Meridiosignum undulatum, Doti & Roccatagliata, 2009

Doti, Brenda L. & Roccatagliata, Daniel, 2009, On the South American species of the genus Meridiosignum (Crustacea: Isopoda: Asellota: Paramunnidae), Journal of Natural History 43 (17 - 18), pp. 1115-1138 : 1116-1124

publication ID	https://doi.org/ 10.1080/00222930902781046
persistent identifier	https://treatment.plazi.org/id/F978878D-FF87-FF90-FE5F-5558CAC1FD98
treatment provided by	Felipe
scientific name	Meridiosignum undulatum
status	sp. nov.

Treatment

Meridiosignum undulatum View in CoL n. sp.

( Figures 2–6 View Figure 2 View Figure 3 View Figure 4 View Figure 5 View Figure 6 )

Material examined

Holotype: brooding ♀ (MACN-In 37527), R / V Aldebarán 2003-02, Sta. R1 ; off the Río de la Plata estuary; 36 ° 46.99S, 54 ° 15.29W to 36 ° 46.69S, 54 ° 14.79W; 129 m, 6 Nov GoogleMaps

2003. Paratypes (same data as for holotype): 10 brooding ♀♀ and 3 non-brooding ♀♀ (MACN-In 37528, MNHNM 1804 View Materials ) GoogleMaps .

Diagnosis

Head anterior margin nearly straight. Eyestalk with red spherical body (photoreceptive pigment?). Pereonites 1 and 4–7 lateral margins produced into single processes, pereonites 2 and 3 lateral margins bilobed. Coxal plates 5–7 rounded. Pleotelson lateral margins with 12–14 small denticles. Pereopod I propodus with one robust seta on ventral margin. Pereopod II carpus without robust setae, propodus with one robust seta on ventral margin. Uropod exopod with one terminal simple seta.

Description of brooding female

(Body description based on the holotype, appendages on the paratype MACN-In 37528-a). Length: 1.46 mm ( Figure 2A, 2B View Figure 2 ). Body width 0.61 length, widest at pereonite 3. Head length 0.37×width, anterior margin nearly straight and smooth, labrum slightly surpassing head anteriorly ( Figures 2B, 2C View Figure 2 , 6A View Figure 6 ). Eyestalks long axis angling forward at approximately 30 °; with red pigment, no specimens with noticeable ommatidia. Pereonites 1 and 4–7 lateral margins with single processes, pereonites 2 and 3 lateral margins bilobed ( Figures 2A, 2B View Figure 2 , 6A, 6B View Figure 6 ). Pereonites 1–4 increasing in length backwards (relative length ratios 1.0:2.2:2.5:3.0), pereonites 5–7 equal to or slightly longer than pereonite 1. Coxal plates rounded, visible in dorsal view on pereonites 5–7 only ( Figures 2B View Figure 2 , 6E View Figure 6 ). Pleotelson width 0.78×length, lateral margins with 12–14 small denticles ( Figures 2B View Figure 2 , 6C View Figure 6 ).

Antennula ( Figure 3A View Figure 3 ), article 1 length 0.68×article 2 length, with one broom and two simple setae; article 2 longest, approximately as long as articles 4–6 combined, with four broom and three simple setae; article 3 length 0.4×article 2 length, with one simple seta; article 4 shortest, with one broom and one simple setae; article 5 glabrous; article 6 subequal to 5, with one aesthetasc, one broom and five simple setae.

Antenna ( Figure 3B View Figure 3 ), articles 1 and 2 glabrous, article 2 with two small teeth on lateral margin, article 3 subequal in length to article 5, with five simple setae (most distal one on process); article 4 with two simple setae; article 5 length 0.88×article 6 length, with two broom and three simple setae; article 6 longest, with five broom and four simple setae; flagellum of seven articles.

Right mandible ( Figure 3C, 3D View Figure 3 ), incisor process with five blunt cusps; setal row with five setae; molar process with one row of teeth and two setae on distal edge, and one accessory row of teeth and one cuticular comb close to distal edge. Left mandible ( Figure 3E View Figure 3 ) as right one except for: incisor process with a four-cusped lacinia mobilis and a setal row of four setae, molar process without distal edge setae and accessory row of teeth.

Maxillula ( Figure 3F View Figure 3 ), lateral lobe with one simple seta close to distal margin and 12 cuspidate setae distally; mesial lobe with two short simple setae and three long (two simple?, one setulate) setae distally.

