Testudinella obscura Althaus, 1957

De, Willem H., 2009, A review of the marine and brackish-water species of Testudinella (Rotifera: Monogononta, Testudinellidae), with the description of two new species, Zootaxa 2092, pp. 1-20 : 8-11

Testudinella obscura Althaus, 1957

( Figs 6 & 7 )

Material examined. Hundreds of specimens collected in psammon samples from the Mediterranean, Mindanao Sea and Red Sea were examined. The localities at which I found T. obscura are as follows:

Mediterranean. (1) France, Bay of Hyères: Île Porquerolles, near wreck of Prosper Schiaffino (Donateur), depth 50 m, distance from shore ~ 4 km, 31 December 2001; Port Cros, La Gabinière Est, depth 43 m, distance from shore 10 km, water temperature 22 °C, 26 June 2006; Cavalaire, wreck of Espignole, depth 29 m, distance from shore 500 m, water temperature 20 °C, 1 July 2006; (2) Spain, Bègur: Canyons de Tamariu, Illa de Fito, Furio de Fito, depth 21–45 m, distance from shore 250 m, 15–27 °C, 13, 14 and 18 August 2006. (3) Italy, Elba Island: Ligurian Sea: Punta della Madonna, Scoglio della Nave Enfola, La Formiche di Ponente, Punta della Madonna di Ponente, Picco Giallo, Scoglietto di Portoferraio; Tyrrhenian Sea: Il Relitto di Pomonte (wreck of Elviscott), La Fonza Esterna; depth 10–40 m, distance from shore ~ 50 m to 1 km, water temperature 21–23 °C, September 2006.

Mindanao Sea, the Philippines: Bohol Island (Garden Eel), Balicasag Island, Siquijor Island (Tubod Sanctuary, Sawang), Apo Island (Cogon, The Chapel), Negros Island (Dauin); April 2007, depth 8–30 m, distance from shore ~ 10 m to 5 km, water temperature 28 °C, April 2007.

Red Sea, Egypt: Sha’ab Maksour, Abu Galawa Sougair, Sha’ab Marsa Alam, Abu Dabbab, El Shona; depth 15–30 m, water temperature 29 °C, October 2006.

Description of female. The lorica ( Fig. 6 ) is more or less elliptical, weakly truncate anteriorly, smooth or occasionally very weakly striated ( Fig. 6 F). Ratio lorica length/lorica width 1.43–1.71 (average 1.54). The dorsal anterior margin shows a broad, flat median part connected by shallow folds to smaller rounded lateral lobes. The ventral margin is slightly convex ( Fig. 6 D, F) to weakly undulate ( Fig. 6 A–C, E), with shallow median indentation. The dorsal anterior margin is not or slightly projecting beyond the ventral margin. The posterior margin is smoothly rounded or very weakly rounded-angular. In cross-section ( Fig. 6 G) the lorica is slightly arched dorsally with shallow elevation near the lateral margins; ventrally almost flat with median part protruding. The foot opening is sub-terminal, on the ventral side; it takes the shape of an inverted U-shaped slit, the lateral margins of which sometimes appear undulate ( Fig. 6 C). The foot is composed of a long wrinkled proximal part, a short penultimate and a longer distal pseudosegment ending in a ciliated cup. The ratio lorica length/position of antennae relative to the antero-dorsal margin varies between 2.40–2.88 (average 2.60) for the dorsal antenna and 1.97–2.23 (average 2.07) for the lateral antennae. Two red eyespots.

Trophi malleoramate ( Fig. 7 ). The rami are elongate triangular with rounded latero-ventral margins, and very short blunt alulae ( Fig. 7 D: a). Basal and subbasal chambers forming single large chamber, opening latero-ventrally by a large common fenestra. Asymmetrical and interlocking median apophyses are apparent in caudal view. The inner margins of the distal rami sections bear 10–16/11–16 (left/right) arched and strongly webbed rami scleropili. The basal apophyses are moderately developed ridges, composed of a series of fused scleropili. The fulcrum is short, plank-shaped, and more or less trapezoid in lateral view. It is composed of a double layer of long and appressed sclerite bodies, the greatest part of which is involved in the formation of the junction with the rami, and another series situated anteriorly which border a distinct proximal opening ( Fig. 7 A: fo). The unci plates are composed of 10–12/11–12 (left/right) straight and strongly webbed teeth, lying parallel. There are three major teeth with distinctly offset club-shaped head in each uncus; the head of the midst tooth is distinctly smaller than the others. The space between the minor teeth is fairly large, and their weakly offset head is cylindrical to elongate-lanceolate. The crescent shaped manubria are composed of a superimposed dorsal, median, ventral and well developed subventral chamber ( Fig. 7 B: sc).

