Milnesium cassandrae, Moreno & Roszkowska & García & Flores & Kaczmarek, 2019

Moreno, Antonio, Roszkowska, Milena, García, Mario Alberto, Flores, José Juan & Kaczmarek, Łukasz, 2019, Current knowledge on Mexican tardigrades with a description of Milnesium cassandrae sp. nov. (Eutardigrada: Milnesiidae) and discussion on the taxonomic value of dorsal pseudoplates in the genus Milnesium Doyère, 1840, Zootaxa 4691 (5), pp. 501-524: 506-513

publication ID

https://doi.org/10.11646/zootaxa.4691.5.5

publication LSID

lsid:zoobank.org:pub:0684AE18-0510-4F7B-B75D-AE5177FBF2A2

persistent identifier

http://treatment.plazi.org/id/0684AE18-0510-4F7B-B75D-AE5177FBF2A2

taxon LSID

lsid:zoobank.org:act:0684AE18-0510-4F7B-B75D-AE5177FBF2A2

treatment provided by

Plazi

scientific name

Milnesium cassandrae
status

sp. nov.

Milnesium cassandrae   sp. nov.

( Table 2 View TABLE 2 , Table 3 View TABLE 3 , Figure 1 View FIGURE 1 a–e, Figure 2 View FIGURE 2 a–e)

Type material: Holotype (female) and 47 paratypes (32 adult females, 13 hatchlings, two juveniles of indeterminate sex), 25 eggs and nine exuviae from piedmont of Sierra Las Mitras (25°44′55.57′′N, 100°24′11.19′′W, ca. 632 m asl), Monterrey, Nuevo León, Mexico. Lichen ( Physcia stellaris   ) on trees ( Parkinsonia aculeta   and Celtis pallida   ), coll. Antonio Moreno - Talamantes, 7 August 2014. GoogleMaps  

Additional material: Thirteen females from a lichen sample and five eggs in exuviae from San Agustin Park (25°39′18.63′′N, 100°20′34.51′′W, ca. 605 m asl), San Pedro Garza García Municipality, Nuevo Leon. Mexico. Lichen ( Nephroma   sp.) on trees ( Fraxinus   sp. and Quercus   sp.), coll. Antonio Moreno - Talamantes, 6 November 2013. Four females from a piedmont of Sierra Las Mitras (25°44′45.98′′N, 100°25′27.68′′W, ca. 700 m asl), Monterrey, Nuevo Leon, Mexico. Lichen ( Physcia stellaris   ) on tree ( Quercus virginiana   ), coll. Antonio Moreno - Talamantes, 8 November 2014. Six females from piedmont of Sierra Las Mitras (25°44′38.55′′N, 100°25′31.65′′W, ca. 719 m asl), Monterrey, Nuevo Leon, Mexico. Lichen ( Physcia stellaris   ) on tree ( Quercus virginiana   ), coll. Antonio Moreno - Talamantes, 8 November 2014. Four females from La Posta (26°00′46.21′′N, 97°58′59.00′′W, ca. 22 m asl), 2.2 km N of Buenavista, Rio Bravo, Tamaulipas, Mexico. Lichen on mesquite tree ( Prosopis glandulosa   ) coll. Antonio Moreno - Talamantes, 19 December 2016.

Species description. Body white or transparent with light yellow to brownish tones before fixation ( Fig. 1a View FIGURE 1 ). Eyes present in all living and mounted adults. Hatchling and juveniles without eyes. Adults cuticle sculptured with pseudopores (0.6 – 1.4 μm in diameter), sparsely distributed and not forming a reticular design. Hatchling and juve- niles with reticular design ( Figs 1b View FIGURE 1 and 2b View FIGURE 2 ). In adults, dorsal side with delineated geometric areas i.e. pseudoplates clearly visible only in FM ( Figs 3 – 4 View FIGURE 3 View FIGURE 4 ). The row I of pseudoplates situated anteriorly to legs I with four (two small and two large) pseudoplates. The row II situated in line with legs I with two triangular pseudoplates connected in the middle. The row III situated between legs I and II with four connected rectangular pseudoplates forming a large rectangle in the midline of the body. The row IV situated in the line of legs II with six rectangular pseudoplates forming a large rectangle in the midline of the body and two pairs of small oval dorsolateral pseudoplates. The row V situated between legs II and III with two rectangular pseudoplates connected in the middle, and two pairs of small oval dorsolateral pseudoplates. The row VI situated in line with legs III with six rectangular pseudoplates forming a large rectangle in the midline of the body and two pairs of small oval dorsolateral pseudoplates. The rows VII to IX situated between legs III and IV (row VII just behind legs III, row VIII in the middle between legs III and IV, row IX just before legs IV). The row VII with a double rectangular paired pseudoplate (the caudal pair poorly developed) and two pairs of small oval dorsolateral pseudoplates. The row VIII with a complex of ten pseudoplates, eight clustered on the dorsal side and two oval placed dorso - laterally. The row IX with a pair of pseudoplates connected in the middle. The pseudoplates arrangements see Remarks below. For pseudoplates in row I and II poorly visible under PCM, but clearly visible in FM. ( Fig. 4 View FIGURE 4 ). The pseudoplates in the hatchlings and juveniles poorly developed.

