ending in acute tips. Pre-orbital spine strong, acute, directed upwards; post-orbital spine short, acute. Basal article of antenna with three spines, one tubercle, not visible in dorsal view. Cheliped long, merus armed with short spines or tubercles, granulated. P2 shorter than cheliped, dactylus much shorter than propodus. Thoracic sternal somite IV with lateral margins straight. Sternite VIII concealed by pleon in males. Male and female pleon with six somites not fused plus telson. Male telson tight-fitting into sterno-pleonal cavity, distinctly triangular. G1 slender, straight, with bilobed apex. G2 slender, straight, tapering distally, short about one fifth of G1 length.
Libinia spinosa H. Milne Edwards, 1834 – Brazil • 1 male, 1 female; Macaé, near Santana Archipelago, PITA stn 12 III (
Macrocoeloma Miers, 1879 s. str. is an amphi-American genus with 12 species. This genus is characterised by the pyriform or triangular carapace, densely covered by short, velvet-like setae; with well-developed bifurcated or parallel rostral spines; the eyes completely protected by the orbits when retracted; orbits composed by the pre-orbital and the post-orbital spines and one or two projections of the basal article of antenna forming a functional, laterally projected protective hood. Although some of these characters can be observed in Pohleus gen. nov., the new genus can be easily distinguished from Macrocoeloma s. str. by a unique combination of characters, which include: (i) carapace relatively more globose in Pohleus gen. nov. (Figs
Pohleus septemspinosus (Stimpson, 1871) gen. nov. et comb. nov. A, B. male, (
In Macrocoeloma, the gonopods are highly variable amongst species, but it is possible to recognise a general pattern with G1 being longer than the thoracic sternal suture IV/V, parallel and usually with a bilobed apex (except in M. concavum, M. intermedium and M. laevigatum that have a unilobed apex). Although Pohleus septemspinosus gen. nov. et comb. nov. (G1 of Pohleus heptacanthus gen. nov. et comb. nov. not examined) can be fitted in this general pattern, the G1 apex is notably more similar to the G1 apex of Libinia Leach, 1815 (Fig.
Thersandrus Rathbun, 1897, is a monotypic genus exhibiting extremely efficient camouflage behaviour as Macrocoeloma and Pohleus gen. nov. However, Thersandrus does not actively decorate itself, presenting crypsis behaviour consisting of matching the body to the environment in shape and colour, being morphologically adapted to live on green algae fronds. For instance: (i) Thersandrus has a carapace covered by long setae giving a felt-like texture (vs. velvet-like and hooked setae in Macrocoeloma and Pohleus gen. nov.); (ii) the carapace and pereopods are flattened in Thersandrus (vs. carapace subtriangular or piriform, not flattened and with cylindrical pereopods in Macrocoeloma and subglobose carapace and cylindrical pereopods in Pohleus gen. nov.); (iii) the orbital spines are reduced, not forming a hood in Thersandrus (vs. orbital spines long, blunt, forming a hood in Macrocoeloma and long, acute and forming a hood in Pohleus gen. nov.); all characters that prevented us from synonymising Thersandrus to Macrocoeloma. However, it is important to note that, based on the molecular results, Thersandrus should be transferred from Majidae to Pisinae as mentioned above.
Generic name in honour of the renowned marine biologist and carcinologist Gerhard Werner Pohle (Atlantic Reference Centre, Huntsman Marine Science Centre). Gender masculine.
Pericera septemspinosa
Stimpson, 1870 (1871): 113 [type locality: West of Tortugas; 65 m depth, type material: non-extant]. – A.
Macrocoeloma septemspinosa – Miers, 1886: 80; Rathbun, 1892: 250; 1898b: 257; 1899: 576.
Macrocoeloma septemspinosum
–
(Here designated).
USA • male neotype, cl 31 mm, cw 35 mm; Florida, West of Sarasota, R/V Oregon, stn 4088, 27°44'N, 83°45'W; 04 Dec 1962, National Marine Fisheries Service exped.; 27 Oct 2014, W Santana det. (
USA • 1 male; North Carolina, 33°48'06"N, 76°34'42"W, 77 m depth; 03 Apr 1981, Duke Univ. for MMS leg.; 1981, P Krikorian det. (
Rostrum width half of interorbital length bifurcated, base elongated, fused, diverging abruptly forming a Y-shape. Pleonal somite II smooth; merus of second pereopod armed with a spine.
