Family BATILLIPEDIDAE Ramazzotti, 1962

Batillipes sp. female, habitus

© Copyright Dr S. Claxton, Camden, NSW

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Introduction

This marine arthrotardigrade family is the most highly derived of all heterotardigrades. Batillipedids lack the slow bear-like gait of most tardigrades and moved very swiftly around and between sand grains. They are extremely well adapted to all kinds of interstitial habitat and even though they are most common in intertidal beaches, they can also be found in subtidal coarse sediments worldwide.

Batillipedids have reduced the telescopic segmentation in the leg only to the femur-tibial link. This telescopic link, however, functions as a piston and the tibia with the toe-carrying foot can be fully retracted into the femur. The leg bears, on each foot, four (first instar larva) or six toes (adult), each composed of a tubular stalk of different length. Each toe terminates in a sucking disc, which has no adhesive glue, but works like a plumber's sucking disc. There is only one genus, Batillipes, in the family after the other genus with sucking rod-shaped toes, Orzceliscus, has been removed to its own family. The different lengths of the toes (giving symmetrical or asymmetrical feet) and the shape of the toe disc (spade-shaped to round) have been used to distinguish species. Other species have been distinguished from each other primarily by the shape or absence of the caudal apparatus, the relative length and shape of the cephalic cirri and primary clava, and the shape of the lateral body projections (Pollock 1971). However, McKirdy (1975) and Kristensen (1978) showed that especially the caudal apparatus (spike(s)) may vary with salinity or other abiotic factors. In his revision of six Batillipes species from Florida, McKirdy (1975) used a very sophisticated model to distinguish species, including features of the bucco-pharyngeal apparatus, pillar patterns of the dorsal cuticle and the features of the female gonopore. The systematic value of the presence/absence of eyes in Batillipes has been questioned, because the so-called lipoid eyes disappear immediately after fixation as does the calcium carbonate encrusted bucco-pharyngeal apparatus. However, the shape and the location of the eyes in live specimens of tidal Batillipes is, in fact, one of the best characters for distinguishing species. It is, therefore, strongly recommended that Batillipes species be observed alive, before fixation.

Batillipes is the most widespread and speciose marine tardigrade genus. Twenty species are described currently, mostly from sandy beaches, but at least 20 other undescribed species are known, especially from subtidal carbonate sand. The family is never recorded from the deep-sea.

The Australian Batillipes species fall into two categories: 1) species from coral sand which are cosmopolitan, e.g. B. similis, B. tubernatis and B. littoralis and 2) species from quartz sand which are probably endemic to Australia. These latter species are not found in the usual Batillipes habitat in the mid tidal zone, but only in the lower surf area of the beach. The Australian species show adaptations to the surf with development of cuticular stabilisers between the legs as only seen elsewhere in the genera Florarctus and Wingstrandarctus.

Ecological Descriptors

Marine.

General References

Kristensen, R.M. 1978. Notes on marine heterotardigrades. 1. Description of two new Batillipes species, using the electron microscope. Zoologischer Anzeiger 200(1/2): 1-17

McKirdy, D.J. 1975. Batillipes (Heterotardigrada): Comparison of six species from Florida (USA) and a discussion of taxonomic characters within the genus. Memorie dell'Istituto Italiano di Idrobiologia 32(Suppl.): 177-223

Pollock, L.W. 1971. On some British marine Tardigrada, including two new species of Batillipes. Journal of the Marine Biological Association of the United Kingdom 51: 93-103

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