Castrada (Castradella) biacantha, Noreña, Carolina, Eitam, Avi & Blaustein, Leon, 2008

Noreña, Carolina, Eitam, Avi & Blaustein, Leon, 2008, “ Microturbellarian ” flatworms (Platyhelminthes) from freshwater pools: New species and records from Israel, Zootaxa 1705, pp. 1-20 : 16-17

Castrada (Castradella) biacantha sp. nov.

( Figure 13 )

Locality. Temporary pool on Mount Kavul and Mount Shekhanya, Lower Galilee.

Material. Few individuals, live observations, squash preparations.

Holotype. One sagittally-sectioned individual deposited in the Department of Zoology at Tel Aviv University, Israel, Catalogue Number VR-25070.

Etymology. The specific name refers to the double spine or thorn at the base of the copulatory organ.

Description. Body spindle-like with narrowed posterior end and slightly rounded anterior end ( Fig. 13 A). Length 1–1.5 mm. Colour transparent white; without zoochlorellae. Rhabdite-tracts well developed in the anterior end of the body. Pharynx rosulatus (length: 0.25mm) at the end of the first half of the body. Both excretory pores open laterally, behind the pharynx and before the genital area.

Testes not well developed in the studied individuals; testes are elongated, sack-like and located laterally to the pharynx. The copulatory organ has a truncheon-like shape, (length: 198 μm) with a proximal vesicula seminalis and distal granular secretion ( Fig. 13 B). The ductus ejaculatorius (56.5 μm) is a double bladder, clearly differentiated from the proximal region of the copulatory organ. The copulatory organ, the bursa copulatrix and one small blind sac open into the atrium copulatorium. The opening of the atrium copulatorium into the atrium genitale is regulated through a sphincter. The bursa copulatrix (227 μm) shows longitudinal folds or small grooves. At the base of the bursa copulatrix there is a handsaw-like, strong spine or hook (spine 1, length: 96.8 μm, Fig. 13 B: Sp 1). Two other spines are located at the base of the copulatory organ (spine 2, length: 22.8 μm) and at the base of the blind sac (spine 3, length: 3 μm, width: 9 μm). The first of these spines (spine 2) resembles a double horn with a circular base ( Fig. 13 B: Sp 2). The second spine (spine 3, Fig. 13 B: Sp 3) resembles a hook (thumbtack like) with a wide base. The atrium also contains a thorny cushion near the copulatory organ.

The well-developed vitellaria are finger-like, strongly branched, stretching from the pharynx to the end of the body. Castrada (Castradella) biacantha is proterandric. All of the studied animals were without eggs.

Ecological features. Castrada (Castradella) biacantha was collected during the spring (March 2002) in two of the largest pools at Manof (pools 1 and 28 in Eitam et al, 2004)

Discussion. Nasonov (1926) divided the genus Castrada into the subgenera Castrada and Castradella , although this division remains controversial ( Papi, 1959; Luther, 1963; Willems, 2005). The subgenera can be distinguished by the different opening of the nephridiopore. Castrada is characterized by one nephridiopore and Castradella by two nephridopores to the outside. Besides this character, other morphological characters could help to distinguish between the taxa, such as the presence of three characteristically shaped (generally sawed) thorns in the atrium copulatorium of the species of Castradella . These characters are not enough to establish a new genus, but sufficient for the formation of a subgenus because they clearly distinguish between two groups of species within the genus Castrada . For a definitive creation or elimination of a subgenus or genus, it would be very advantageous to carry out an exhaustive revision of the genus Castrada and its diagnostic characters. Therefore, we prefer to await this revision and, following the criteria of authors such as Papi (1959), Schwank (1980) and Heitkamp (1982), describe the new species as Castrada (Castradella) biacantha .

Given these considerations, seven species constitute the subgenus Castradella : C. baldi (Steinböck 1949) , C. gladiata Schwank, 1980 , C. granea Braun, 1885 , C. lutheri Papi, 1959 , C. mochella Schwank, 1980 and C. triacetabula Heitkamp, 1982 . Of these seven species, C. baldi , C. gladiata and C. granea are most similar or closely related to C. biacantha . These four species show well-developed spines within the atrium copulatorium, but the size, number and shape of the spines are very different among these species ( Table 2 ).

Spines number, shape: size in µ m Another difference between C. gladiata and C. biacantha is the pseudocuticularized ductus ejaculatorius of C. gladiata , which is absent in C. biacantha .

Presently, Castrada (Castradella) biacantha is only known from the temporary pools on the slopes of Mount Kavul and Mount Shekhanya, Lower Galilee.

Diagnosis. Castrada (Castradella) species with three spines within the atrium copulatorium, the first spine (spine 1) saw-shaped, the second spine (spine 2) double shaped with a circular base and the last spine (spine 3) short and with a rounded base.

Figures

FIGURE 13: Castrada (Castradella) biacantha sp. nov. A. Habitus. B. Male copulatory organ. C. Detail of the spines.

Tables

TABLE 2. Comparative account of the number, size and shape of the spines of Castrada (Castradella) baldi, Castrada (Castradella) gladiata, Castrada (Castradella) granea, and Castrada (Castradella) biacantha sp. nov.

species	1	2 3	4	5
C. baldi	Handsaw: 117	smooth horn: 97 thumbtack: 33	triangular serrated plate: 58	nipple: 22
C. gladiata	Handsaw: 32-40	serrated horn: 55 thumbtack: 8-13	-	-
C. granea	Handsaw: 30-40	shark tooth: 14-20 thumbtack: 6-16	-	-
C. biacantha	Handsaw: 96.8	double horn: 3 thumbtack: 22.8	-	-