Genus Meiodorvillea Jumars, 1974

Type-species. Protodorvillea minuta Hartman, 1965 [13]

Type locality. Block Canyon, off New England (USA), 39˚58’24"N, 70˚40’18"W

Amended diagnosis. Prostomium pear-shaped. One pair of simple and clavate dorsal antennae (Fig 3A and 3B). One pair of simple and clavate lateral palps, sometimes absent, shorter than antennae (Fig 19A and 19B). Jaw apparatus (Fig 12) with paired and medially fused butterfly-shaped mandibles. Maxillae with one pair of V-shaped dorsal carrier-like structures and one pair of ventral basal plates, each one fused posteriorly, and free from each other. Inner margin of basal plates smooth, rarely dentate. Ten to 15 pairs of maxillary plates in two rows, anteriorly to the basal plates, denticulate on its margin, absent in M. apalpata . Two peristomial rings. Small dorsal cirri sometimes present, without acicula (Fig 4A and 4B). Small ventral cirri present (Fig 10). Supra-acicular chaetae: (1) capillaries (Fig 11A), (2) geniculates (Figs 11C and 21A) and (3) furcates (Figs 11B, 11H and 16 A-16D). Sub-acicular chaetae: (4) compound falcigers and/or spinigers (Figs 11E–11G and 21C) and (5) cultriforms (Figs 16H and 21D). Pygidium with two pairs of cirri (Fig 9E and 9F).

Remarks. Jumars [17] erected Meiodorvillea naming M. minuta as type species, describing M. apalpata, and raising M. chilensis (previously Protodorvillea gaspeensis chilensis Hartmann-Schröder, 1965 [18]) to species. Meiodorvillea chilensis and P. gaspeensis Pettibone, 1961 [22] have short biarticulated palps, so that the latter was considered to belong to a new genus [23] and assigned as type species of Marycarmenia Núñez, 1998 [24]. The jaw apparatus of this genus is markedly different from Meiodorvillea in the absence of maxillary carrier-like structures and the presence of denticles on the anterior margin of mandibles [24]. Meiodorvillea chilensis was described based on one specimen, and although it was well described and illustrated, the jaw apparatus was not examined, which makes its determination questionable [19]. Given the lack of information about its jaw apparatus, M. chilensis must remain as species inquirenda possibly also belonging to Marycarmenia . The character “biarticulated palps”, proposed by Jumars [17], has been removed from the diagnosis, as it only occurred in M. chilensis .

Eibye-Jacobsen & Kristensen [23] proposed the erection of a new genus to M. apalpata, suggesting that it could be a sister group of Meiodorvillea sensu stricto . However, Jumars [17] stated that no ‘free denticles’ (maxillary plates) remained in the specimens, which did not allow distinguishing a real absence from a handling artifact. Therefore, maxillary plates could be present, but this could not be assessed in handled specimens. Although M. apalpata is the only one with lacking palps, it shares characters, such as absence of dorsal cirri, shape of mandibles, absence of denticles on its anterior margin, and presence of maxillary carrier-like structures. Furthermore, the absence of furcate chaeta is also verified in other species, either in the anterior or posterior region. As proposed by Wolf [19], our analysis found no significant morphological differences to support the erection of the new genus proposed by Eibye-Jacobsen & Kristensen [23]. Therefore, M. apalpata should remain within Meiodorvillea until more specimens will be carefully examined, especially regarding the jaw apparatus.

The present revision allowed including new morphological character states in the generic diagnosis, such as presence and shape of geniculate, furcate and cultriform chaetae and details of jaw apparatus.

The posterior peristomial ring frequently covers the anterior ring in specimens where the contraction of the anterior region is markedly visible (Fig 14A and 14B), which apparently demonstrates the presence of one ring (Figs 1C and 3B) [13, 17]. Although this is not a diagnostic character, this variation is mentioned in the descriptions as being rather variable and dependent on the state of contraction caused by fixation of the specimens.

The free denticles, terminology adopted by Jumars [17], Oug [25], and Eibye-Jacobsen & Kristensen [23], are here referred as the paired maxillary plates (placed anteriorly to basal plates), following Wolf [26] and Purschke [27]. Each maxillary plate contains denticles on its margin.