Neonesidea holdeni, 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 : 489-496

Neonesidea holdeni n. sp.

( Figs. 2 , 24–27 )

Etymology. For John C. Holden, who was the first to undertake comprehensive identifications of Ostracoda from the Hawaiian Islands and Midway.

Material. One adult male.

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 3908M, L 786 μm, H 375 μm.

Description. Carapace (24A–H, 25F–I) elongate-siliquose, streamlined; greatest height and width located about at midlength (0.49); transparent, lacking any patch pattern, surface smooth. Left valve lateral outline subtriangular, with nearly straight anterodorsal and posterodorsal margins sloping steeply anteriorly and posteriorly from distinct, rounded mid-dorsal angle; no posterodorsal angle; anteroventral margin broadly but obliquely rounded; midventral margin straight, without ventral indentation; posteroventral margin curved, rising gradually to caudal process located a little below one-third height (0.29); posterior end narrowly rounded, obliquely truncated, forming a slightly acute angle; caudal process humped, but no posterodorsal concavity above it. Broad-based, flat, triangular terminal spine projects at posterior end of LV; complementary spine at end of RV smaller, more transparent, may be extension of chitinous flange rather than calcified; no marginal denticles on anteroventral or posteroventral margin of either valve. Fused zone very narrow, vestibules deep and broad, false RPC not observable. NPC numerous, conspicuous, many with ring-walls. AMSP not clearly observable; adhering muscles form a small, central, wedge-shaped cluster.

Carapace armed with a ferocious array of setae of many sizes ( Figs. 24 A–H, 25F–I, 26H); those of anterior region mostly quite short, those in posterior region longer; all simple in form, tapering to a point; most directed posteriorly in streamlined fashion, with a few diverging posterodorsally and posteroventrally in protective fashion. No barbed or polyfurcate setae observed. Eyelash setae unusually long, conspicuous, evenly spaced in uniform row along all margins, curving outward. About 6–8 fan-shaped, pinnate caudal setae located in row along dorsal edge of caudal process in both valves, just above terminal spine; having thick, cylindrical shafts and flattened, palmate crowns; each with 30 or more thin, close-spaced, featherlike barbs or vanes on each side, producing a stiff, densely fringed fan; these flat fans overlap tightly to form a stiff, brown, protective wall above the terminal spine.

Hook of male antennal claw ( Figs. 24 I–J, 26C–D) slender, long, with delicate, spine-like anterior and posterior horns, both horns sharply bent near tip; outer horn continues smooth profile of claw; inner horn thinner; sigmoid groove between horns.

Hemipenis ( Figs. 25 D–E, 26A, G) with narrow basal segment. Median segment longer, broader, lamellar, rounded-oblong in outline; inner-upper edge broadly arched, flared, and reinforced with a chitinous strip, forming a channel to house and support the arched copulatory tube; extending distally beyond terminal segment as a narrow, bluntly truncated, thumb-like plate. Terminal segment elongate-oblong, boomerang-shaped, with a broad base, thickest medially, slightly tapered distally; with slightly concave margins and a square, smooth, right-angled termination; indented at distal-outer edge by broad groove for copulatory tube; it functions as a brace, holding the arched inner edge of the median capsule in place and closing the half-socket through which the copulatory rod exits. Copulatory tube long, thin, tapering, flexibly coiled.

Kauplatte of masticatory organ with about 10–14 small, unevenly terminated teeth, divided by an indistinct cleft into 5–7 teeth on either side, the 2 end teeth set apart by a gap from and not as long as the others, some of the middle teeth small and spine-like or fused at the base with neighbors.

Comparisons. In carapace shape N. holdeni belongs to a complex of rather elongate species of the N. schulzi species-group, which are widely distributed in the Pacific Ocean, and which are not yet easily discriminated. These include, among others, N. woodwardiana (Brady 1880, Puri & Hulings 1976, Titterton et al. 2001; off Tongatapu, Fiji), N.? sp. aff. N. woodwardiana of Titterton & Whatley (1988a, Solomon Islands); Bairdia crosskeiana of Brady (1880, not 1866) of Holden (1967, Hawaiian Islands), N. ifalikensis Maddocks (1969, Ifalik Atoll, Caroline Islands), N. gierloffi (Hartmann, 1959) of Holden (1976; Hawaiian Islands, Midway), N. michaelseni Hartmann (1982, 1984; Western Australia, Rangiroa), and N. supercaudata Whatley, Jones & Wouters (2000, Easter Island). For most of these species the soft anatomy and carapace details (i.e. patch pattern, terminal spine, marginal denticles, setae) are not documented. As Figure 2 shows, populations identified at different localities display significant discrepancies in size.

