Munnogonium diplonychia, Doti, Brenda L. & Roccatagliata, Daniel, 2013
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Munnogonium diplonychia n. sp.
Etymology. The specific epithet is derived from the Greek diplous, double and onychia, claws, in reference to the bifid claws of the pereopods II–IV.
Type locality. Puerto Deseado (Santa Cruz Province), 23 Jan 2007, Sta. 20, 47º 43.76 ’S, 65 º 50.26 ’W, 15 m.
Material examined. Holotype. Brooding ♀, 1.25 mm (MACN-In 39190), here designated.
Paratypes. Same data as holotype: 14 brooding ♀, 5 ♀ and 11 ♂ (MACN-In 39191).
Other material. Puerto Deseado (Santa Cruz Province), 23 Jan 2007, Sta. 1, 47º 39.55 'S, 65 º 47.47 'W, 15 m: 1 brooding ♀ (MACN-In 39192). Sta. 3, 47º 40.14 'S, 65 º 47.62 'W, 16 m: 7 brooding ♀ (MACN-In 39193). Sta. 15, 47º 48.89 'S, 65 º 51.25 'W, 15 m: 6 ♀, 6 ♂ (MACN-In 39194). Sta. 17, 47º 45.37 'S, 65 º 50.75 'W, 20 m: 1 brooding ♀ (MACN-In 39195). Sta. 19, 47º 42.58 'S, 65 º 49.12 'W, ca. 15 m: 1 brooding ♀ (MACN-In 39196). Sta. 23, 47º 43.56 'S, 65 º 49.27 'W, 15 m: 8 brooding ♀, 1 ♂ and 2 juvs (MACN-In 39197). Sta. 24, 47º 43.58 'S, 65 º 49.13 'W, 15 m: 4 brooding ♀, 1 ♂, 3 juvs (MACN-In 39198). Puerto Deseado (Santa Cruz Province), 0 7 Feb 2006. Sta. 10, 47º 45.76 'S, 65 º 53.90 'W, less than 10 m: 1 brooding ♀ (MACN-In 39199). Comodoro Rivadavia (Chubut Province), 0 5 Feb 2006. Sta. 4, 45º 51.44 'S, 67 º 27.82 'W, 9 m: 1 brooding ♀ (MACN-In 39200). Sta. 5, 45º 51.63 'S, 67 º 27.23 'W, 13 m: 6 brooding ♀, 9 ♂ and 2 juvs (MACN-In 39201). Sta. 6, 45º 51.36 'S, 67 º 27.13 'W, 13.8 m: 1 ♀ (MACN-In 39202). Sta. 11, 45º 51.44 'S, 67 º 27.77 'W, 9 m: 1 brooding ♀, 3 ♂ and 1 juv. (MACN-In 39203). Rada Tilly (Chubut Province), 0 9 Feb 2006, Sta. 23, 45º 55.39 'S, 67 º 32.13 'W, ca. 10 m: 1 brooding ♀ (MACN-In 39204).
Description. Body width 0.53 length in female (0.38 in male), widest at pereonite 3 in both sexes. Head length 0.54 width; length posterior to eyestalks 0.52 anterior length (0.46 in male). Frontal margin broadly rounded with tuft of setae medially (at low resolution this tuft of setae looks like a short blunt median projection), without angular lateral margins adjacent to antennae. Eyestalks vestigial, length 1.0 width in female (0.75 in male), long axis angling forward at approximately 20 ° in female (17 ° in male), with 4 ocelli.
Pereonites 1–4 lateral margins not projecting, coxae not visible in dorsal view; pereonite 1 in female greatest sagittal length 2.83 midline length, in male 1.66 midline length. All pereonites lateral margins rounded.
Pleon length 1.77 width in female (1.67 in male). Pleonite 1 width 0.8 distance between uropods, length 0.5 width. Pleotelson lateral margin rounded and smooth, lacking inflection between lateral and proximal margins; ventral length proximal to pleopods 0.15 total pleotelson length (see Figs. 8 View FIGURE 8 A, 11 C); posterior margin apex pointed, evenly curving into lateral margin.
Antennula article 1 extending beyond eyestalk apex and reaching to pereonite 1 lateral margin, shorter than article 2, tubular and subequal in width to article 2; articles 4–6 subequal in length, all shorter than article 3.
Antenna article 3 in ventral view tubular, width 0.25 length, article 5 1.84 longer than article 4; flagellum with 6 articles, proximal article subequal to distal ones.
Mandible molar process distally flared, triturative surface oval-shaped.
Pereopod I basis dorsal margin smooth, length 3.8 width; merus ventral margin with 1 robust seta distally; carpus triangular, distal width 0.61 ventral margin length, ventral margin with 3 subequal robust setae and crenate ridges; propodus narrowing distally, with crenate ridge. Pereopods II–IV carpus and propodus ventral margins with row of elongate stiff robust setae; dactylus dorsal and ventral claws thin, elongate and bifid, both claws longer than dactylus (in males dorsal claw simple and ventral claw shorter than dactylus). Pereopods V–VII carpus and propodus ventral margins with short robust setae, dactylus dorsal and ventral claws thick and robust, dorsal claw near length of dactylus, ventral claw much shorter than dactylus.
