Durckheimia De Man, 1889

Ahyong, Shane T. & Brown, Diane E., 2003, Description of Durckheimia lochi n. sp., with an annotated checklist of Australian Pinnotheridae (Crustacea: Decapoda: Brachyura), Zootaxa 254, pp. 1-20 : 2-4

Durckheimia De Man, 1889

Durckheimia de Man, 1889 : 422 [Type species: D. carinipes de Man, 1889, by monotypy and original designation. Gender: feminine].

Pinnotheropsis Kubo, 1939: 57 [Type species: P. yo ko ta i Kubo, 1939, by monotypy and original designation. Gender: feminine].

Dürckheimia . — Tesch, 1918: 245, 246, 287. — Balss, 1922: 140 [misspelling].

Duerckheimia . — Guinot, 1967: 279 [misspelling].

Diagnosis of females (males unknown). Carapace subtrapezoid to subcircular, well calcified; regions undefined; dorsum with or without longitudinal median carina; front strongly produced, completely obscuring eyes in dorsal view, with distinct median notch. Third maxilliped endopod with ischium and merus indistinguishably fused; palp 2­ or 3­segmented; propodus longer than carpus; dactylus (when present) digitiform, inserted near midlength of ventral margin of propodus. Chelae symmetrical. Walking legs similar and symmetrical from left to right; dactyli falcate with spiniform apex.

Included species. Third maxilliped with 3­segmented palp: D. caeca Bürger, 1895 from Palau (host: Lima squamosa Lamarck , Limidae ); D. carinipes de Man, 1889 from the Red Sea (host unknown); D. lochi n.sp. from Australia (hosts: Ctenoides ales (Finlay) , Lima lima vulgaris (Link) , Limidae ); and D. yokotai ( Kubo, 1939) n.comb. from Japan (hosts: Lima sowerbyi Deshayes (Limidae) , Chama reflexa Reeve (Chamidae) . Third maxilliped with 2­segmented palp: D. besutensis Serène, 1967 , from Peninsular Malaysia (host: Lithophaga sp., Mytilidae ).

Remarks. Kubo (1939), apparently unaware of de Man’s (1889), Bürger’s (1895) and Balss' (1922) papers dealing with Durckheimia , described a new genus and species from Japan, Pinnotheropsis yokotai . Like Durckheimia , Pinnotheropsis was characterised by a carapace with a longitudinal median carina and strongly produced, upturned margins. Sakai (1955) synonymised P. y o k o t a i with D. caeca and therefore Pinnotheropsis with Durckheimia . Although we concur with the synonymy of Pinnotheropsis with Durckheimia , we believe Sakai (1955) was incorrect to synonymise P. y o k o t a i with D. caeca . Based on comparison of the account and figures of D. caeca by Bürger (1895) with that of P. y o k o t a i by Kubo (1939) and Sakai (1976, as D. caeca ), Kubo’s species is clearly distinct, and is herein removed from synonymy. Durckheimia yokotai n. comb. differs from D. caeca in the following features: 1) the median carina of the carapace is interrupted by a distinct notch instead of being entire; 2) the anterolateral margins of the carapace are more strongly rounded; 3) the median frontal notch of the carapace is relatively broad and Ushaped instead of narrow and slit­like; and 4) the dactylus of the third maxilliped palp distinctly overreaches instead of just reaching the apex of the propodus. Balss's (1922) record of D. caeca from Japan requires verification; it is probably based on D. yokotai .

Recent revisionary studies on the Pinnotheridae (e.g. Manning 1993a, b, c, Campos 1989, 1990, 1996, 2002), following Bürger (1895), have increasingly focussed on limb segment proportions, segmentation and morphology of the third maxilliped, and features of the carapace. Principally on the basis of segmentation of the third maxilliped, several recent studies have suggested heterogeneity within Durckheimia (see Manning 1993b, Campos 1996) to the effect that D. besutensis should be excluded from the genus.

Serène (1967) acknowledged the atypical characters of his species, but in determining its generic placement, focussed on the subtrapezoid carapace shape and distinctive frontal carapace margin that united D. besutensis with other species of Durckheimia . As in other species of the genus, the frontal carapace margin of D. besutensis bears a distinct median notch and is strongly produced, completely obscuring the eyes in dorsal view. Serène (1967) and Campos (1996) together indicated that Durckheimia besutensis differs from congeners in having the exopod of the third maxilliped with concave instead of convex margins and a 1­ instead of 2­segmented flagellum, the presence of a knob or ridge and strong concavities (‘fausse orbite’) dorsolateral to the orbits, distinctly pitted or eroded instead of generally smooth carapace surfaces, subcylindrical meri of the walking legs, and most importantly the 2­ instead of 3­segmented third maxilliped palp, the absence of a median carina on the carapace, and the absence of upturned lateral and posterior carapace margins.