Cephalothorax and appendages sparsely covered with short, velvet-like pubescence. Carapace subglobose wider than long, convex, with long lines of hooked and simple setae in all carapace regions, denser in rostral and lateral spines. Rostrum width half of interorbital length bifurcated, base elongated and fused, abruptly diverging forming a Y-shape, ending in acute tips. Interorbital region slightly depressed medially. Hepatic region broad. One metagastric spine. Four long, strong, conical lateral spines (two in each branchial region), in line with the cardiac spine. One short intestinal spine. Orbital region very prominent, eyes completely protected in orbit when retracted, ocular peduncle visible when not retracted. Pre-orbital spine acute, directed upwards, tip curved, longer than post-orbital spine, ventral margin of pre-orbital spine with a small crenulation; post-orbital spine curved upwards.
Antennular fossae wider than long, margins smooth. Interantennular septum elongated, compressed laterally, forming distinct, ventrally-directed lobe. First and second antennal articles fused to epistome, suture between antenna and epistome visible, antennal gland opening near suture line. Basal article of antenna with three spines, one tubercle, not visible in dorsal view. Antennal flagella longer than rostral spines, behind rostrum in dorsal view.
Epistome anterior margin narrower than antennular fossae, smooth. Buccal field sub-quadrate, narrower at posterior edge with acute spine at anterolateral angle in line with antennal spines. Third maxillipeds completely covering buccal field. Exopod long, nearly reaching distal margin of merus. Pterygostomial region subtriangular, slightly inflated, separated from subhepatic region by marked groove, one long, strong spine slightly curved upwards on medial margin, visible in dorsal view.
Chelipeds equal, longer than pereopods in adults, more robust in adult males; females chelipeds shorter than males, slender. In males, ischium, merus, carpus and propodus segments granulate. Ischium with one prominent tubercle laterodistally. Merus with one spine on proximal half, one on distal margin. Carpus with four tubercles sparsely distributed. Dactylus arched in adult males, a small gap between fingers, distinctly shorter than palm. Cutting edges with sub-equal teeth in distal half, one distinct proximal tooth in larger males; distal half with dark brown colour in fixed specimens. Female ischium, merus, carpus and propodus with smaller tubercles than males, dactylus slightly arched, without gap between fingers.
Pereopods short, slender, cylindrical. P2 longest, P3−P5 progressively decreasing in length. P2 merus with distinct spine in distolateral margin. Dactylus slightly curved, shorter than propodus, smooth ventrally, with corneous tip.
Male thoracic sternites I–IV fused, broadly triangular, smooth, anterior half declivous in ventral view, forming a carina along the sterno-pleonal cavity margin. Thoracic sternal somite IV with lateral margins straight. Telson fully fitted to cavity, anterior margin smooth. Sternite VIII concealed by pleon. Episternites IV and V forming a continuous line with the sternite, slightly downward directed.
Pleonal somites I–VI, telson free in males and females, slightly raised medially forming low longitudinal ridge. Male telson sub-triangular, apex rounded. Female pleon markedly arched, with row of setae marginally. Female telson transversally ovate.
G1 longer than thoracic sternal suture IV−V, stout, straight, parallel, with torsion in distal half, apex bilobed; mesial lobe short, with tip curved upwards; lateral lobe long, slightly arched, ending in an acute tip; lateral margin smooth. G2 slender, straight, very short (one fifth of G1 length), with disto-medial process.
Carapace light brown; cephalothorax ventral, pleon and pereopods pinkish to purple (Fig.
USA, Florida, west of Sarasota, 27°44'N, 83°45'W.
Geographic distribution. Western Atlantic: USA (from North Carolina); Gulf of Mexico; Bahamas; Venezuela and Brazil (from Ceará to Bahia) (Fig.
Geographic distribution Pohleus heptacanthus (Bell, 1836) gen. nov. et comb. nov.; orange circles = distribution based on examined material; green star = type locality and Pohleus septemspinosus (Stimpson, 1871) gen. nov. et comb. nov.; red circles = distribution based on examined material; yellow star = neotype locality.
The type material of Pericera septemspinosa was probably lost in the Great Chicago Fire in 1871 (see
Pohleus septemspinosus gen. nov. et comb. nov. can be distinguished from its Pacific congener, Pohleus heptacanthus gen. nov. et comb. nov., by the following characters: (i) rostrum width half of the interorbital length in P. septemspinosus gen. nov. et comb. nov. (vs. rostrum with one-third or less of the interorbital length in P. heptacanthus gen. nov. et comb. nov.; Fig.