Female operculum width 0.68 length, distal part tapering with concave distolateral margins. Male pleopod I lateral lobes distinctly projecting from midlateral margin, width 0.4 distance to midline, apex with tuft of simple setae and 1 thick seta with distal pore; distal projection length 0.31 pleopod total length, forming acute angle, with rounded apices.
Uropods dorsal and adjacent to lateral margins of pleotelson.
Size. Largest female 1.53 mm, largest male 1.27 mm.
Distribution. From Comodoro Rivadavia / Rada Tilly (Chubut Province) to Puerto Deseado (Santa Cruz Province).
Remarks. In Munnogonium diplonychia n. sp. the chaetotaxy of pereopods II–IV differs from that of pereopods V–VII, both in females and males (see Table 1 View TABLE 1 ). This bipartite arrangement has not been reported for any other species of the genus. Bifid claws are an easy-to-use character, although high magnification is required to observe them.
Munnogonium quequensis n. sp. and M. diplonychia n. sp. are distinguished from the remaining five species of the genus by having a tuft of setae on the anterior margin of the head. These two new species mainly differ from each other by the following characters (those of M. diplonychia in parentheses): antenna flagellum of 4 articles (6 articles); pereopod I propodus with 1 robust seta (without robust seta); claws of all pereopods simple (claws of pereopods II–IV bifid); and pleotelson with a proximal neck (pleotelson without such basal constriction).
So far, three species of the genus Munnogonium have been reported from the southern tip of South America, viz.: M. falklandicum (Nordenstam, 1933) described from the Malvinas Islands, M. globifrons (Menzies, 1962) described from the Magellan Strait and M. tillerae (Menzies & Barnard, 1959) described from California and reported from the Magellan Strait by Winkler (1994).
According to Nordenstam (1933) Munnogonium falklandicum has elongate stiff robust setae on the carpus and propodus of the pereopods II, VI and VII (pereopods III–V are missing in the female described by Nordenstam. We can assume, however, that these pereopods are also furnished with elongate stiff robust setae). In contrast, in M. quequensis n. sp. and M. diplonychia these carpal/propodal elongate setae are present on the pereopods II–IV only. Regarding the claws, Jean Just (pers. comm.) has had the opportunity to examine the female of M. falklandicum described by Nordenstam and he confirmed to us that this specimen has simple (not bifid) claws on the pereopod II.
M. globifrons was briefly described by Menzies (1962) and a redescription of this species is badly needed. Regarding, the specimens of M. tillerae from the Magellan Strait, Winkler (1994) wrote “it seems that this species [ M. tillerae ] occurs in the Magellan Strait” and pointed out that the setae on the propodus and carpus of the pereopods II–VI are longer than those illustrated by Bowman & Schultz (1974). These, together with the fact that the type locality of M. tillerae is southern California, hints at the possibility of a misidentification of the Magellan specimens.
In the Argentine Sea, two biogeographic provinces have been recognized as the Argentine Biogeographic Province (ABP) and the Magellan Bioeographic Province (MBP) (see López Gappa et al. 2006, and references therein). Except for M. quequensis n. sp., all other species of Munnogonium have been reported from the MBP ( Fig. 13 View FIGURE 13 ). M. quequensis n. sp. is reported from only one locality of the ABP, and most specimens (80 of the 92 specimens collected) were found attached to the surface of the asteroid Astropecten brasiliensis . Associations between isopods and echinoderms have previously been mentioned by many authors (Hatch 1947; Harty 1979; Setubal Pires 1995; Doti et al. 2008, and references therein).
In some asellote species, the terminal males show a pronounced sexual dimorphism. Usually such dimorphic males have some pereonites or appendages enlarged (see Just & Wilson, 2004; Cunha & Wilson, 2006; Doti & Wilson, 2010; Riehl et al. 2012). Within Paramunnidae , the most common changes in these final males are in the pereonite 1, whose lateral parts are enlarged, and in the pereopod I which become more robust (Just & Wilson, 2004). Of the two new species described herein, only M. quequensis depicted sexual dimorphism. In this species, however, the pereonite 1 and its corresponding pereopod I are not displaying any change. In contrast, the basis and ischium of the pereopods II and III are enlarged (see remarks of M. quequensis ). It is noteworthy that Bowman and Schultz (1974) and Wilson (1997) reported a similar sexual dimorphism in the pereopod II of Munnogonium tillerae and M. cf. tillerae , respectively.
|Pereopods II–IV||Pereopods V–VII|
|Carpus and propodus ventral margins with||elongate robust setae in both sexes.||short robust setae in both sexes.|
|Dactylus dorsal and ventral claws||In females, both claws bifid, thin and longer than dactylus. In males, dorsal claw simple and longer than dactylus, ventral claw bifid and shorter than dactylus.||In both sexes both claws simple and thick; dorsal claw almost as long as dactylus and ventral claw much shorter than dactylus.|
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