Figure left: A entire holotype, note protruded genital cone. B dorsal posterior view. C fold around mouth, long cilia from pedal pit. D pedal groove spicules, anterior to right. Figure right: holotype

Copulatory spicules (figure left) hollow, fluted, curved, in paired bundles numbering up to 15 spicules per bundle varying in length from 15 to 200 µm, the shorter with the same morphology as the distal ends of the longer ones (figure left).

A-F, semischematic drawings of reproductive system from histologic sections, anterior (A) to posterior (F). G, posteroventral view of individual with cuticle turned back from shallow mantle cavity showing free proximal ends of copulatory spicule sacs. 1 seminal receptacle, 2 lower gametoduct, 3 copulatory spicule sac, 4 upper gametoduct, 5 exterior of genital cone.

Most epidermal spicules rimmed, nearly oval, somewhat asymmetrical, narrowest at flattened base, with medial bump, to 25 µm long by 14 µm wide; curved paddle-shaped spicules few, 20 by 9 µm; spicules beside pedal groove (at right) 38 to 58 µm long to 16 µm wide, overlapped in flat, paired ventral longitudinal rows; all spicules <2 µm thick.

Appearance mossy, height <0.5 mm, body narrowing posteriorly before broadening at posterior end, width greatest ventrally (A-C). Cuticle <2 µm thick, epidermis to 11 µm thick; anterodorsal midgut coecum paired, large; with a pedal commissure sac anteriorly (Scheltema, 1981).

Radula 0.2 mm long with 20 to 30 rows, those near proximal end opening into pharynx, distal half held vertically in single anteroventral radular pocket, teeth 30 to 35 µm long with 2 median denticles.

Reproductive system. -- The paired upper gametoducts are short and enter the lower gametoducts dorsolaterally presumably shortly after the dorsomedial union of the lower gametoducts with the pair of large, ventral, lobate seminal receptacles (B, C). The upper gametoducts were clearly distinguished in 3 sectioned individuals (D), but neither their origins from the pericardial cavity nor their union with the lower gametoducts were discerned. The paired lower gametoducts are surrounded by circular muscles, which become more pronounced after fusion of the two gametoducts to form a cone (G) similar to that in the genera Genitoconia Salvini-Plawen (1967) and the lepidomeniid Nierstrassia Heath (1918, pl. 6 fig. 11). The mantle cavity runs as a shallow space beneath the lower gametoducts, genital cone, and copulatory spicule sac (D). The proximal ends of the copulatory spicule sacs lie free in the mantle cavity (A-C, G); distally they lie within the body cavity (D, E). The relationship of the openings of the copulatory spicule sacs and the genital cone into the mantle cavity were not clear from the sections. The copulatory spicules are apparently deciduous, with new spicules forming in a rosette of cells within the copulatory spicule sacs (see Scheltema et al., 1994, fig. 23D). Spermatophores, not reported in any other species of Aplacophora, occur in the lower gametoducts and genital cone (figure above).
In G. pellucida, the union of the lower gametoduct and seminal receptacle was figured but interpreted as the union of upper and lower gametoducts ( Odhner, 1921, fig. 85); the upper gametoducts, which are difficult to see, were not figured.

Remarks. -- Gymnomenia virgulata is placed in the genus Gymnomenia on the basis of body shape, striped appearance due to the midgut sacculations, mouthfold of everted pharynx, and structure of the gametoducts. It is distinguished from species belonging to Wirenia Odhner (=Aesthoherpia Salvini-Plawen, 1985; see Salvini-Plawen, 1997) by spicule morphology and from Genitoconia Salvini-Plawen by the separation of mouth and vestibule and by the presence of midgut sacculations. G. virgulata differs from G. pellucida in height, which is greater and even throughout the body in G. pellucida, in number of copulatory spicules, and in presence of a large, paired midgut coecum, which is small and single in G. pellucida.
A pedal commissure sac with its contained bodies found in Gymnomenia also occurs in Genitoconia and Wirenia. Its fine structure has been described in Wirenia (Haszprunar, 1986 [as Aesthoherpia ]; Scheltema et al., 1994).

From Ophelia 51 (1): 1-28 (1999).

Gymnomenia virgulata Scheltema, 1999

Gymnomenia sp., Scheltema, 1981, figs. 2m, n, 4a-g; Scheltema et al. 1994, figs. 13c, 23b, d, 24a.
 

Type locality. -- Off Walvis Bay, Namibia, 23°00'S, 12°58'E, 619-622 m (RV ATLANTIS II Cruise 42, Stn. 188, 16.v.1968).
 

Holotype. -- USNM 880314 (alcohol specimen, spicule slide). 4.1 mm long, height 0.4 and 0.3 mm anteriorly and posteriorly, respectively . Paratype 1. -- USNM 880315 (dissected alcohol specimen, spicule slide including copulatory spicules). Paratype 2. -- USNM 880316 (alcohol specimen). Paratype 3. -- USNM 880317 (radula slide only). All from type locality.
 

Etymology. -- gymno = bare; virgulata = stripes