This group has had an unstable history, and its validity needs further testing, though Sugi (1987) stated that Rivula Guenée should be excluded from the Catocalinae + Ophiderinae assemblage. Kitching (1984) could not find any characteristic that supported its monophyly, but placed it tentatively in a basal position in the Noctuidae, whereas Kitching & Rawlins (1998) included it in the Hypeninae. The phragma lobes between the first two abdominal tergites are very large as in the core Hypeninae (see p. 173). However, without a much more detailed study of this feature, it is unclear whether this extreme size is a potential synapomorphy (see also Speidel & Naumann (1995)). Edwards, in Nielsen et al. (1996), recognised the subfamily as distinct, as did Fibiger & Lafontaine (2005) and Lafontaine & Fibiger (2006).
Fibiger & Lafontaine (2005) defined the group on larval features, following Beck (1960, 1999-2000), but these have not been confirmed to occur widely through the current rather heterogeneous concept of the genus (see below) apart from the barbed or plumose primary setae. On A1 and A2, the SV3 seta moves dorsolaterally to share a pinaculum with L3, leaving the SV-group apparently bisetose. All prolegs are fully developed. Speidel et al. (1996a, b) noted a potential adult apomorphy: a unique microsculpture of the tongue. The clypeofrons is fully scaled. The mode of pupation appears to be constant and distinctive within the type-genus at least (see below), and most host records for Rivula are from monocotyledonous plants, particularly grasses (Sugi, 1987).
The family-group name Rivulinae is also used in Pisces (Holloway, 2005: 30; Speidel & Naumann, 2005) with greater frequency and stability than in Lepidoptera; Speidel & Naumann suggested that, though usage in Lepidoptera had priority, stability might best be served by ceding Rivulinae to Pisces and using Rivulainae until the concept of subfamily status can be more firmly substantiated for the lepidopteran group. This proposal was not adopted by Fibiger & Lafontaine (2005) or Fibiger & Hacker (2005).
Bornean species currently placed in Rivula show considerable morphological diversity, though with a few distinctive features that are relatively widely distributed, as discussed below. The two Rivulinae taxa included in the molecular analyses of Mitchell et al. (2006) were not associated with each other in the results. The representative of Rivula was placed in a clade with the Lymantriidae and Arctiidae as discussed on p. 4. Lafontaine & Fibiger (2006) placed the Rivulinae as a basal group within their quadrifine noctuid assemblage.
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