Paeduma Rathbun, 1897

Hendrickx, Michel E. & Visauta-Girbau, Eva, 2013, New record and description of the male gonopods of Paeduma cylindraceum (Bell, 1859) from the tropical eastern Pacific (Decapoda, Brachyura, Hexapodidae), Zoosystema 35 (1), pp. 89-96 : 90-95

Genus Paeduma Rathbun, 1897

Paeduma cylindraceum ( Bell, 1859) ( Figs 1 ; 2 )

Amorphopus cylindraceus Bell, 1859: 27 .

Paeduma cylindraceum . – Rathbun 1897: 163. — Guinot 2006: 559, figs 1, 2 (complete synonymy). — Ng et al. 2008: 86 (list). —- Guinot et al. 2010: 287, fig. 1E.

MATERIAL EXAMINED. — 1 ♂ (CW 13.7 mm; CL 9.0 mm), off Santa Maria la Reforma Bay (24°44’42”N, 108°02’04”W), Sinaloa, Mexico, 02.IV.2007, trawl net, 3.5 m depth (coll. J. Madrid-Vera and E. Visauta-Girbau) (EMU-8270) .

DISTRIBUTION. — The record from Galápagos for the holotype of P. cylindraceum has been questioned (see Guinot 2006 for details). The locality reported by Guinot et al. (2010: Gulf of Tehuantepec) corresponds to station 5 visited by the R/V The Stranger in 1939: off “Tenela Bar” (certainly “Tonala Bar”; approximately 15°53’48”N, 93°54’36”W), 24- 33 m. Present record in the Gulf of California confirms that P. cylindraceum is not a Galápagos endemic as previously thought but rather a species with a wide geographic distribution along the tropical east Pacific region. Assuming that the Galápagos record is in error, P. cylindraceum would be part of the continental “Panamic tropical fauna” as defined by Garth (1946), occurring in the Gulf of California (the “Cortés” Province) and in the Gulf ofTehuantepec (within the Panamic Province). As observed for many species of Brachyura and other decapod crustaceans (see Garth 1946; Hendrickx 1992; Wicksten & Hendrickx 2003), the vast majority of species occurring in the Gulf of California and south of this enclosed sea are likely to be found in Central America or even further south, to Colombia, Ecuador or northern Peru.We might therefore expect to find it in similar habitats between Mexico and Peru, within or close to shallow tropical bays, whenever adequate sampling is performed.

REMARKS

The male specimen represents a range extension of about nine degrees of latitude to the north and is in excellent condition, with all pereiopods attached and the abdomen intact ( Fig. 1A, B ). All characters described and illustrated by Guinot et al. (2010) are clearly observed in the specimen. These include the typical transverse-cylindrical form; strongly convex and laterally pitted carapace; conspicuously narrow abdomen with abdominal somites 3-5 fused, and a strong, proximal constriction in somite 6; the arrangement and size of thoracic sternites 1-8; and the apodemal platelet at the base of coxa 4. The apodemal platelets are more reduced in the specimen examined than in the holotype on the left side, and even smaller (not discernible on Fig. 1B due to the angle between the coxa and the carapace) on the right side.

DESCRIPTION OF GONOPODS

Guinot (2006:557) noted in her emended diagnosis of Paeduma that a description of the male gonopods was impossible due to the dry condition of the holotype, the only male specimen available to that time. The examination of the gonopods was feasible because the male examined herein was originally preserved in formalin, and transferred to 70% ethanol shortly after. Gonopod 1 as illustrated. Shaft long, slender, slightly sinuous, slightly inflated basally ( Fig. 1C ); terminal opening slit-like ( Fig. 2A ); inner face of shaft with one series of about 10 strong spines extending from just below tip in approximately distal 1/5 of shaft length ( Fig. 2A ); outer face of shaft with rows of spinules extending from tip in approximately distal ⅓ of shaft length ( Fig. 2A ); a few, dispersed, similar spinules on dorsal section of the shaft, near tip ( Fig. 1C ); in ventral view, tip of gonopod with crowded concentric series of strong, downwards-pointing, conical spines located next (mesial) to terminal opening and further below, one small patch of five or six similar, slightly curved spines located lateral to terminal opening ( Fig. 2B ); in dorsal view, tip of gonopod roughly rounded, rugged, with two strong lateral, conical spines, rugged area extending proximally as a roughly triangle-shaped rugged area with series of slender spines, subterminal crown of four or five strong, conical spines, similar to those in ventral view below triangle-shaped area, these spines overhanging a subcircular fleshy fold bordered with few strong spines ( Fig. 2C, D ). As predicted by Guinot (2006:

(1976); C, Manning & Hothuis (1981); D, Huang et al. (2002); E, this contribution.

