Ilyodromus amplicolis De Deckker, 1981

Martens, Koen, 2017, On the affinity of Isocypridinae and Herpetocypridinae, with redescriptions of four species of Ilyodromus Sars, 1894 (Crustacea, Ostracoda), Zootaxa 4318 (1), pp. 47-81 : 51-58

Ilyodromus amplicolis De Deckker, 1981

Figures 2 to 5

1981 Ilyodromus amplicolis n. Sp. — De Deckker: 54–56, FigS 8 , 9 l–r h.

nov. comb. 2011 Isocypris amplicolis ( De Deckker, 1981) —MartenS & SaVatenalinton: 50.

Type locality. Granite rock pool on top of Boyagin Rock, between Brookton and Pingelly, Western Australia, Australia ( De Deckker 1981). Approximate coordinates: S 32° 28’ 14.92”, E 116° 53’ 10.29” ( Figure 1 ).

Material investigated. Holotype female with soft parts dissected on a sealed slide (J1171a) and valves stored dry in a micropalaeontological slide (J1171b); one male paratype with soft parts dissected on a sealed slide (J1172a) and valves stored dry in a micropalaeontological slide (J1172b); two female paratypes with carapaces stored dry on micropalaeontological slides (J1173a, J1174a).

One female topotype recollected from type locality with soft parts dissected on a sealed slide and valves stored dry in a micropalaeontological slide (WAM57208); one male topotype recollected from type locality with soft parts dissected on a sealed slide and valves stored dry in a micropalaeontological slide (WAM57209). Three female topotypes recollected from type locality with carapaces stored dry in micropalaeontological slides (WAM57210 to WAM57212), three male topotypes recollected from type locality with carapaces stored dry in micropalaeontological slides (WAM57213 to WAM57215).

Many in toto topotype specimens in EtOH recollected from type locality by RS on the 24th September 2013 stored in two vials ( WAM 57226, WAM 57227 - granite rock pool on top of Boyagin Rock, between Brookton and Pingelly, Western Australia, Australia).

Measurements (in µm). ♀ RV: L = 1875–2027 (n = 4), H = 914–975 (n = 4). LV: L = 1711–2057 (n = 5), H = 848–989 (n = 4). Cp: L = 2290 (n = 1), W = 1048 (n = 1).

♂ RV: L = 1373–1558 (n = 2), H = 615–714 (n = 2). LV: L = 1368–1537 (n = 2), H = 552 (n = 1).

Diagnosis. Adults large, up to 2000 µm in length, valve surfaces with deep, broad striations and finer striations nested within them. CIL of both valves broad anteriorly and posteriorly, extending inwardly by approximately 1/4 of valve length, and with a blunt anteroventral peg (remnants of reduced inner list) in LV. A1 third segment with dorsal seta shorter than ventral seta, and RO 0.3 times length of second segment of A1. A2 with longest natatory setae 0.7 times length of second endopodal segment. Males with L5 Rpp and Lpp almost symmetrical, Hp with ls broad and rectangular, with almost straight distal margin, proximally with lateral rounded protrusion; ms with rounded edge, reaching almost as far as ls.

Differential diagnosis (see electronic supplementary file, Table S1). This species can be distinguished from all others by the Hp having a broad and rectangular ls. In females, the lengths of the natatory setae on the A2 are unique, with the longest being flanked by four short setae on one side, and a seta of intermediate length on the other.

Description. Carapaces dark green to dark blue in colour. Female carapace elongate ( Figure 2 A & B), with anterior and posterior edges pointed in dorsal and ventral view, but with anterior one more elongated than posterior one. Greatest width situated at mid-length.

In lateral view ( Figure 2 A & B), dorsal margin almost straight along dorsal hinge for about half of its length, sloping in caudal direction, and with slight concavity in front of the anterodorsal hinge. Ventral margin slightly sinuous at mid-length. Anterior margin slightly broader than posterior one, with apex of both anterior and posterior margins below mid-height. LV only slightly overlapping RV around entire margin. Greatest height situated at approximately 1/4 from anterior. All external valve surfaces with deep, broad striations, with finer striations nested within them ( Figure 2 I).

In interior view, RV and LV with similar shape, mainly differing in size with LV being slightly larger ( Figure 2 C & D). Both valves with CIL broad, and extending around entire valve, aside from dorsal hinge area; CIL extending inward, by approximately 1/4 of valve length anteriorly, and by approximately 1/5 of valve length posteriorly, much narrower ventrally at mid-length. Ventral margin sinuous at mid-length ( Figure 2 C–F). CIL in LV with a blunt anteroventral peg (remnants of reduced inner list) ( Figure 2 G–H). Central muscle scars consisting of a central group of five scars with two other large scars set apart anteroventrally from central group.