Buccal apparatus of the Milnesium   type ( Figs 1c View FIGURE 1 and 2c View FIGURE 2 ). Buccal tube in adults wide and short (standard width on average 56% of its length) and funnel - shaped, wider anteriorly (posterior diameter on average 89% of the anterior diameter); buccal tube in hatchling and juveniles is more slender (standard width on average 35% of its length) and funnel - shaped, wider anteriorly (posterior diameter on average 80% of the anterior diameter). Six peribuccal papillae and six peribuccal lamellae (of unequal size, 4+2) around the mouth opening present. Two cephalic papillae positioned laterally. The peribuccal papillae longer than the cephalic one. Pharyngeal bulb elongated and pear - shaped, without placoids or septulum.

Claws of the Milnesiidae   type ( Figs 1 View FIGURE 1 d–e and 2d–e). Primary branches on all claws with small accessory points. Secondary branches of all claws with rounded basal thickenings. Transverse cuticular bars present under claws I – III. In adult specimens, internal secondary branches on legs I–III with three points, external with two points. Secondary branches of anterior claw on legs IV with three points, posterior claws with two points. In hatchling and juvenile specimens all secondary branches on all legs with two points. Milnesium cassandrae   sp. nov. exhibits an early positive internal CC (claw configuration [2 - 2/3] - [2/3 - 2]); in other words, changes in claw configuration ( CC) occur between the hatchling/juvenile stages [2 - 2] - [2 - 2], and adults [2 - 3] - [3 - 2].

Males: not observed.

Eggs: Oval, smooth and deposited in exuvium as in all other known Milnesium   species.

Type depositories: The holotype (slide ELITE - 1/053) and 11 paratypes (slide: ELITE - 1/052, ELITE - 2/054 - 055 - 056 - 057, ELITE - 4/089, ELITE - 5/091 - 092 - 093, ELITE - 30/ 1068 - 1069), one exuviae with four eggs (slide ELITE - 30/1067) are deposited at Colección Carcinológica - FCB - UANL at Facultad de Ciencias Biológicas, Universidad Autónoma de Nuevo León, San Nicolás de los Garza, Nuevo León, Mexico, nine paratypes (slides ELITE - 12/878, ELITE - 14/881, ELITE - 43/ 1097 - 1098 - 1099, ELITE - 44/ 1100 - 1101 - 1102, ELITE - 52/1115), one exuviae and eight eggs ( ELITE - 52/1114) are preserved at the Department of Animal Taxonomy and Ecology, Adam Mickiewicz University, Poznań, Uniwersytetu Poznańskiego 6, Poznań, Poland and 27 paratypes (slides: ELITE - 3/058 - 060, ELITE - 13/879 - 880, ELITE - 28/1060, ELITE - 29/ 1065 - 1066, ELITE - 35/ 1084 - 1085, ELITE - 36/ 1086 - 1087, ELITE - 37/1089, ELITE - 40/1092, ELITE - 41/1094, ELITE - 42/1096. ELITE - 45/1103, ELITE - 47/1106, ELITE - 49/ 1108 - 1109, ELITE - 50/ 1110 - 1111, ELITE - 53/1116, ELITE - 54/ 1119 - 1120, ELITE - 58/1139, ELITE - 59/ 1140 - 1141), eight exuviae with 13 eggs (slides: ELITE - 27/987, ELITE - 29/1064, ELITE - 36/1088, ELITE - 38/1090, ELITE - 39/1091, ELITE - 53/1117, ELITE - 54/1118) are deposited in the collection of first author.

Etymology: The new species is dedicated to Cassandra Moreno Perales, the first author’s youngest daughter.

Remarks: To clarify the nomenclature of the pseudoplates arrangement we propose the system which is similar to that used for the numbering of gibbosities in Doryphoribius   and Isohypsibius   species by Michalczyk & Kaczmarek (2010). In this system all rows of pseudoplates are named and assigned to a specific place on the dorsal cuticle and the number of pseudoplates is counted:

row I of pseudoplates situated anteriorly to legs I,

row II of pseudoplates situated in line with legs I,

row III situated between legs I and II,

row IV situated in line with legs II,

row V situated between legs II and III,

row VI situated in line with legs III,

row VII situated between legs III and IV (just behind legs III),

row VIII situated between legs III and IV (in the middle between legs III and IV),

row IX situated between legs III and IV (just before legs IV).

