Amerus troisi (Berlese, 1883)

AVANZATI, A. M., SALOMONE, N., BARATTI, M. & BERNINI, F., 2003, Taxonomic revision of Amerus troisi (Berlese, 1883) (Acari, Oribatida, Ameridae) using morphological and biochemical characters, Journal of Natural History 37 (7), pp. 797-819 : 798-808

Amerus troisi (Berlese, 1883)

Belba Troisii Berlese, 1883 , A.M.S.It., Cryptostigmata, fasc. 3, n. 5, figure 59. [ Frosinone , Latium, Italy; holotypus: presumably lost], neotypus stated here.

Amerus troisii: Berlese, 1896 , A.M.S.It., Cryptostigmata, fasc. 79, n. 7.

Amerus troisii: Berlese, 1914: 130–131 .

Amerus troisi: Van der Hammen, 1952: 40–41 .

(partim) Amerus troisi: Mahunka and Mahunka-Papp, 1995: 139 .

Diagnosis

Ameridae . Trilobed rostrum. The medial tooth is larger, roundish and curves downward. The prodorsum and anterior notogastral portion are flat. The sejugal suture is absent, but there is a pair of deep humeral foramina between the ta and te notogastral setae. The exobothridial prodorsal setae are as long as the rostral and lamellar setae. Interlamellar setae cross each other medially. Bothridial border with four small abaxial teeth. Ten pairs of notogastral setae differing in length: marginal setae p –p the shortest, te, ti, ms and r are longest. Plethotrichy (about 14 pairs) 1 3 1

at the aggenital setae. Lyrifissures iad located in anterior corner of anal plates.

Redescription of the adult

The analysis of material preserved in the Berlese Collection at the Istituto Sperimentale per la Zoologia Agraria in Florence (hereon referred to as ISZA) revealed that no specimens are labelled ‘typus’ or ‘typicus’ or ‘tipico’ or ‘cotipi’. Only slide 25/21 bears the label ‘ubi? tipico?’; it is an extremely broken specimen not suitable for study. The only reliable indication is given by the locus typicus, ‘ in agri romani (Frosinone) muscis ’. Therefore, one of us (F.B.) collected soil samples around Frosinone (a city which has greatly expanded since the end of 19th century). The large conspecific population of Amerus , collected in the small wood ‘Bosco Faito’ on the outskirts of Frosinone, is the source of our revision material because this area is reported to be the locus typicus restrictus of Belba Troisii Berlese, 1883 . Measurements. The mean size of 10 randomly selected specimens is 914 m m× 527 m m. The specimen selected as neotypus measures 900 m m× 510 m m; it is a male just esclosed (figure 4b, c).

Colour. Reddish brown.

Cerotegument. The whole body is covered by a waxy cerotegumental layer of varying thickness and consisting of spherical elements (figure 1g). This layer is particularly thick in the dorso-sejugal depression, around the humeral foramen (figure 1c), ventrally in the epimeral furrows and legs (figure 1b).

Cuticle. The body surface is generally smooth, but the cuticle of the rostrum and around the humeral foramen, the anal plates, and pedotecta I and II is covered by very small tubercles visible under the SEM (figure 2d).

Prodorsum. Due to the absence of the sejugal suture, this part of the body is typically not well delimited. Like the anterior notogastral area, comprising the humeral foramen and setae te (figure 1b, c), it is very flat. The anterior border of the rostrum is divided in three by two deep incisions. The medial tooth is larger and longer than the two lateral teeth; it is apically rounded and curves downwards (figure 1i). The prodorsal setae are generally long, rugose, basally thick and apically slender: ro and le are sagittally curved (figures 1c, figure 4b) while ex are directed anteriorly (figure 1b, l). The interlamellar setae (in) are shortest; they are slender and sagittally directed so that they cross each other apically (figure 5b). Externally, the bothridium is tube-like; internally, it has a tetradentate border on the antiaxial side (figure 1h). The sensillus protruding from the cup-like structure is long, slender, apically flagelliform, rugose and is generally directed laterally (figure 1b).

