Cotylegaleata perplexa, De, Willem H., 2007

De, Willem H., 2007, Cotylegaleatidae, a new family of Ploima (Rotifera: Monogononta), for Cotylegaleata perplexa gen. et sp. nov., from freshwater benthos of Belgium, Zootaxa 1425, pp. 35-43 : 36-42

Cotylegaleata perplexa sp. nov.

( Figs 1–20 )

Material examined. Females (number of specimens): (3), 16.02.1997, – 8 m; (11), 16.03.1997, – 8 m; (4), 16.03.1997, – 9 m; (2), 20.02.1999, – 8 m; all from type locality.

Holotype. An adult female in a permanent, glycerin glass slide mount deposited in the Koninklijk Belgisch Instituut voor Natuurwetenschappen (K.B.I.N.), Brussels, Reg. no. IG 30410.

Paratypes. Nine paratypes in wholemount slides: one in K.B.I.N., 2 in the American Academy of Natural Sciences of Philadelphia, and 5 in the Department of Biology, University of Antwerp; 3 stubs each with one trophi preparation for SEM each in the Department of Biology, University of Antwerp

Type locality. Grote Put, Muisbroek, Ekeren, Province of Antwerpen, Belgium. Superficial benthos, between –8 and – 9 m.

Etymology. From the Latin adjective perplexa , perplexing, enigmatic.

Description. Adult female ( Figs 1–12 ). Moderately loricate. Head relatively small, offset from trunk by neckfold, more or less oval in dorsal view, covered by dorsal shield composed of four median plates and two lateral plates; shield not retractile. Mouth opening ventrally, at anterior edge of almost circular oral field in large, ventral, shallow cup-shaped structure. Cup-shaped structure with stiffened walls, showing two folds antero-laterally from mouth opening. Wall of mouth opening and short buccal tube strengthened. Corona reduced, inserted antero-dorsally from cup-shaped structure, with three rows of cilia at least. Dorsal antenna conspicuous, in shallow depression at posterior of head. Trunk rectangular in dorsal view, slightly compressed dorso-ventrally, in cross section weakly convex dorsally and more or less flattened ventrally; two ventro-lateral longitudinal folds. Tail short. Lateral antennae small, laterally near posterior ¼ of trunk. Foot long, placed ventro-distally, consisting of four pseudosegments; distal pseudosegment longest, bearing two toes, with sensory pit near mid-length dorsally, and two offset, slightly curved ventro-lateral spurs distally. Foot opening small. Toes relatively long, in dorsal view straight, elongate conical, slightly narrowing near mid-length, tapering to acute tips; in lateral view slightly decurved ventrally.

Eyespot(s) absent. Brain fairly large, saccate. Retrocerebral sac hemispherical, relatively large, at posterior of brain. Two strongly light refracting ducts opening in ciliary field. Subcerebral glands present. Oesophagus short. Stomach very large, continuing into intestine without constriction. Gastric glands latero-ventrally, strongly lobed (multiple?), apparently without stalks; with connection to mastax. Bladder normal. Pedal glands very long, extending into proximal foot pseudosegment, each with small reservoir in distal pseudosegment. Vitellarium characteristic, more or less tubular and J-shaped, located in left or right half of trunk, anterior part extending till gastric glands, posterior part curled in posterior of trunk; developing egg transversely projecting on tubular part; eight nuclei; intestine running below or above developing egg. Ovary small, spherical, connected to anterior end of vitellarium by short stalk.

The three immature females ( Figs 11–12 ) studied, showed a proportionally narrower trunk than the adults.

Trophi ( Figs 13–20 ) virgate, symmetrical. Rami strongly bent dorsally; basal parts elongate triangular, blunt anteriorly, with long pointed alulae postero-laterally; prior to the ramus apex a shallow cavity, the postero-ventral margin of which is formed by a shallow rim; frontal rami plates triangular, less sclerified, almost semi-circularly recurved dorso-distally; each ramus with large cavity ventrally, and opening near base of alulae dorsally. Fulcrum long, c. twice ramus length, in lateral view shallow, decreasing in height distally; in dorsal view gradually broadening distally; distal part weakly recurved dorsally. Unci small, composed of a triangular basal plate, bearing 5–6 long and free interlocking teeth; uncinal seams very weakly indicated. Manubria relatively small, rod-shaped, caudum recurved dorsally, head narrow, with tubular dorsal chamber displaying elongate opening postero-laterally; opening of shaft elongate, laterally, near distal end of dorsal chamber. Epipharynx two relatively long stiletto-shaped elements, apparently connected to proximal part of fulcrum, pointing outwards; a small rounded opening ventro-distally each.

Male unknown.