Species First gonopod description

Hexapinus buchanani Shaft stout, almost vertical, basally narrow and of almost similar width throughout

(Monod, 1956) (C) its length, long setae on inner and outer margin; tip subacute, with more densely set setae.

Hexapinus granuliferus (Campbell & Shaft stout, basally wide, strongly curved; distal ²⁄³ with long, dense (inner margin)

Stephenson, 1970) (C) and short, scarse (outer margin) setae; tip description not available.

Hexapus anfractus Shaft moderately long, basally wide and robust, tappering to a strongly bent

(Rathbun, 1909) (C) distal section, the latter with fringes of setae on inner and outer margins; no distal ornamentations.

Hexapus estuarinus Shaft moderately long, slender, bent at a 45° angle at about mid-length; distal

Sankarankutty, 1975 (A) (bent) half of shaft with few marginal setae; proximal half with marginal plumose setae; a flared part along inner margin near tip, the latter subacute and without ornamentations.

Hexapus sexpes (Fabricius, 1798) Shaft stout, basally wide, strongly curved; distal ²⁄³ with long, dense (inner margin)

(B) and scarse (outer margin) setae; tip subacute, without ornamentations.

Hexalaughlia orientalis Shaft long, wide basally, narrowing regularly to a strongly bent (180°) terminal

(Rathbun, 1909) (B, C) section forming a “S” (doubly recurved), this section about ¹⁄³ the length of the rest of the shaft; terminal (inverted) “S”-shaped sections of left and right gonopods forming a “8”, tips acute, without ornamentations.

Parahexapus africanus Shaft long, narrow, basally sigmoid, distal ²⁄³ slightly curved; mid-section of shaft

Balss, 1922 (C) with series of strong conical spines and sparse setae;distal section naked,tappering to an acute tip without ornamentations.

Pseudohexapus platydactylus Shaft stout; tip curved, bent at an angle of 90°, a series of subterminal short setae

Monod, 1956 (C) on inner margin, tip without ornamentations.

Spiroplax spiralis (Barnard, 1950) Shaft short, robust, base wide, mid-shaft 3-spired; distal ¹⁄³ bent at c. 60°, margins

(C) with short setae; tip acute, without ornamentations.

Thaumastoplax anomalipes Shaft long, narrow, without spines or long setae (“almost naked”), strongly sigmoid

Miers, 1881 (C) in proximal ²⁄³, distal ¹⁄³ slightly bent; tip acute, no distal ornamentations.

Tritoplax stebbingi (Barnard, 1947) Shaft basally very wide, proximal ²⁄³ robust,tappering and strongly curving distally;

(C) distal end slender, bent at a 90° angle in a vertical position, fringed with minute setae on inner margin; tip acute, no distal ornamentations.

Tritoplax stephenseni (Serène & Shaft stout, basally wide, moderately curved; distal ¹⁄³ with long, scarse setae on

Soh, 1976) (B) inner margin,outer margin with scarse setae in mid-third; tip slightly bent,subacute, with a subterminal conical tooth.

Latohexapus granosus Huang, Shaft moderately long, slender, bent at a 45° angle at about mid-length; distal

Hsueh & Ng, 2002 (D) (bent) half of shaft with strong spines in the outer margin,and similar, slightly longer spines in the inner margin of proximal half; tip subacute, without ornamentations.

Paeduma cylindraceum ( Bell, 1859) Shaft long, basally narrow, slightly sigmoid; distal ¹⁄³ with short setae in outer

(E) margin, inner margin with a row of strong conical spines in distal ¹⁄ 5; tip rounded, ornamentated with crown of numerous conical, subterminal spines and short setae.

559), the gonopods of P. cylindraceum are “neither recurved posteriorly nor doubly recurved into an 8-shaped figure as in Hexalaughlia ”.

Gonopod 2 as illustrated. Short, about 1/6 total length of gonopod 1, slightly curved, tip bent at almost 90° with shaft, suboval, flat in dorsal view, with few short setae ( Fig. 1D ).

