Crenoicus Nicholls, 1944

Wilson, George D. F. & Ho, L. E., 1996, Crenoicus Nicholls, 1944 (Crustacea, Isopoda, Phreactoicidea): Systematics and biology of a new species from New South Wales, Records of the Australian Museum 48 (1), pp. 7-32: 9-10

publication ID 10.3853/j.0067-1975.48.1996.279


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Crenoicus Nicholls, 1944


Crenoicus Nicholls, 1944  

Crenoicus Nicholls, 1944: 21-23   .

Type species. Crenoicus mixtus Nicholls,   1944.

Generic diagnosis. Eyes absent. Head length subequal to width in dorsal view, maxillipeds inserting near posterior margin of head. Dorsal surface with scattered fine setae, lacking tubercles or ridges. Pereonites lacking epimeral plates, all coxae visible in lateral view. Pereopodal coxae lacking distinct lateral projections. Gut with minimal typhlosole, "u" shaped in cross section. Pleonites with well-developed ventral epimera, pleopodal protopods not visible in lateral view. Pleotelson depth greater than length; posteriorly trilobed in dorsal or ventral view; medial tip not cleft, not distinctly longer than lateral lobes; ventral margin anterior to insertion of uropods with row of simple robust setae. Antennula terminal article shorter and narrower than subterminal articles, roughly globular. Right mandible lacking lacinia mobilis. Maxillula medial lobe narrower than lateral lobe, with 4 large plumose setae and 2 small simple setae (6 plumose setae sometimes occurring). Pereopod I male propodal palm with short, broadly conical, dorsally angled setae on low ridge; female propodal palm with row of broad based simple setae. Male pereopod IV subchelate between dactylus and propodus, propodal palm with proximal large broad based setae. Penes smooth, lacking setae, strongly curved posteriorly, tapering distally to rounded point. Pleopod I exopod distally pointed, widest at midlength; endopod without setae. Male pleopod 11 appendix masculina curved, distally stylet-like, distal tip spatulate or spine-like with long single subdistal seta. Uropodal protopod distoventral margin with 1 robust distally spinose seta; propodal medial margin lacking distal projection; rami distally pointed, spine-like.

Remarks. Nicholls (1944) classified his genus Crenoicus   , an exclusively Australian genus, in the subfamily Phreatoicinae   which otherwise contains New Zealand forms. His subfamily concept may be too broad because the elongate subterranean genera Phreatoicus Chilton, 1883   and Neophreatoicus Nicholls, 1944   can be distinguished from the more typically shaped species of Crenoicus   and Notamphisopus Nicholls, 1944   . Nevertheless, Poore et at. (in press) expand the definition of the subfamily to include genera of Paraphreatoicinae Nicholls, 1944 plus Uramphisopus Nicholls, 1943   , and raise this group to family level. We do not diagnose the family Phreatoicidae   because the family level systematics of the Phreatoicidea   should be reviseu using phylogenetic methods.

With this new composition of the Phreatoicidae   , more genera must be compared with Crenoicus   . The New Zealand species of Phreatoicus   and Neophreatoicus   are much more elongate than other Phreatoicidae   and have a pleotelson whose length is greater than its depth. Crenoicus   can be distinguished from Colacanthotelson Nicholls, 1944   , Mesacanthotelson Nicholls, 1944   and Onchotelson Nicholls, 1944   by the lack of any unusual alterations of the dorsal cuticle, the pleotelson tip or the coxae (i.e. the cuticle is not rugose, the pleotelson does not have an elongate tip and the coxae are not laterally expanded). The other phreatoicid genera Uramphisopus Nicholls, 1943   , Colubotelson Nicholls, 1944   , Metaphreatoicus Nicholls, 1944   , Paraphreatoicus Nicholls, 1944   and Notamphisopus Nicholls, 1944   are more similar to Crenoicus   . Unlike Knott (1975) and Poore et al. (in press), we are uncertain whether the genera Metaphreatoicus   , Colubotelson   and Paraphreatoicus   should be synonymised into Uramphisopus   . Uramphisopus pearsoni Nicholls, 1943   has a large medial extension of the uropodal protopod, while none of the species attributed to other three genera have this feature. Other characters, such as the setation of the pleopodal endopods and the uropods, also suggest more diversity than a single genus should contain. Consequently, we prefer to recognise these genera until the suborder is revised. All of these genera, however, lack a distally pointed appendix masculina seen in Crenoicus   and instead have a typically rounded tip with multiple setae. These genera also differ in other details such as the setation of the first pleopod and the number of spinose setae on the distal margin of the uropodal protopod. While most Australian Phreatoicidae   have eyes, Crenoicus   species are completely blind, although the head may have a cuticular remnant of the eyes. Crenoicus   species also have a subcuticular white patch of unknown function in the ocular region of the head.

Species included. Crenoicus mixtus Nicholls, 1944   ; C. shephardi ( Sayce, 1900)   ; C. harrisoni Nicholls, 1944   and C. buntiae   n.sp. Nicholls (1944: 31) noted another undescribed species from the New England region of New South Wales. The morphological conservatism of this genus coupled with substantial intrapopulation variation in some characters (discussed later in this paper) makes identification of species difficult. A complete species inventory for Crenoicus   , therefore, will require careful morphometric and genetic studies.

Distribution of Crenoicus   species. Throughout springs and swamps of Victoria and New South Wales: near Ballarat (c. mixtus   ), Plenty Range near Melbourne Vic. (c. shephardi   ), Barrington Tops NSW (c. harrisoni   ), Boyd Plateau NSW (c. buntiae   n.sp.), Otway Range Vic. ( Crenoicus   sp.-undescribed). Our collecting activities have shown other undescribed species of Crenoicus   to be widespread in NSW springs and marshes above 1000 m (see Fig. 1 View Fig ).












Crenoicus Nicholls, 1944

Wilson, George D. F. & Ho, L. E. 1996


Nicholls, G. E. 1944: 23