Measurements. Female, adult, N=13, [juvenile, N=3]: total length 212–251 (mean 227) µm, [173–177 µm]; head shield, length 38–45 (mean 42) µm, [41–44 µm]; head, width 30–33 (mean 32) µm, [31 µm]; sucker, diameter 23–28 (mean 24) µm, [18–23 µm]; trunk, length 95–120 (mean 106) µm [50–64 µm]; trunk, width 70–74 (mean 72) µm [38–39 µm]; trunk, height 46–61 (mean 53) µm [28 µm]; foot 70–86 (mean 77) µm [65–73 µm]; toe 22–26 (mean 24) µm [21–22 µm]; spur 3.5–4.5 (mean 4.5) µm [3.5–4.3 µm]; trophi, adult (N=3), [juvenile N=1]: ramus 5.2–7.4 (mean 6.0) µm [6.6 µm], fulcrum 9.9–15.4 (mean 13.0) µm [13.6 µm], manubrium 7.0–12.1 (mean 9.3) µm [10–11.2 µm], uncus 2.2–3.0 (mean 2.5) µm [2.7 µm], epipharyngeal element 3.1–5.1 (mean 4.2) µm [4.6 µm].

Comments. C otylegaleata perplexa gen. et sp. nov. is characterized by a combination of features, viz. the body shape, the cup-shaped structure surrounding the mouth opening, the head shield, the distal foot pseudosegment bearing two ventro-lateral spurs, the J-shaped vitellarium and the specialized virgate trophi with stilletto-shaped epipharyngeal sclerites, which clearly differentiate it from all other Ploima . As it can not be assigned to any known family (e.g. Koste 1978), and neither its relationship to the other families be established on morphological grounds, the creation of a new family seems justified.

The new taxon shows some superficial similarities with the Lepadellidae , concerning the general shape of the body, the presence of a head shield, and the shape of the foot and toes. The new taxon can be mistaken for a Lepadella by its outline, however, its lorica lacks the indentations for the head, the head shield is non-retractile whereas retractile in Lepadella , and the dorsal antenna is located in a perforated depression of the head shield and not directly on head, under the shield, as in Lepadella . Contrary to the uniform head shields in Lepadella , and in the other lepadellid genera Colurella , Paracolurella and Squatinella , the shield of Cotylegaleata perplexa is apparently composed of several fused plates. The not retractile foot with long pointed toes and its sensory pit on the distal pseudosegment also is reminiscent of Lepadellidae which, however, never show two latero-ventral spurs associated with the toes. Such accessory projections are rare in monogononts and only Trichocercidae (e.g. Koste 1978) show a variable number of characteristic spine-like appendages or substyli. However, any other resemblances with the Trichocercidae , which usually display an asymmetric body shape and strongly asymmetric virgate trophi, are lacking. The symmetrical virgate trophi of Cotylegaleata perplexa moreover differentiate the new taxon unequivocally from Lepadellidae which possess malleate trophi with rather short, characteristically enlarged fulcra ( Figs 21–26 ). The reduced unci and manubria, and the stiletto-shaped epipharyngeal elements indicate a highly specialized virgate type. To date, stiletto-shaped epipharyngeal elements have only been demonstrated in Dorystoma caudata (Bilfinger, 1894) of the family Notommatidae . Other similarities with Notommatidae are yet lacking. The tubular J-shaped vitellarium with transversely placed developing egg and anteriorly situated stalked ovary is apparently unique in monogononts, which usually show spherical, irregularly lobed, and more rarely band-like or horsheshoeshaped vitellaria (e.g. Remane 1929 –33; Koste 1978). The ovary normally lies close to the vitellarium, with the cytoplasmic bridges between the vitellarium and each ovocyte (Clẻment & Wurdak 1991) not differentiated into a short stalk as in Cotylegaleata perplexa .

The most characteristic, major apomorphic trait of the new taxon is the cup-shaped structure surrounding the mouth opening. This structure and the shape of the trophi suggest that the new taxon is a food specialist, and likely an ectoparasite. The cup-shaped structure must probably be interpreted as a sucker, used for the attachment to some kind of animal or animal life stage e.g. eggs, cocoons, etc. (vascular plants and large algae are absent at the depth the species is living) and for the intake of food. The proportionally very long and distally broadened fulcrum suggests a strong pumping capacity likely to generate a negative pressure in the sucker and to suck the food. The strengthened head shield could then be a formation providing support, preventing collapse of the sucker cavity and deformation of the head under the negative pressure. The relatively small mallei with tiny unci and short manubria, and the apparently stiffened mouth-rim and buccal tube suggest that the food must be liquid or soft. Reasoning on, it sounds plausible that the stiletto-shaped epipharyngeal elements are used to pierce the body wall of some host (or its products), as is the case in Dorystoma caudata where they serve to pierce algae. A still more important reduction of the unci also ocurred in the latter species where unci are even reported absent (confirmation by SEM needed). The strongly reduced corona in Cotylegaleata most probably plays a minor role in locomotion, suggesting that the new taxon displays a close and more permanent association with its host/feed.

