Neonesidea bacata, Maddocks, Rosalie F., 2013

Maddocks, Rosalie F., 2013, New and poorly known species of Neonesidea (Bairdiidae, Ostracoda, Crustacea) from French Frigate Shoals, the Hawaiian Islands, Zootaxa 3608 (6), pp. 457-510 : 496-502

Neonesidea bacata n. sp.

( Figs. 28–34 )

Etymology. Latin bacatus, set with pearls, referring to the papillate microornament of the carapace.

Material. One adult male.

Types. Holotype male 3912M.

Type locality. French Frigate Shoals, Hawaiian Islands, station FFS–TC–11, 23 o 47.7 N, 166 o 0 4.97 W, 13 Sep 2000. E perimeter backreef, 14 km due E of East Island, depth 4– 6 m.

Dimensions. Holotype male 3912M, L 605 μm, H 285 μm. See also Figure 34 .

Description. Carapace ( Figs. 28 A–G, 29A–F, 30A–H) oblong, inflated; thickness greater than height, greatest height and greatest thickness both located distinctly anterior to midlength (0.38, 0.39). Surface of valves nearly smooth medially, with a velvety, micropapillate texture elsewhere; marginal regions visibly papillate. Microornament of numerous, tiny, hemispherical granules or papillae; 1 to 4 μm in diameter, larger and more densely packed near valve edge. Adductor muscle scars expressed externally as smooth regions outlined by rows of micropapillae. Lateral outline of LV subrhomboidal, tapering posteriorly; dorsal margin distinctly tripartitite, with broadly curving, anterodorsal and posterodorsal angles; nearly straight, sloping anterodorsal segment, gently arched, slightly sloping median segment, and straight, steeply sloping posterodorsal segment; anteroventral margin slightly convex, obliquely truncated; ventral indentation broad, shallow, distinct; posteroventral margin curving obliquely upward to posterior end; posterior end not caudate, bluntly rounded, located at one-fifth of height (0.20); no caudal process, no posterodorsal concavity. Posteroventral margin of LV with numerous, fairly large, triangular marginal denticles, whose long axis is oriented posteroventrally; narrow flange wraps around posterior angle. Anterior margin of RV with broad chitinous flange and indented selvage; posterior margin with deeply indented selvage and narrow chitinous frill or flange around posterior angle. NPC large, conspicuous, not especially numerous, mostly about the same diameter, some with narrow to fairly broad walls.

Carapace setae ( Figs. 28 A–G, 29A–F, 30A–H) conspicuous, not especially abundant, mostly about the same length; of simple form, smooth, tapering to point, standing erect or oriented posteriorly; with a few longer ones located on posterior lateral surfaces. On each valve, about three exceptionally long, thick anchor setae originate posteromedially and posteroventrally (near but not at posteroventral margin), project outward, and trail posteriorly. Simple setae of uniform size and spacing are aligned along all free margins of both valves, curving outward like eyelash setae, but not differing in size or structure from other simple setae elsewhere. No feathered caudal setae observed.

Male antennal claw ( Figs. 31 J–N, 32C–D) nearly straight, slightly tapering; anterior horn continues smooth profile of claw; anterior horn slightly shorter and distinctly thinner than posterior horn, nearly straight and rodlike in some views, slightly tapering with pointed termination in other views; posterior edge of anterior horn nearly straight (only weakly sigmoid); cleft between horns tapering (only weakly sigmoid); posterior horn broadly pointed, with obliquely beveled or faceted anterior edge, which may facilitate forced overlap of the two horns in scissors-fashion.

Hemipenis ( Figs. 31 C–G, 33D) with stout trapezoidal basal segment; median segment oblong to ovate with rounded margins, broadly flared or sinuous lamellar edge, with asymmetrically tapering distal process extending beyond terminal segment; terminal segment a bluntly truncated, hook-shaped lamellar plate, with broad indentation on outer edge. Copulatory tube thin, arched, tapering, barely reaching distal end of terminal segment.

Kauplatte ( Fig. 31 O, 33E) of masticatory organ with smooth, gently curved, toothless perimeter; with central cleft; end teeth broad, offset by wide gap.

Comparisons. In anatomical characteristics this species is indisputably allied with Neonesidea . No other known species of Neonesidea has a papillate carapace.

The tuberculate ornament of N. bacata is reminiscent of that in Mydionobairdia and Papillatabairdia , though on a finer scale and more subtly developed. Species of Mydionobairdia have fewer but much larger, flat-topped, volcano-like tubercles, together with conspicuous anterior and posterior marginal spines. In Papillatabairdia the tubercles are broader, low-hemispherical in shape, and may be arrayed in uniform rows. Species of Papillatabairdia are also distinguished by reniform lateral outlines, with distinctly indented ventral margin and broadly rounded anterior and posterior margins. The relationships among Mydionobairdia, Papillatabairdia , and Triebelina have been evaluated at length by Keij (1974, 1976), Bentley (1881), Warne (1986), Titterton & Whatley (1988a), Maddocks (1991), Maddocks & Wouters (1990), and references cited therein.

