DECKENIIDAE Ortmann, 1897

Reed, Sadie K. & Cumberlidge, Neil, 2006, Brachyura: Potamoidea: Potamonautidae, Platythelphusidae, Deckeniidae (), Zootaxa 1262 (1), pp. 1-139 : 1-139

FAMILY DECKENIIDAE Ortmann, 1897

Type genus. Deckenia Hilgendorf, 1869 , by original designation.

Diagnosis. Carapace sub­circular, texture smooth, postfrontal crest lacking; front with protruding medial lobe; antennules folding vertically. Paired efferent respiratory channel openings at tips of long upwardly­directed tubes, openings level with the frontal margin, either side of medial frontal lobe; respiratory tubes formed by partly rolled elongated endopod of first maxilliped applied to corresponding grooved channels in endostome. Medial part of lower orbital margin deflected diagonally to meet edge of elongated endopod of first maxilliped close to frontal margin. Merus of third maxilliped with broadlyrounded anterolateral margin; mandibular palp 2­segmented, terminal segment simple; anterior sternum slim, sternite s4 narrow; abdominal segment a1 completely concealed by posterior margin of carapace (visible abdomen appearing to have only 6 parts: a2–a6 plus telson (a7); terminal article of gonopod 2 extremely long, flagellum­like, equal in length to subterminal article of gonopod 2.

Distribution. Somalia, Kenya, Tanzania. An updated account of the distribution of Deckenia is available in Marijnissen et al. (2005).

Remarks. This unusual East African family comprises a single genus with two species. Bott (1955) mistakenly attributed authorship of this family to Bott (1955) that was corrected to Ortmann (1897) by Ng et al. (1995). This family was revised by Ng et al. (1995) who provided detailed illustrations of the carapace and gonopods of both species. For this reason these characters have not been redrawn here, but photographs of both species have been included (Plates XV and XVI).

Natural history and conservation status. The Deckeniidae are semi­terrestrial crabs that dig burrows into the banks of rivers, ponds and marshes (S. Marijnissen, pers. comm.). The highly arched, untoothed carapace and modified anterior respiratory openings of Deckenia are the hallmarks of those species of semi­terrestrial freshwater crabs that regularly breathe air ( Ng et al. 1995).

Deckenia Hilgendorf, 1869 (Figs. 187–188, plates XV, XVI)

Type species. Deckenia imitatrix Hilgendorf, 1869 .

Deckenia Hilgendorf, 1869a: 2 ; 1869b: 77; 1898: 23; Rathbun, 1906: 69; 1921: 434; Balss, 1929: 353; Chace, 1942: 225; Ng et al., 1995: 582–583.

Diagnosis. As for family.

Distribution. Somalia, Kenya, Tanzania.

Remarks. This genus was recently reviewed by Ng et al. (1995) who provided detailed comparisons between the two species. Bott (1955) separated D. imitatrix from D. mitis by differences in five characters: the form of the exorbital tooth, the armature of the ischium, merus and carpus of the cheliped, and the shape of the terminal segment of gonopod 1. Bott (1955) provided whole animal photographs of both species and sketches of their first gonopods. Differences between the two species were tabulated by Ng et al. (1995) who added new characters and provided illustrations of the gonopods, the mandibles and the mouthparts of the two species.