Ilyodromus sensaddito, Koenders, 2017

Koenders, Annette, 2017, Patterns of genetic divergence in the Ilyodromus amplicolis lineage (Crustacea, Ostracoda), with descriptions of three new species, Zootaxa 4318 (1), pp. 1-46 : 17-24

Ilyodromus sensaddito n. sp.

Figures 10 to 14

Diagnosis. Adult females up to 1950 µm in length; both valves with apex of anterior and posterior margins below mid-height in lateral view, calcified inner lamella broad anteriorly and posteriorly, extending inwardly by approximately 1/4 of valve length anteriorly and 1/5 posteriorly, and with a blunt antero-ventral peg (remnants of reduced inner list) in LV. A1 third segment with dorsal seta longer than ventral seta, and second segment with seta alongside RO. A2 with natatory setae very reduced, less than 0.05 times length of second endopodal segment. Males with L5 Rpp and Lpp almost symmetrical, Hp ls narrow proximally, pointed medially, and widening to rounded latero-distal margin, proximally with lateral rounded protrusion; ms elongated with near parallel margins and rounded distal margin, reaching as far as ls.

Differential diagnosis. The feature that distinguishes this species from all others of Ilyodromus , and perhaps all other Cyprididae (preliminary survey in Smith & Matzke-Karasz 2008), is the seta based alongside the RO on the A1 second segment. Additional characters that distinguish this species from others of the Ilyodromus amplicolis lineage include the Hp ls being pointed medially, and having a rounded latero-distal margin. In other species the Hp ls has a straight lateral margin (as in I. armacutis n. sp.), or is sub-rectangular (as in I. amplicolis ). The occurrence of five very reduced natatory setae flanked by one longer set on the A2 of I. sensaddito n. sp. is unique compared to other species of this lineage. In I. amplicolis , the longest seta is flanked by four short setae on one side and a seta of intermediate length on the other; in I. armacutis n. sp. the two longest setae are flanked by three very reduced setae on one side, and a seta of intermediate length on the other; in I. hiatus n. sp., one natatory seta is flanked by four reduced natatory setae on one side, and a longer seta on the other.

Etymology. The name of this species is derived from the latin words ’addito’ (meaning additional or extra) and ’sensus’ (meaning sensory), for the unusual presence of a secondary structure (seta) alongside the sensory organ (RO) on the ventral side of the A1 second segment.

Type locality. Granite rock pool on Frog Rock, near Southern Cross, Western Australia, Australia. Coordinates: S 31° 29’ 53.484”, E 119° 13’ 51.096” ( Figure 2 ).

Type material. Holotype male with soft parts dissected on a sealed slide (WAM57844) and valves stored dry in a micropalaeontological slide (WAM57844); one male paratype with soft parts dissected on sealed slides (WAM57845) and valves stored dry in a micropalaeontological slide (WAM57845); four male paratypes with carapaces stored dry on micropalaeontological slides (WAM57849, WAM57850, WAM57851, RS698). One male paratype with valves stored in a micropalaeontological slide, and soft parts used for DNA extraction (WAM57856). One male paratype critical point dried with RV removed stored in a micropalaeontological slide (WAM57858). Allotype female with soft parts dissected on a sealed slide (WAM57843) and valves stored dry in a micropalaeontological slide (WAM57843); one female paratype with soft parts dissected on sealed slides (WAM57842) and valves stored dry in a micropalaeontological slide (WAM57842); three female paratypes with carapaces stored dry on micropalaeontological slides (WAM57846, WAM57847, WAM57848). Four female paratypes with valves stored in micropalaeontological slides, and soft parts used for DNA extraction (WAM57852, WAM57853, WAM57854, WAM57855). One female paratype critical point dried with RV removed stored in a micropalaeontological slide (WAM57857).

Many in toto paratype specimens in EtOH recollected from type locality by RS on 18 September 2013 stored in a vial ( WAM 57859 - Granite rock pool on Frog Rock, near Southern Cross, Western Australia, Australia).

Measurements (in µm). ♀ RV: L = 1831–1926 (n = 5), H = 877–930 (n = 5). LV: L = 1856–1957 (n = 5), H = 908–950 (n = 5). Cp: L = 1881–1950 (n = 3), W = 685–710 (n = 2), H = 898 (n =1).

