Alpheus

The Family Alpheidae Rafinesque, 1815


Arthur Anker, A. Rich Palmer and Nancy Knowlton

        The caridean shrimp family Alpheidae presently includes 46 genera (see list of genera below) and about 600 valid species.   It is numerically one of the most important and ecologically diverse families of decapod crustaceans.   Most alpheids occur in marine, shallow tropical and subtropical waters, especially on coral reefs, although some species also live in temperate waters, as far north as Alaska, Norway and Hokkaido, and as far south as New Zealand, Cape Horn, and Amsterdam and St. Paul Islands in the southern Indian Ocean.   A few species have colonized oligohaline or freshwater habitats, while others are stygobitic or stygophilic, living in caves or cracks of anchialine pools.   Many alpheids also live in mangroves and estuarine areas, as well as in the deep sea, with maximum recorded depths being just over 1000 m.

       All alpheids are strictly benthic and rarely if ever swim; some heavily calcified forms (e.g., species of the most speciose genera Alpheus and Synalpheus) resemble mini-lobsters more than typical shrimps, and thus appear to have evolved towards a "reptantian life style".   On marine hard and soft substrates, alpheids are among the most frequently encountered shrimps, and are often the dominant decapods (except perhaps for crabs) both in number of species and number of individuals.   Endolithic species play an important part in the biological erosion of corals and other hard rocks.   Numerous alpheids live in permanent symbiosis with other marine organisms, including sponges, cnidarians, molluscs, echinoderms, other crustaceans, echiurans and gobiid fishes.   Biological aspects of these associations, such as inter-specific communication, protandric hermaphroditism, host protection and eusociality are fascinating.   For these reasons, alpheids are particularly attractive to field biologists.

        The family Alpheidae is also morphologically one of the most diversified decapod families.   Alpheid chelipeds come in a remarkable variety of forms, ranging from small, unspecialized, symmetrical chelipeds that are not much different from those of other caridean shrimps, to greatly enlarged, often highly asymmetrical chelipeds, sometimes very specialized and odd in shape.   Cheliped polymorphism and sexual dimorphism occur in many genera.  The evolutionary origins of these unusual cheliped forms remain decidedly obscure.

        In most species (Alpheus, Synalpheus and three smaller genera), one of the first pereiopods (= chelipeds) bears a voluminous claw with a complex snapping mechanism on the fingers: the famous snapping claw.   The snapping claw is a powerful and multifunctional tool that is used as both a defensive and aggressive weapon in interspecific and agonistic interactions.   The loud snap resulting from the rapid closure of the dactylus (movable finger of the claw) is one of the most audible of underwater noises, detectable as far away as 1 km.   The closure of the dactylus is among the most rapid movements in the animal kingdom.   The crackling noise produced by numerous snapping shrimps may interfere with submarine sonar system, which resulted in extensive investigations following World War II to the present day.   Most early workers studying the snapping mechanism in Alpheus and Synalpheus believed that mechanical impact of the dactylus onto the fixed finger (pollex) caused the snapping sound.   However, recent studies in Alpheus heterochaelis revealed that the snapping sound results from implosion of a cavitation bubble caused by water rapidly ejected from a socket in the fixed finger by a plunger (specialized tooth) on the dactylus (Versluis et al., 2000).   Even more curious, a byproduct of this implosion is a short flash of light.   This mode of light production - appropriately named "shrimpoluminescence" - is truly unique among animals (Lohse et al., 2001).   However, some endolithic Alpheus species may not produce a directed water jet and instead may use the mechanical impact of the dactylus to split off substrate particles.   The snapping mechanism of Synalpheus species remains to be investigated.

        The alpheid frontal region is also unique among caridean shrimps and Decapoda in general.   In the vast majority of species, the eyes are covered dorsally by frontal projections of the carapace, forming so-called orbital hoods.   The orbital hoods are particularly well developed in Alpheus, covering the eyes not only in dorsal and lateral view, but sometimes also in frontal view.   In many other species, orbital hoods conceal the eyes dorsally, and usually laterally, but remain open frontally.   A few species, however, like species of Athanas and Automate have partly or even completely exposed eyes.

