Dendrocephalus (Dendrocephalus) thieryi Rabet

Rabet, Nicolas, 2006, A new species of Brazilian Dendrocephalus (Anostraca, Thamnocephalidae), Zootaxa 1370, pp. 49-57 : 50-55

Dendrocephalus (Dendrocephalus) thieryi Rabet sp. nov.

(figs. 1–4)

Holotype: mature male, total length 24 mm, cercopods 3.5 mm ( MNRJ 20166).

Allotype: mature female, total length 24.5 mm, brood pouch 5 mm reaching 3/10 of the 5th abdominal segment, cercopods 3.9 mm ( MNRJ 20167).

Paratypes from type locality: males ranging 21.0 to 26.8 mm, mean = 24.4 ± 1.4 mm (n=17), cercopods 2.9 to 3.9 mm, mean = 3.4 ± 0.3 mm (n=17). Females ranging 20.5 to 25, mean 22.3 ± 1.3 mm (n=32), brood pouch 4.1 to 6.6 mm, mean = 5.3 ± 0.6 mm (n=32), cercopods 3.0 to 3.9 mm, mean = 3.2 ± 0.2 mm (n=27). Two males, 2 females in MZUSP (17152), 2 males, 2 females in MNHN (Bp799), 2 males, 2 females in USNM (1092272), and 1 male, 1 female in Alain Thiéry and in D. Christopher Rogers collections. Other specimens are kept in NR personal collection and in MNRJ (5453).

Type locality. Temporary pool in Buritizeiro (ca. 17°22’S; 44°56’W) in the state of Minas Gerais, Brazil. The pool is localized in a sunny place of the Caatinga ecosystem and had a very high turbidity at the time of the collect (W. Costa personal communication). Etymology. Named in honor of Dr Alain Thiéry for his contributions to the ecology and systematics of large branchiopods.

Description

Male: Eye pedunculate, ovoid in lateral view, with a prominent spine at the posteroventral edge in line with main axis (fig. 1a). Spine about 15–20 % of length of the eye (fig.1a).

Antenna-like outgrowth slender, lying between first antennae and second antennae.

Second antennae with proximal antennomeres fused basally on the anterior of the head. Proximal antennomere bearing mediodistally a stout digitiform process ornamented with setae. Distal antennomere weakly sclerotized, evenly curved medially, and ornamented on medial surface with “scale-like” transverse ridges; terminus acute.

Frontal appendage with the basal arms with three or four strong spines on anterior margin (fig. 1b) and a row of medial spines extending to the terminal branches (fig. 1b). Branch 1V distally ramified in two sub-branches, both with longitudinal row of medial spines (fig. 1d). Anterior sub-branch generally longer than posterior. Anterior sub-branch broadened distally with row of posterior spines and with a larger spine at the tip. Posterior sub-branch ending acutely in short spine (fig. 1d).

Frontal appendage branch 2D (fig. 2a) with 3 distal sub-branches (from left to right I, II, III). Sub-branch I (most proximal) with row of short spines on medial side, sometimes ending acutely. Sub-branch II half as long as sub-branch I, ending acutely in two long spines, sometimes posterior spine clearly longer (fig. 2a). Sub-branch III as long as subbranch I, but with twice times the basal diameter, cylindrical proximally and flattened distally, bearing a large spiniform process and a smaller spine arising proximally; distal flattened portion with three spines on posteriolateral side, the longest spine arising proximally, and with five to seven short spines near anterior edge (fig. 2a).

Frontal appendage branch 2V (fig. 1e, 3a and 3d) cylindrical ending in a cluster of 5 to 7 cell pads on a bulge. The posterior and distal surfaces present numerous microstructures interpreted as sensorial elements (fig. 3d and 3e). Medial surface with a conical outgrowth and three clusters of cell pads (fig. 1e and 3a): one row of 4 large cell pads, a second row of 4 smaller inclined cell pads on a bulge and a cluster of small cell pads (fig. 3a, 3b and 3c).

Frontal appendage branch 2A (fig. 1c) cylindrical and heavily sclerotized on its anterior podiform end. One long cell pad present proximally, parallel to main axis and a “cell pad” like on a bulge more laterally (fig. 1c, 3f and 3g). A long spiniform process is present basally (fig. 1c).

Endopodite of first pair of thoracopods with a basolateral lobe ending in three or four smooth spines; distolateral non-prominent border with 3–5 spines (fig. 2b). Endopodites of limbs 2 with prominent distolateral border ornamented with 12–13 spines and a strong basolateral spine (fig. 2c). Endopodites of limbs 3 with prominent distolateral border ornamented with 8–9 spines (fig 2d). Endopodites of limbs 4 with only 8 small spines on distolateral corner (fig. 2e).

Basal part of penes short and massive with a short conical outgrowth medially. Everted part of the penes ornamented with several rows of strong spines (fig. 4a). Cercopods plumose.

Female: Shorter than male. As for other dendrocephalid species, no frontal appendage, no posterior spine in eye, no antenna-like outgrowth. Short antenna, flat and rounded at the top. No modification in endopodites. Brood pouch elongated. Cercopods plumose.

Cyst: Polyhedral with rounded ridges intersecting to form large polygons with circular depressions (fig. 4b). Sometimes in addition to large depressions there are small polygons. Average diameter of cyst 238,4 +/- 5 Μm (n = 30).

Distribution. Known only from the type locality. Natural Coloration. Unknown.

Differential diagnosis

Dendrocephalus species are mainly separated by several male characters: presence/ absence of eye spines, form of the frontal appendage, form of the first three thoracopod pairs, and the armature of the penes. Similarities can be observed between different species for each specific character but the combination of characters is unique for each species.

The species is most similar to D. thieryi is D. affinis Pereira, 1984 . Both species share the presence of several spines on the base of the frontal appendage, the form of the branch 1V anterior sub-branch, the podiform branch 2A, the first thoracopod endopodite with a basolateral spiny lobe, and second and third thoracopod endopodites with prominent distolateral border. However, D. thieryi differs from D. affinis by the following combination of characters: frontal appendage branch 2D lacks the hand-like projection in sub-branch III, sub-branch II has only 2 distal spine, and sub-branch I lacks the large basal spine. Furthermore, the endopodites of D. thieryi lack the spiny prominent distolateral border in thoracopod 1 and spiny basolateral lobe in thoracopods 2 and 3.

D. thieryi shares the proximal spines on the base of frontal appendage, the podiform branch 2A, the spiny basolateral lobe of endopodite 1, and the prominent spiny distolateral lobe of the endopodites 2 and 3 with D. goiasensis Rabet & Thiéry, 1996 , but lacks the acute apex of the anterior sub-branch of the branch 1V and the long basal spines on subbranches I and II of branch 2D, which D. goiasensis has.

Dendrocephalus . thieryi and D. brasiliensis Pesta, 1921 both have the branch 1V anterior sub-branch broadened distally and bearing spines, the branch 2D sub-branch II short (less than the half the length of sub-branch I) and terminating in two spines, and a podiform branch 2A. However, D. thieryi bears an eye spine (absent in D. brasiliensis ), bears spines on the base of frontal appendage, presents prominent spines in the thoracopod endopodites, lacks the large basal spines in branch 2D sub-branch I, and has a long branch 1V posterior sub-branch.