Maxilla ( Figure 3G View Figure 3 ), lateral and middle lobe with one pectinate and three simple setae distally; mesial lobe with two pectinate setae and six simple setae (with rounded tip) on distal margin, and two setulate setae on or near medial margin.

Maxilliped ( Figure 4A View Figure 4 ), endite with two or three coupling hooks (in other specimens dissected both maxillipeds with two coupling hooks), distal margin with five unequal serrate setae, ventral surface with two fan setae, dorsal surface with two serrate setae (only their insertion points depicted in the detail of Figure 4A View Figure 4 ), one large setulate seta, and cuticular combs. Epipod subtriangular, width 0.44×length (0.55× in another brooding female examined).

Pereopod I ( Figure 4B View Figure 4 ), basis longest article with three simple setae. Ischium 0.5×basis length, with three simple setae and one cuticular comb. Merus as long as wide, with six simple setae and two cuticular combs. Carpus 0.9×ischium length; dorsal margin with one simple seta distally; ventral margin with two robust setae, four simple setae and some tooth-like hyaline lamellae; anterior surface with one cuticular comb. Propodus subequal in length to ischium, dorsal margin with four simple setae (one halfway along article and three distal), ventral margin with one robust seta, three simple setae and two hyaline lamellae, anterior surface with one simple seta and several cuticular combs. Dactylus with four simple setae near distal end and two simple setae between unguis and ventral claw, unguis longer than dactylus, ventral claw 0.5×unguis length.

Pereopod II ( Figure 4C View Figure 4 ), basis longest article, with three simple setae. Ischium 0.7×basis length, with five simple setae. Merus distodorsal corner with two simple setae, ventral margin with four simple setae. Carpus slightly shorter than ischium, dorsal margin with one broom and two simple setae, ventral margin with four simple setae. Propodus 0.7×ischium length, dorsal margin with one broom and three simple setae, ventral margin with one robust seta and four simple setae. Dactylus, setae arrangement as in pereopod I, unguis longer than dactylus, ventral claw weak, 0.25×unguis length.

Pereopod VII ( Figure 4D View Figure 4 ), basis longest article, with one broom and two simple setae. Ischium 0.8×basis length, with three simple setae. Merus with two simple setae on each distal corner. Carpus slightly longer than ischium, dorsal margin with one broom and two simple setae, ventral margin with three simple setae. Propodus 0.9×ischium length, distodorsal corner with one broom and two simple setae, ventral margin with one robust seta and three simple setae. Dactylus as in pereopod II except for ventral claw 0.2×unguis length.

Operculum ( Figure 5A, 5B View Figure 5 ) ovoid, width 0.67×length, with 6 simple setae on ventral surface, 2 at distal end, and many on lateral margins.

Pleopod III ( Figure 5C View Figure 5 ), endopod width 0.62×length, with three plumose setae distally. Exopod articles not fully separated; with one long simple seta, which extends as far as tips of endopod setae.

Pleopod IV ( Figure 5D View Figure 5 ), endopod width 0.39×length, exopod not reaching distal end of endopod, lateral margin with fringe of tiny setae.

Pleopod V ( Figure 5E View Figure 5 ) width 0.4×length.

Uropod ( Figures 5F View Figure 5 , 6D View Figure 6 ), exopod 0.44×endopod length, with one simple seta distally; endopod with three simple setae subapically and six broom setae distally.

Size ranges

Non-brooding females: 1.2–1.4 mm; brooding females: 1.07–1.46 mm.

Distribution

Only known from the type locality ( Figure 1 View Figure 1 ).

Etymology

The epithet, from the Latin undulatus meaning ‘‘wavy’’, alluding to the lateral bilobed margins of the pereonites 2 and 3.

Remarks

Meridiosignum undulatum n. sp. can be easily distinguished from the remaining species of the genus by having the lateral margins of pereonites 1 and 4–7 produced into single processes, and those of pereonites 2 and 3 bilobed. M. undulatum n. sp. is most similar to M. disparitergum n. sp.; the main differences between these two species are discussed in the remarks section of the latter one.

Wilson (1997) reported two paramunnid species having some brooding females with fully developed male pleopods (protogynous hermaphroditic forms). Our sample consisted exclusively of 14 females (11 of which were brooding), and all of them had the characteristic female operculum. Thus, this sample with a skewed sex ratio did not include hermaphroditic forms.