Dicranophorus cambari Wulfert, 1957

De Smet, Willem H. & Verolet, Michel, 2016, Epibiotic rotifers of Gammarus pulex (L.) (Crustacea, Amphipoda), with descriptions of two new species and notes on the terminology of the trophi, Zootaxa 4107 (3), pp. 301-320 : 312-314

Dicranophorus cambari Wulfert, 1957

( Figs 8 , 9 )

The specimens seen largely fit the original description, except for some minor details, in particular the less concave lateral ramus margins.

Redescription of trophi by SEM. Trophi ( Fig. 9 ) large, stout, almost symmetrical. Rami elongate triangular, terminating distally in distinct, slightly incurved tip dorsally and very slightly outward curved tip ventrally; between dorsal and ventral tip three inwardly directed apical rami teeth at right angle to trophi axis ( Fig. 9 I: at); inner margins almost straight, outer margins weakly concave, postero-ventral margins running obliquely to fulcrum, postero-dorsal ones only weakly oblique; median rami opening elongate wedge-shaped; alulae stout, triangular, pointing caudo-laterally; distal ¼ of inner margins with comb of 7−8 delicate caudally directed teeth ( Fig. 9 E: rt), comb apparently movable (inwardly directed in Fig. 9 C or dorsally directed and lying against rami in Figs 9 A, B); subbasifenestrae fairly large, rounded triangular, basifenestrae medium-sized, elongate. Fulcrum ramus length, laminar, tapering to rounded end in lateral view. Unci widening proximally and distally; right uncus ( Fig. 9 G) with median stout tooth and symmetrically placed lateral apophyses of similar shape and length; left uncus ( Fig. 9 H) tricuspidate, asymmetrical with a strong ventral tooth bearing shallow blunt projection at ventral margin 1/3 from tip, and a smaller median and dorsal tooth; dorsal tooth with small blunt apophysis dorsally at base of head; left uncus with large rounded-triangular epiuncus ( Figs 9 H, I: e) at base of median and dorsal teeth. Manubria almost straight in dorsal view, very weakly curved dorsally in lateral view; head small, median chamber with small rounded opening at inner surface, dorsal chamber lamellar, rounded dorsally, ventral chamber vestigial; caudae not expanded. Epipharynx ( Figs 9 D −F) complex, usually taking shape of two mirror S-shaped elements in trophi preparations, composed of interconnected pairs of well-sclerified combs and less stiffened laminae, connected to the unci by a pair of strong ligaments; two types of combs are present: a pair of small ones ( Figs 9 D −F: sc) bearing 7−8 fairly sharp spaced teeth, and a pair of large ones ( Figs 9 D −F: lc) bearing c. 12 blunt, appressed and fan-wise placed teeth provided with a seam.

Measurements. Body (N=5): total length 164−300 µm, toe 24−47 µm; trophi (N=7) 31.8−35.5 µm, ramus 18.3−22.6 µm, fulcrum 14.6−16.0 µm, uncus (l & r) 15.8−19.1 & 16.5−20.0 µm, manubrium (l & r) 32.2−36.7 & 32.5−37.1 µm, epipharynx (N=4): minor comb 3.9 × 2.4−3.1 µm, major comb 5.1−5.4 × 2.6−3.1 µm.

Comments. Dicranophorus cambari belongs to the D. hauerianus Wiszniewski species group which is still subject of taxonomic confusion. The general morphology of the different taxa is largely similar, and their differentiation mainly relies on the trophi. However, at the moment of description several taxa with apparent differences in trophi structure were treated as of infrasubspecific rank, but still more unfortunate, the descriptions of their trophi are often not detailed enough to allow for a clear distinction. It is now recognized that the trophi of Dicranophorus species are highly specialised and species-specific structures ( Hauer 1959; De Smet 1997). In the original description of D. cambari Wulfert (1957) states that the rami are characterized by a strongly curved outer margin, somewhat lyrate in shape, with sharply projecting lateral alulae. Specimens attributed to the species by Hauer (1959) and our specimens show less curved outer rami margins, but show the characteristic double-S-shaped epipharynx only reported in D. cambari . To our knowledge, the epipharynx of the other species of the D. hauerianus complex consists of a pair of simple comb-shaped elements, which we consider homologous to the pair of large combs demonstrated by SEM ( Figs 9 D −F: lc). The rami teeth of D. cambari are pictured more or less needle-shaped, spaced and caudally directed by Wulfert (1957), Hauer (1959) and Koste (1978), which agrees fairly well with our observations by SEM. Shape of the rami teeth turns out to be a good diagnostic feature as well, as shown by the differently shaped, flattened and more or less parallel-sided teeth found in D. siedleckii Wiszniewski ( De Smet 1997, SEM pictures Pl. 6). Hauer (1959) suggests that D. hauerianus var. brachygnathus described by Wiszniewski (1939) might be identical to D. cambari , but synonymization would be preliminary without precise information on the epipharynx and the rami teeth.

The term epiuncus (Greek epi, upon) is proposed for the small sclerite body lying outside at the base of the unci teeth ( Figs 9 H, I: e). To date, such a structure has never been reported in rotifer trophi, but a small epiuncus appears also present on the left uncus of the related D. siedleckii ( De Smet 1997, Pl. 6, Fig. 3 ), which is the only other member of the D. hauerianus Wiszniewsi species group of which trophi were studied by SEM.

Distribution and ecology. Dicranophorus cambari is now known from Germany and France. It lives in the branchial cavities of the freshwater crayfish Orconectes limosus (Rafinesque) (syn. Cambarus affinis (Say)) and Austropotamobius torrentium (Schrank) where it feeds on other epibionts. The intestine of the specimens seen contained the peritrichous ciliate Epistylis sp. and trophi of Embata laticeps .

Figures

FIGURE 3. Pectines, SEM photographs. A. Cephalodella hoodii, complete set of trophi, ventral; B. ibidem, detail; C. C. maior, ventro-frontal; D. C. boettgeri, ventro-fontal; E. C. panarista, ventro-frontal; F. C. stenroosi, ventro-frontal. aa: apical ramus apophysis; dc: dorsal ramus chamber; f: flabellum; p: pecten. Scale bars: A, C − F: 10 µm, B: 5 µm.

FIGURE 8. Dicranophorus cambari Wulfert, habitus live female. A. dorsal; B. lateral.

FIGURE 9. Dicranophorus cambari Wulfert, SEM photographs of trophi. A. complete set, ventral; B. ibidem, oblique lateral; C. ibidem, dorsal; D − F. epipharynx, dorsal; G. teeth of right uncus; H. left uncus; I. rami tips and unci teeth. at: apical rami teeth; e: epiuncus; lc: large epipharyngeal comb; rt: rami teeth; sc: small epipharyngeal comb. Scale bars: A − C: 50 µm; D − I: 10 µm.