♂ RV: L = 1592–1623 (n = 3), H = 752–754 (n = 2). LV: L = 1606–1652 (n = 3), H = 758–777 (n = 3). Cp: L = 1428–1652 (n = 3), W = 563–598 (n = 2), H = 663 (n = 1).

Description. Female carapace up to 1950 µm and elongate ( Figure 10 A, C & E), with anterior and posterior edges pointed in dorsal and ventral view, but with anterior one more elongated than posterior one ( Figure 10 C & E). Greatest width situated at mid-length. In lateral view ( Figure 10 A), dorsal margin almost straight along dorsal hinge for about half its length, sloping more sharply in caudal direction. Ventral margin straight. Anterior and posterior margins with apex well below mid-height. LV only slightly overlapping RV dorsally and ventrally. Greatest height situated along middle third. All external valve surfaces with deep, broad striations, with finer striations nested within them ( Figure 10 B).

In interior view ( Figure 10 G–J), RV and LV with very similar shape and size. Both valves with calcified inner lamella broad, and extending around entire valve, aside from dorsal hinge area; calcified inner lamella extending inwardly, by approximately 1/4 of valve length anteriorly and 1/5 of valve length posteriorly. LV calcified inner lamella with a blunt antero-ventral peg (remnants of reduced inner list) ( Figure 10 K–L). Central muscle scar consisting of a central group of five small scars with one additional small scar set apart antero-dorsally, and another large elongated scar set apart antero-ventrally from the central group.

A1 ( Figure 11 A) seven segmented (with first two fused segments counted as only one segment). Length of first segment approximately twice the width, with one dorsal seta and two longer ventral setae. Length to width ratio of second segment approximately 1:1, this segment medio-dorsally with a long seta; medio-ventrally with another seta ( Figure 11 B) with length almost that of the segment, and a RO with length approximately 0.2 times the length of the segment; this RO ( Figures 11 B, 12A & B) two segmented, with distal flagella. Third A1 segment elongate, with length approximately 2.5 times the width, with one ventral seta of similar length to that of the segment, and a slightly longer dorsal seta. Fourth segment with length approximately 1.5 times the width, carrying two ventral setae, the ventral-most shorter, and two dorsal setae of the same length as the longer ventral seta. Fifth segment with length approximately twice its width, with two dorsal natatory setae, and two shorter ventral setae, the latter approximately half the length of the dorsal natatory setae, the ventral-most being the shortest and broadest. Sixth segment with length approximately twice its width, apically with three long reduced setae, dorsal to this group one seta of less than half the length of the others. Seventh segment with length approximately twice its width, distally carrying two short setae, a broader ventral claw-like seta and a dorsal aesthetasc Ya with length approximately half the other short setae.

A2 ( Figure 11 C) first protopodal segment with two latero-distal setae, as typical of Cypridoidea. Second protopodal segment (fused with first) with one distal seta on inner side of the segment. Exopod a small rudimentary plate, with three setae, the anterior-most shorter than the segment, the middle seta under 1/2 this length, and the posterior-most very short. First endopodal segment with aesthetasc Y elongate and two segmented; distally this segment with all natatory setae reduced ( Figures 11 D & 12C), flanked by another longer seta, the five reduced setae being less than 0.2 times the length of the anterior-most seta, and less than 0.05 times the length of the second endopodal segment; ventro-distally this segment with a large bristled seta, with length approximately 0.7 times that of the segment. Second endopodal segment with four medio-ventral t-setae, two medio-dorsal setae on the opposite segment margin, three subapical z-setae, three distal claws (G1–G3) and a short aesthetasc (y2); G1 and G2 of similar length, approximately 1.5 times the length of the second endopodal segment with G3 shorter. Terminal segment approximately twice as long as its basal width, distally with Gm a seta, and GM a claw, reaching as far as G1–G2, and approximately 1.4 times the length of Gm; one solitary g seta and one seta fused at the base with aesthetasc y3, y3 and g seta being under half the length of GM.

