In vertical haul 0-22 m.
See remarks for scotti.
After Dias (1996), the specimens off the coastal region of Espirito Santo (Brazil) differ from the description by Ramirez (1971), who found 4 spines and 3 branched setae on the terminal segment of the male's A1. The Dias' specimens had 1 plumose seta, in addition to the ones described by Ramirez. A1 females were described with 1 seta and 4 spines on segment 2; 1 seta and 3 smooth setae on segment 3 and 5 smooth setae, and 3 branched setae and 4 spines on segment 4. The Dias' specimens have 1 smooth setae and 5 spines on segment 2; 2 smooth setae and 1 spine on segment 3; and 5 spines, 5 smooth and 3 branched setae on segment 4. The males are somewhat shorter than previously reported.
Suarez-Morales (2000 c, p.111) remarks: Isaac (1975) included this species in the unvalid genus Strilloma, which was created as an interpretation of the partial separation of the genital double somite present in some species of Monstrilla; this very variable feature ha been considered to have a questionable taxonomical value. Hence, having 3 or 2 somites between the genital and the caudal rami in the male and the female, this species is correctly placed in the genus Monstrilla.
For Suarez-Morales & al. (2013, p.625) the size and morphometric variations found in M. grandis even in geographically adjacent areas (i.e. The Mediterranean), its wide distribution and the idea supposedly cosmopolitan species among Monstrilloida could represent species complexes highlights the need for a deeper analysis to define whether this nominal species represents a species complex. It will be useful to determine the status of records of M. grandis from other geographic regions than those of the central and south american coasts which could be conspecific.
Suarez-Morales & al. (2017, p.1827) underline a degree of intraspecific variability in the same locality as observed in the Gulf of Trieste. The comparative analysis of the cephalic ornamentation in females shows some variation among specimens from Trieste, always resembling the pattern observed in the males, with an anteriiomost set of bud-like processes arranged in two vertical rows, with 4 or 5 elements on each row (Figs.12c and 13c) or with an asymmetrical alignement of these rows (Fig.12d), the latter pattern depicted also by Huys & Boxshall (1991) and Chang (2014). A similar, but tighter pattern of these elements was observed by Suarez-Morales (2000c) in material from Toulon. The presence of frontal sensilla (Figs.12c and 13g) is also a variable intra-population character, it was absent in some specimens from Trieste (Fig.12d). In all populations compared female M. grandis lack a cephalic ventral protuberance (Fig. 12b and 13c)described in some males of this species.
The female A1 armature in specimens from Trieste showed some coincidences when compared with that of the male in pre-geniculation segments; elements 2v2,3 are the longest of group 2v-d (Figs.12 a and 13b) and element 4v1 is the longest of group 4v-d.
Also, the female genital double-somite has an incomplete suture visible on dorsal view and reaching halfway around the lateral margin (Figs. 12f and 13d) and observed in other populations as well (Dolgopolskaya, 1945; Huys & Boxshall, 1991; Suarez-Morales 2000c; Chang, 2014), but not in Argentinian specimens, in which the suture appears to be more extended around the ventral surface of the somite (Ramirez, 1971, figs.2 and 4).
The female P5 has, in all the populations compared, a thumb-like inner process on the exopodal lobe, it was clearly present in the specimens from Trieste (arrows in Figs. 12h and 13d-f, h,i). Giesbrecht's 1893 [1892] illustration of this appendage could be deemed as incomplete as noticed by Chang (2014)
It is requisite to use molecular evidence to solve taxonomic problem in which morphological patterns are not informative enough.
This presumably widespread species was originally described from the SW Atlantic (49°S, 65°W) by Giesbrecht (1891); the male was depicted from specimens collected at the Gulf of Naples (Giesbrecht, 1893 [1892], later, Suarez-Morales (2000 c) described the male from Toulon Bay. The species has been recorded from different geographic areas of the world, including the Black-Sea (Dolgopolskaya, 1948), the China Seas (Shen & Bai, 1956), the Carribbean area (Fish, 1962; Nutt & Yeaman, 1975), Argentina (Ramirez, 1971, geographically closest to the type locality), the Mediterranean (Isaac, 1974, 1975), Chile (Marin & Antezana, 1985), Costa Rica (Suarez-Morales & al., 2013), Korea (Chang, 2014)
The relative length of the cephalothorax with respect to the total body length: the shortest cephalothorax (43 %) in the Costa Rica population, followed by specimens reported by Giesbrecht (1892) from Naples and by Ramirez (1971) from Argentina (47 %), by Suarez-Morales (2000c) from Toulon (48 %), Dolgopolskaya (1948) from the Black Sea (48.7 %, Shen & Bai (1956) from China (49 %) and a range of 49.2-50.5 % was observed in the male specimens from Trieste.