The median carina of the carapace is broad and blunt in D. carinipes , uninterrupted and cristate in D. caeca , and cristate but interrupted in D. yokotai and D. lochi n.sp. Durckheimia carinipes , D. caeca , D. lochi , and D. yokotai all share a 3­segmented third maxilliped palp (probably plesiomorphic) and uniquely share the median carina and strongly produced carapace margins that wrap around the front, sides and rear. Therefore, these four species appear to be more closely related to each other than either is to D. besutensis . The present recognition of D. lochi and D. yokotai reinforces the contention that D. besutensis is either outside of the main group of Durckheimia or erroneously assigned.

If the condition of the carapace front is convergent, then D. besutensis is unrelated to Durckheimia sensu stricto rendering the frontal similarities superficial. If, however, the strongly produced front and medially notched frontal margin of the carapace in D. besutensis is homologous with that of its congeners, then Serène’s species would be the sister to the remaining species of Durckheimia . Durckheimia carinipes would thus represent an intermediate between D. besutensis and the remaining species of the genus. Either way, the absence of the median carina of the carapace in D. besutensis is plesiomorphic as no other pinnotherids bear such a structure. Clearly, D. besutensis warrants further study. Irrespective, however, of whether D. besutensis is sister to the remaining congeners or only distantly related, it can be excluded from the genus without threatening the monophyly of Durckheimia sensu stricto. Removal of D. besutensis will enable a more uniform diagnosis of Durckheimia .

Previous workers (de Man 1889, Serène 1967) have recognised the similarity between the type species of Xanthasia , X. murigera White, 1846 (having a 2­segmented third maxilliped palp) and species of Durckheimia (those with a 3­segmented third maxilliped palp) in the upturned lateral and posterior carapace margins. Xanthasia murigera and the 3­segmented third maxilliped palp species of Durckheimia also share a similar third maxilliped exopod in which the margins are convex and the flagellum is 2­segmented. They differ obviously in dorsal carapace ornamentation, the subcylindrical versus dorsally cristate meri of walking legs and segmentation of the third maxilliped palp. Based on Serène (1967), D. besutensis resembles X. murigera in the following ways: 1) the shape of the segments of the third maxilliped palp — the propodus is spatulate and longer than the carpus, tapering to a blunt apex, and the ischiomerus has a concave outer margin and relatively straight inner margin; 2) the meri of the walking legs are subcylindrical; 3) the carapace is dorsally and ventrally irregularly pitted, but much less so in X. murigera ; and 4) a ventral knob or ridge is present lateral to the orbits. Durckheimia besutensis differs from X. murigera in having concave margins and a 1­segmented flagellum on the third maxilliped exopod, a strongly pitted and eroded carapace, and most significantly in carapace ornamentation. In D. besutensis the lateral and posterior carapace margins are not upturned, the median dorsal tubercle and carinae are absent, and the eyes and outline of the orbits are not visible dorsally. Aside from carapace characters, D. besutensis and X. murigera bear a strong phenetic resemblance and might ultimately prove closely related. Xanthasia itself, however, requires further attention because of the presence of X. whitei , de Man, 1887, which has a 3­ instead of 2­segmented third maxilliped palp. In any case, Serène's species cannot be placed in Xanthasia , for X. murigera and D. besutensis share no unique characters.

Durckheimia besutensis cannot be accommodated in any existing genus without significant generic modification. The strongly produced frontal carapace margin that completely obscures the eyes from dorsal view, the distinct median frontal notch, and deep excavations dorsolateral to the orbits exclude D. besutensis from all other genera. Durckheimia besutensis should eventually be removed to a new monotypic genus. Such an action would be premature, however, in lieu of specimens of D. besutensis , and that we have neither examined type nor other specimens of the poorly known D. carinipes (the type of the genus). In the absence of further comparative material and phylogenetic data, and in view of the strong similarities in frontal form between D. besutensis and other species of Durckheimia , we provisionally recognise the unity of the genus. Presently, Durckheimia can be distinguished from other pinnotherid genera, by the strongly produced frontal and anterolateral margins of the carapace that completely obscure the eyes in dorsal view, and the presence of a distinct median frontal notch in the carapace. Males are presently unknown for any species of Durckheimia .