number and relative sizes of placoids or rod-shaped 

 concretions within the bulbous muscular pharynx can be 

 diagnostic. 



Members of at least six genera {Archechiniscus. 

 Batillipes. Coronarctus, Echiniscoides, Parastygarctus, and 

 Stygarctus) display sexual dimorphism in the shape and 

 location of gonopores. Females possess rosette gonopores 

 located midventrally at considerable distance anterior to 

 the anus. In males, the gonopore is circular or tubular, 

 mid-ventral and only slightly anterior to the anus. In 

 members of the genus Halechiniscus, dimorphism is 

 exhibited in the relation of the length of clavae relative to 

 the lateral cirri. In males, clavae are longer than lateral 

 cirri, while the opposite is true of females. Sex determi- 

 nation in other marine tardigrades is based on presence of 

 mature gametes in the gonad or on the fact that males 

 possess two vasa deferentia while females have a single 

 oviduct. 



Tardig^ada develop directly. Excepting their dispropor- 

 tionately longer cephalic appendages and their reduced 

 number of claws per leg, juveniles resemble miniature 

 adults. Growth in Tardigrada is accomplished through 

 periodic molting of all cuticular structures, including the 

 linings of the foregut and hindgut. Apparently internal fluid 

 pressure is reduced enough to permit defecation, oviposi- 

 tion, and sperm penetration only during an intermolt period. 



Other aspects of the morphology and anatomy of marine 

 tardigrades lie beyond the scope of this presentation. 

 Interested readers are referred to monographs by Marcus 

 (1936), Rudescu (1964), and Ramazzotti (1972), and to a 

 recent review by Renaud-Mornant and Pollock (1971). 



ECOLOGY 



In recent years, ecological studies of marine Tardigrada 

 have focused largely on those living interstitially among 

 grains of sand (Renaud-Debyser 1959a; Schmidt 1968, 1969; 

 Pollock 1970c; Lindgren 1971). Tardigrades are found 

 throughout portions of intertidal beaches which undergo 

 periodic drainage and replenishment of interstitial water. 

 Most interstitial meiofauna, including tardigrades, are 

 absent or uncommon in beaches of fine sand (mean grain 

 diameter less than 300 /im) and in beaches of larger grain- 

 size but where fine silt and debris clog pore spaces and 

 restrict circulation. 



Tardigrada occupy specific portions of littoral beaches 

 creating patterns of zonation both horizontally along the 

 beach surface and vertically within the sediment. A "typical 

 pattern" of species composition and distribution on a single 

 beach becomes evident from studies of temperate, quartz 

 sand beaches. An abundant species and from one to several 

 less common species of Batillipes occupy superficial sand 



(occurring somewhat deeper in beaches under the influence 

 of heavy surf). The abundant Batillipes dominates mid-beach 

 sand while other Batillipes often are relegated to more 

 landward or seaward locations. A comparatively denser 

 concentration of Stygarctus often occurs deeper within the 

 beach approaching the deepest sediments undergoing tidal 

 drainage of interstitial water. 



Less frequently, marine tardigrades are reported from 

 other habitats. Sublittoral specimens have been collected to 

 a depth of 4,700 m (Renaud-Mornant 1974). Their 

 comparative scarcity in most deepwater surveys suggests 

 either that Tardigrada are less successful here than are 

 many other meiofaunal groups or that sampling and/or 

 observational techniques commonly used fail to include such 

 small members of the meiofauna. Certain Tardigrada occur 

 on seaweed ranging from intertidal Enteromorpha and 

 Lichinia to offshore Sargassum. Among the several 

 Tardigrada reportedly living ectocommensally with various 

 other marine invertebrates, Tetrakentron synaptae Cuenot, 

 1892 alone possesses obvious morphological adaptations to 

 such a life style and has been found exclusively in such a 

 relationship. 



COLLECTING METHODS 



A complete discussion of techniques for working with 

 interstitial meiofauna generally and marine Tardigrada 

 specifically may be found in Hulings and Gray (1971). 

 Quantitative extraction of tardigrades from sand requires 

 rigorous procedures since most species are strongly 

 thigmotactic and vigorously resist dislodgment. Anestheti- 

 zation by flooding a small sand sample with 3.5% MgCl2 may 

 be effective for removing Tardigrada from sediments 

 gathered in areas of low to moderate wave activity; 

 however, this technique is not effective quantitatively on 

 samples from "high-energy" beaches (Gray and Rieger 

 1971). Soaking small quantities of sand (e.g., 10 cm' or less) 

 in 10 times that volume of 3.5% ethanol is more effective for 

 anesthetization. This can be followed by three or more 

 rinses of seawater to provide revived and apparently 

 unharmed Tardigrada quantitatively. 



Marine Tardigrada can be preserved well in either 5-7% 

 neutralized Formalin or in 70% ethanol. McGinty and 

 Higgins (1968) described a widely used technique for mount 

 ing marine tardigrades. Specimens preserved in 7% 

 Formalin are transferred to a 1:10 glycerin-Formalin 

 solution which then is allowed to evaporate to glycerin (a 

 glycerin-alcohol solution works for specimens preserved in 

 alcohol). Tardigrades prepared by this technique can be 

 mounted in glycerine, glycerine jelly, or Hoyer's medium. 

 Phase contrast microscopy is necessary for fine observa- 

 tions, especially if Hoyer's medium is used. 