A1 ( Figure 3 B & C) seven segmented (with first two fused segments counted as only one segment). Length of first segment approximately twice the width, with one short dorsal seta and two long ventral setae. Length to width ratio of second segment approximately 1:1, this segment with a long medio-dorsal seta and a RO of approximately half the length of the segment; this RO ( Figure 3 D) two-segmented, with distal flagella rarely visible. Third A1 segment elongate, with length approximately twice the width, additionally with one ventral seta, approximately 1.5 times the length of the segment and a longer dorsal seta with length over twice that of the segment. Fourth segment with length to width ratio approximately 1:1, carrying two ventral setae, the ventral-most one c 0.75 times the length of the other, and two dorsal natatory setae, both of these much longer than the ventral setae. Fifth segment ( Figure 3 C) with length approximately twice its width, with two dorsal natatory setae, and two shorter ventral setae, the latter less than half the length of the dorsal natatory setae, the ventral-most being the shortest and broadest. Sixth segment with length approximately twice its width, with an apical group of three reduced setae, dorsal to this group one very short seta, and ventral to this group one seta of approximately half the length of the three reduced setae. Seventh segment with length approximately twice its width, distally carrying one long seta, one short seta, a broader ventral claw-like seta and a dorsal aesthetasc Ya with length shorter than any of the other setae.

First protopodal segment of A2 ( Figure 3 A) 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 of similar length to the segment, the middle seta approximately 1/2 this length, and the posterior-most very short. First endopodal segment with aesthetasc Y elongate and two-segmented, with distal segment approximately half the length of the proximal one; distally this segment ( Figure 3 E) with four very reduced and one short natatory setae, flanked by another short adjacent seta, the four reduced setae being less than 0.2 times the length of the anterior-most seta, and less than 0.1 times the length of the second endopodal segment; ventro-distally this segment with a large bristled seta, of similar length as the segment. Second endopodal segment with four medio-ventral t-setae, two medio-dorsal setae on the opposite segment margin, three subapical z-setae and three distal claws (G1–G3), the latter all of similar length, approximately twice the length of the second endopodal segment, and a short aesthetasc (y2). Terminal segment approximately twice as long as its basal width, distally with two claws, the larger one (GM) reaching as far as G1–G3, and about 1.8 times the length of the shorter claw on this segment (Gm); one solitary seta g and one seta fused at the base with aesthetasc y3, all being approximately as long as the length of claw Gm.

Md coxa ( Figure 3 G) 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 3 F) with length ratios of four palp segments 4:1:2:1. First palp segment the largest, with length approximately 1.6 times 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, the more proximal S1 straight, the distal S2 bent; α seta short and spine-like distally, but with a broad base; total length of α seta approximately 0.4 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 of similar length as the S setae; terminal seta in this group originating more distally, about half the length of the S setae, and covered with rows of long setules; this segment also with a group of three antero-dorsal setae, two of which smooth, with similar length to the S setae, and the most distal one shorter, 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, the three most distal ones of similar length as the first palp segment, the most proximal one slightly shorter; distal margin of third palp segment with γ seta anteriorly (missing in illustrated holotype in Figure 3 F), and a row of three additional setae, γ seta elongate and with short setules covering the distal half, three neighbouring setae of similar length (two missing in illustrated holotype); 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 longer than the other two, and four setae of similar length to the shorter claws.

Rake-like organ (not illustrated) with elongate proximal arm, broadening abruptly to a 7–9 toothed rake structure.

Mx ( Figure 4 A) endopodite two-segmented. First segment with six setae on the dorsa-apical margin, three of these setae smooth and of similar length, two slightly longer and hirsute, the most proximal 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 distally with two strongly developed but smooth claws positioned between seven setae dorsally (one not visible in illustrated holotype), 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. Chaetotaxy of endites I and II not elaborated. Respiratory plate (not illustrated) with approximately 26 rays, six of these reflexed.

L5 ( Figure 4 B) protopod with two a-setae of similar length, based proximally on the anterior margin, one long and hirsute 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 hirsute distal setae, one longer than the other two. Exopodite a respiratory plate with 6 setae (not shown).

L6 ( Figure 4 C) a walking limb, with first two segments bearing d1 and d2 setae antero-distally, with d2 being approximately 1.5 x longer than d1. Endopod four-segmented. First endopodal segment with e-seta (damaged and missing in illustrated holotype); posterior margin hirsute and arranged into four groupings. Second endopodal segment with f-seta antero-distally and approximately the same length as the third endopodal segment. Third endopodal segment with g-seta antero-distally, plus one shorter seta, approximately half the length of the g-seta, and less than half the length of the third endopodal segment. Terminal segment with h2 developed into a long serrated claw, about 2.6 times the length of the third endopodal segment, seta h3 0.7 times the length of h1, h3 approximately twice the length of the terminal segment. Length ratios of first to fourth endopodal segments approximately 8:6:5:2.

L7 ( Figure 4 E) 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, approximately half the length of the f-seta, a reflexed seta h3 slightly longer than the f-seta.

CR ( Figure 4 F) symmetrical and elongated, each with three serrated claws and apical Sa seta. Claw Ga nearly half the length of the ramus. Length ratios of claws Sa, Ga, Gp and Sp to ramus 0.1, 0.5, 0.5 and 0.2, respectively. Attachment of CR ( Figure 4 D) with slightly bent main stem, bearing an obvious branch at proximal end, and a distal bifurcation.