Lateral characters. Amerus lacks a tutorium. Pedotectum I is a very large lamina, rounded along its outer border; pedotectum II is smaller, but always easily distinguishable (figure 2c). Acetabulum III lies on a protuberance which bears the large, rounded discidium (figure 2c). Acetabulum IV also lies on a protuberance.

Notogaster. As there are no traces of the dorsosejugal suture, an imaginary line connecting the left and right humeral teeth (the pointed lateral apophysis located before the setal insertion ta) (figure 1b), is considered the boundary between the prodorsum and notogaster. A lateral rectangular lamina and, paraxially, the humeral foramen lie posterior to this line (figure 1b, f) beyond which the body surface rises. The 10 pairs of notogastral setae are of varying length: the marginal setae p –p 1 3 are very short and contiguous to the notogastral surface (figures 1d, e, 4c), the centrodorsal setae te, ti, ms and r are longest, while the remaining ta, r and r are 1 3 2

of intermediate length (figures 1c, 4c). Whatever their length, the centronotogastral setae lying almost in the same longitudinal row are all basally thick, apically slender and rugose or spiny (figure 1a) while the marginal setae are smooth. The ti pair is generally sagittally curved.

The position of the lyrifissures and the opening of the latero-abdominal gland gla are illustrated in figure 4c. It is worth noting the closed position of the gla opening to the anteriorly displaced im and ip lyrifissures. The latero-abdominal glands are large and globular (figure 4c).

Ventral characters. In this genus the fourth epimeral furrow, and not the sejugal one, is largest. It is very deep and laterally has two pairs of condyles; the remaining epimeral furrows are hardly visible (figure 2a).

The epimeral setae follow the usual 3-1-3-3 formula; setae 1b, 1c, 3c and 4c are very long, while the others are about half their length (figure 2a, c).

The ventral plate is characterized by the plethotrichy (multiplication of setae) of the aggenital pair: 14–15 pairs of these setae are inserted around the genital plates (figure 2a). The other genito-anal setal numbers are as usual: six genital pairs, two anal pairs and three adanal pairs. All these setae represented in figures 2a and 4c are slender, relatively long and smooth. The lyrifissures iad are situated near the anterior angle of the anal plates (figure 4c).

Gnathosoma . The infracapitulum is diarthric as is usual in this group of families; the other features of this part of the body are also normal (figure 2b). The palp setal formula is 0-2-1-2-7 (+1 solenidion); the solenidion is long, thick and accumbent. Setae cha are as long as setae chb and they are equally ciliate.

Legs. All legs are monodactylous with the following chaetotactic and solenidiotactic formulae (from trochanter to tarsus; numbers of solenidia in parentheses): (I) (1-6-3(1)-4(2)-20(2)-1); (II) (1-5-3(1)-4(1)-16(2)-1); (III) (2-3-3(1)-4(1)-15-1); (IV) (1-2-3-4(1)- 12-1).

The solenidions are short and not tactile; those proper to tarsus and tibia I inserted on distinct tubercles. The proral setae are eupathidic on tarsus I and reduced to very short on tarsi II, III and IV.

The normal setae are often modified and thickened: setae v on femora of all legs are spadiform, while on tarsi II, III and IV the setae pv are thick, ceratiform with large cilia.

Immatures. We found no immatures in the collected material, but Dr R. Nannelli bred this species and obtained a larva. According to Grandjean (1965), this is the one missing stasis in the development of the genus.

Variations. The diagnostic characters are reasonably constant in all examined populations, except for those of two specimens found in Tangier ( Morocco). In these specimens the rostral morphology and the length of the notogastral setae are in perfect agreement with A. troisi , but the interlamellar setae are shorter and more similar in length to A. polonicus and the new species to be described (figure 5c). With great reserve, we consider the two specimens to belong to A. troisi ; we are waiting for a greater number of specimens from other Riffian and/or southern Spanish populations for morphological and biochemical analyses. It should be noted (see below) that, outside of Italy, A. troisi is only found at this Moroccan site. We will discuss this later along with the biogeographical aspects of this finding.

