Meridiosignum menziesi ( Winkler, 1994 )

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 : 1130-1136

Meridiosignum menziesi ( Winkler, 1994)

( Figures 12–15 )

Paramunna kerguelensis Vanhöffen, 1914 ; Menzies 1962, p. 22, 47, figure 7, tables 3, 4. Paramunna kerguelensis Vanhöffen, 1914 ; Doti et al. 2005, table 2.

Paramunna menziesi Winkler, 1994, p. 255 –258, figures 9–12 (synonym of Menzies’ P. kerguelensis ); Just and Wilson 2004, table 1; Doti et al. 2005, tables 2, 3.

Meridiosignum menziesi ( Winkler, 1994) ; Just and Wilson 2007, p. 18, 21, table 1.

Material examined

Holotype: adult „, appendages mounted in the slides ZMB 4198–4200 (26932) . Paratypes: appendages of a female mounted in the slide ZMB 4201 (26932) , appendages of an adult male mounted in the slides ZMB 4202–4203 (26932) , and 9 specimens preserved in ethanol (2 adult „„, 2 immature ♀♀ and 5 mancas, ZMB 26932) .

Additional material examined: Puerto Deseado , Santa Cruz Province. Mouth of the Deseado River estuary, 5–10m, 7 Feb 2006. Sta. 12, 47 ° 45.4129S, 65 ° 52.6389W: 1 brooding ♀, 1 non-terminal „, 1 juvenile. Off mouth of the Deseado River estuary, Coast guard ship ‘‘ Río de la Plata’ ’, 15 m, 23 Jan 2007. Sta. 20, 47 ° 43945.60S, 65 ° 50915.70W: 26 brooding ♀♀, 12 non-brooding ♀♀, 4 terminal „„, 7 non-terminal „„, 4 mancas. Sta. 15, 47 ° 48953.50S, 65 ° 51914.90W: 1 brooding ♀, 2 juveniles. Sta. 19, 47 ° 42934.60S, 65 ° 49907.30W: 1 brooding ♀, 1 non-brooding ♀, 1 terminal „. Sta. 23, 47 ° 43933.40S, 65 ° 49916.30W: 10 brooding ♀♀, 3 non-brooding ♀♀, 4 terminal „„, 1 non-terminal „, 3 juveniles. All the specimens from Puerto Deseado were catalogued under the number MACN-In 37531. Argentine navy vessel ARA ‘‘Alférez Sobral’’, Beagle Channel. Sloggett Bay, 55 ° 00.09S, 66 ° 20.69W, 15–30 m, 9 Feb 2001: 2 nonbrooding ♀♀, 1 non-terminal „. Moat Mount, 55 ° 01.59S, 66 ° 41.79W, 15–25 m, 9 Feb 2001: 1 brooding ♀. All the specimens from the Beagle Channel were catalogued under the number MACN-In 37532 .

Diagnosis

Head anterior margin nearly straight. Eyestalk with a few ommatidia. Lateral margins of pereonite 1 rounded; 2–4 linear; 5, 6 rounded and 7 tapering into a small tooth. Coxal plates 5–7 with one small tooth. Lateral margins of pleotelson with 11 strong denticles. Pereopod I propodus with one or two robust setae on ventral margin. Pereopod II carpus without robust setae, propodus with one robust seta on ventral margin. Uropod exopod with two terminal simple setae.

Description of the terminal male

(Based on three specimens from Puerto Deseado, MACN-In 37531a–c). Length: 1.22 mm ( Figure 12A, 12B ). Body width 0.51×length, widest at pereonites 2 and 3. Head length 0.42×width, anterior margin nearly straight ( Figures 12A , 15A ). Eyestalks elongate, apically rounded and with six ommatidia, long axis angling forward at approximately 30 °. Pereonite 1 greatly enlarged laterally, midline length 0.28×maximum length ( Figures 12A, 12B , 15A, 15B ). Lateral margins of pereonite 1 rounded; 2–4 linear; 5, 6 rounded and 7 tapering into small tooth (see detail Figure 12A ). Pereonite 1 shorter than subequal pereonites 2–4 at midline, pereonites 5–7 increasing in length backwards (relative length ratios 1.0:1.2:1.6). Coxal plates visible in dorsal view on pereonites 1 and 5–7; those of last three pereonites with one small tooth each (see detail Figure 12A ). Pleotelson almost as wide as long, lateral margins with 11 strong denticles.

Antennula ( Figure 14B ), article 1 length 0.8×article 2 length, with one broom and three simple setae; article 2 longest, 1.06×length of articles 4–6 combined, with four broom and three simple setae; article 3 length 0.44×article 2 length, with one simple seta; article 4 shortest, with one broom seta; article 5 glabrous; article 6 slightly longer than article 5, with one aesthetasc, one broom and four simple setae.

Pereopod I ( Figure 14D ), basis longest article, with crenate ridge and four simple setae. Ischium 0.69×basis length, with three simple setae, one hyaline tooth, and two cuticular combs. Merus approximately as long as wide, with four simple setae, two hyaline teeth, and two cuticular combs. Carpus ovate, 0.77×ischium length; distodorsal corner with one simple seta; ventral margin with two thick robust setae, four simple setae, and some tooth-like hyaline lamellae, anterior surface with one cuticular comb. Propodus slightly longer than carpus, dorsal margin with four simple setae (one halfway along article and three distal), ventral margin with two small robust setae, three simple setae, and one hyaline lamella, anterior surface with one simple seta and cuticular combs. Dactylus with four simple setae near distal end and two simple setae between unguis and ventral claw, unguis slightly longer than dactylus, ventral claw approximately 0.5×unguis length.