The trunk is distinctly smaller in juveniles than in adults, whereas the dimensions of the head shield, sucker, toes and trophi prove almost equal. Differences in growth rate of different regions of the body in the pre-reproductive phase are well known for other rotifers as well (e.g. Lehmensick 1926; Magis 1962), whereas trophi size appears unrelated to either age or body size in monogononts, as has been shown by Fontaneto & Melone (2005, 2006) in their studies on the postembryonic development of trophi. The similar dimensions of the trophi, head shield and sucker in juveniles and animals in the reproductive phase might indicate that they are functionally connected as suggested above.

Aspelta psitta Harring & Myers, 1928: 2 Bdelloidea indet.: 1, 4

Cephalodella forficula (Ehrenberg, 1832) : 1, 4 C. gibba (Ehrenberg, 1832) : 3, 4

C. intuta Myers, 1924: 4

C. panarista Myers, 1924: 1 , 2, 3

C. stenroosi Wulfert, 1937: 1 , 2, 4

Cephalodella sp.: 1, 2, 3, 4

Cotylegaleata perplexa gen. et sp. nov.: 1, 2, 3, 4 Dicranophorus luetkeni (Bergendal, 1892) : 3 Dissotrocha macrostyla (Ehrenberg, 1838) : 1, 2, 3 Encentrum saundersiae (Hudson, 1885) : 2, 3, 4 Encentrum sp.: 1, 2, 3

E. uncinatum (Milne, 1886) : 1, 2, 3, 4 Euchlanis dilatata Ehrenberg, 1832: 2 Keratella cochlearis (Gosse, 1851) : 1, 3, 4 K. quadrata (Müller, 1786) : 1, 2

Lecane closterocerca (Schmarda, 1895) : 4 L. stenroosi (Meissner, 1908): 1, 2, 3

Notholca labis Gosse, 1887: 1 , 2, 3, 4

Paradicranophorus hudsoni (Glascott, 1893) : 1, 2, 3, 4 Rotaria neptunia (Ehrenberg, 1832) : 1, 2, 3, 4 Synchaeta oblonga Ehrenberg, 1832: 2 , 3, 4 S. pectinata Ehrenberg, 1832: 2 , 4

Wierzejskiella velox (Wiszniewski, 1932) : 1, 2

1: 16.02.1997, – 8 m; 2: 16.03.1997, – 8 m; 3: 16.03.1997, – 9 m; 4: 20.02.1999, – 8 m

Figures

FIGURES 1 – 2. Cotylegaleata perplexa gen. nov., sp. nov. 1. Adult female, lateral view. 2. Same as 1, dorsal view. Scale bar: 50 µm.

FIGURES 3 – 12. Cotylegaleata perplexa gen. nov., sp. nov. 3. Adult female, ventral view. 4. Same as 3, lateral view. 5. Cross-section of trunk. 6. Distal foot pseudosegment and toes, ventral view. 7. Same as 6, lateral view. 8. Head, ventral view. 9. Head, dorsal view. 10. Head, lateral view. 11. Juvenile female, dorsal view. 12. Same as 11, lateral view. Scale bars: 3 – 5, 11, 12: 50 µm; 6 – 10: 10 µm.

FIGURES 13 – 14. Cotylegaleata perplexa gen. nov., sp. nov., trophi. 13. Ventral view. 14. Dorsal view. Scale bar: 10 µm.

FIGURES 15 – 20. Cotylegaleata perplexa gen. nov., sp. nov., SEM photographs of trophi. 15. Ventral view. 16. Dorsal view. 17. Lateral view. 18. Detail, dorso-frontal view. 19. Same as 15, detail of incus. 20. Detail, ventro-frontal view. Scale bars: 15 – 19: 10 µm; 20: 1 µm. m: membrane, e: epipharyngeal element.

FIGURES 21 – 26. Lepadellidae, SEM photographs of trophi. 21, 22. Colurella adriatica Ehrenberg, 1831. 21. Incus, dorsal view; manubria, inner view. 22. Incus, ventral view; unci and manubria, outer view. 23, 24. Lepadella patella (Müller, 1786). 23. Incus dorsal view; unci and manubria, inner view. 24. Incus, ventral view; unci and manubria, outer view. 25, 26. Squatinella bifurca (Hudson, 1886). 25. Incus, dorsal view; manubria, outer view; unci, inner view. 26. Incus, ventral view; unci, outer view; manubria, inner view. Scale bars: 10 µm.