Thoriellidae Lowry & Stoddart 2011, fam. nov.

Thoriellidae fam. nov.

(Figs 6, 7)

Diagnostic description. Head exposed or partially covered by coxa 3; much deeper than long, extending well below insertion of antenna 2, without cheek notch. Antennae calceoli present or absent in male. Antenna 2 peduncular article 3 without distal hook. Epistome with proximal portion not produced. Mouthpart bundle subquadrate. Mandible incisors well developed, symmetrical or asymmetrical, left convex or straight, minutely serrate, right convex or straight, smooth; left lacinia mobilis absent; accessory setal row with 5 or less robust setae, without distal setal tuft; molar absent; palp absent. Maxilla 1 inner plate with pappose setae along medial margin or with 2 apical pappose setae; outer plate with setal-teeth in modified 8/3 crown arrangement, setal-teeth large; palp large, without apical robust setae. Maxilla 2 inner plate subequal to or slightly shorter than outer plate, inner plate without oblique row of facial setae. Maxilliped outer plate present, medial setae vestigial or absent, without apical setae; palp 2-articulate, 1-articulate or absent.

Gnathopod 1 simple; coxa vestigial; ischium short (length up to 2 × breadth); carpus short; propodus small or large; dactylus slightly curved or vestigial. Gnathopod 2 coxa short, subequal in size to coxa 3 or vestigial. Pereopods all simple; propodus with or without spurs. Pereopod 4 coxa with posteroventral lobe weak or absent. Pereopod 5 coxa posterior lobe deeper than anterior lobe.

Uropod 3 present or absent; if present then rami vestigial or absent. Telson absent.

Type genus. Thoriella Stephensen, 1915.

Included genera. The Thoriellidae includes 4 genera: Chevreuxiella Stephensen, 1915, Danaella Stephensen, 1925, Parachevreuxiella Andres, 1987 and Thoriella Stephensen, 1915.

Remarks. Only cebocarids and thoriellids have the first and second coxae vestigial and maxilla 1 with the setal-teeth in an 8/3 crown arrangement. Thoriellids differ from cebocarids and all other lysianassoid families in having uropod 3 vestigial or absent and the telson absent.

There is little information on the biology of this abyssopelagic group. Herring (1981) reported bioluminescence in live specimens of Thoriella islandica, Chevreuxiella metopoides, Danaella mimonectes and other entities in the Chevreuxiella / Danaella group. Parker (1999) reported an unusual antennal reflector associated with bioluminesence in an undescribed species of thoriellid.

Thoriellids have been very rarely reported in the literature. From the North Atlantic Ocean there have been one record of Chevreuxiella (Stephensen 1915), two records of Danaella (Stephensen 1925), one record of Parachevreuxiella (Andres 1987) and two records of Thoriella (Stephensen 1915 and Shoemaker 1945). There are three records of Danaella from the Southern Ocean (Andres 1983, Birstein & Vinogradov 1962 and Piatkowski et al. 1994), one record of Thoriella from the Red Sea (K.H. Barnard 1937) and one record of Thoriella from the eastern South Pacific Ocean (Vinogradov 1990). According to Thurston (2010, in litt.) there are possibly as many as 15 thoriellid ‘entities’ among more than 100 or so specimens collected in the mid-water north-east Atlantic. Uncertainty as to the number of species arises from radical ontogenetic change and the difficulty of recognising whether differences are intra- or inter-specific. The description of these taxa may lead to changes in the family diagnosis.