Limnadopsis Spencer & Hall, 1896

Timms, Brian V., 2009, A Revision of the Australian Endemic Clam Shrimp Genus Limnadopsis Spencer & Hall (Crustacea: Branchiopoda: Spinicaudata: Limnadiidae), Records of the Australian Museum 61 (1), pp. 49-72 : 50-52

Genus Limnadopsis Spencer & Hall, 1896

Diagnosis. Umbo poorly developed, but present; carapace with many well expressed growth lines; growth lines in some species projecting as carinae along dorsal margin of carapace; head with a frontal organ on the apex of a posteriorly situated pyriform appendage; first antennae bar-shaped bearing many (5–13) lobes; 24–32 pairs of thoracopods; male with anterior-most two pairs of thoracopods modified as claspers, with the movable finger terminating in 1–3 spines, instead of a suctorial organ as in other limnadiids. First spine of the dorsal spine row of the telson large and protruding from the general alignment of the telson’s dorsal surface.

Remarks

In the original diagnosis by Spencer & Hall (1896), emphasis was placed on the 10–15 clearly marked growth lines, the “dorsal line, which is raised into a much-compressed spiney keel”, and the large number (26–32 pairs) of limbs. Henry (1924) and Daday (1925) continued in this vein, oblivious to the virtual lack of spiny outgrowths (i.e. carinae) and the large number (ca 30) of growth lines in L. brunneus . Likewise Novojilov (1958) was most impressed by the spiny dorsal outgrowths, so much so that he erected the subfamily Limnadopsinae based on this character, containing Limnadopsis and his Limnadiopsium . Straškraba (1965a), and Thiéry (1996) followed Novojilov (1958) in their definitions of the subfamily Limnadopsinae , using the spiny outgrowths as their only diagnostic feature. Given that in L. brunneus , L. parvispinus , and five new species described below, these spiny outgrowths are absent or minimally expressed, this character cannot be used alone as a major distinguishing feature of Limnadopsis or the subfamily.

Many of the other characters mentioned in the diagnosis are also not unique to Limnadopsis , or are not universal in the genus. However, all species of Limnadopsis have the first spine of the dorsal spine row of the telson large and protruding from the general alignment of the telson’s dorsal surface.All species also have, well-expressed lines of growth on the carapace. However in L. parvispinus the lines are less well expressed than in other species, but still quite different from the few poorly expressed lines that are typical for the remainder of the Limnadiidae , except in Metalimnadia ( Straškraba, 1965a) . Metalimnadia differs from Limnadopsis in lacking a frontal organ, in having a well-developed umbo, and only two lobes on the first antennae. Finally, and first introduced in the generic key provided by Richter & Timms (2005), all species of Limnadopsis have spines on the tip of the movable finger of the clasper, not a sucker as in other species of Limnadiidae . This unique character, together with the large and protruding first spine of the telson spine rows can be used to diagnose the genus, with limited reference as well to the numerous well-marked growth lines and dorsal carinae, The general appearance of specimens of Limnadopsis is shown in Figs. 1 , 2 .

Species descriptions

Figures

Fig. 1. General view of Limnadopsis pilbarensis n.sp. Drawn by Jane McRae.

Fig. 2. Photographs of whole specimens of species of Limnadopsis. (A) L. birchii; (B) L. tatei; (C) L. parvispinus; (D) L. minuta; (E) L. multilineata; (F) L. occidentalis; (G) L. paradoxa; (H) L. pilbarensis. Scale bars 5 mm.