Md coxa ( Figure 11 E) distally with teeth accompanied by few setae, and more proximally from largest tooth an elongate seta covered in stiff setules, as typical of Cypridoidea. Md palp ( Figure 11 F) with length ratios of four palp segments 5:1:2:1. First palp segment the largest, with length approximately twice the width; this segment with a group of four setae; the most proximal seta long and smooth, followed by an S1 seta of similar length, an α seta, then most distally a broader S2 seta, both S setae of similar length and carrying rows of long setules; α seta short and spine-like distally, but with a broad base; total length of α seta approximately 0.2 times the length of the S setae. Second palp segment stout, its width about twice its length, and with six setae posteriorly; β seta short and stout, covered with long setules, and almost of the same length as the α seta; four subsequent setae all slightly longer than the S setae; last seta in this group originating more distally, about half the length of the S setae, and covered with rows of setules; this segment also with a group of three antero-dorsal setae, two of which smooth, and the most distal one shortest, with long setules over the distal half of its length. Third palp segment elongate with length approximately 1.5 times its width, antero-distally with four smooth setae, all of similar length to the first palp segment; distal margin of third palp segment with γ seta anteriorly, and a row of three additional setae, γ seta elongate and with short setules covering the distal half, three neighbouring setae of similar length; ventral margin of third segment with two subapical setae, one very short, the other long, approximately the same length as the S setae. Terminal palp segment short, with length approximately 1.5 times its width; distally with a group of three claws, one shorter than the other two, and three setae approximately 2/3 the length of the longest claw.

Mx ( Figure 13 A) endopodite two segmented. First segment with six setae on the dorso-apical margin, three of these setae smooth and of similar length, two slightly shorter and hirsute, the most proximal one slightly longer; a seventh seta being the shortest, based more medially than the others, and pointed posteriorly. Second endopodal segment spatulate, distally with three claws and three setae. Third endite with one proximal seta on ventral margin, distally with two strongly developed but smooth claws positioned between seven setae dorsally, and one seta ventrally, all setae on the distal margin of similar length, apart from one seta based slightly more proximal, this seta stout, bent, covered with long stiff setules, and approximately one third of the length of the other setae (not shown in illustrated specimen). Chaetotaxy of endites I and II not elaborated. Respiratory plate with approximately 24 rays, six of these reflexed.

L5 ( Figure 13 B) protopod with two a-setae of similar length based proximally on the anterior margin, one long b-seta on ventral margin, and a long, hirsute d-seta based anteriorly. Endite with 14 setae lining the antero-distal margin of varying length and shape. Endopodite with three distal setae, one longer and less hirsute than the other two. Exopodite a respiratory plate with six rays.

L6 ( Figure 13 C) a walking limb, with first two segments bearing d1 and d2 setae antero-distally, with d2 being approximately 0.7 times the length of d1. Endopod four-segmented. First endopodal segment with e seta; posterior margin hirsute and arranged into five groupings. Second endopodal segment with f seta antero-distally of approximately 0.6 times the length of the third endopodal segment. Third endopodal segment with g seta anterodistally, plus another shorter seta alongside. Terminal segment with h2 developed into a long serrated claw, about 2.4 times the length of the third endopodal segment, seta h3 0.8 times the length of h1, h3 approximately 1.5 times the length of the terminal segment. Length ratios of first to fourth endopodal segments approximately 8:6:5:2.

L7 ( Figure 13 D) a cleaning limb, basal segment with setae d1 and d2 on anterior margin, and seta dp posterodistally; seta dp slightly longer than and d1 and d2. First endopodal segment the longest, and bearing a bristled antero-distal e seta with length approximately the same as d2 seta. Second and third endopodal segments fused, with a bristled f seta approximately in the middle of this fused segment, this seta approximately half the length of the e seta. Third endopodal segment without g seta. Terminal segment fused with third endopodal segment to form a pincer organ, and bearing three setae: seta h1 forming a comb-like seta, h2 short, under half the length of the f seta, a reflexed seta h3 shorter than the f seta.

CR ( Figures 12 D & 13F) symmetrical and elongated, each with two serrated claws, an apical Sa seta, and with Sp claw-like but with serration on all sides ( Figure 13 D). Claw Ga approximately 0.4 times the length of the ramus. Length ratios of claws Sa, Ga, Gp and Sp to ramus 0.15, 0.4, 0.35 and 0.2, respectively. Attachment of CR ( Figure 13 E) with slightly bent main stem, bearing an obvious branch at proximal end, and a distal bifurcation.

