Pachycheles chubutensis Boschi, 1963

Miranda, Ivana, Schubart, Christoph D. & Mantelatto, Fernando L., 2014, Morphological and molecular data support the distinctiveness of Pachycheles laevidactylus Ortmann, 1892 and Pachycheles chubutensis Boschi, 1963 (Anomura, Porcellanidae), Zootaxa 3852 (1), pp. 118-132 : 124-126

Pachycheles chubutensis Boschi, 1963

( Figs. 2 A–C)

Pachycheles chubutensis Boschi, 1963: 35 , 36, figs. 2, 3; 1979: 137.— Da Silva et al., 1989: 133, 135.— Veloso & Melo, 1993: 173, 177, 184.— Harvey & De Santo, 1996: 713.— Melo, 1999: 227, 232, fig. 154.— Rodríguez et al., 2005: 554, 555, 570, 572, 574.— Ferreira, 2009: 59.— Osawa & McLaughlin, 2010: 112.

Type locality. Golfo San Matías, Chubut, Argentina. The holotype of Pachycheles chubutensis (male with 10 mm carapace length) is in the Museo Argentino de Ciencias Naturales (Buenos Aires, Argentina) (Col. Museo Arg. Cienc. No. 21.244) ( Boschi, 1963). Not examined.

Material examined. 1 female, 1 male (CCFurg 381), Porto Belo, Santa Catarina, Brazil, coll. Silva, B., 23.Mar.1987; 2 males (CCFurg 370), Rio Grande do Sul (RS), Brazil, coll. Silva, B., 27.Jun.1986; 1 female, 1 male (CCFurg 920), Parcel do Carpinteiro, RS, Brazil, coll. Feijó, F.A., Jul.1988; 1 female ( CCDB 860), Mar del Plata, Argentina, coll. Ocampo, E., 14.Feb.2003; 2 females ( CCDB 2800), La Restinga, Mar del Plata, Argentina, coll. Ocampo, E., 22.Mar.2010; 1 female ( CCDB 2801), La Restinga, Mar del Plata, Argentina, coll. E. Ocampo, Oct.2008; 1 male ( CCDB 2802), La Restinga, Mar del Plata, Argentina, coll. Ocampo, E., 22.May.2008; 1 male ( CCDB 2804), La Restinga, Mar del Plata, Argentina, coll. Ocampo, E., Oct.2008.

Diagnosis. Frontal region with tuft of plumose setae. Chelipeds without prominent granules, external surface with plumose setae and some simple setae on margins. Telson consisting of 7 plates. Second pleopods present in males.

Redescription. Carapace. Carapace slightly longer than broad; surface of branchial and postlateral regions wrinkled, more prominent in some specimens. Tufts of short and simple setae present on metagastric region of some specimens. Front trilobed in frontal view, with medium lobe more prominent in some specimens; a dense tuft of plumose setae present, smaller tufts can be found on hepatic region. Orbital region well defined, continuing on a curved crest that constitutes an accentuated angle with the lateral carapace borders. Lateral walls divided into a large piece followed by one or more (two to three) smaller posterior pieces.

Antennule. Basal segment of antennule armed with 3–5 strong spines on medial anterior margin (visible from dorsal-lateral view), 7 or 8 spines on anterolateral dorsal surface.

Antenna. Basal segment of antenna with projection on the anterior margin, configuring a well defined cavity for the eyes together with the border of orbits; second segment with a small protuberance on the anterior margin; third segment smooth to slightly granulose on anterior margin; flagellum with tiny bristles just visible under great magnification.

Pereiopod 1 (Chelipeds). Chelipeds unequal, strong, with a thin and weak granulation, more intense from the medial region to the external margin of carpus, propodus, and dactylus. Merus with rounded projection on inner margin; presence of parallel series of small bristles following wrinkles in inner-outer border direction; dorsal surface of carpus, propodus and dactylus sometimes covered by tufts of plumose setae originating from base of granules, alternating with long and simple setae, the last ones especially on external borders. Density and distribution of these tufts is variable among individuals from different localities. Anterior margin of carpus armed with projecting lobe subdivided into 2–4 lobes of variable sizes; distal ones being better delimited. Inner border of pollex of major cheliped with 1–4 large tubercles; lines of short bristles present; dense tuft of plumose setae at the base of pollex filling the gap between fingers. Internal margin of dactylus with 7 or 8 small tubercles; both fingers of minor cheliped with a cutting inner border.

