Kiwetinokia sp.

Kiwetinokia sp. ?

Fig. 6M View Fig .

Material.—USDG 001–5, several isolated triradiate spicules from the middle Cambrian at the Cerro El Mogallón, Arivechi, Sonora.

Description.— Occasional triradiate or Y-shaped spicules occur in the assemblage, associated with dissociated stauractines of diverse sizes. Triactine-like prodiaene spicules have presumed proximal rays 5.5 mm long, and two somewhat longer, presumed distal rays, with maximum ray lengths of 10.3 mm (mean = 5.5 mm). Basal ray diameter in largest spicules is 0.40–0.50 mm.

Remarks.— Walcott (1920) proposed the genus Kiwetinokia , designating the new species K. utahensis as the type, to include clusters of scattered spicules in the absence of any articulated material. Similar disarticulated remains from Little Métis, Quebec ( Dawson and Hinde 1889) were reassigned to the genus from Hyalostelia . There is thus a severe risk that the spicule assemblage is itself not natural, although the name is effectively tied to the most distinctive spicules, consisting of triradiate spicules, Y-shaped spicules resembling demosponge prodiaenes, and spicules with helically twisted rays. Walcott (1920) considered the cruciform spicules associated with the more distinctive morphologies to be characteristic of species included in that genus. Fink and Rigby (2004) and other authors considered that the twisted spicular rods may be part of the basalia of the co-occurring (at Little Métis) Palaeosaccus Hinde, 1893 . It is therefore possible that Kiwetinokia may be a junior synonym of Palaeosaccus , although the full range of distinctive spicules included in the genus is unlikely to be accommodated in that way. Until articulated remains are discovered, the genus remains recognisable as a spicule assemblage.

In the Arivechi material the spirally twisted triradiate spicules are not yet known. However , from the early Cambrian of the Caborca , northern Sonora, McMenamin (2008) described one spicule of this type, assigning it to Kiwetinokia .