Eutardigrada: Distribution at Eniwetok Atoll, Marshall Islands1 RONAL H. MEHLEN 2

ABSTRACT: Six species of Eutardigrada were found at Eniwetok Atoll, represent­ ing two families (Macrobiotidae and ) and three genera (Hypsibius, Macrobiotus, and ). Hypsibius (Calohypsibius) truncatus was found in sand samples from the thalassosupralittoral fringe at Runit and Eniwetok islets. H. (Isohypsibius) augusti was found in sand of the thalassosupralittoral fringe on Engebi Islet. Macrobiottts allani was found on Muti Islet; M. harmsUlorthi on Bogallua, Engebi, Roijoa, Eniwetok, Muti, and Igurin islets; M. richtersi on Japtan and Muti islets; all three species from tree-borne lichens and mosses. Milnesium tardigradum was commonly recovered from lichens and mosses on Muti and Igurin islets. The total number of individuals collected was small compared to collections in the temperate zone. No morphological anomalies were noted.

THE FAUNA of Micronesia has promptly brought to the laboratory on Eniwetok been neglected; the prime objective of this Islet and processed according to the methods of study, therefore, was to extend the range of Mehlen (1969a, b, and in press). After being collecting to provide more extensive data on soaked overnight in tap water in beakers or tardigrade distribution, and the secondary ob­ petri dishes, the samples were squeezed out jectives were to acquire specimens for long-term over a petri dish to recover the , studies on comparative morphology, intraspe­ which were then killed and fixed by heating cific variability, and life history. on an electric hot plate. Under examination with a binocular dissection microscope the ani­ mals were picked out with an Irwin loop and METHODS stored in vials of 70 percent ethanol prior to After a preliminary survey of the atoll, 11 subsequent study as glycerol or lactophenol islets were selected for study on the basis of mounts. accessibility by motorboat and of habitat diver­ sity. These islets include those with topography DESCRIPTION OF SPECIES severely, partially, or very slightly damaged Hypsibius (Calohypsibius) truncatus Thulin during W orId War II, atomic bomb testing, or Diagnosis both of these destructive events. The native Cuticle unornamented. Body length small. names of the islets follow the Decision List Claws small; outer claw almost twice as large 4414 of the Board on Geographical Names and as inner claw; primary branch of outer claw the code names used by the military are included twice as large as secondary branch. Gullet nar­ in parentheses. row, moderate in length. Apophyses large. Sand, lichen, and moss samples were Pharynx oval. Macroplacoids three in number,

1 This paper is a result of research at the Eniwetok ovoid in shape; first shorter than second, third Marine Biology Laboratory operated by the U.S. the longest. Microplacoid absent. Distance from Atomic Energy Commission, whose support is grate­ stylet support to anterior margin of pharynx fully acknowledged. Manuscript received 1 March equal to half the gullet width. 1971. 2 Texas A. & M. University, Biology Department, Atoll Distribution College Station, Texas 77843. Present address: Bow­ man Gray School of Medicine, Microbiology Depart­ This species was occasionally recovered from ment, Winston-Salem, North Carolina 27103. sand samples taken at the supralittoral fringe on 223 224 PACIFIC SCIENCE, Volume 26, April 1972