Material examined

When not otherwise indicated, the samples were collected by F. Bernini.

Italy: Bosco Faito, surroundings of Frosinone ( FR), Latium, U. T.M. 33TUG6008: humus under Quercus pubescens and Q. cerris , 26 December 1979 (47); locus typicus restrictus; Margheria dei Boschi ( IM): without indication of habitat, 1150 m, 31 August 1980 (1) (Coll. R. Poggi); M. Ravinet eastern slopes, Ligurian Alps ( SV), U. T.M. 32 TMP 3289: humus under Fagus sylvatica wood, 900 m, 10 April 1977 (1) (Coll. S. Zoia); Loano, M. Carno slopes ( SV), U. T.M. 32 TMP 4088: humus under Fagus sylvatica wood, 900 m, 11 March 1979 (1) (Coll. Benedetti Briganti); Cabella Ligure, Rosano, eastern Ligurian Apennines, U. T.M. 32TNQ0849: humus under oak wood near stream, 16 August 1979 (22) (Coll. C. Torti); S. Colombano- Certenoli, eastern Liguria, U. T.M. 32TNQ2713: humus under Castanea sativa wood, 13 March 1978 (18); Monte di Portofino ( GE), U. T.M. 32TNQ1508: forest humus, 1 September 1976 (1) (Coll. S. Zoia); ibidem: 6 June 1977 (1) (Coll. R. Poggi); Traso, Bargagli ( GE), U. T.M. 32TNQ0522: forest humus, 22 October 1978 (4) (Coll. R. Poggi); S. Stefano d’Aveto ( GE), M. Groppetto, eastern Ligurian Apennines, U. T.M. 32TNQ3633: forest humus, 1300 m, 1 October 1978 (26) (Coll. S. Zoia); Colli Berici, U. T.M. 32TPR93: forest humus, 21 October 1971 (34); Mt Altissimo, Apuan Alps, U. T.M. 32SNP9878: humus under Fagus sylvatica wood, 1000 m, 12 June 1984 (7); Mt Freddone, Apuan Alps, U. T.M. 32SPP0378: humus under Fagus sylvatica and Castanea sativa , 900 m, 29 October 1969 (1) (Coll. R. Dallai); Badia Prataglia, Tuscan Apennines, U. T.M. 32TQP3253: humus under Fagus sylvatica wood, 1100 m, 5 August 1972 (4) (Coll. R. Dallai); Boboli Garden ( FI), U. T.M. 32TPP8148: humus under Quercus ilex , 23 May 1970 (7); Elba island, Tuscan Archipelago, Valle delle Conche, U. T.M. 32TNN9540: humus under Mediterranean maquis, 250 m, 25 November 1976 (12); Montalbuccio ( SI), surroundings of Siena, U. T.M. 32TPN8598: humus under Quercus ilex wood, 350 m, 15 December 1974 (2); ibidem: 20 December 1978 (8); ibidem: 10 June 1981 (48); ibidem: 15 January 1982 (54); ibidem: humus under Quercus ilex and Q. pubescens wood 350 m, 6 March 1990 (78); Farma Valley, Carpineta ( SI), U. T.M. 32TPN8372: humus under Quercus ilex , 15 January 1972 (3); ibidem: riparian forest humus, 27 February 1979 (1) (Coll. G. Callaini); ibidem: humus and litter under Quercus ilex , 250 m, 27 February 1979 (9); ibidem, Bosco della Bandita ( GR), U. T.M. 32TPN8372: humus under Taxus baccata , 25 September 1977 (1) (Coll. G. Callaini); ibidem: humus under Taxus baccata , Fagus sylvatica , Quercus ilex and Castanea sativa wood, 3 October 1977 (13) (Coll. G. Callaini); ibidem: humus under Taxus baccata near Troscia pond, 29 October 1978 (1) (Coll. G. Callaini); ibidem: humus under alder wood near Troscia pond, 20 March 1986 (1); ibidem: humus under Taxus baccata and Fagus sylvatica near Troscia pond, 20 March 1986 (9); ibidem: Il Belagaio ( GR), U. T.M. 32TPN8073: humus under Fagus sylvatica , 14 December 1979 (2); ibidem: humus in mixed wood of Fagus sylvatica , Quercus cerris and Castanea sativa along river, 21 April 1988 (4); Mt Amiata slopes, 1° Refuge, U. T.M. 32TQN1252: moss and forest humus under Fagus sylvatica wood, 1320 m, 18 December 1970 (2); Puzzolaia del Palazzo, Pietri Neri ( SI), Mt Zoccolino slopes, U. T.M. 32TQN1858: humus under Alnus ornus , 650 m, 24 August 1976 (2); ibidem: forest humus, 650 m, 8 November 1981 (3); Mt Zoccolino ( SI), Amiata Massif, U. T.M. 32TQN1856: humus under Fagus sylvatica and Corylus avellanae , 900 m, 5 February 1984 (2); ibidem: idem, 5 May 1984 (1); Frontigliano d’Ussita ( MC), Sibillini Mountains, U. T.M. 33TUH4856: moss and humus under Fagus sylvatica wood, 1550 m, 11 September 1976 (1); Monteporzio Catone ( RM), Latium, U. T.M. 33TUG1032: forest humus, 700 m, 15 February 1972 (10); Foresta Umbra, Gargano Promontory, U. T.M. 33TWG8129: forest humus, 600 m, 10 April 1970 (3) (Coll. R. Lampariello); Galdo ( SA), Mts Alburni U. T.M. 33TWE2989: humus under Castanea sativa , 700 m, 4 September 1970 (1) (Coll. M. T. Di Gasero); Bosco di Rifreddo ( PZ), Basilicata, U. T.M. 33TWF7091: humus under Fagus sylvatica, 1200 m , 22 May 1984 (5); Pollino Massif, Mormanno ( CS), U. T.M. 33SWE8614: humus under Quercus ilex , 700 m, 15 October 1976 (2); ibidem: Mt Dragone slopes, U. T.M. 33SWE9617: humus under Fagus sylvatica wood, 1300 m, 14 October 1976 (14); ibidem: humus under Pteridium aquilinum and grasses, 1300 m, 14 October 1976 (1); Sicily, Nebrodi Mountains, Cesarò ( ME), U. T.M. 33SVB6994: humus under Quercus cerris, 1050 m , 25 March 1972 (2); ibidem: humus and litter of Fagus sylvatica 1200 m , 25 March 1972 (8); ibidem: Peloritani Mountains, Malabotta Forest, U. T.M. 33SVC0401: moss in beech wood, 1215 m, 15 May 1981 (1) (Coll. R. Arcidiacono); ibidem: humus of Fagus sylvatica, 1215 m , 26 October 1981 (7) (Coll. R. Arcidiacono); ibidem: humus of Quercus cerris, 1185 m , 26 October 1981 (11) (Coll. R. Arcidiacono).