In their extensive review of the West African brachyuran crabs, Manning & Holthuis (1981: 166) presented a synthesis of all the species included in the family Hexapodidae at that time (11 genera, 16 spe - cies). They also presented a compilation of a key to genera in which they considered the shape and size of male first gonopods as an important diagnostic character for some genera. Furthermore, they provided illustrations (some of very poor definition and quality) of the male first gonopods for nine species belonging to eight genera (see Table 1): Hexapinus buchanani (Monod, 1956) and Hexapinus granuliferus (Campbell & Stephenson, 1970) ; Hexapus anfractus (Rathbun, 1909) ; Paeduma orientale (Rathbun, 1909) (now included in the genus Hexalaughlia Guinot, 2006 fide Guinot 2006); Parahexapus africanus Balss, 1922 ; Pseudohexapus platydactylus Monod, 1956 ; Spiroplax spiralis (Barnard, 1950) ; Thaumastoplax anomalipes Miers, 1881 ; and Tritoplax stebbingi (Barnard, 1947) . Manning & Holthuis (1981: fig. 34) also provided an illustration of the male abdomen of Lambdophallus sexpes Alcock, 1900 , showing the first gonopods with an acute tip, apparently devoid of any ornamentation. Manning & Holthuis (1981) did not reproduce the description of the male first gonopod of Hexapus estuarinus Sankarankutty, 1975 , and overlooked the contribution of Serène & Soh (1976) who illustrated the first gonopods of their new species Hexapus stephenseni Serène & Soh, 1976 (transfered to Tritoplax Manning & Holthuis, 1981 ; see Ng et al. 2008), and of two previously described species, Hexalaughlia orientalis (Rathbun, 1909) , as Thaumastoplax Miers, 1881 , and Hexapus sexpes (Fabricius, 1798) . The first gonopods of the family have also been illustrated for Latohexapus granosus Huang, Hsueh & Ng, 2002 ( Table 1; Fig. 3 ). We are not aware of other descriptions of the male first gonopods in other species of hexapodids.

When comparing the major characteristics of gonopods of each species (see Table 1; Fig. 3 ), it becomes clear that there is a wide variety in the shape of gonopods among members of the Hexapodidae as currently recognised. The first gonopods can be either short and stout, long (filiform) and curving, or even short and spiralling. In most cases, the tip is acute to subacute, straight to strongly bent or even doubly recurved, and without any ornamentations (distal setae present in some cases), except in the case of Paeduma cylindraceum , where rows and a complex crown of stout conical spines are observed. These variations could reflect the diversity of genera within the family, as does the presence or absence of sternal grooves or trenches (see Manning & Holthuis 1981), or the variation in the abdominal holding mechanism (see Guinot et al. 2010). Guinot (2006) indicated that a review on the position of Hexapodidae within the Brachyura is in progress. These variations will certainly prove to be of importance among other morphological features, and characters derived from first gonopods structure will certainly contribute to clarify the phylogenetic position of Hexapodidae within the Brachyura .

Figures

FIG. 1. — Paeduma cylindraceum (Bell, 1859), male (EMU-8270), CW 13.7 mm: A, dorsal view; B, ventral view; C, right first gonopod, ventral view; D, right second gonopod, ventral view, and dorsal view of tip. Scale bars: C, 1 mm; D, 0.5 mm.

FIG. 2. — Paeduma cylindraceum (Bell, 1859), left first gonopod of male (EMU-8270): A, distal section of shaft, ventral view; B, same, details of tip; C, distal section of shaft, dorsal view; D, same, details of tip. Scale bars: A, C, 250 µm; B, 300 µm; D, 100 µm.

FIG. 3. — First gonopod of species of Hexapodidae Miers, 1886: A, Hexapinus buchanani (Monod, 1956); B, Hexapinus granuliferus (Campbel & Stephenson,1970);C, Hexapus anfractus (Rathbun,1909);D, Hexapus estuarinus Sankarankutty,1975;E, Hexapus sexpes (Fabricius,1798); F, G, Hexalaughlia orientalis (Rathbun, 1909); H, Parahexapus africanus Balss,1922;I, Pseudohexapus platydactylus Monod, 1956; J, Spiroplax spiralis (Barnard, 1950); K, Thaumastoplax anomalipes Miers, 1881; L, Trioplax stebbingi (Barnard, 1947); M, Tritoplax stephenseni (Serène & Soh, 1976); N, Latohexapus granosus Huang, Hsueh & Ng, 2002. A-C, G-L, from Manning & Holthuis (1981); D, from Sankarankutty (1975); E, F, M, from Serène & Soh (1976); N, from Huang et al. (2002).