Pereiopods 2–4. Merus and carpus of first pereiopods slightly granulated, covered by wide plumose setae on dorsal surface; propodus with wide lines of plumose setae on dorsal and lateral margins, ventral surface with 3–5 spines, 2 on distal border, 1 subdistal, shaping a triangle with the first 2 and 1 or 2 other medial spines located proximally; dactylus ending in a strong spine, inner border with 4 or 5 spines decreasing in size. Second pereiopod with the same pattern of setae distribution for merus, carpus and propodus, more dense when compared to the first pair; ventral surface of propodus with three to five spines, two at distal border, followed by one medial and immediately above, forming triangle with first 2, and 1 or 2 medial, located proximally; dactylus ending in a strong claw; inner border with 4 spines decreasing in size. Third pereiopod equal to the second. Fourth pereiopod smooth, carpus with rolls of long and simple setae on dorsal, ventral and lateral surfaces, brush-like.

Telson . Telson 7-plated in males and females.

Pleopods. Second pleopod present in males.

Measurements. Males with carapace width 8.0–12.0 mm, females 8.1–12.4 mm.

Color. All the material analyzed was preserved in alcohol or formalin, being impossible to report the color in life. There is no previous information to be found in the literature.

Ecology. Pachycheles chubutensis occurs infralittorally, preferentially on hard, mussel-free bottoms ( Bremec & Cassaniga 1984; González-Pisani et al. 2009), associated to tubes of Litofaga patagonica (d'Orbigny, 1846) ( González-Pisani et al. 2006) and also on sand bottoms at depths between 3 to 28 m ( Boschi 1963; Melo 1999; Scelzo et al. 2008). Bremec & Cassaniga (1984) have recorded the species occurring at the inner zone of the Bahía Blanca Estuary, a region that suffers considerable variations of salinity and temperature throughout the year. Despite their importance in the bioenergetics marine cycle, as an adult in the benthos, and as larvae in the water column, information about their biology and population ecology is scarce. Larvae are an important component of the zooplankton in the embayment of Chubut Province ( Dellatorre & Baron, 2007), while as an adult it is preyed upon by cephalopods ( González-Pisani et al. 2009) and some benthic fish ( González-Pisani et al. 2006), integrating the trophic networks. Observations provided by Bremec & Cazzaniga (1984) suggest an annual life cycle of the species in Argentina, with recruitment season in summer (September to March), when it can be found abundantly in the lower intertidal zone ( González-Pisani et al. 2006).

Remarks. Some differences were found in relation to the original text of the description and they were here incorporated. In the original description, the author mentioned the carapace as slightly broader than long, especially in males. This revision could not find any specimen fitting this proportion. The description of the basal antennule segment is presented here and also the description of the antenna is more detailed.

The morphology of the lateral walls is variable, but in most cases it follows the original description. One exception is a specimen (CCDB 2801) which presented four smaller pieces after the most anterior and larger one. Presence, quantity and distribution of the setae on the cheliped surface is extremely variable, as cited firstly by Harvey & De Santo (1996), from less and short setae more concentrated on the outer margins of merus, carpus, propodus and dactylus to a dense coverage on these segments. All the material from Brazil had the whole surface of chelipeds covered by short and plumose setae together with long and simple setae, especially on external margins. In Argentina, we found animals with fewer and shorter setae distributed on the wrinkles and base of the granules. The number of tubercles on the inner border of pollex (major cheliped) ranged from one to four instead of three to four, being one unique medial tubercle very frequent. We extend here the range for the number of spines on propodus and dactylus of first pereiopods to three to five instead of four, as cited in the original description. Descriptions of the second, third and fourth pereiopods were added. The original description mentioned females, in general having a five-plated telson , sometimes with the small posterior plates half segmented; the first condition was not observed by us, while the second was observed once.

Distribution. Brazil on Rio de Janeiro ( Ferreira 2009), from Santa Catarina to Rio Grande do Sul ( Da Silva et al. 1989) and Rawson, Chubut Province, Argentina ( Boschi 1963).

Figures

FIGURE 2. Pachycheles chubutensis Boschi, 1963. A) General dorsal view (male, CCFurg 920); B) Minor cheliped, glabrous form (CCDB 2802, male, dorsal view); C) Telson with 7 plates (CCDB 2802, male, ventral view). Scale bar in A) = 1 cm.