The A1 length with respect to the total body length shows some variation: 48 % (Naples), 55 % (Argentina), 56 % (China), 57 % (Black Sea), 60 % (Costa Rica), 61 % (Toulon), 59.3 % - 64.8 % (Trieste)
There are subtle differences on the position of the oral papilla along the cephalothorax: 44 % (Naples), 45-43 % (Trieste), 46 % (Costa Rica), 49 % (China), 53 % (Toulon);
The relarive lengths of the male 4th antennular segment: 20 % (Black Sea), 23 % (China), 24.4 % (Argentina), 26 % (Naples), 26.6 % (Toulon), 27 % (Costa Rica), 28-32 % (Trieste)
The body size is remarkably variable: less than 0.8 mm (Naples, Black Sea, Costa Rica) up to more than 1.5 mm (Naples, Barbados, Argentina, Brazil, Scotland); in the samples from Trieste, the male specimens length ranged between 0.64-1.05 mm (average = 0.86 mm, n = 15).
The cuticular ornamentation of the ventral surface of the cephalothorax was described only in the specimens from Toulon Bay (Suarez-Morales, 2000 c) and the pattern differs from the Costarrican male (Suarez-Morales & al., 2013); in the former specimens, there is only 1 pair of strongly chitinised nipple-like processes vs 3 pairs of such structures (plus an additional medial one) in the Costarrican specimen, these arranged in a relatively tight pattern (Suarez-Morales & al., 2013, fig.2E. In specimens from Trieste the ornamentation resembles that of Costarrican specimens, with 3 pairs of nipple-like processes, but in in our specimens these are arranged in a more separate pattern and, instead of having a single medial papilla-like structure posterior to this group, there are additional bud^like structures grouped either in a transverse row of 3 (arrows in fig.9, b, e, f) or in 2 symmetrical inclined rows each with 2-4 such elements §fig. 11, b, d); these bud-like groups are associated to a ventral cephalic protunerance, which is pronounced in our specimens (arrows in fig. 9 f and 11 b) and in those reported by Giesbrecht (1892), but is weakly developed in the specimens from Toulon (Suarez-Morales, 2000 c, fig. 2C) and Costa Rica §Suarez-Morales & al., 2013, fig. 2D).
Also, the Toulon male specimens have 1 pair of protuberant processes on the inner and outer margins of the caudal rami (Suarez-Morales, 2000 c, fig. 3G); these have not been reported in any other of the examined records, including the males from Trieste (fig. 10 f and 11 g);
The length of the single P5 seta is similar in all cases, reaching midlength of the caudal rami or even slightly beyond it when stretched backwards (fig. 10 f, g and 11 g, i).
Details of the male antennulary armature (Grygier & Ohtsuka, 1995) of our specimens can be compared only with records from Toulon (Suarez-Morales, 2000 c) and Costa Rica (Suarez-Morales & al., 2013): In the 1st segment, element 1 has some variation, even in individuals from Trieste; it can be as long as a segment (fig. 10 b) as in the Toulon specimens (Suarez-Morales, 2000 c, fig.2E) or about half its length (fig. 11 e) as in the Costarrican specimens (Suarez-Morales & al., 2013, fig. 2 C). In the 3 groups compared, elements 2 v2,3 are the longest of group 2 v-d. This is also discernable from illustrations by Giesbrecht (1892) (Naples), Shen & Bai (1956) (China) and Ramirez (1971) (Argentina). On the 4th segment, element 4 v1 is consistently the longest of the setal group 4 v-d in the populations compared (Giesbrecht, Ramirez, Suarez-Morales, 2000 c and Suarez-Morales & al., 2013), but showed some variation in size among the specimens from Trieste (fig. 10 b and 11 e).
At least two of the males from Trieste showed a modified (proximally expanded) caudal seta (fig. 10 d, r), but the other specimens observed have normal caudal setae (fig. 10 a, f and 11 a, g). It is to mention that some females showed an expansion on the 2 caudal setae (arrows in fig. 13i)
In addition, P3 basipodal seta is relatively longer in our specimens (fig. 11 f) than in the specimen from Costa Rica (Suarez-Morales & al., 20013, fig.3 C)