Pereopod II ( Figure 14E ), basis longest article, with crenate ridge and four simple setae. Ischium 0.77×basis length, with four simple setae. Merus distodorsal corner with two simple setae, ventral margin with four simple setae. Carpus as long as ischium, dorsal margin with one broom and three simple setae, ventral margin with six simple setae, anterior surface with cuticular combs. Propodus 0.79×ischium length, dorsal margin with one broom and three simple setae, ventral margin with one robust seta and four simple setae. Dactylus, chaetotaxy as in pereopod I, unguis longer than dactylus, ventral claw 0.33×unguis length.

Pereopod VII ( Figure 14F ), basis longest article with two broom and three simple setae. Ischium 0.95×basis length, with four simple setae. Merus with five simple setae. Carpus 1.14×ischium length, dorsal margin with one broom and two simple setae, ventral margin with five simple setae and cuticular combs. Propodus 0.95×ischium length, dorsal margin with one broom and three simple setae, ventral margin with one robust seta, three simple setae and cuticular combs. Dactylus, chaetotaxy as in pereopod I, unguis as long as dactylus, ventral claw 0.28×unguis length.

Size ranges

See Table 1.

Distribution

Formerly recorded from the Magellan Strait from the tidal belt to 9 m depth ( Menzies 1962; Winkler 1994). Now, found in the Beagle Channel and Puerto Deseado at 15–30 m and 5–15 m depth, respectively ( Figure 1 ).

Remarks

All the specimens of M. menziesi from Puerto Deseado and Beagle Channel had denticles on coxal plates 5–7 and the lateral margins of pereonite 7 ( Figures 12 , 13A, 13B ). Just and Wilson (2007) examined the type material of Paramunna menziesi Winkler, 1994 and confirmed the presence of distinct coxal plates on pereonites 5–7. After staining the nine paratypes of P. menziesi and re-examining them under high magnification, we found that one immature female and one adult male had denticles on the coxal plates 5–7 and the last pereonite (see Figure 13C ). These denticles were wrinkled and extremely translucent, and all paratypes were somewhat deteriorated. Therefore, the examination of fresh material of M. menziesi from the type locality is badly needed to decide whether these denticles are actually absent in some individuals of this species.

For several species in the Paramunna complex, Just and Wilson (2004) described males (termed ‘‘terminal males’’) that were larger than normal ones. These terminal males had pereonite 1 inflated into broad rounded ‘‘shoulders’’, and pereopods I much larger. The terminal males of M. menziesi also show some additional differences from the non-terminal ones, namely: (1) eyestalks elongate; (2) carpus of pereopod I ovate with stouter robust setae; (3) propodus of pereopod I with two robust setae; and (4) carpi and propodi of pereopods II and VII slender.

In addition to the differences between non-terminal and terminal males mentioned above, we observed that the length/width ratio of article 2 of the antennula ( Figure 14A, 14B ) and the number of robust setae on the propodus and carpus of pereopod I ( Figure 14C, 14D ) vary among instars in both sexes. The intraspecific variation found among the specimens collected at Sta. 20 from Puerto Deseado is summarized in Table 1. Article 2 of the antennula is more elongated in brooding females than in the other instars. Additionally, on the carpus of pereopod I there is only one robust seta in the mancas but two in the remaining instars, and on the propodus of pereopod I the number of setae increases from one to two as the specimens become older (see Figure 14C, 14D ). It is worth noticing that the four specimens examined from the Beagle Channel also agree with this general pattern.

Figures

Figure 1. Distribution of the South American species of the genus Meridiosignum: (Z) M. undulatum n. sp.; (O) M. disparitergum n. sp.; (m) previous records; (n) new records of M. menziesi (Winkler, 1994).

Figure 12. Meridiosignum menziesi (Winkler, 1994). Terminal „ (MACN-In 37531-a). (A) habitus in dorsal view and detail of coxal plates 5–7; (B) habitus in lateral view. Scales: 0.5 mm.

Figure 13. Meridiosignum menziesi (Winkler, 1994). (A) habitus in dorsal view of nonterminal „ (MACN-In 37531-c); (B) habitus in dorsal view of brooding ♀ (MACN-In 37531- d); (C) detail of coxal plates 5–7 of immature female (paratype ZMB 26932). Scales: 0.5 mm.

Figure 14. Meridiosignum menziesi (Winkler, 1994). (A, C) non-terminal „ (MACN-In 37531- e); (A) antennula; (C) pereopod I. (B, D–F) terminal „ (MACN-In 37531-b); (B) antennula; (D–F) pereopods I, II and VII. Scales: 0.1 mm. A and B share the same scale bar, as do E and F.

Figure 15. Meridiosignum menziesi (Winkler, 1994). SEM photographs. (A, B) terminal „ (MACN-In 37531-f), habitus in dorsal and lateral views; (C) brooding ♀ (MACN-In 37531-g), habitus in dorsal view. Scale: 0.2 mm. A–C share the same scale bar.