Neonesidea plumulosa, 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 : 483-487

Neonesidea plumulosa n. sp.

( Figs. 5 E–F, 18–23)

Etymology. Latin noun plumula, diminutive of pluma, a soft feather, down; plus adjectival suffix -osus, full of, prone to; referring to the caudal setae.

Material. One adult male specimen, holotype male specimen 3960M.

Dimensions. Holotype male specimen 3960M, LVL 1008 μm, LVH 563 μm.

Type locality. French Frigate Shoals, FFS–TC–09, 23 o 52.9 N, 166 o 15.1 W, 12 September 2000. N forereef, N of Tern Island, depth 10– 15 m.

Description. Carapace ( Figs. 18 A–J, 19A–D) elongate-ovoid, streamlined, siliquose, moderately inflated, tapering, greatest thickness and greatest height located a little anterior to midlength (0.42). Surface smooth, not punctate, with fine granular microtexture visible in transmitted light. Lateral outline of left valve elongate-ovate, with smoothly curved, low-arched dorsal margin, no anterodorsal or posterodorsal angles; anteroventral margin obliquely rounded, evenly curved; ventral margin straight to very slightly convex, without ventral indentation; posteroventral margin slightly curved, rising gradually to slightly caudate posterior end; caudal process obliquely truncated, humped, slightly flared and thickened dorsally beneath weak posterodorsal concavity; posterior end narrowly rounded, forming symmetrical obtuse angle, located at about one-third of height (0.35). Anteroventral margin of LV smooth, except for extremely short, triangular granules or minute denticles, regularly spaced with wide gaps, located between RPC, barely visible. Posteroventral margin of LV edged with numerous, easily visible, asymmetrical, triangular denticles, with long axis oriented posteroventrally, increasing in size toward posterior, then decreasing in size dorsally; no terminal spine. Anterior and posterior margins of RV with extremely narrow chitinous flange; short, flaring, ragged chitinous frill at caudal process. Marginal fused zone narrow, vestibules deep and broad; NPC and false RPC numerous but not clearly observed because of preservation. AMSP large, rosette-shaped, not clearly seen; obscured by oval opaque patch located centrally; indistinct somewhat opaque regions located mid-dorsally, anteroventrally and posteroventrally.

Carapace setae ( Figs. 5 E–F, 18E–F, H, J, 19A–D) numerous, easily visible though not conspicuous, yellow, closely spaced; of various sizes, most relatively short, none excessively long; all simple in form, tapering to a single point. Barbed setae suspected to be present but not clearly observed. Eyelash setae numerous, close-spaced, short, thin-walled, arranged in even row along all free margins, curving out and up. About 6 caudal setae located along posterodorsal edge of humped caudal process in each valve; each with 15–20 close-spaced, fairly short, lateral vanes or barbs alternating along both sides; outline leaf-like but not palmate or fringed.

Male antennal claw ( Figs. 20 C–D, G, J, 21A–B) relatively short, wide, slightly curved; distal edge of outer horn continues smooth profile of claw; outer horn weakly curved with narrowly rounded termination; inner horn shorter, thinner, tapering, distal edge nearly straight, ending in sharp point; sigmoid groove between horns.

Hemipenis ( Figs. 19 E–H, 20B, 22F) with large, wedge-shaped, basal segment; shorter, curled, lamellar median segment, which is straight-edged and polygonal as seen in life position but circular in outline as compressed in dissection mount; terminal segment short, with two tapering chitinous ribs or spines supporting a thin, slightly curved wall between, enclosing a cuspate space, distal (outer) spine a little longer and thinner than proximal (inner) spine; copulatory tube short, inflexible, nearly straight, barely reaching terminal segment, ending in short, rigid copulatory rod.

Kauplatte ( Figs. 20 F, 21E) of masticatory organ with 8 broad marginal teeth of unequal sizes, with triangular or irregular terminations, two center teeth broadest and highest; end teeth separated from others by gaps; 2 straight thin spines at ends, longer than teeth.

Comparisons. N. plumulosa is easily distinguished from species of the N. schulzi species-group by its softly rounded, sinuous, subtly caudate lateral outline (rather than elongate-subtriangular or teardrop-shaped) and the absence of a terminal spine in the LV. The caudal setae are leaf-like, not fringed and lamellose as in N. schulzi .

N. plumulosa is distinct from another complex of species, which includes N. woodwardiana (Brady, 1880, off Tongatabu, Fiji Islands; as redescribed by Puri & Hulings 1976, Titterton et al. 2001), N.? sp. aff. N. woodwardiana of Titterton & Whatley (1988a, Solomon Islands), and N.? sp. aff. N. woodwardiana of Gou (1990, Hainan Island, South China Sea), by its more gently curving contours, conspicuous marginal denticles, and absence of a patch pattern, as well as significant size discrepancies.

