Neonesidea credibilis Maddocks 2021, n. sp.

Neonesidea credibilis n. sp.

(Figure 3 A–N)

1995 Neonesidea sp. CR: Maddocks: 206, Pl. 1, figs. 9–10; Plate 10, figs. 7–8; Graph 1.

Holotype: Male carapace containing fragmentary dry soft parts, specimen 500M, collected at R. V. Anton Bruun station 412C, 12 o 47’S, 47 o 42’E, 23 m depth, near Nosy Be, Madagascar.

Other material. Eleven subfossil valves in shallow-water sediment collected among patch reefs in the Lac du Cratère, Nosy Be, Madagascar.

Etymology: Latin adjective credibilis, worthy of belief, likely, credible.

Dimensions: Male specimen 500M, LVL 0.81 mm, LVH 0.46 mm, RVL 0.80 mm, RVH 0.43 mm. See also Maddocks (1995, Graph 1).

Distribution. R. V. Anton Bruun station 412C, 12 o 47’S, 47 o 42’E, 23 m depth; and Lac du Cratère, near Nosy Be, Madagascar.

Supplemental description. The carapace is somewhat thick-walled, inflated, with moderate left-right asymmetry. The lateral outline is boxy, rhomboidal, with flattened venter, beveled anteroventral margin, high-peaked dorsal margin, steeply sloping posterior margin, and subacute, noncaudate posterior angle, located only slightly above the venter. The carapace exterior is smooth (not punctate, as originally stated), with numerous, conspicuous NPC. The posterior margin of the LV has well developed denticles; the anterior and posterior margins of the RV have narrow, irregular fringes. No row of plumose setae is visible above the caudal angle. The middle third of each vave is occupied by an elaborate opaque patch pattern, which encloses one or more small clear regions.

The distal claw of the A2 is stout, slightly sinuate, does not taper, and ends in a large bifid claw. The fused claw is longer than usual and smooth.

The plate of the esophageal apparatus is flat, rather broad, symmetrical, with uneven lateral edges, shallow beveled scroll, and striated chevron-groove. The posterior perimeter is banded (brown and tan) and striated (where bristles of the ventral brush show through). The posterior edge is symmetrically scalloped, with six broad, arcuate lobes or low mounds, but no corner teeth and no significant gaps. The ventral bracket consists of two subpyramidal mounds. Thick spines project posterolaterally from the posterior end of the bracket, and the anterior faces are tuberculate.

Remarks. This uncommon species was not recognized by Maddocks (1969) but became apparent later after more specimens were picked (1995). The soft anatomy is that of Neonesidea, and the scalloped but toothless plate shows similarities to the N. dinochelata species-group (informal). The inner chitinous lining of the carapace is clear (not brown), and the AMS is less exaggerated than usual for that group. The complex patch pattern has analogues in the N. tenera species-group and also in Paranesidea. Species of similar aspect elsewhere are poorly understood.