Deckenia mitis Hilgendorf, 1898

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

16. Deckenia mitis Hilgendorf, 1898 (Fig. 188, plate XVI)

Deckenia mitis Hilgendorf, 1898: 24 , fig. 8; Ortmann, 1902: 306; Bott, 1955: 221, fig. 5, pl. 1 fig. 2a–d; Ng et al., 1995: 583–585, figs 1A, 2, 3, tables 1, 2; Cumberlidge, 1997: 574; 1998: 195.

Type material examined: TANZANIA: Tabora, Wembere Steppe near Tabora, male (cw 48, cl 38 mm, lectotype, designated by Bott 1955: 221), 6–7.vi.1892 (F. Stuhlmann) ( ZMB 9444 ) .

Additional material examined: TANZANIA: Singi (= Zingi ), Dodoma, female, 25 v.1926 (A. Loveridge, Smithsonian­Chrysler Expedition) ( USNM 82330 ) ; Dodoma, female, 10 v.1926 (A. Loveridge, Smithsonian­Chrysler Expedition) ( USNM 82331 ) ; Tanga, female (Jierra) ( USNM 30030 ) ; Taro, adult male, (cw 40.9 mm), juvenile (cw 26.6 mm) (O. Neumann) ( ZSM 1235 /1); South Pare Mountains ( T. R. Williams) ( NMU TRW­ EA 62.34); Amani, Usambara ( T. R. Williams) ( NMU TRW1964.04 ) ; Ruaha River , Iringa­ Dodoma road (Joy) ( NMU TRW1975.10 ) ; Kiono Forest , ( T. R. Williams) ( NMU TRWIII.1990.a) . KENYA: Taveta ( T. R. Williams) ( NMU TRW1968.13 ) ; Murangía (formerly Fort Hall ), (Joy) ( NMU TRW07.2001 .f) .

Diagnosis. Exorbital tooth low, blunt; infraorbital margin lined with short, flat, peglike teeth; epibranchial tooth small, blunt­tipped; ischium of cheliped with low blunt tooth; lower margin of merus of cheliped lined with rounded teeth/granules; upper margin of merus of cheliped with blunt tooth; anterior inferior margin of merus of cheliped with small, rounded, distal tooth; outer margin of carpus of cheliped with two low teeth; first and second carpal teeth on inner margin of carpus of cheliped subsequal rounded teeth; inner/outer margins of carpus of p2 lined with low subdistal granules; dorsal margin of merus of p2–p5 with blunt subdistal tooth; interior margin of propodus of p2–p5 with row of small, blunt teeth; terminal article of gonopod 1 clearly separated from subterminal segment by distinct line; proximal region of terminal article slim, subconical, tapering to cylindrical distal part. Chelipeds of adult males equal­sized, not markedly heterochelous.

Distribution. Tanzania and Kenya. The type locality is Wembere Steppe near Tabora (5°02’S, 32°50’E) in Tanzania, and Ng et al. (1995) reported on material from Kilimantinde (5°52’S, 34°55’E), Dar es Salaam, and at a non­specific locality in southern Tanzania near Lake Malawi (as Nyassa Lake). The combination of all known localities for D. mitis ( Marijnissen et al. 2005) indicates that this species is found in both inland and coastal localities in Tanzania (Dodoma, Tanga, Iringa, Mount Meru, Amani, South Pare Mountains, Kibno, Kilimantinde and Dar es Salaam) and in Kenya (Murangía, Taveta and Mombasa).

Remarks. Photographs of the whole animal are available in Bott (1955), and illustrations of the gonopods, the mandibles and the unusual mouthparts of Deckenia mitis are available in Ng et al. (1995).

Natural history and conservation status. Deckenia mitis prefers marshes and lowlying wetlands, and is an air­breathing amphibious species. Williams et al. (1964) provided some observations on the habitat of D. mitis caught in an arid area of northern Tanzania close to Mount Meru. Specimens of D. mitis were collected in warm stagnant surface waters, and never in the cooler streams flowing down mountain slopes. Deckenia mitis and P. obesus share the same habitat and burrow deeply into the soil at the waters edge, often causing extensive damage to drainage ditches. The conservation status of D. mitis is categorized as vulnerable (VU) ( Table 4) because despite its wide range of occurrence well above the threshold for vulnerable (VU), it may have an increasingly restricted area of occupancy due to declining wetlands in the region that would qualify for vulnerable (VU) status. It is difficult to estimate the population status and trends of this species, but it is likely that its population is declining based on indirect factors such as the lack of recent specimens from many parts of its range, its poor representation in museum collections and increasing habitat disturbance from loss of wetlands associated with growing human populations in the region ( IUCN 2004). Marijinissen et al. (2005) argued for the upgrading of the conservation status of D. mitis to VU based on new field studies and new population estimates.