Male unknown.

Distribution and ecology. The species was originally described ( Althaus 1957b) from littoral mesopsammon (3 mm), 15–20 m from the shore, of the Bulgarian part of the Black Sea at Spatnite pjasatzi near Varna, July, salinity ~18 %. Only a few more, but undocumented records exist from Russia (White and Barents Sea), Europe (the Channel, Mediterranean), USA (Gulf of Mexico) and a tidal river on Peninsular Malaysia. Studying zooplankton in 104 arctic rockpools of different salt content along the shores of the islands in the White and Barents Sea, Ghilarov (1967) reports the species from (percentages of water bodies the species was found in the areas of the respective seas bracketed) fresh (14 and 25 %), brackish (3 and 17 %) and marine (25 and 60 %) waters. The records from the Channel, Europe are by d’Hondt (1970), who found in total four specimens among Enteromorpha in a puddle at Roc’h kroum and the harbour of Roscoff, and in a nursery tank of the Station Biologique (July, October). Menéndez & Comín (1986) and Forés et al. (1986) reported T. obscura from coastal lagoons of the Ebro Delta (N. E. Spain), located at the western part of the Mediterranean. Studying rotifer distribution in interstitial sand of a small brackish-water beach in Florida, USA (Okalossa Isl., Santa Rosa Sound), Turner (1993) collected T. obscura in the top 4 cm of sand of the intertidal zone (August, water temperature 38 °C, pH 6.5). Green (1995) found a single specimen in plankton of the Chukai river estuary opening into the South China Sea, Malaysia (28.2 °C, 3,800 µScm at high tide). Speaking from my experience with marine rotifers, I have not found yet the species in samples, both psammon or periphyton, from the North Sea, the Channel, and arctic rockpools or littoral from Svalbard ( Spitsbergen) and Greenland, and neither did Godske Eriksen (1968), Godske Björklund (1972) observe it in rock-pools and shore-pools, or among sub-littoral algae and bottom sediments from western Norway and southern Finland. I therefore consider the observations by Ghilarov (1967) and d’Hondt (1970) as misidentifications of e.g. young T. clypeata (Müller, 1786) .

From the observations considered valid it follows that the species is widespread ( Fig. 1 ) and apparently perennial. The water temperatures of 15–38 °C it was found, suggest that it prefers warm waters. It occurs from the intertidal zone to at least 10 km off shore, up to a depth of 50 m, and I agree with Turner (1993) that T. obscura appears to be an interstitial element and may live only in that habitat (the single specimen report from plankton by Green (1995) must be considered as an accidental introduction). Testudinella obscura was present in 24 of the 38 subtidal psammon samples studied here and as such it was the most frequent, and often even only species observed. It usually was also the most abundant rotifer and only outnumbered locally by the monogonont Lindia gravitata (Lie-Pettersen, 1905) and the bdelloid Rotaria laticeps Wulfert, 1942 .

The variation of the lorica ( Fig. 6 ) was not related to any sampling locality or area.

Figures

FIGURE 1. Map indicating sampling areas and distribution of Testudinella bicorniculata sp. nov., T. elongata sp. nov. and T. obscura Althaus. S, Spain; F, France; E, Egypt; I, Italy; P, Philippines.

FIGURE 6. Testudinella obscura. A – E. Loricae, ventral view. F. lorica, dorsal view. G. Lorica, caudal view. H. Foot pseudosegments. Scale bars: A – G: 50 µm, H: 25 µm.

FIGURE 7. Testudinella obscura, scanning electron microscope photographs of trophi. A. Complete set, frontal view. B. Detail left manubrium. C. Complete set, caudal view. D. Complete set, lateral view. Scale bars: 10 µm. a: alula, dc: dorsal chamber, fo: fulcrum opening, mc: median chamber, sc: sub-ventral chamber, vc: ventral chamber.