Abrochtha meselsoni, Jr & Ricci & Melone & Fontaneto, 2011

Jr, C. William Birky, Ricci, Claudia, Melone, Giulio & Fontaneto, Diego, 2011, Integrating DNA and morphological taxonomy to describe diversity in poorly studied microscopic animals: new species of the genus Abrochtha Bryce, 1910 (Rotifera: Bdelloidea: Philodinavidae), Zoological Journal of the Linnean Society 161 (4), pp. 723-734 : 726-729

ABROCHTHA MESELSONI SP. NOV.

Type material: The holotype and eight paratype specimens were isolated from a clonal lab culture obtained from one individual named Angl2.7b, collected from the type locality on 15 June 2005 by C. W. B. They are represented by slide mounts deposited in the Academy of Natural Sciences , Philadelphia, accession numbers ANSP 2052 (holotype) and 2053 to ANSP 2060 (paratypes), and by the COI sequence deposited in GenBank with accession number GU989432 .

Type locality: Angelfish Pool , on the east rim of Squirrel Canyon ( Fish Creek ), Virginia Dale, Coloado, USA, 40°57 ′ 21.6 ′′ N, 105°22 ′ 19.4 ′′ W, altitude 2190 m .

Etymology: The new species is dedicated to the work of Matthew Stanley Meselson, from Harvard University, on the evolutionary genetics of bdelloid rotifers.

Differential diagnosis: Morphologically, A. meselsoni resembles the other two species of the genus, Abrochtha carnivora Ricci, Melone & Walsh, 2001 and Abrochtha intermedia ( de Beauchamp, 1909) . Nevertheless, it may be easily distinguished from these by the wider rostrum and the higher number of major teeth on unci plate of trophi: 4/ 4 in A. meselsoni , 3/ 3 in A. intermedia , and 2/ 2 in A. carnivora . Moreover, A. carnivora is a much larger animal (> 500 Mm) and is the only known predatory bdelloid.

General morphology: The three usual body regions of bdelloids can be distinguished: head, trunk, and foot ( Figs 2 , 3 ).

The head is roundish and narrower than the trunk. Dorsally a single antenna is present, comprising two pseudosegments, with a terminal tuft of cilia. The apical part of the head bears the dorsal rostrum, which is wide and long. It is lined dorsally by a small bilobed lamella, with a sensory area present under the lamella. The rostrum is always clearly visible when the rotifer is creeping, and also when it is swimming, exceeding the trochi in length. The small trochi sit on small pedicels, well separated from each other, and appear as small auricles. The area between the trochi pedicels is covered by the upper lip, which, under the scanning electron microscope, appears flat on the head with square borders. The ventral part of the head is almost completely covered by a Y-shaped wide ciliated field, encircled laterally by a pair of small arched structures (cheeks). The mouth is ventral, at the bottom of the Y-shaped field. A series of ciliated structures is present between the mouth and the upper lip. Two red bright eyespots are present on the brain and are clearly visible when the animal is creeping, and when it is contracted in the tun shape.

The trunk is divided in three major sections: the first one forms a broad neck connecting the head with the main part of the trunk. This is stout and cylindrical, offset from the neck and laterally and dorsally lined by a series of folds. No folds, either longitudinal or transversal, are visible on the ventral surface. This median part of the trunk is not narrower at its posterior end and is distinctly offset from the following part. The third part ends with the opening of the cloaca, and is much narrower than the two previous trunk sections; because of its shape, it may appear as the first segment of the foot. The majority of the internal space of the trunk is occupied by the stomach; this lies between paired vitellaria, each with eight large nuclei.

The foot proper starts after the opening of the cloaca, and consists of four pseudosegments, the first two clearly visible and forming the longest part of the foot; the third one bears the spurs, and the last one bears four toes. The dorsal toes are smaller than the ventral ones. As in other bdelloids, pedal glands open on the tips of both spurs and toes.

The trophi are ramate, as in other bdelloids, with paired symmetrical rami, unci, and manubria ( Fig. 4A, B ). Each ramus is provided with a strong apophysis close to the ventral end, widening in the median part of the trophi, where the apophyses are connected. The two rami articulate at the ventral tips and at the apophyses. Each ramus also has an elongated process on which unci plates lay. A series of small denticles, called scleropilia, are present on the interior margin of the elongated process of each ramus. Each uncus plate consists of a large number of teeth, with four small minor teeth in the proximal part, usually four sharp major teeth on each plate, but occasionally five major teeth on one uncus plate, and 16 to 19 distal minor teeth. Each major tooth is bordered by two smaller teeth variably fused to it. The arched manubria border the uncus plates; they are narrow bands, with one extremity at the base of the proximal minor teeth on the uncus and the other extremity at the junction with the tip of each ramus.

Measurements: Total length, 150–300 Mm; trunk length, 80–180 Mm; trunk width, 50–80 Mm; head width, 30–45 Mm; rostrum, 10–15 Mm; antenna, 9–12 Mm; foot, 30–40 Mm; spur, 5–6 Mm. Trophi, ramus length from SEM, 16.93 ± 0.93 (SD) Mm (N = 42).

Distribution and ecology: This new species is known from the type locality only. Angelfish Pool is a temporary pool in a depression in granite bedrock, approximately 0.02 m deep and 1.5 m wide, in open ponderosa pine, Douglas fir, and juniper forest in the Montane zone at the southern end of the Laramie Mountain range at an altitude of 2190 m. The pool is filled occasionally by snowmelt and/or rainwater.

DNA barcoding: The partial COI sequence of Angl2.7b has been deposited in GenBank with accession number GU989432 . Additional partial COI sequences from other specimens collected in the wild in the type locality, belonging to the same species have been deposited with GenBank accession numbers DQ078535 (Angl1.1) and GU989433 to GU989438 (Angl2.8, 3.6, 3.5, 3.4, 3.10, 3.11, respectively) .

Figures

Figure 2. Abrochtha meselsoni sp. nov. A, habitus in dorsal view; B, lateral view. Scale bar = 50 Mm.

Figure 3. Abrochtha meselsoni sp. nov. Scanning electron microscopy pictures of details of body morphology. A, habitus, lateral view; B, head; C, foot; D, antenna; E, rostrum; F, epidermis. Scale bars = 25 Mm (A), 10 Mm (B, E), 5 Mm (C, D), 2 Mm (F).

Figure 4. Scanning electron microscopy pictures of trophi of Abrochtha meselsoni sp. nov. (A, B) and Abrochtha kingi sp. nov. (C, D). A, C, caudal view; B, D, cephalic view. Scale bar = 5 Mm.