PODOCOPIDA Sars, 1866

Savatenalinton, Sukonthip & Martens, Koen, 2009, On a freshwater species of the genus Sanyuania Zhao and Han, 1980 (Crustacea, Ostracoda, Loxoconchidae) from Thailand, with a discussion on morphological evolution of the freshwater Loxoconchidae, Journal of Natural History 43 (5 - 6), pp. 259-285 : 261-270

publication ID	https://doi.org/ 10.1080/00222930802590885
persistent identifier	https://treatment.plazi.org/id/03DF565C-151B-0D67-5490-F101C73533B2
treatment provided by	Felipe
scientific name	PODOCOPIDA Sars, 1866
status

Treatment

Order PODOCOPIDA Sars, 1866 View in CoL

Family LOXOCONCHIDAE Sars, 1925

Diagnosis (modified from Athersuch et al. 1989)

Carapace in lateral view reniform, ovate, rhomboidal, quadrate, rectangular or subtriangular, sometimes with a caudal process. Valves smooth, pitted or reticulated, sometimes with tubercles and/or alae. Inner lamella relatively broad; marginal pore canals few, usually simple but occasionally branching, anterior and posterior vestibula usually present. Pores normal, with or without sieve plates, with or without rim, sometimes with distinct pore conuli (sensu Athersuch et al. 1989). Muscle scar pattern set with a vertical or arcuate row of four adductor muscle scars, frontal scars U-, V-, Y-, C-shaped or subtriangular, sometimes with a second small, rounded scar in front, sometimes mandibular scars visible. Hinge typically gongylodont, occasionally henodont, invicidont or adont. Eye tubercles often present.

A1 with five or six segments. Endopodite of A2 with three segments and two terminal claws, exopodite mostly two-jointed, occasionally undivided. Respiratory plate on Md-palp with two to four setae (rays). Respiratory plate on Mx1 with a single aberrant seta. Legs usually slender. Caudal ramus with two or three setae.

Genus Sanyuania Zhao and Han, 1980 View in CoL

Type species

Sanyuania psaronius Zhao and Han, 1980 View in CoL

Diagnosis (modified from Zhao and Whatley 1992)

Carapace small (c. 280–350 Mm), in lateral view subovate to subtriangular, anterior margin broadly rounded, posterior margin rounded to bluntly pointed; in dorsal view laterally compressed and with (slightly) pointed ends, in some species with large and pointed posterior expansion. Valve surface smooth, reticulate, punctate or pits. Eye tubercles present, sometimes inconspicuous. Sieve pores present, radial pore canals few, simple. Hinge (reduced) invicidont. Adductor muscle scars set in an oblique row of four adductor muscle scars, frontal muscle scars U-shaped or triangular. A1 slender, five or six-segmented. Legs slender, setal formulae of basal segments of T1–T3: (1+1:2:1), (1+1:1:1), (1+1:1:1).

Differential diagnosis

Sanyuania is similar to Loxoconcha and Pseudolimnocythere . It can be distinguished from them by the invicidont hinge, the chaetotaxy of the penultimate segments of A1 and A2, the morphology of the valve surface and sieve pores. In addition, Sanyuania differs from P. hartmanni in the absence of selvages on both LV and RV, the presence of eye tubercles and the divided exopodite of the A2.

Sanyuania segersi sp. nov.

( Figures 1–5 View Figure 1 View Figure 2 View Figure 3 View Figure 4 View Figure 5 )

Type locality

Lopburi River (TH 140), Muang district, Lopburi Province, Thailand (14 ° 47955.50N, 100 ° 38929.80E). The river ran slowly and the bank was sparsely covered by grass and water hyacinth [ Eichhornia crassipes (Mart.) ]. Some submerged macrophytes ( Hydrilla verticillata Presl. ) were found along the littoral zone. Accompanying ostracod fauna were Chrissia sp. , Cypris subglobosa, Cypridopsine undetermined, Fabaeformiscandona cf. japonica , Hemicypris sp. , Physocypria sp. , Stenocypris sp.1, Stenocypris sp.2, Bradleystrandesia lineata , Strandesia weberi , Strandesia sp. , Vestalenula sp.

Type material

Approximately 30 females were collected on 5 October 2007 by S. Savatenalinton.

Holotype: female (OC. 3014) soft part dissected and kept in glycerine-mounted slide, valves stored dry in a micropalaeontological slide.

Paratypes: two females (OC. 3015, MSU-ZOC. 004) dissected and stored dry as the holotype, two undissected females (OC. 3016, MSU-ZOC. 005) stored in micropalaeontological slides. All these paratypes have been coated for scanning electron microscopy. Nineteen remaining specimens kept in 70% ethanol (MSU-ZOC. 008).

