Macrobiotus caymanensis, Meyer, Harry A., 2011

Meyer, Harry A., 2011, Tardigrada of Grand Cayman, West Indies, with descriptions of two new species of eutardigrade, Doryphoribius tessellatus (Hypsibiidae) and Macrobiotus caymanensis (Macrobiotidae), Zootaxa 2812, pp. 28-40 : 35-38

Macrobiotus caymanensis sp. n.

( Figs. 13–18 , Tables 2–3)

Diagnosis. A Macrobiotus of the polyopus -group with minute cuticular pores, two macroplacoids and a microplacoid, a relatively short buccal tube and posterior stylet support insertion (pt 77.5–79.3) and eggs, laid free, with ornamented shell of reticular design with hexagonal mesh and a small number (9–12 in the circumference and 9–13 in the hemisphere) of large, conical processes (9–20 μm high).

Type material examined. Holotype, seven paratypes, one embryonated egg: sample 4b ( Table 1 ), Salina Reserve , East End District, Grand Cayman, Cayman Islands, West Indies, 1921ʹ0 0.3ʺ N and 8105ʹ48.7ʺ W, 9.1m asl, dry tropical forest, squamulose lichen.

Description of holotype. Body length 452.7 μm, colourless. Sex undetermined. Cuticle smooth, with numerous, uniformly distributed small, circular pores about 1.0 μm in width ( Fig. 13 ). Eyes present. No granulation on any leg.

Mouth opening terminal with ten small peribuccal lamellae ( Fig. 14, 15 ). Buccal cavity small. Buccal armature very simple and difficult to see with light microscopy, system of 3 very thin transversal ridges present with posterior band of very small teeth ( Fig. 15 ). Buccal tube 39.2 μm long and 6.9 μm [17.6] wide. Ventral lamina 21.6 μm [55.1] long, double the length of the stylet sheaths. Stylet supports inserted on buccal tube at 30.4 μm [77.6].

Oval pharyngeal bulb with apophyses, two rod-shaped macroplacoids decreasing in length and a small, rodshaped microplacoid ( Fig. 14 ). First macroplacoid 11.0 μm [28.1] long, with a central constriction. Second macroplacoid 7.0 μm [17.9] long, not constricted. Microplacoid 2.9 μm [7.4] long. Macroplacoid row 19.8 μm [50.5] long, entire placoid row 23.5 μm [59.9] long.

Claws of hufelandi - type, short (especially the common basal tract) and stout ( Fig. 16 ). External claw lengths: leg I primary branch 10.5 μm [26.8], secondary branch 8.7 μm [22.2]; leg II pb 10.4 μm [26.5], sb 8.7 μm [22.2]; leg III pb 11.2 μm [28.6], sb 9.6 μm [24.5]. Posterior claw lengths: leg IV pb 13.3 μm [33.9], sb 9.0 μm [23.0]. Primary branches of all claws with very well-developed accessory points. Small, smooth lunules present on all legs (leg II, 3.1 μm [7.9] wide; leg IV, 4.1 μm [10.5] wide). No cuticular bars visible on legs.

Morphometric data and summary statistics for the holotype and seven paratypes are given in Table 2. Four paratypes (50%) lacked discernable eyes when examined immediately after mounting.

Eggs laid freely ( Fig. 17 ), with small number of large processes (9–12 around the circumference, 9–13 in the hemisphere). Egg shell areolated, six polygonal areolae around each process present ( Fig. 18 ). Egg shell otherwise smooth. Processes conical, tapering to a sharp point with very faint annulations. Measurements of some structures from five eggs are given in Table 3.

Remarks. Eighty-two additional specimens were found in samples 1, 2a, 2b, 3, 4a, 4d, 4f. 4h and 4i ( Table 1 ) in foliose and squamulose lichen, bark and moss. Macrobiotus caymanensis sp. n. is widely distributed on Grand Cayman.

Etymology. The specific name is a masculine adjective commemorating the Cayman Islands, where the species was collected.

Type repository. The holotype and three paratypes ( SMLA 9401) are deposited in the W.A.K. Seale Museum, Department of Biology and Health Science, McNeese State University in Lake Charles, Louisiana, U.S.A. Four paratypes ( NTCI 9402) are deposited with the National Trust for the Cayman Islands.

Differential diagnosis. Macrobiotus caymanensis sp. n. belongs to the polyopus -group of species, which have in common a pharyngeal bulb with two macroplacoids and a small or absent microplacoid, short claws and egg shells with reticular design with hexagonal mesh ( Pilato 2006). Five species are currently attributed to this group: M. polyopus Marcus, 1928 in Sumatra, M. mandalaae Pilato, 1974 in southern China, M. insularis Pilato, 2006 in the Andaman Islands, M. ocotensis Pilato, 2006 in southern Mexico and M. alvaroi Pilato & Kaczmarek, 2007 in Costa Rica.

Macrobiotus caymanensis sp. n. differs from other known species in the polyopus group in having a shorter buccal tube (28.2 μm long in a M. caymanensis sp. n. specimen 282.1 μm long, 29.2–38.8 μm in specimens of similar length from the other species) and a more posterior stylet support insertion (pt 78.3 in the new species, pt 71.1– 73.4 in the other described species). Macrobiotus caymanensis sp. n. further differs from M. polyopus in having a microplacoid, more robust claws, stronger accessory points and fewer processes on the egg (18 around the circumference and 39 in the hemisphere in M. polyopus , 9–12 around the circumference and 9–13 in the hemisphere in the new species). It differs from M. mandalaae in having a wider buccal tube (pt 12.4 in M. mandalaae and pt 15.7 in the new species), in lacking leg granulation and in having fewer and larger egg process (24–26 around the circumference, 70–75 in the hemisphere, 3.4–4.7 μm high, 3.2–4.5 μm wide in M. mandalaae ; 8.3–20.0 μm high, 12.3– 19.2 μm wide in M. caymanensis sp. n.). Macrobiotus caymanensis sp. n. differs from M. insularis in having fewer and larger egg processes (35 in the hemisphere, 7.7–8.8 μm high and 10.9–13.2 μm wide in M. insularis ). The new species differs from M. ocotensis in lacking leg granulation, in having a wider buccal tube (pt 8.2–10.6 in M. ocotensis and 13.7–18.2 in the new species) and fewer and larger egg processes (25 around the circumference, 100 in the hemisphere, 4.7–6.0 μm high and 4.9–6.0 μm wide in M. ocotensis ). The new species differs from M. alvaroi in having a wider buccal tube (pt 10.1–10.9 in M. alvaroi ) and fewer and larger egg processes (23–26 around the circumference, 100 in the hemisphere, 3.6–6.1 μm high and 3.3–4.1 μm wide in M. alvaroi ).

Figures

FIGURES 13 – 16. Macrobiotus caymanensis sp. n. (13) Cuticular pores (arrows). (14) Buccopharyngeal apparatus. (15) Buccal cavity, with arrows indicating peribuccal lamellae and transverse ridges. (16) Claw, leg II. Scale bars: 13, 15 – 16, 10 μm; 13, 20 μm.

FIGURES 17 – 18. Macrobiotus caymanensis sp. n. (17) Egg. (18) Egg shell with processes and hexagonal areolation. Scale bars: 10 μm.