Runit Islet (site Yvonne) and Eniwetok Islet with two mouth rings, each with eight lamellae. (site Fred). At Eniwetok Islet it was rarely Gullet moderate to wide, length tending to be accompanied by very small numbers of Macro­ about five times the width. Macroplacoids rod­ biotus harmsworthi. shaped, three in number, relative lengths vari­ able but third usually longest and second short­ est, third often with slight terminal knob. Hypsibius (Isohypsibius) augusti Murray Microplacoid large, located midway between Diagnosis third macroplacoid and posterior margin of pharynx, comma-shaped. Distance from stylet Cuticle unornamented. Body length small. supports to anterior margin of pharynx equal to Claws small. Ocelli anterior to furcae. Gullet or slightly less than gullet width. narrow and moderate in length. Pharynx slightly oval. Macroplacoids three in number, Atoll Distribution rod-shaped; first slightly shorter than second, This species was rarely recovered from the third the longest. Microplacoid absent. Distance supralittoral fringe at Bogallua Islet (site from stylet supports to anterior margin of Alice), Engebi Islet (site Janet), Roijoa Islet pharynx equal to about half the gullet width. (site Ursula), and Eniwetok Islet (site Fred). Atoll Distribution On Muti Islet (site David) and Igurin Islet (site Glenn) it was commonly found in lichen, This species was occasionally recovered from but at Igurin, in moss also. sand samples taken along the seaward supra­ littoral fringe on Engebi Islet (site Janet), being the only tardigrade in the samples. Macrobiotus richtersi Murray Diagnosis Macrobiotus allani Murray Cuticle unornamented. Body length small to Diagnosis medium. Claw moderate size, with lunule, pri­ mary branch with accessory spines. Mouth with Cuticle unornamented. Body length small. one mouth ring, lamellae present. Gullet mod­ Claws moderate sized, secondary branch half as erately wide. Apophyses large. Macroplacoids long as primary; lunule simple. Mouth with one rod-shaped, three in number, first and third mouth ring, lamellae present. Gullet narrow nearly equal but second always shortest, third and short. Pharynx nearly round. Macroplacoids with terminal knob: Microplacoid small. Dis­ round, three in number. Microplacoid very tance from stylet supports to anterior margin of small, located very close to third macroplacoid. pharynx about one-third the gullet width. Distance from stylet supports to anterior margin of pharynx about equal to three times the width Atoll Distribution of gullet. This species was commonly collected from tree-borne lichens on Japtan Islet (site Broce) Atoll Distribution and Muti Islet (site David). This species was rarely encountered in lichen samples from Muti Islet (site David), accom­ panied by numerous individuals of Macrobiotus Milnesium tardigradum Doyere harmsworthi and Milnesium tardigradum. Diagnosis Cuticle unornamented. Body length from Macrobiotus harmsworthi Murray small to large. Basal claw equal to or slightly shorter than the terminal claw; basal claw with Diagnosis one or two secondary branches, depending on Cuticle unornamented. Body length small to instar. Gullet very wide, rather short; mouth moderate. Claws moderate sized, with lunule; surrounded by six oral papillae. Pharynx primary branch with accessory spines. Mouth elongated, striated, without placoids. Stylets Distribution of Eutardigrada at Eniwetok-MEHLEN 225 small, somewhat arrow-shaped. Cephalic papil­ stable substratum because of wind and wave lae located rather laterally, two in number. restructuring of the area. The fauna of this fringe appeared best developed during late Atoll Distribution summer and early autumn, which are periods Found both in moss and lichen, this species of higher cloudiness and rainfall but lesser was commonly recovered from Muti Islet (site wind intensity. David) and Igurin Islet (site Glenn). In contrast to the thalassosupralittoral fringe, the lichen- and moss-associated faunas were composed of many genera, species, and individ­ DISCUSSION uals. The phytophilic tardigrades included: With limited distribution and paucity of Milnesium tardigradum, Macrobiotus allani, M. numbers compared to collections in the temper­ harmsworthi, and M. richtersi. The distribution ate zone, the genus Hypsibius was rather poorly from islet to islet probably reflects nothing on represented. Yet it did appear as the dominant tardigrade distribution characteristics per se but, tardigrade of the thalassosupralittoral fringe rather, reflects the absence of mosses and lichens and its presence there is surprising because on most of the islets; mosses and lichens became distribution is, in general, halo­ more scarce the closer one came to the islets phobic. However, it may be significant to note used during the testing of atomic weaponry. In that the only marine eutardigrade (H. stenosto­ spite of the potential genetic damage from the mus) is in this genus. The absence of Hypsibius atomic testing, no morphological anomalies from the lichens and mosses is as surprising as were noted in the tardigrades. its appearance in the thalassosupralittoral fringe and neither is presently very well understood. LITERATURE CITED M. harmsworthi was present in the thalasso­ supralittoral fringe only during the rainy period MEHLEN, R. H. 1969a. New Tardigrada from in autumn; when the trade winds became estab­ Texas. Amer. MidI. Nat. 81(2) :398-404. lished in December, this species no longer was ---. 1969b. Tardigrada: and dis­ collected. The thalassosupralittoral fringe ap­ tribution in Costa Rica. Trans. Amer. Micr. peared to be a precarious place for the develop­ Soc. 88(4) :498-505. ment of a tardigrade fauna, being subject to ---. In press. Tardigrada. In Peter Gray high-intensity tropical sunlight, salt spray, and [ed.] Encyclopedia of microscopy and micro­ variable salinity; dependent on the wind-driven technique. Reinhold Publishing Corporation, spray and the rainfall; and possessing an un- New York.