Repository

Holotype and two paratypes (one dissected, one undissected) are held in the Ostracod Collection of the Royal Belgian Institute of Natural Sciences (Brussels, Belgium). Two paratypes (one dissected, one undissected) are deposited in the Natural History Museum , Mahasarakham University (Mahasarakham, Thailand).

Derivation of name

This small but interesting species is named after Dr Hendrik Segers (Brussels, Belgium), in recognition of his significant contributions to research on rotifers, as

well as to the career of the first author. Both authors herewith acknowledge years of friendship and stimulating collaboration.

Diagnosis

Carapace small (c. 300 Mm long), in lateral view subtriangular, in dorsal view elliptical with characteristically spearhead-like, protruding posterior extremity; valve surface with small, shallow, round pits and with dispersed setae, sieve plates centrally without pore and setae; A1 five-segmented, penultimate segment with four apical setae (three anterior, one posterior), aesthetasc ya of A1 shorter than accompanying seta (less than half the length of accompanying seta); aesthetasc Y on A2-penultimate segment short (not reaching the end of segment), exopodite of A2 long, divided; respiratory plate on Md-palp with four setae; end claw of T1–T3 slender, with the bottle-necked tip.

Differential diagnosis

Sanyuania segersi View in CoL sp. nov. is similar to S. cuneata Zhao and Whatley, 1992 View in CoL and S. abei ( Choe, 1988) . It can be distinguished from the former by the absence of alae situated at the junction between lateral and ventral surface, the morphology of the anterior margin and posterior extremity, the ornamentation of the valve surface and the number of segments of A1 and from the latter by the shape of valves and frontal muscle scars, and the number and feature of radial pore canals. The morphology of soft parts of S. abei has not been illustrated so no comparison of limbs between S. segersi View in CoL sp. nov. and S. abei was possible.

Additional description of female

Carapace small (c. 300 Mm long), in dorsal view ( Figure 1A View Figure 1 ) elliptical, with spearhead-like protruding posterior extremity and pointed anterior extremity; greatest width situated slightly behind the middle; eye tubercles ( Figure 1A,F View Figure 1 ) situated at about one third of the length.

Carapace in ventral view ( Figure 1B View Figure 1 ) with outer list at both valve margins.

Both LV and RV in external view ( Figure 1D,E View Figure 1 ) subtriangular; greatest height situated at the anterior one third of the body length; anterior margin broadly rounded; dorsal margin moderately sloping down from the greatest height to the posterior margin; ventral margin straight at the middle, posterior half curved upward to the posterior margin; eye tubercles situated slightly behind the highest point; two and three carinae (ridges) present along anterior and posterior margins respectively.

Valve surface ( Figure 1F,G View Figure 1 ) ornamented with small, shallow, round pits and dispersed setae; sieve plates centrally without a pore with seta (sensillum) ( Figures 1H–K View Figure 1 , 9A View Figure 9 ).

LV and RV in internal view ( Figure 2A–H View Figure 2 ) subtriangular; anterior margin broadly rounded, without selvage; inner lamella wide along anterior, ventral and posterior margins, wider anteriorly than posteriorly; ventral margin straight, with central undoubled portion.

Hinge ( Figure 2A–D,G,H View Figure 2 ) invicidont, LV with smooth cardinal bar, anteriorly with three rounded teeth, posteriorly with four sockets, RV with complementary intercardinal groove, anteriorly with three sockets, posterior with four teeth.

Radial pore canals simple, c. 18 anteriorly, c. 9 posteriorly. Muscle scar pattern ( Figure 2E,F View Figure 2 ) set with a vertical row of four equal adductor muscle scars and a large subtriangular frontal muscle scar; mandibular scars visible; two dorsal muscle scars present (one situated above the row of four adductor muscle scars and one above the frontal muscle scar).

A1 ( Figure 3A View Figure 3 ) five-segmented, first segment without seta; second and third segments with one long apical seta; penultimate segment undivided, medially with two long setae and distally with a group of three unequal and one long apical setae; terminal segment long, with three long setae and aesthetasc ya, the latter less than half the length of accompanying seta.

A2 ( Figure 3B View Figure 3 ) with exopodite long and divided (divided point situated at about two thirds of its length); endopodite three-segmented: first endopodite with long apical seta (almost reaching the end of penultimate segment); penultimate segment undivided, distally with an apical seta, medially with a short anterior seta and a group of a long posterior seta and a short aesthetasc Y (about half the length of the long seta, not reaching the end of segment); terminal segment with one subapical claw and one apical claw.