Male Cp smaller than that of female ( Figure 10 D–F) and valves with calcified inner lamella extending inward less than in females ( Figure 10 I & J), but otherwise of similar appearance.

Male L5 prehensile palps symmetrical ( Figures 14 B, C & 12E) with first segment over twice central width; subapically with two sensory organs; second segment narrow and hook shaped with distal sensory organ.

Male Hp ( Figures 14 A, Figure 12 F) ls narrow proximally, pointed medially, and widening to rounded laterodistal margin, proximally with lateral rounded protrusion; ms elongated with near parallel margins and rounded distal margin, reaching as far as ls.

Distribution and habitat. This species has only been recorded from its type locality: Granite rock pool at base of Frog Rock, near Southern Cross, Western Australia, Australia; a large pool with marginal emergent macrophytes (Supplementary file, Table S3). As with other species of this lineage, and many others of the genus, the reduced natatory setae on the A1 and A2 ( Figure 12 C) suggest this species is adapted to benthic life.

Figures

FIGURE 2. Geographic origin of material of the Ilyodromus amplicolis lineage examined from Western Australia, showing the locality of each species represented by a corresponding symbol colour (colour only visible in electronic version). Symbols placed on circles originate from the centre of that circle, and represent pools that were positioned on the same rock outcrop.

FIGURE 10. Ilyodromus sensaddito. n. sp. (RTJ 7) from granite rock pool at base of Frog Rock, near Southern Cross, Western Australia, Australia A – L. A. CpRl ♀ (WAM 57847). B. CpD ♀ detail of valve striation pattern (WAM 57848). C. CpD ♀ (WAM 57848). D. CpD ♂ (WAM 57849). E. CpV ♀ (WAM 57846). F. CpV ♂ (WAM 57850). G. LVi ♀ (WAM 57842) indicating anterior peg. H. RVi ♀ (WAM 57842). I. LVi ♂ (WAM 57844) indicating anterior peg. J. RVi ♂ (WAM 57844). K. Lvi ♂ detail of anterior peg (WAM 57844). L. LVi ♀ detail of anterior peg (WAM 57842). Scales: A, C – J = 1000 µm, B = 30 µm, K – L = 100 µm

FIGURE 11. Ilyodromus sensaddito. n. sp. ♀ (WAM 57843) from granite rock pool at base of Frog Rock, near Southern Cross, Western Australia, Australia A – F. A. A 1. B. A 1, detail of RO. C. A 2. D. A 2, detail of natatory setae. E. Md coxa. F. Md palp. Scales: A, C, E – F = 200 µm, B, D = 22 µm

FIGURE 12. Ilyodromus sensaddito. n. sp. from Drummond Pool, Western Australia, Australia A – F. A. ♀, (WAM 57857) Left and right A 1, detail of RO (red) and additional seta. B. ♀ (WAM 57857), Left A 1, detail of RO (red). C. ♀ (WAM 57857), A 2, detail of natatory setae (red). D. ♀ (WAM 57857), CR, detail of Sp (red). E. ♂ (WAM 57858), Left and right L 5, detail of prehensile palp first (blue) and second (yellow) segments. F. ♂ (WAM 57858), Hp, detail of ls (blue) and ms (yellow). Colour only visible in electronic version. Scales: A, C = 50 µm, B = 10 µm, D = 150 µm, E = 100 µm, F = 200 µm

FIGURE 13. Ilyodromus sensaddito. n. sp. ♀ (WAM 57843, RTJ 7) from granite rock pool at base of Frog Rock, near Southern Cross, Western Australia, Australia A – F. A. Mx palp and endites, without detail on second and third endites. B. L 5. C. L 6. D. L 7. E. CR attachment. F. CR. Scales: A – F = 150 µm

FIGURE 14. Ilyodromus sensaddito. n. sp. ♂ (WAM 57844) from granite rock pool at base of Frog Rock, near Southern Cross, Western Australia, Australia A – C. A. Hp. B. Prehensile palp of right L 5. C. Prehensile palp of left L 5. Scales: A – C = 77 µm.