        The taxonomy of the Alpheidae is difficult.   Many genera, e.g., Alpheopsis and Leptalpheus, need redefinitions and no less than seven genera are currently in process of description (see list below).   Despite extensive taxonomic effort, all larger genera are yet to approach revisions at species level.   Cryptic species pairs and complexes occur in several genera, notably in the two most specious genera Alpheus (with over 300 species) and Synalpheus (with 160 species).   To date, most of these complexes remain unresolved, especially in the vast Indo-West Pacific region.   Intraspecific variation, including cheliped polymorphism, further complicates alpheid systematics.



List of all presently known alpheid genera

(updated in July 2008)

1. Acanthanas Anker, Poddoubtchenko and Jeng, 2006 (1 species, IWP)

2. Alpheopsis Coutière, 1896 (>30 species, WW) [generic complex]

3. Alpheus Fabricius, 1798 (>>300 species, WW)

4. Amphibetaeus Coutière, 1896 (1 species, IWP)

5. Arete Stimpson, 1860 (6-7 species, IWP)

6. Aretopsis De Man, 1910 (1-2 species, IWP)

7. Athanas Leach, 1814 (>30 species, IWP, EA) [generic complex]

8. Athanopsis Coutière, 1897 (5 species, IWP)

9. Automate De Man, 1888 (>12 species, WW) [generic complex]

10. Bannereus Bruce, 1988 (2 species, IWP)

11. Batella Holthuis, 1955 (3 species, IWP)

12. Bermudacaris Anker and Iliffe, 2000 (4 species, WW except EP)

13. Betaeopsis Yaldwyn, 1971 (3 species, IWP) [= Hamalpheus Bruce and Iliffe, 1991]

14. Betaeus Dana, 1852 (15 species, WW) [generic complex]

15. Coronalpheus Wicksten, 1999 (2 species, IWP, EP)

16. Coutieralpheus Anker and Felder, 2005 (1 species, WA)

17. Deioneus Dworschak, Anker and Abed-Navandi, 2000 (1 species, EA)

18. Fenneralpheus Felder and Manning, 1986 (WA, 2 species)

19. Harperalpheus Felder and Anker, 2007 (1 species, WA)

20. Jengalpheops Anker and Dworschak, 2007 (1 species, IWP)

21. Leptalpheus Williams, 1965 (>12 species, WW except WA) [generic complex]

22. "Leptathanas" De Grave and Anker, submitted (1 species, EA)

23. Leslibetaeus Anker, Poddoubtchenko and Wehrtmann, 2006 (1 species, EA)

24. Metabetaeus Borradaile, 1898 (2-3 species, IWP)

25. Metalpheus Coutière, 1908 (>3 species, WW)

26. Mohocaris Holthuis, 1973 (1 species, WA)

27. Nennalpheus A.H. and D.M. Banner, 1981 (2 species, IWP)

28. Notalpheus Méndez and Wicksten, 1982 (1 species, EP)

29. Orygmalpheus De Grave and Anker, 2000 (1 species, IWP)

30. Parabetaeus Coutière, 1896 (3-4 species, WW) [= Neoalpheopsis Banner, 1953]

31. Pomagnathus Chace, 1937 (1 species, EP)

32. Potamalpheops Powell, 1979 (13 species, WW)

33. Prionalpheus A.H. and D.M. Banner, 1960 (8 species, WW)

34. Pseudalpheopsis Anker, 2007 (1 species, WA)

35. Pseudathanas Bruce, 1983 (1 species, IWP)

36. Pterocaris Heller, 1862 (1 species, IWP)

37. Racilius Paulson, 1875 (1 species, IWP)

38. Richalpheus Anker and Jeng, 2006 (2 species, IWP)

39. Rugathanas Anker and Jeng, 2007 (2-3 species, IWP)

40. Salmoneus Holthuis, 1955 (>30 species, WW) [generic complex]

41. Stenalpheops Miya, 1997 (2 species, IWP)

42. Synalpheus Bate, 1888 (>>160 species, WW) [incl. Zuzalpheus Ríos and Duffy, 2007]

43. Thuylamea Van Xuan, 2001 (1 species, IWP)

44. Vexillipar Chace, 1988 (1-2 species, IWP)

45. Yagerocaris Kensley, 1988 (1 species, WA)

46. "Triacanthoneus" Anker, in prep. (2 species, WA, EP)