N. holdeni is significantly smaller than the specimens identified as B. crosskeiana Brady (1880, not 1866) by Holden (1967, figs. 6 h–l) from Hawaii. Both of the Hawaiian species are substantially smaller than the dimensions reported by Brady (1880), which may apply to an unknown species from another locality. Holden (1976) identified Cenozoic fossils from Midway as Neonesidea gierloffi (Hartmann, 1959) , and he included the Hawaiian records of B. crosskeiana by Brady (1880) and Holden (1967) in that synonymy. The discrepancies shown in Figure 4 do not support this conclusion.

N. holdeni differs from N. gierloffi (as described by Hartmann from El Salvador) in many anatomical details, including setation and podomere proportions of the fifth limb and furca. The antennal claw of N. holdeni is thinner with sharply pointed, needle-like horns, the inner horn being markedly shorter; whereas the claw of N. gierloffi is thicker and more compact, with a flared hook and sinuously curved horns. The hemipenis of N. gierloffi has different proportions and construction: the median segment is oval and tapers basally, the terminal segment is broader than high and bluntly terminated, there is no thumblike lamellar projection, and the copulatory tube does not extend beyond the terminal segment.

N. holdeni is close in size and shape to N.? sp. aff. N. woodwardiana (Brady) of Titterson & Whatley (1988a, Solomon Islands), but it is smooth rather than finely punctate and lacks the spinose anterior and posteroventral marginal denticles in the LV. The lectotype of N. woodwardiana (Brady) is much larger, has a distinctive patch pattern, has a more broadly arched dorsal margin, ends in a bluntly upturned, obtusely beveled caudal process, and lacks the terminal spines (Puri & Hulings 1976; Titterton et al. 2001, off Tongatabu).

N. holdeni is much smaller than N. ifalikensis , with a more streamlined carapace; both horns of the antennal claw are sharply angled and finely pointed (not bluntly rounded), the podomere proportions and claws of the walking legs are more compact; and the terminal segment of the hemipenis is less tapered and lacks the distal setose projection.

N. holdeni is much smaller than N. michaelseni (as originally described from Sharks Bay, Western Australia, by Hartmann 1982). It lacks the patch pattern and the numerous, long, anterior and posterior marginal denticles. N. holdeni can also be distinguished by the tapering, lamellar shape of the terminal segment of the hemipenis (vs. ovate in N. michaelseni ) and the long, flexible copulatory rod (not reaching beyond terminal segment in N. michaelseni ).

Hartmann (1984) had about 50 specimens of both sexes in the population identified as N. michaelseni from Rangiroa, Tuamotu Islands. The dimensions (reported only as ranges) suggest two clusters, of which one agrees with the holotype of N. michaelseni (from Australia), but the other is much smaller (though significantly larger than N. holdeni ). If all specimens are adults, as stated, then at least two species may be represented in the Rangiroa population. From the information provided, it is not possible to determine whether the anatomical structures he illustrated belong to the larger or the smaller species. The long, flexible copulatory rod and the proportions of the hemipenis are similar to N. holdeni , except for the distally stepped end of the terminal segment (bluntly rounded in N. holdeni ). The RV illustrated as N. michaelseni by Gou (1990, pl. 1, fig. 7) is similar in lateral outline to N. michaelseni from Rangiroa but is minutely punctate rather than smooth.

N. supercaudata Whatley, Jones and Wouters (2000) is significantly larger than N. holdeni and has angulate, diamond-shaped outlines with an unusually low-set, extended caudal process.

Figures

FIGURE 24. Neonesidea holdeni n. sp., all male specimen 3908 M: A, B, right and left exteriors of entire animal; C – F, RV and LV exteriors; G, H, anterior margins of LV and RV with setae and chitinous edge-strip, eyelash setae are longer and anteriorly directed; simple setae are shorter and ventrally directed; the chain of black dots near the inner margin is a row of gland cells (?) in the underlying epidermis; I, J, left antennal claw with hook. Scale bar = 50 μm.

FIGURE 25. Neonesidea holdeni n. sp., all male specimen 3908 M. A, right side of body; B, masticatory organ; C, masticatory processes and palp of maxillule; D, E, hemipenes; G – J, posterior ends of LV and RV to show humped caudal process, terminal spine, caudal setae, and simple setae. Scale bar = 50 μm.

FIGURE 26. Neonesidea holdeni n. sp., all male specimen 3908 M. A, G, hemipenes and furca; B, furca; C, D, antenna; E, mouth; F, segregated setae of maxillule with wedge-shaped terminations; H, one caudal seta; I, masticatory organ.

FIGURE 27. Neonesidea holdeni n. sp., all male specimen 3908 M. A, sixth limb; B, seventh limb; C, fifth limb; D, brushshaped organ; E, mandible; F, palp and masticatory processes of maxillule.

FIGURE 2. L – H scatter plot for Hawaiian records of Bairdia amygdaloides of Brady (1880) and similar species.

FIGURE 4. L – H scatter plot for Pacific records of Bairdia crosskeiana of Brady (1880) and similar species.