A small Dondersiidae to 3.2 mm long with a rough but glistening spicular coat. Like Dondersia and Ichthyomenia greatest height near anterior end, to 0.5 mm, but tapering rapidly to an anterior point; height near posterior end to 0.4 mm, tapered to a fingerlike projection above a bulbous ventral lobe containing the copulatory spicule sac (lacking in immature specimens), mantle cavity a shallow depression beneath the fingerlike projection; body narrowest somewhat anterior to posterior end, to 0.3 mm in height. Cuticle and epidermis 5 µm and 7 to 8 µm thick, respectively. Contracted mouth opening bilobed; contracted pedal pit indistinct; pedal groove ending on ventroposterior lobe. Dorsoterminal sense organ not distinguished.

Epidermal spicules of two types : first type elongate, slender, to 100 µm long by 9 µm wide and up to 5 µm thick, but most only 2 to 3 µm thick, width same throughout, thickest proximally, with slight distal trough sometimes with a distal ridge; second type ovate with distal end drawn out into a point, rimmed proximally, 2 µm or less in thickness, to 20 µm long by 13 µm wide on midbody and to 34 µm long at posterior end; spicules from beside pedal groove rimmed, to 52 µm long by 20 µm wide and 4 µm thick at rim.

Radula (4 examined) with 8 rows of monostichous teeth 50 µm in height by 40 µm wide, base with a faint line of bumps or serrations pointed distally; denticles deeply curved (Figs 3C, D).

Copulatory spicules not paired, formed of two elongate pieces, one about 150 µm long, flared and troughlike proximally, accompanied ventrally by clustered, small accessory spicules about 40 µm long; the other copulatory spicule with a proximal collar, about 80 µm long, partly wrapped around the longer, flared piece.

The reproductive system has not been unambiguously described for Lyratoherpia. In L. incali the gonopericardial ducts are paired (B). Paired seminal vesicles open posteriorly from the pericardium (C) and empty into the upper gametoducts (F), which descend vertically to join the narrow, paired lower gametoducts far posteriorly. Paired saclike seminal receptacles lie anterior to and above the lower gametoducts and are distally bifurcate (E); they enter the anterior ends of the lower gametoducts through stalks (D). Beneath the lower gametoducts is a single voluminous copulatory spicule sac, anteriorly glandular and surrounded by a thick layer of circular muscles (F). This gland may have been mistaken for the fused portion of the lower gametoducts in L. carinata, in which copulatory spicules were not detected (Salvini-Plawen, 1978). The copulatory spicule sac narrows posteriorly to form the portion containing the unpaired group of copulatory spicules (G), their former presence before dissolution marked by matrices in histologic sections (above, arrow). The sac opens dorsally into the shallow depression serving as a mantle cavity. The lower gametoducts remain narrow and paired until their union shortly before emptying ventrally into the shallow mantle cavity depression and anterior to the opening of the rectum (H).

A, reconstruction from histologic sections, anterior to left. B-H, semischematic cross-sections, somewhat skewed, midgut and rectum not shown except in H (see text for description). 1 pericardial cavity, 2 gonopericardial duct, 3 seminal vesicle, 4 upper gametoduct, 5 lower gametoduct, 6 seminal receptacle, 7 glandular portion of copulatory spicule sac, blind end indicated in E, 8 spicule-containing portion of copulatory spicule sac (see histologic section above), 9 mantle cavity, 10 rectum, 11 gonad. (A, modified from Scheltema et al., 1994.)

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