The row numbers are always in Roman numerals and the number of pseudoplates is always listed in Arabic numerals. For example, in this system a configuration of pseudoplates (CP) in Mil. cassandrae   sp. nov. will be: (CP: I:4; II:2; III:4; IV:10; V:6; VI:10; VII:8; VIII:10; IX:2, Figs 3 – 4 View FIGURE 3 View FIGURE 4 ).

Differential diagnosis. Based on having a sculptured dorsal cuticle, Mil. cassandrae   sp. nov. belongs to the granulatum group ( Michalczyk et al. 2012a, b). The new species with claw configuration [2 - 3] - [3 - 2] in adults, is most similar to Mil. krzysztofi Kaczmarek & Michalczyk, 2007   and Mil. beasleyi Kaczmarek et al., 2012   , but it differs from:

1. Milnesium krzysztofi   by: different dorsal sculpture (very dense pseudopores, but not forming a reticular design in adults of Mil. cassandrae   sp. nov. vs. a fine reticular design in Mil. krzysztofi   ), presence of eyes, a higher pt of the standard buccal tube width ([41.6–67.2] in Mil. cassandrae   sp. nov. and [33.1–38.4] in Mil. krzysztofi   ), and the presence of pseudoplates (but see Discussion, below).

2. Milnesium beasleyi   by: presence of eyes, having higher pt buccal tube width ([47.4–66.2], [41.6–67.2], [39.9– 61.1] anterior, standard and posterior, respectively in Mil. cassandrae   sp. nov. vs. [35.3–41.8], [31.2–39.8], [33.2–39.6] anterior, standard and posterior, respectively in Mil. beasleyi   ), higher standard width/ length ratio of buccal tube (42% – 67% in Mil. cassandrae   sp. nov. vs. 31% – 40% in Mil. beasleyi   ), smaller lateral papillae (4.0 – 6.5 in Mil. cassandrae   sp. nov. vs. 7.5 – 10.3 in Mil. beasleyi   ), and presence of pseudoplates (but see Discussion, below).

In addition, Mil. cassandrae   sp. nov. is similar to other species with the claw configuration [2 - 3] - [3 - 2] i.e. Mil. lagniappe Meyer et al., 2013   , Mil. reductum Tumanov, 2006   , Mil. reticulatum Pilato et al., 2002   , Mil. tardigradum   tardigradum Doyère, 1840   , Mil. tetralamellatum Pilato & Binda, 1991   and Mil. vorax Pilato et al., 2016   , but it differs from:

3. Milnesium lagniappe   by: larger number of peribuccal lamellae (six in Mil. cassandrae   sp. nov. vs. four in Mil. lagniappe   ), different dorsal sculpture (very dense pseudopores, but not forming a reticular design adults of Mil. cassandrae   sp. nov. vs. reticulated pattern of irregular polygons in Mil. lagniappe   ), presence of eyes, stylet supports inserted in less caudal position ([58.7–67.6] in Mil. cassandrae   sp. nov. vs. [69.7–73.4] in Mil. lagniappe   ), and lower pt of buccal tube width ([47.4–66.2], [39.9–61.1] anterior and posterior, respectively, in Mil. cassandrae   sp. nov. vs. [68.0–77.5], [61.8–70.8] anterior and posterior, respectively, in Mil. lagniappe   ).

4. Milnesium reductum   by: sculptured dorsal cuticle, presence of accessory points on primary branches of claws, stylet supports inserted in more anterior position (16.5 – 26.0 in Mil. cassandrae   sp. nov. vs. 29.2 – 28.1 in Mil. reductum   ), smaller claws IV (see Table 2 View TABLE 2 in this work and Table 5 in Tumanov (2006) for the exact differences in dimensions of claws), and presence of pseudoplates (but see Discussion, below).

5. Milnesium reticulatum   by: larger number of peribuccal lamellae (six in Mil. cassandrae   sp. nov. vs. four in Mil. reticulatum   ), absence of cuticular gibbosities, different dorsal sculpture (very dense pseudopores, but not forming a reticular design in adults of Mil. cassandrae   sp. nov. vs. pseudopores arranged in nine sculptured bands, forming a reticular design in Mil. reticulatum   ), higher pt of the standard buccal tube width ([45.6–67.2] in Mil. cassandrae   sp. nov. vs. [30.4–37.4] in Mil. reticulatum   ), and higher pt of claws II, III and IV (see Table 2 View TABLE 2 in this work and Table 2 View TABLE 2 in Pilato et al. (2002) for the exact differences in dimensions of claws).

