Tanaidacea: Families

Kim Larsen

Gulf Coast Research Laboratory
Department of Coastal Sciences
Ocean Springs
MS-39564-7000, USA
tanaids@hotmail.com

Introduction

Tanaidaceans are a group of small malacostracan crustaceans, belonging to the superorder Peracarida. Currently more than 700 species exist within the Tanaidacea but the order is estimated to contain several thousand species (Dojiri & Sieg, 1997). Tanaids range from 1 mm to several cms, but the majority are around a few mm in length.
 
The order is divided into four suborders: Anthracocaridomorpha, Apseudomorpha, Neotanaidomorpha and Tanaidomorpha (Sieg, 1983). The suborder Anthracocaridomorpha is known from fossils only and not treated in this key. Members of the different suborders have characteristic life-styles. Neotanaidomorphans are free-living, tanaidomorphans are tube-dwellers and the apseudomorphans are mostly burrowers (Sieg, 1983).

While the vast majority of tanaidaceans are marine, a small number of species are found in brackish water. They can occur in high densities. In shallow water, they often exceed 10,000 individuals/m}{\fs24\super 2}{\fs24 and populations sizes above 140.000 individuals/m2 have been reported (Delille et al., 1985). However, tanaids have their greatest ecological importance on the abyssal plain, where they are often the most abundant crustaceans (Marshall, 1979) and, on the level of order, the dominant and most diverse faunal component, rivalling that of polychaetes (Cosson et al., 1997). Estimates of their abundance range from 13% (Cosson et al., 1997), 19% (Wolff, 1977) to 22% (Sokolova, 1972) of the total fauna. The continental shelf and slope also contain numerous tanaids (Sieg & Heard, 1989).

The abundance of tanaids is strong evidence of their ecological importance. Despite this, they have been neglected in most ecological surveys (Baldinger & Gable, 1996). This ecological ignorance of the Tanaidacea is caused by the immense difficulties associated with identifying these animals. Identifying tanaids is notoriously difficult and, in particular members of the suborder Tanaidomorpha present problems (Larsen, 2001). While this is partly due to their small size, the identification of tanaidomorphans is particularly confounded by the high sexual and ontogenetic variation that they display. This polymorphism is a consequence of a peculiar reproductive strategy involving protegynous hermaphroditism (Buckle-Ramirez, 1965). Since the majority of taxonomic studies have ignored this variation, the diagnostic characters of tanaid taxa are often misleading.

Therefore the systematics of Tanaidacea is not fully resolved at this stage and the families are thus not very stable or well defined. However, while some families might change in the future, a key to the currently valid families are presented here for the first time since Sieg and Winn in 1978. The systematics follows that of Larsen & Wilson (in press) for the Paratanaoidea and that of Gutu & Sieg (1999) for other families. A few new discoveries are also included in this work. The families can, however, be identified in this key using a minimum of character combinations. Due to the small size of most Tanaidacea and particularly members of the suborder Tanaidomorpha, identification to family level cannot always be achieved without dissection of mouthparts.

The observant reader will note that the family Tanapseudidae Bacescu, 1978a, is not included in the key. The Tanapseudidae consisted until recently of only two genera Paradoxapseudes Gutu, 1991 and Tanapseudes Bacescu, 1978. Recently Bamber (2000) removed Tanapseudes to the Spyrapidae and the Paradoxapseudes is currently being transferred to the Kalliapseudidae (pers. comm., Heard & Gutu).

Due to the systematical difficulties mentioned above, it is possible that some species will not key out to the correct family. Users of this key should be aware of the unstable systematics of Tanaidacea and it is my hope that they will report any potential discrepancies or inconsistencies to the author on tanaids@hotmail.com.

Monographs Monograph and Interactive Keys Interactive Key

Tanaidacea Families

Monograph Interactive Key

Agathotanaidae

Monograph Interactive Key (not available)

Anarthruridae

Monograph Interactive Key (not available)

Anuropodidae

Monograph Interactive Key (not available)

Apseudellidae

Monograph Interactive Key (not available)

Apseudidae

Monograph Interactive Key (not available)

Colletteidae

Monograph Interactive Key (not available)

Gigantapseudidae

Monograph Interactive Key (not available)

Kalliapseudidae

Monograph Interactive Key (not available)

Leptocheliidae

Monograph Interactive Key (not available)

Leptognathiidae

Monograph Interactive Key (not available)

Metapseudidae

Monograph Interactive Key (not available)

Neotanaidae

Monograph Interactive Key (not available)

Nototanaidae

Monograph Interactive Key (not available)

Numbakullidae

Monograph Interactive Key (not available)

Pagurapseudidae

Monograph Interactive Key (not available)

Parapseudidae

Monograph Interactive Key (not available)

Paratanaididae

Monograph Interactive Key (not available)

Pseudotanaidae

Monograph Interactive Key (not available)

Pseudozeuxoidae

Monograph Interactive Key (not available)

Sphyrapidae

Monograph Interactive Key (not available)

Tanaellidae

Monograph Interactive Key (not available)

Tanaidae

Monograph Interactive Key (not available)

Tanzanapseudidae

Monograph Interactive Key (not available)

Whiteleggiidae

Monograph Interactive Key (not available)

Cite this publication as: Larsen, K. (2002 onwards). 'Tanaidacea: Families.' Version: 2 October 2002. http://crustacea.net/.