Ascomata subcuticular. In vertical section the upper wall of unopened ascomata up to 30-40 µm thick, narrower toward edges and at the centre of the ascomata. Upper wall comprising mostly dense, black tissue with no obvious cellular structure, except for the inner part of the wall along the future line of opening, where it comprises thin-walled, hyaline cells. In opened ascomata the upper wall is up to 60-80 µm thick, becoming gradually thinner toward the base of the wall, and toward the ascomatal opening. A few poorly developed, hyaline, cylindric cells initially line the exposed face of the broken upper wall, but these cells are not persistent. Lower wall 5-10 µm thick, of 1-2 layers of brown to pale brown, angular to cylindric cells. Upper and lower walls extending up to 300-400 µm beyond hymenium.

Paraphyses 1.0-3.5 µm diam., undifferentiated or slightly and irregularly swollen near apices, extending 5-10 µm beyond asci. Asci 110-180 x 10-12 lam, clavate-stipitate, tapering gradually to small, truncate apex, wall undifferentiated at apex, 8-spored, spores restricted to upper half of ascus. Ascospores 32-45 x 2.5-4.5 µm (average 37.9 x 3.0 µm), in face view cylindric, tapering slightly to base, with slight or sometimes well-developed constriction near centre of spore, 0-1-septate, surrounded by gelatinous sheath. In many asci ascoconidia are produced from both ends of unreleased ascospores. Asci often becoming packed with the 2.5-6.0 x 1 µm, cylindric, hyaline, 0septate ascoconidia.

Conidiomata subcuticular. In vertical section lenticular in shape, upper wall 5 µm thick, comprising dense, brown tissue with no visible cellular structure. Lower wall of 1-2 layers of cylindric to angular, brown to dark brown, thick-walled cells. Lower wall lined with 1-2 layers of thin-walled, hyaline cells on which the conidiogenous cells develop. Conidiogenous cells 6-11 x 1.5-2.5 µm, cylindric, percurrent proliferation, wall thickened, and sometimes flaring, at the single, apical conidiogenous locus. Conidia 3.0-5.0 x 1.0-1.5 µm, cylindric, straight, ends rounded, 0-septate, hyaline.

CHARACTERISTICS IN CULTURE: Ascospores from PDD 46709 germinated within 24 hours on agar plates. Ascoconidia did not germinate. Cultures on OA 60 mm diam. after 8 weeks, aerial mycelium white, coarse, cottony, tufted, agar surface grey-green to olivaceous with black patches. Scattered, globose, black-walled conidiomata, conidiogenous cells as described from host material, conidia longer, 5-7 x 1-1.5 µm.

ETYMOLOGY: carinatum = keeled; refers to ascomatal shape, with keel-like ridge along opening slit.

NOTES: H. carinatum is easily confused with two other species with similarly sized asci and ascospores, H. campanulatum and H. alborubrum. H. carinatum can be distinguished by its very broad ascomata, greater than I mm wide, and by the keel-like ridge along the ascomatal opening.

The appearance in vertical section of the upper wall of unopened ascomata of H. carinatum is similar to that of H. cookianum. Both species have an ascomatal upper wall thinner along the future line of opening, and with no persistent layer of differentiated cells along the edge of the ascomatal opening. As in other Hypoderma species the ascomata are subcuticular, and the inner part of the upper wall along the future line of opening comprises cells thinner-walled and paler than those of the rest of the wall, the paraphyses are undifferentiated at the apex, and the asci are clavate-stipitate.

See also notes under H. campanulatum, H. alborubrum.