6. Milnesium tardigradum tardigradum   by: having sculptured dorsal cuticle and presence of pseudoplates (but see Discussion, below).

7. Milnesium tetralamellatum   by: larger number of peribuccal lamellae (six in Mil. cassandrae   sp. nov. vs. four in Mil. tetralamellatum   ), sculptured dorsal cuticle, and presence of pseudoplates (but see Discussion, below).

8. Milnesium vorax   by: sculptured dorsal cuticle, longer % external base + secondary branch/external primary branch I to III in Mil. cassandrae   sp. nov. (see Table 2 View TABLE 2 in this work and Table 1 View TABLE 1 in Pilato et al. (2016) for the exact differences), and presence of pseudoplates (but see Discussion, below).

TABLE 3. Measurements and pt values of selected morphological structures of 13 hatchling and juvenile specimens (instar I and II) of Milnesium cassandrae sp. nov. mounted in PVA medium. Range refers to the smallest and the largest structure among all measured specimens. The pt values are provided in italics; N, number of specimens or structures measured; SD, standard deviation.

Character N Range µm     pt   Mean µm pt SD µm pt
Body length 13 131 202     179   20  
Peribuccal papillae length 3 3.3 4.2 16.2 19.7 3.7 17.9 0.4 1.7
Lateral papillae length 5 2.3 3.4 11.3 16.5 3.0 14.6 0.4 2.1
Buccal tube
Length 13 18.2 22.6     20.7 1.2
Stylet support insertion point 13 10.3 14.8 56.5 70.5 13.8 66.3 1.1 3.4
Anterior width 13 7.2 9.6 38.1 47.1 8.8 42.3 0.7 3.2
Standard width 13 6.1 7.8 28.2 39.4 7.2 34.6 0.5 3.0
Posterior width 13 6.3 7.3 29.6 36.1 7.0 33.6 0.3 2.0
Standard width/length ratio 13 28% 39%     35% 3%
Posterior/anterior width ratio 13 74% 88%     80% 4%
Claw 1 lengths
External primary branch 13 7.4 10.4 35.1 52.8 8.9 42.9 0.9 5.7
External base + secondary branch 12 6.5 7.9 30.1 39.7 7.3 35.1 0.4 2.6
External branches length ratio 12 72% 96%     84% 10%
Internal primary branch 13 7.6 9.8 35.8 48.4 8.7 42.1 0.7 4.1
Internal base + secondary branch 13 6.2 8.2 30.2 39.6 7.1 34.3 0.5 2.9
Internal branches length ratio 13 74% 94%     82% 6%
Claw 2 lengths
External primary branch 13 7.6 11.0 35.4 60.5 9.3 45.2 0.9 6.5
External base + secondary branch 13 6.7 8.1 30.9 40.9 7.5 36.3 0.5 3.5
External branches length ratio 13 65% 94%     81% 7%
Internal primary branch 12 7.6 9.7 37.4 53.5 9.0 43.3 0.6 4.3
Internal base + secondary branch 13 6.4 8.9 29.9 40.9 7.2 34.7 0.7 3.4
Internal spur 1 1.8 1.8 10.1 10.1 1.8 10.1 ? ?
Internal branches length ratio 12 70% 96%     80% 9%
Claw 3 lengths
External primary branch 12 8.5 10.3 39.4 48.9 9.4 44.7 0.5 3.2
External base + secondary branch 13 6.0 8.3 31.3 38.5 7.3 35.1 0.6 2.3
External branches length ratio 12 71% 90%     79% 6%
Internal primary branch 12 8.6 9.7 39.0 47.2 9.3 44.4 0.4 2.8
Internal base + secondary branch 13 6.7 7.6 30.4 40.0 7.1 34.2 0.3 2.7
Internal branches length ratio 12 70% 83%     76% 4%
Claw 4 lengths
Anterior primary branch 11 8.4 11.2 41.5 54.9 10.2 49.7 0.8 3.6
Anterior base + secondary branch 13 5.9 8.1 26.1 40.7 7.1 34.4 0.5 3.7
Anterior branches length ratio 11 61% 80%     71% 6%
Posterior primary branch 11 9.5 11.8 45.8 56.7 10.7 52.3 0.7 3.3
Posterior base + secondary branch 13 6.6 8.2 30.6 40.9 7.5 36.1 0.5 3.1
Posterior branches length ratio 11 65% 77%     70% 4%
FM

Department of Nature, Fujian Province Museum

VI

Mykotektet, National Veterinary Institute

PCM

Polish Collection of Microorganisms

CC

CSIRO Canberra Rhizobium Collection

UANL

Universidad Autonoma de Nuevo Leon