Md-palp ( Figures 4A,B View Figure 4 , 5F View Figure 5 ) four-segmented; first segment bearing a long subapical seta, a long, smooth apical a seta and a respiratory plate with 4+1 rays, the latter a special small and broad seta at the base of the respiratory plate ( Figure 5H View Figure 5 ); second segment posteriorly with a pair of long subapical setae, laterally with one long seta and a plumose b seta, anteriorly with one long apical seta; penultimate segment posteriorly with one long apical seta, laterally with c seta, anteriorly with five unequal, long apical setae; terminal segment bearing three claws; Md-coxa ( Figure 4C View Figure 4 ) anteriorly with a plumose, short seta, apically with about seven blunt teeth.

Mx1-palp ( Figure 4D View Figure 4 , 5G View Figure 5 ) two-segmented, basal segment with a group of four unequal, long setae, one long seta and one spine-like, short seta ( Figure 5G View Figure 5 ); terminal segment with three claws; first endite basally with one large, long seta; Mx1-respiratory plate ( Figure 3F View Figure 3 ) bearing c. 16 long setae and one aberrant seta, the latter not always reflexed.

T1 ( Figure 3C View Figure 3 ) with first segment bearing one long posterior proximal seta, medially two unequal, long anterior setae, and apically two unequal anterior setae (the shorter one slightly more than half the length of the long one); second segment with a short anterior apical seta (reaching the end of the next segment); penultimate segment short (length about twice the width), without seta; terminal segment short (length c. 2.5 times the width), with end claw slender, but unevenly tapering, with the bottle-necked point about one third of its length.

First segment of T2 ( Figure 3D View Figure 3 ) with one long posterior proximal seta, medially two unequal but long anterior setae, apically with one long anterior seta (about half the length of the next segment); second segment with a short anterior apical seta (reaching the end of the next segment); penultimate segment short (length c. 2.3 times the width), without seta; terminal segment long, with end claw slender, bottle-necked point about two fifths of its length.

First segment of T3 ( Figure 3E View Figure 3 ) with a long posterior proximal seta, medially with two (one long, one short) anterior setae (the short one about half the length of the long one), apically one long anterior seta (less than half the length of the next segment); second segment long (length c. 9–10 times the width), with a short anterior apical seta (reaching end of next segment); penultimate segment short (length c. 2.5 times width); terminal segment long, with end claw slender, bottle-necked point about two fifths of its length.

Thoracopod attachment ( Figure 3G View Figure 3 ) with one anterior cell and two posterior cells.

CR ( Figure 4E View Figure 4 , 5J View Figure 5 ) with two setae.

Female abdomen ( Figure 4E View Figure 4 ) triangular, with needle-like posterior end and long setae along the border; genital lobe rounded.

Male unknown.

Measurements (in M m)

Carapace (n 52): L5296–301, W5129–134; LV (n 52): L5299–304, H5166–170; RV (n 52): L5293–306, H5165–173.

Remarks

So far, the male of S. segersi sp. nov. has not yet been found, although one of us (S.S.) sampled this locality three times, on 20 September 2005, 6 February 2006 and 5 October 2007. Only in the third sample were females of this new species found; the species was absent in the first two samples. Males could be absent because of seasonal occurrence of males, because males only rarely occurred, or because the population was fully parthenogenetic. Parthenogenesis is much more common in freshwater than in marine environments, so it is conceivable that it is also more common in freshwater loxoconchids than in marine representatives of this group. This would not exclude the fact that sexual populations of this species might exist elsewhere.

Phylogenetic analyses

In most generated trees, support for the nodes was quite weak. Various combinations of deleted characters, ordered/unordered character states and weighted characters almost invariably yielded unresolved topologies. Of the combinations that could be justified with biological reasons (e.g. the higher weight for characters related to hinge structure and segment fusions), the present ones were retained.

The results of the MP and NJ analyses yielded slightly different topologies for the relationships among the freshwater loxoconchids. In the MP tree ( Figure 6 View Figure 6 ), S. segersi sp. nov. clusters with the Loxoconcha species , and this clade subsequently joins with Pseudolimnocythere , which in turn clusters with Cytheromorpha . Elofsonia is closest to the basal lineage in this tree. The topology of the NJ tree ( Figure 7 View Figure 7 ) shows that Pseudolimnocythere clusters with Loxoconcha ; this clade subsequently joins with S. segersi sp. nov., which in turn clusters with Cytheromorpha . In both MP and NJ trees, S. segersi sp. nov. has been separated from the other genera and has either Pseudolimnocythere or Loxoconcha as its sister clade. Elofsonia is the most basal lineage in both trees. Additionally, P. hypogaea and P. hartmanni form a wellsupported cluster in both trees, with bootstrap values 81 and 100 for MP and NJ, respectively.