Soft parts have been described for only one species of Mydionobairdia . The soft anatomy of Triebelina appears to be close to that of Paranesidea , but no males have been described. The anatomy of Papillatabairdia is unknown.

The elongate-subrhomboidal lateral outline of N. bacata , with low-set, tapered posteroventral angle and flattened ventral surface, is distinct from the upward-curving, caudate posterior end that is typical for species of Triebelina (always visible in the RV if not so much in the LV outline). Species of Triebelina have much greater valve asymmetry and pronounced anterodorsal and posterodorsal LV overlap.

As compared to Mydionobairdia tulearensis Maddocks (1991, the only species of that genus for which the soft parts have been described), N. bacata is less elongated medially in lateral outline, with a gently curving rather than perfectly straight mid-dorsal segment, and with a more acutely extended (rather than rounded) posteroventral angle. The surface tubercles are smaller, more numerous, lower except near the edge, mostly low granules or papillae rather than the isolated, flat-topped table-mounts of M. tulearensis . N. bacata also lacks the two sizes of simple setae, the smaller trifurcate setae, the three long anteromarginal tubercles, and the four long posteroventral marginal tubercles of M. tulearensis , and there is no record of anchor setae in M. tulearensis .

N. bacata is similar in L/H proportions to Bairdia hanaumaensis Holden (1967) but smaller, with a more extended posteroventral end but a more rounded (less acute) posteroventral angle; other distinctions include the several long anchor setae, the LV posteroventral marginal tubercles, the LV anteroventral marginal fringe, and the RV marginal fringe or flange. Holden described B. hanamauensis as finely pitted, evenly covered with short hairs, and uniform brown in color, comparing it to Bairdia acanthigera Brady, 1880 and Bairdia tuberculata Brady, 1880 . [It is unclear whether Holden intended the latter name to refer to the punctate species described from Mauritius by Brady (1868), which was perhaps a species of Triebelina , or the spinose species described from the Admiralty Islands by Brady (1880), which was probably a species of Mydionobairdia (later reported from New Caledonia by Brady (1890). Holden's drawing shows a species that is distinct from both of these species, being more elongate, with markedly angular contours, and entirely lacking marginal denticles.] Holden (1976) identified B. hanaumaensis from Midway (on the basis of a single juvenile RV, unillustrated) and reclassified it in Triebelina .

The configuration of the hemipenis and the shape of the Kauplatte of the masticatory organ are unique in Neonesidea .

Figures

FIGURE 28. Neonesidea bacata n. sp., all male specimen 3912 M. A, B, RV and LV exteriors, with simple setae and anchor setae; C, dorsal view of LV, focused at ventral edge; D, dorsal view of RV, focused at mid-height; E, left exterior view of entire animal before dissection; F, G, RV and LV exteriors with AMSP, NPC, setae, and numerous small papillae. Scale bar = 50 μm.

FIGURE 29. Neonesidea bacata n. sp., all male specimen 3912 M. A, posteroventral lateral region of LV to show simple setae, anchor seta, small papillae; B, dorsal view of LV, focused at ventral edge, to show anchor setae, striate anterior chitinous edgestrip, papillate texture, eyelash setae; C, tilted dorsal view of RV, focused at ventral edge, to show inset selvage at anterior and posterior ends, neat row of anterior and posterior eyelash setae; D, E, dorsal views of LV and RV, focused below hinge, to show simple hinge, short simple setae, NPC, papillate texture; F, posteroventral region of LV, to show marginal denticles, setae, papillae. Scale bar = 50 μm.

FIGURE 30. Neonesidea bacata n. sp., all male specimen 3912 M. A, B, anterior region of RV at mid-height to show papillate texture, setae, NPC; C, posterior end of RV, to show marginal setae, short chitinous fringe around posterior angle, inset selvage; D, posterior end of LV, to show triangular marginal denticles, chitinous flange, and setae; E, posteroventral margin of LV, to show triangular marginal denticles and setae; F, enlarged view of three marginal denticles from D; G, H, RV and LV exteriors to show AMSP, NPC, setae, and papillae. Scale bar = 10 μm.

FIGURE 31. Neonesidea bacata n. sp., all male specimen 3912 M. A, B. left and right sides of body; C, E – G, I, hemipenes and furcae, before and after dissection; D, mouth; H, testes and spiral vas deferens; J, K, right antennal claw; L – N, left antennal claw in natural position before dissection and after dissection, to show slender anterior horn, V-shaped cleft, and obliquely beveled anterior surface of posterior horn; O, masticatory organ. Scale bar = 10 m.

FIGURE 32. Neonesidea bacata n. sp., all male specimen 3912 M. A, maxillule; B, mandible; C, D, antennae.

FIGURE 33. Neonesidea bacata n. sp., all male specimen 3912 M. A, fifth limb; B, sixth limb; C, seventh limb; D, hemipenis, furca and post-abdominal bristle; E, masticatory organ; F, mouth.

FIGURE 34. L – H scatter plot for Neonesidea bacata n. sp., Bairdia hanaumaensis Holden, and Indo-Pacific species of Papillatabairdia.