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

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 ).

Figures

Fig. 1. Known distribution of species of Crenoicus in New South Wales and Victoria, Australia. Numbers within parentheses indicate the number of sites where specimens were found. Site numbers marked with an asterisk indicate overlapping sites, only one symbol shown in figure. Plus symbols may also overlap.