At first glance, N. plumulosa appears to resemble some species of the N. pateriformis species-group, but its lateral outline is more elongate and more caudate, and in dorsal view it is less compressed. The caudal setae appear to have more numerous, more closely spaced vanes and do not taper like those of N. tenera .

N. plumulosa is the same size as N. sp. CP of Maddocks (1995, Nosy Be) and is similar in lateral outline, although its lateral outline curves more gracefully, and it has conspicuous marginal denticles. Maddocks (1995, pl. 10, fig. 1) illustrated enlarged pores on the dorsal edge of the caudal process for N. sp. CP, which may indicate the presence of caudal setae in life.

N. plumulosa is substantially smaller than B. ritugerda Holden (1967, Hawaii) and more elongate, with a smoothly arching dorsal margin, a longer, more nearly straight mid-dorsal segment, a curved (rather than straight) anterodorsal segment, indistinct anterodorsal and posterodorsal angles, and a curved rather than straight anteroventral margin. It is more elongate and much smaller than B. kauaiensis Holden (1967, Hawaii).

N. plumulosa is somewhat similar in lateral outline to N. lenitiphila Hartmann (1984, Rangiroa), though less elongate through the midsection, and it lacks many distinctive details, including the unique hemipenis with wartlike terminal tubercles. It is much larger than N. anfieldingae Hartmann (1984, Rangiroa), lacks the bushy, many-branched carapace setae, and most details of the hemipenis are different.

N. plumulosa is similar in size, lateral outline and marginal denticles to N. michaelseni Hartmann (1982, Sharks Bay, Western Australia), except that the posterior end is slightly less acutely extended, and it lacks the terminal spine in the LV. Hartmann's drawing of the hemipenis (1982, fig. 49) is generalized but resembles that of N. plumulosa in its compact proportions, oblong terminal part, and short, straight copulatory tube.

N. plumulosa has much larger carapace size than the specimens identified as N. michaelseni by Hartmann (1984, Rangiroa), and it differs in lateral outline (weakly convex ventral margin, more symmetrically extended caudal process). Hartmann stated that he had about 50 adults of both sexes, and that Polynesian populations often are smaller than the same species in Australian waters. The ranges of adult dimensions reported by Hartmann (1984, p. 123) are excessive for a single cluster, however ( Fig. 23 ). It is likely that his population included juveniles as well as adults, and perhaps more than one species. Hartmann provided excellent SEM illustrations of the Polynesian male and female, displaying evident sexual dimorphism, but unfortunately he did not report the individual dimensions or magnifications. He meticulously illustrated many carapace details, including eyelash setae, caudal setae, simple setae, marginal denticles and the terminal spine. Hartmann's drawings of the hemipenis (1984, figs. 27, 28) show a more elongate central capsule, a tapering terminal part with stepped margin, and a long, flexibly coiled, tapering copulatory rod and tube. This record from Rangiroa cannot be confidently identified with either N. michaelseni (Sharks Bay, Australia) or N. plumulosa .

Geography. Known at present only from French Frigate Shoals in the Hawaiian Islands.

Figures

FIGURE 5. Caudal setae and simple setae on caudal process. A, C, Neonesidea tenera Brady, female specimen 3905 F, LV and RV exteriors. B, D, Neonesidea tenera Brady, juvenile female instar A – 1 specimen 3957 J, RV and LV exteriors. E, F, Neonesidea plumulosa n. sp., male specimen 3960 M, LV and RV exteriors. Scale bar = 10 μm.

FIGURE 18. Neonesidea plumulosa n. sp., all male specimen 3960 M. A, B, E, I, interior of LV containing entire body, E also shows caudal setae and marginal denticles; C, D, right and left exteriors of intact carapace; F, G, RV exteriors, showing opaque patch and AMSP; H, right anterior margin of carapace, showing eyelash setae and simple setae; J, RV exterior with NPC and setae. Scale bar = 50 μm.

FIGURE 19. Neonesidea plumulosa n. sp., all male specimen 3960 M. A, left posterior end of carapace to show caudal setae and simple setae; B – D, right posterior end of carapace to show angulate, slightly humped caudal process, caudal setae, simple setae, and zigzag chitinous frill around terminal angle; E, left and right hemipenes; F, both hemipenes; G, detail of F to show copulatory tube and terminal segment. Scale bar = 10 μm.

FIGURE 20. Neonesidea plumulosa n. sp., all male specimen 3960 M. A, left side of entire body; B, dorsal view of both hemipenes and furcae; C, left antennal hook before dissection with too-slender proportions, because the hook is slightly bent and rotated relative to the plane of the claw and limb, to show how perspective alters shape; D, G, same left antennal hook after dissection, seen straight-on, enlarged to show corrugated surface of anterior horn; J, right antennal hook; E, maxillule; F, masticatory organ; H, I, spermatophore. Scale bar = 10 μm.

FIGURE 23. L – H scatter plot for Neonesidea plumulosa n. sp. and similar Indo-Pacific species.