Chillagoeidae Lowry & Myers, 2012

King, Rachael A., Stringer, Danielle N. & Leijs, Remko, 2023, Carnarvonis gen. nov. and Warregoensis gen. nov.: Two New Genera and Species of Subterranean Amphipods (Crangonyctoidea: Chillagoeidae) Described from North-eastern Australia, Records of the Australian Museum (Rec. Aust. Mus.) 75 (4), pp. 447-457 : 449

Chillagoeidae Lowry & Myers, 2012

Type genus. Chillagoe Barnard & Williams, 1995

Diagnosis. (After Lowry & Myers, 2012) Body laterally compressed. Eyes absent. Antennae 1–2 calceoli crangonyctoid (type 9). Antenna 1 longer than antenna 2; peduncular article 1 subequal to, or longer than article 2; article 2 longer than article 3; article 3 shorter than article 1; peduncular articles 1–2 not geniculate; accessory flagellum short. Mandible molar triturative; palp symmetrical. Maxilla 1 basal endite setose along medial margin or apically setose; palps symmetrical. Maxilla 2 basal endite with oblique setal row of 2–3 setae. Labium inner lobes vestigial or absent. Coxal gills on pereopods 2–6 or 2–7, stalked (without proximal restriction); sternal gills present, simple, paired; sternal blisters absent; oostegites fringing setae simple. Coxa 1 distinctly smaller than coxa 2, as long as broad, with a robust seta at the posterodistal corner and additional simple seat along distal margin; Coxae 2–3 similar, longer than broad with a robust seta at the posterodistal corner and additional simple seat along distal margin; coxa 4 similar length to coxae 2–3, as long as broad, with small but distinct excavated corner on the posterior margin, with a robust seta at the posterodistal corner and additional simple setae along distal margin. Coxae 5–6 similar, approximately half length of coxae 2–4, anteroventral lobe distinct, posteroventral lobe indistinct, with setae along posterior margin. Coxa 7 similar length to coxae 5–6, rounded, with setae along posterior margin. Gnathopod 1–2 subchelate, similar in males and females (not sexually dimorphic); gnathopod 1 smaller (or weaker) than or similar in size to gnathopod 2; gnathopods 1–2 propodus lateral face with distinct excavation above and parallel to palm margin, palm without robust setae along palm margin, with rows of 1–5 robust setae either side of palm corner (where dactyl fits to the propodus). Pereopods 3–4 not sexually dimorphic. Pereopod 4 basis without distinct posteroventral lobe. Pereopod 5 shorter than pereopod 6. Pereopod 7 subequal in length to, or longer than pereopod 6. Pleonites 1–3 without dorsal carinae. Urosomites 1–3 free; with slender or robust dorsal setae. Urosomite 1 with distoventral robust seta. Urosomites 1–2 with paired dorsolateral robust setae. Uropod 1 with or without basofacial robust setae on lateral margin of peduncle, distal margin of peduncle with group of 1 large and 2 small robust setae laterally and 1 large robust seta medially. Uropod 2 distal margin of peduncle with group of 2 small robust setae laterally and 1 small robust seta medially. Uropod 3 not sexually dimorphic; uniramous, without plumose setae. Telson cleft; apical robust setae present.

Remarks. Examination of type material for the family and comparison of this to material of the two new taxa described herein has led to a revision of diagnostic characters of the Chillagoeidae . New characters to the diagnosis are highlighted in bold text. Significant changes include the morphology of the maxilla 2 and the setation of the uropod 1 peduncle. Firstly, the original description of Chillagoe thea indicated that maxilla 2 basal endite was missing an oblique row of setae, which was included as a family-level character by Lowry & Myers (2012). However, subsequent examination of the holotype and paratype material showed that while there was variation between individuals, there was an oblique setal row of at least 2–3 setae that is also present in the new genera described herein. Secondly, in the original diagnosis of Chillagoeidae the presence of a robust basofacial seta on the uropod 1 peduncle was included as an important family-level character ( Lowry & Myers, 2012) but we conclude that this character is variable among genera.

More importantly, we find that the distinct gnathopod, coxal and uropodal morphology of all three genera now included within the Chillagoeidae should be raised to family-level diagnoses. This includes the sculpturing of gnathopods 1–2 propodus lateral face (with distinct excavation above and parallel to palm margin) as well as setation of the palm corner (with rows of 1–5 robust setae either side of where the dactyl fits to the propodus; coxal morphology (coxae 1 short, coxae 2–4 similar length, coxae 5–7 half length of coxae 1–4); and the setation of uropods 1–2 peduncle distal margin (uropod 1 with group of 1 large and 2 small robust setae laterally and 1 large robust seta medially, uropod 2 with group of 2 small robust setae laterally and 1 small robust seta medially). Together, a suite of characters is formed that clearly defines the family.

Chillagoeidae taxa are most easily separated from the albeit poorly defined Paramelitidae by the uniramous uropod 3 as well as urosomites 1–2 with paired dorsal robust setae. Two other Australian groundwater-associated families are also characterized in-part by a uniramous uropod 3: Uronyctidae (erected for the monotypic Uronyctus longicaudus Stock & Iliffe, 1990 from sinkholes in Mt Gambier, South Australia) and Giniphargidae (erected for the monotypic Giniphargus pulchellus ( Sayce, 1899) from Gippsland, Victoria). Both of these species show significantly more “vermiform” slender bodies typically associated with true stygobiotic lifestyle, compared to Chillagoeidae taxa. In addition, U. longicaudus further differs from Chillagoeidae taxa in that it has sexually dimorphic gnathopods with distinctive propodus morphology, coxal gills on pereopods 2–7, coxa 4 without a distinct excavated corner on the posterior margin, pereopod 5 much shorter than pereopods 6–7 and an extremely elongate uropod 3 outer ramus. G. pulchellus has reduced coxae 1–7 of similar lengths, a robust antenna 2 peduncle, gnathopods with distinctive propodus morphology, coxa 4 without a distinct excavated corner on the posterior margin, and an elongate uropod 3 outer ramus of two equally sized articles.