Diastylopsis Smith, 1880

Gerken, Sarah, 2014, Eleven New Species and a New Genus of Diastylidae (Crustacea: Cumacea) from Australia and One New Species from Canada, Records of the Australian Museum 66 (1), pp. 1-62 : 19

Diastylopsis Smith, 1880

Type species. Diastylopsis dawsoni Smith, 1880

Diagnosis. Female and subadult male. Carapace elongate. Pereonites 2 and 3 separated ventrally. Pereonites 3–4 may be fused dorsally, free ventrally. Pereopods 3–4 with or without rudimentary exopods in the female. Telson with post-anal portion, with or without lateral setae, 2 or rarely 3 terminal setae. Adult male. Antennae extending to end of pleon. With 2 pairs of pleopods.

Remarks. There are no previous records of the genus from Australian waters. There are two problematic species currently ascribed to Diastylopsis , D. diaphanes Zimmer, 1913 and D. bosphorica Băcescu, 1982 . It is clear from the published descriptions and figs. that D. diaphanes properly belongs in Litogynodiastylis Gerken, 2001 , as the Zimmer (1913) figs. clearly show a male without pleopods, and the first pereopod without a brush of long setae on the propodus. Thus, D. diaphanes Zimmer, 1913 is formally transferred to Litogynodiastylis as the new combination Litogynodiastylis diaphanes ( Zimmer, 1913) . The description and figs. of D. bosphorica clearly show a truncate mandible, and there is no reason to suspect that this is an error, thus D. bosphorica properly belongs in Diastyloides . Therefore, D. bosphorica Băcescu, 1982 is formally transferred to Diastyloides as the new combination Diastyloides bosphorica ( Băcescu, 1982) .

The placement of the new species Diastylopsis senta and D. trisetosa in Diastylopsis could be disputed, with an alternate placement within Makrokylindrus , based on telson proportions. Makrokylindrus and Diastylis seem to constitute a continuous series in the proportions of the pre- and post-anal portions of the telson, as discussed in Day, 1980, with Diastylis generally having the pre-anal portion shorter than the post-anal portion, and Makrokylindrus having a tubular telson with the pre-anal portion longer than the post-anal portion. However, there are species ascribed to each genus that merge this boundary, so that the current generic definitions are insufficient to clearly discriminate two discrete groups. This problem will only be resolved with a phylogenetic study of the Diastylidae .

My placement of Diastylopsis trisetosa in Diastylopsis rather than Makrokylindrus rests in part on the elongate carapace ornamented with concentric semi-vertical ridges, which is shared with the majority of species currently accepted as Diastylopsis , and unusual within Makrokylindrus . In Makrokylindrus the carapace is very commonly globular, and distinctly not elongate. My placement of D. senta in Diastylopsis rather than Makrokylindrus also relies on the elongate carapace. In addition, while pereopods 3–5 of D. trisetosa and D. senta may not be extremely stout, they are distinctly not slender. The new Australian species that I have placed in Makrokylindrus ( M. eirmoacanthus ) more clearly fits with the other known species of Makrokylindrus in that it has the expected globular carapace.

All species. Diastylopsis annulata ( Zimmer, 1902) ; D. crassior Calman, 1911 ; D. dawsoni Smith, 1880 ; D. elongata Calman, 1911 ; D. goeki Roccatagliata & Heard, 1992; D. incompta n. sp.; D. senta n. sp.; D. tenuis Zimmer, 1936 ; D. thilenuisi ( Zimmer, 1902) ; D. trisetosa n. sp.