Morocco: Cap Spartel (Tangier): humus under maquis, 1 September 1972 (2).

F.B. analysed the specimens labelled Amerus troisi preserved in Berlese’s collection housed in the Istituto Sperimentale per la Zoologia Agraria in Florence: (1) Ceresole d’Alba (155/21-22); (2) Padola, Cadore, bellissimo (147/46); (3) Populonia, musco (147/47); (4) Boboli, muschio (147/48); (5) Boboli, cortecce (147/50; 29/44, 30/8 and 148/1); (6) Firenze, musco (38/6) (the label bears the correction of Amerus on Belba troisi ); (7) Ubi? Tipico? (25/21) (the slide belongs to the old collection and bears an extremely broken specimen with missing notogastral setae; it is therefore not suitable for study).

Geographic distribution and ecology

Amerus troisi is a rather rare, classic entity localized in Europe (Van der Hammen, 1952). For many years it has been cited without making a real taxonomic distinction from A. polonicus Kulczynski, 1902 . Specimens of Amerus attributed to A. troisi were recorded in Italy (Berlese, 1883; Zangheri, 1966; Mahunka and Paoletti, 1984; Bernini et al., 1991, for a review), Austria (Schatz, 1983), Germany (Sellnick, 1929; Willmann, 1931; Weigmann and Kratz, 1981), Switzerland (Schweizer, 1922), The Netherlands (Van der Hammen, 1952), Czech Republic, France and Greece (Schuster, 1959), Slovenia and Croatia (Tarman, 1977), Hungary (Balogh, 1943, 1963, 1965, 1972), Poland (Olszanowski et al., 1996), Ossetia, Georgia, Armenia and Crimea (Karppinen et al., 1987), southern Spain (Andalucia) (Kahwash et al., 1991), perhaps Portugal (Pérez-Iñigo, 1997), Algeria (Michael, 1890), Morocco and western Sahara (Subias et al., 1992), the Canary Islands (Pérez-Iñigo, 1976; Pérez-Iñigo and Peña, 1996) and Madeira (Willmann, 1939; Pérez-Iñigo, 1988).

As for its ecology, this species is believed to be a southern element and a climatic indicator (Schuster, 1959) for its absence from northern Europe, Great Britain and Russia.

Owing to the confused systematics of this species and related taxa, no definite conclusions can be drawn on the basis of data from previous works. In particular, some reports can be immediately attributed to A. polonicus on the basis of the drawings of, e.g. Sellnick (1929), Willmann (1931) and Balogh (1943). Furthermore, some central European authors, such as the late Prof. M. Kunst (personal communication) and S. Mahunka (personal communication), believe that all or almost all the central-European citations of A. troisi should be attributed to A. polonicus . The identity of the latter species is not certain: Bulanova-Zachvatkina (1975) identified A. polonicus with A. troisi . We have addressed this issue in another paper, now in advanced preparation, which aims to redescribe the Polish species and define its geographic distribution.

Other reports can be safely attributed to a new taxon described below: these citations relating to Algeria (Michael, 1890), Morocco and western Sahara (Subias et al., 1992, 1994), Canary Islands (Pérez-Iñigo, 1976; Pérez-Iñigo and Peña, 1996) and many Italian sites were directly or indirectly checked by us. They will be discussed after the description of the new species.

Lastly, the Tangier report, and consequently those relating to southern Spain (Kahwash et al., 1991) and Madeira (Willmann, 1939), are dubious.

The above-mentioned data indicate that the distribution of A. troisi is certain only in Italy, and confirms that A. troisi is a southern element with a definite preference for forest humus.

Comparative remarks

The original description only bears the generic characters. The 1914 description, an appendix to the description of A. laticephalus , is much more interesting. In this redescription Berlese explains the differences found by Kulczynski (1902) for A. polonicus with respect to A. troisi , and states that the three known species can be distinguished based on: (1) the length of the notogastral setae, (2) the length of the interlamellar setae and (3) the rostral morphology (rounded in A. laticephalus and pointed in A. polonicus ). This is true in a general sense because the analysis of a larger number of populations has revealed the consistency of diagnostic characters. Nevertheless, Berlese in 1914 had two species before him, A. troisi and another previously unknown one (later described). In fact, the rostral morphology of A. troisi , described by Berlese, is almost certainly related to this new species because ‘due brevi processi cilindrici, quasi trasparenti, che sono l’apice delle mandibole’ hampered detailed observations. Dissection of the animal or SEM observations are necessary for detailed descriptions of the rostrum. Berlese’s redescription allows a correct analysis and determination of the character-states of A. troisi and will facilitate the characterization of other congeneric species.