The southeast record of this species as Espírito Santo State, in Brazil (Serejo et al. 2006: fig. 8C) is not valid, since the specimen (MNRJ 17062) was re-identified as Macrocoeloma concavum. Therefore, the distribution of to Pohleus septemspinosus gen. nov. et comb. nov. is corrected to the Brazilian coast, from Ceará to Bahia.
Pohleus septemspinosus (Stimpson, 1871) gen. nov. et comb. nov. A, B. female (
Pericera heptacantha
Bell, 1836: 173 [type locality: Puerto Potrero, Central America, 23.7 m depth; type material: syntypes, 1 male (non-extant), 1 female (
Macrocoeloma heptacantha
–
Macrocoeloma heptacanthum
–
(Here designated).
Costa Rica • 1 female, cl: 35 mm, cw: 43 mm; Central America, Puerto Potrero, 23.7 m depth; H Cumming leg. (
Mexico • 1 juv. female; Off Cape San Lucas, R/V Albatross, stn 2829, 22°52'00"N, 109°55'00"W, RKY leg., 56.6 m depth, 74.1 °F; 01 May 1888, M J Rathbun det. (
Rostrum width less than one-third of interorbital length, bifurcated, base elongated, fused, diverging abruptly forming a Y-shape, ending in acute tip. Pleonal somite II with one spine or tubercle. Merus of second pereopod smooth.
(male characters modified from
Antennular fossae wider than long, margins smooth. Interantennular septum elongate, laterally compressed, forming distinct ventrally-directed lobe. First and second antennal articles fused to epistome, with suture between antenna and epistome visible, antennal gland opening near suture line. Basal article of antenna with two spines, not visible in dorsal view: proximal spine smallest. Antennal flagella longer than rostral spines, behind rostrum in dorsal view.
Epistome anterior margin narrower than antennular fossae, smooth, posterior margin slightly depressed. Buccal field sub-rectangular, narrower at posterior edge with one acute spine in anterolateral angle aligned with antennal spines. Third maxillipeds covering buccal frame when closed, leaving a small gap between ischia. Exopod long, nearly reaching distal margin of merus. Pterygostomial region subtriangular, slightly inflated, separated from subhepatic region by marked groove, with one long, strong spine slightly curved upwards on medial margin, visible in dorsal view.
Male chelipeds equal, longer than pereopods; covered with sparse granulation, unarmed. Dactylus arched in adult males, leaving small gap between fingers, distinctly shorter than palm. Cutting edges with sub-equal teeth in distal half, one distinct proximal tooth in larger males; distal half with light brown colour in fixed specimens. Pereopods short, slender, cylindrical. P2 longest; P3-P5 progressively decreasing in length. Dactylus slightly curved, covered with short setae.
Female chelipeds equal, longer than pereopods, slender and smooth. Dactylus arched in adult, shorter than palm, sub-equal teeth in distal half. Pereopods, slender, cylindrical. P2 longest, P3-P5 progressively decreasing in length. Dactylus slightly curved, shorter than propodus, smooth ventrally, with corneous tips.
Male thoracic sternites I–IV fused, broadly triangular, smooth, anterior half declivous in ventral view. Telson fully fitted to cavity, anterior margin smooth.
Female pleonal somites I–VI markedly arched, telson free, transversally oval, with a row of setae on margin and one small spine in first somite. Male pleon rather prominent, pleonal somites I–VI, telson free, somite II with a mesial tubercle. Somite III with slight elevations. Somite VI longest, with a mesial tubercle and a small projection each side.
Light brown, covered with darker hair, first pair of pereopods reddish (Bell 1936b).
Costa Rica, Central America, Puerto Potrero, in sand at a depth of 23.7 m.
Eastern Pacific: Mexico (Cape San Lucas), Costa Rica (Guanacaste) and Panamá (Panama Bay) (Fig.
Bell (1836) described Pericera heptacantha, based on two specimens as syntypes, one male and one female. The male syntype is considered lost and the female is deposited in the dry crustacean collection of the Oxford University Museum (
We are grateful to Rafael Lemaitre and Karen Reed (
Table S1
Data type: Species data
Explanation note: Taxa included in the molecular phylogenetic analyses to place the newly described taxa within the context of the family Pisidae.