Male Cp smaller than females and with CIL of both valves extending inward far less than in females ( Figure 2 E & F, the latter deformed because of decalcification), but otherwise of similar appearance.

Male L5 prehensile palps ( Figure 5 B & C) with first segment approximately twice its central width; subapically with two sensory organs of similar length; second segment narrow and hook shaped with distal sensory organ; Rpp second segment broader than Lpp second segment, but otherwise left and right prehensile palps symmetrical.

Male Hp ( Figure 5 A) ls broad and rectangular, with nearly straight distal margin, protruding slightly further than ms, proximally with lateral globular protrusion; ms with broad base narrowing to rounded distal margin, 0.8 times the width of ls at mid-length, with additional proximal lobe over ls.

Remarks. Ilyodromus amplicolis was described in 1981 from a granite rock pool on top of Boyagin Rock, between Brookton and Pingelly, Western Australia, Australia ( De Deckker 1981). In these descriptions, several features of the valves and appendages were not clearly visible in illustrations and were not described. Here, type and topotype material for this species is used in a redescription that includes these features.

Distribution and habitat. This species mainly occurs in temporary rock pools ( Bayly 1982; De Deckker 1981), but has also been found in pit gnammas (Timms 2014), roadside ditches ( De Deckker 1981) and lakes ( Cale et al. 2004) in Western Australia. At the type locality, this species was not observed swimming in open water, but instead rapidly ’running’ across the sediment surface. The reduced natatory setae on the A1 and A2 ( Figure 3 ) support this notion of the species being a true benthic form, as was observed for many other Ilyodromus species by Sars (1894).

Figures

FIGURE 1. DiStribUtion of Ilyodromus redeScribed in the preSent StUdy, ShoWing the locality of each SpecieS repreSented by a correSponding Symbol.

FIGURE 2. Ilyodromus amplicolis. from granite rock pool on top of Boyagin Rock, betWeen Brookton and Pingelly, WeStern AUStralia, AUStralia A – I. A. CpRl ♀ (Paratype NMV J 1174 a). B. CpLl ♀ (Paratype NMV J 1173 a). C. RVi ♀ (Holotype NMV J 1171 a) indicating anterior peg. D. LVi ♀ (Holotype NMV J 1171 a). E. LVi ♂ (Paratype NMV J 1172 a) indicating anterior peg. F. RVi ♂ (Paratype NMV J 1172 a, note ValVe diStorted by decalcification). G. LVi ♂, detail of E (Paratype NMV J 1172 a) indicating anterior peg. H. LVi ♀, detail of C (Holotype NMV J 1171 a) indicating anterior peg. I. CpRl, detail of A (Paratype NMV J 1174 a). ScaleS: A – F = 1000 µm, G = 50 µm, H = 400 µm, I = 30 µm.

FIGURE 3. Ilyodromus amplicolis. ♀ (Holotype NMV J 1171 b) from granite rock pool on top of Boyagin Rock, betWeen Brookton and Pingelly, WeStern AUStralia, AUStralia A – G. A. A 2. B. A 1, firSt foUr SegmentS. C. A 1, SegmentS fiVe to SeVen. D. A 1, detail of RO. E. A 2, detail of natatory Setae. F. Md palp. G. Md coxa. ScaleS: A – C = 200 µm, D = 30 µm, E = 15 µm, F – G = 150 µm.

FIGURE 4. Ilyodromus amplicolis. ♀ S from granite rock pool on top of Boyagin Rock, betWeen Brookton and Pingelly, WeStern AUStralia, AUStralia A – F. A. Mx palp and enditeS, WithoUt detail on Second and third enditeS (Holotype NMV J 1171 b). B. L 5 (Holotype NMV J 1171 b). C. L 6 (Holotype NMV J 1171 b). D. CR attachment, broken in tWo pieceS (WAM 57208). E. L 7 (Holotype NMV J 1171 b). F. CR (Holotype NMV J 1171 b). ScaleS: A – F = 150 µm.

FIGURE 5. Ilyodromus amplicolis. ♂ (Paratype NMV J 1172 b) from granite rock pool on top of Boyagin Rock, betWeen Brookton and Pingelly, WeStern AUStralia, AUStralia A – C. A. HemipeniS. B. PrehenSile palp of left L 5. C. PrehenSile palp of right L 5. ScaleS: A – C = 77 µm.

FIGURE 8. Ilyodromus dikrus ♀ (Paratype NMV J 1184 b) from dam at WaSley Well, near Nallan, 21 km NNE of CUe, WeStern AUStralia, AUStralia A – F. A. Mx palp and enditeS, WithoUt detail on Second and third enditeS. B. L 5. C. CR. D. CR attachment. E. L 6. F. L 7. ScaleS: A, C = 77 µm, B, F = 102 µm, D, E = 150 µm.

FIGURE 9. Ilyodromus dikrus ♂ (Holotype NMV J 1182 b) from dam at WaSley Well, near Nallan, 21 km NNE of CUe, WeStern AUStralia, AUStralia A – C. A. HemipeniS. B. PrehenSile palp of left L 5. C. PrehenSile palp of right L 5. ScaleS: A = 68 µm, B – C = 108 µm.