Proales gammaricola, De Smet, Willem H. & Verolet, Michel, 2016

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 : 309-312

Proales gammaricola n. sp.

( Figs 5 , 6 )

Diagnosis. Female 155−170 µm long. Body elongate, slender, fusiform in dorsal view, slightly bent in lateral view, semi-loricate. Trunk vase-shaped. Head almost as long as wide, narrower than trunk, offset by distinct neckfold. Tail prominent, broadly rounded. Foot long, c. 1/3 total length, two pseudosegments of similar length, distal pseudosegment laterally indented. Toes straight, margins almost parallel-sided, tapering to moderately long tubular tips. Two fused small frontal red eyespots. Trophi weakly asymmetrical. Rami broadly U-shaped with acute alulae; rami tips broad, truncate; caudal margin of rami with rounded projection bearing small cavity. Left major uncus tooth with strongly developed head, preuncinal tooth and transverse process. Cauda of manubria incurved at right angle.

Type locality. Canal Font Rome, Aubenas, France; 24 May 2009, epibiotic on G. p u l e x (L.).

Holotype. A female in a permanent, glycerine glass slide mount deposited in the Royal Belgian Institute of Natural Sciences ( RBINS), Brussels, Belgium, IG 33143, RIR 260.

Paratypes. One female from type locality in RBINS, IG 33143, RIR 261; 5 mounted paratypes and 8 SEM trophi preparations in Department of Biology, University of Antwerp.

Etymology. The specific name gammaricola is derived from the genus name of the basibiont, Latin gammarus for an indefinite crustacean, and the Latin cola, meaning ‘who inhabits’ (colere, to inhabit).

Description of female. Body ( Figs 5 A −C) elongate, slender, fusiform in dorsal view, slightly bent in lateral view, semi-loricate. Trunk vase-shaped in dorsal view; in lateral view arched dorsally and more or less flattened ventrally. Head almost as long as wide, narrower than trunk, offset by distinct neckfold; an indistinct transversal fold near mid-length dorsally. Tail prominent, broadly rounded in dorsal view. Foot long, c. 1/3 total length, stout; two pseudosegments of similar length, with narrow joint between; proximal pseudosegment with transversal fold ventrally, distal one laterally indented. Toes ( Figs 5 D, E) straight, margins slightly narrowing distally in dorsal and lateral view, terminating in moderately long, in dorsal view offset and basally swollen tubular tips; in lateral view tips tubular, without basal swelling, distinctly offset ventrally. Corona slightly oblique. Dorsal antenna in posterior third of head. Brain saccate, large. Two fused small frontal red eyespots. Proventriculus well developed. Stomach and intestine weakly separated by shallow fold. Gastric glands lobed, stalks distinct. Pedal glands large, extending into trunk with long ducts. Vitellarium with 8 nuclei.

Trophi ( Figs 5 F, 6) malleo-virgate, weakly asymmetrical. Elements connected by strong ligaments. Rami bent dorsally at obtuse angle, broadly U-shaped with caudo-laterally directed acute alulae; rami tips broad, truncate with short ventral and dorsal projection; large, elongate dorsal basifenestrae; subbasifenestrae indistinct; caudal margin of rami with rounded projection bearing small cavity near base of rami. Left basal apophysis large, crenated, right a smaller one and a superimposed large crenated ramus tooth; right inner ramus margin with beak-shaped projection. Catenae ( Fig. 6 C: c) composed of distinct basal, median, and distal part; basal part composed of rounded sclerite bodies, showing ventro-lateral opening; median part a chain of transversely placed cylindrical sclerite bodies each with small dorso-lateral protuberance; distal part filamentous, composed of very small, rounded sclerite elements. Fulcrum rod-shaped in dorsal view, in lateral view knife-shaped, with straight dorsal margin and slightly oblique ventral margin, broadly rounding subterminally. Unci plate-shaped, with 4−5 (left) and 5 (right) teeth with offset head decreasing in length dorsally, and an oblique rod-shaped dorsal element; major teeth with preuncinal tooth and transverse process ( Fig. 6 C: tp) at 1/2–1/3 from base at ventral margin; head, preuncinal tooth and transverse process of left major tooth most strongly developed. Subuncus a plate with short scleropili. Manubria long, strongly incurved at right angle distally; head ½ manubrium length, ventral chamber with opening at inner side, median and dorsal chamber with opening at outer side.

Measurements. Body (N=5): total length 160−170 µm, toe 21−23 µm; trophi (N=5) 23−24 µm, ramus ~ 4.7−5.1µm, fulcrum 4.8−5.2 µm, uncus (l & r) 7.3−7.9 × 5.1−5.6 & 7.0−7.3 × 4.5−5.2 µm, manubrium (l & r) 15.6−18.1 & 15.1−16.8 µm.

Distribution and ecology. Proales gammaricola n. sp. is to date only known from its type locality as epibiont of G. pulex .

Comments. The shape of the body and the trophi of P. gammaricola n. sp. indicate a close relationship with P. globulifera (Hauer) and P. minima (Montet) . It can be distinguished from the latter by its more fusiform shape, its stouter foot with the distal foot pseudosegment distinctly indented laterally in dorsal view, and the shape of the toes which are less slender and less gradually tapering, with offset tubular tips. The gastric glands are lobate instead of rounded as in P. globulifera and P. minima . Similar to P. globulifera the pedal glands are large, extending into the trunk and not minute and restricted to the distal foot pseudosegments as in P. m i n i m a. Its body size (160–170 µm) falls within the range of P. globulifera (130−200 µm) but is larger than in P. minima (70–120 µm); light-refracting globules as present in the body cavity of P. globulifera were not observed. The head, preuncinal tooth and transverse process of the left major uncus tooth are more strongly developed in P. gammaricola , and the rounded projections at the caudal ramus margins are absent in P. globulifera and P. minima .

Proales gammaricola n. sp. keys out near P. globulifera and P. minima in the key by De Smet (1996).

The species pictured by Wiszniewski (1953) and attributed to P. g am m ar i (Plate) may concern the new species, but the necessary detailed information on the trophi to differentiate between the small Proales species is not provided. Proales gammari described by Plate (1886) from the gills of G. pulex is unrecognizable, and was successively thought not unlikely P. reinhardti (Ehrenberg) by Harring & Myers (1924) and Koste (1978), belonging to the P. daphnicola (Thompson) – P. sigmoidea (Skorikov) group by Remane (1933), or synonymous with P. daphnicola (now relocated to Epiphanes ) according to de Beauchamp (1923). In the ‘candidate List of Available Names in Zoology, part Phylum Rotifera’ ( Jersabek & Leitner 2013; Jersabek et al. 2015) P. gammari is considered species inquirenda.

The term catena (Latin catena, chain) is proposed for the paired filamentous ( Figs 6 C, 7A: c), ribbon-shaped ( Figs 7 B, C: c) or more or less irregular rod-shaped (Fig. D: c) elements composed of a chain of sclerite bodies attached to the ventro-distal part of the rami and interconnecting with the head of the manubria and/ or proximal part of the unci. Catenae are less visible by LM and often lost during trophi preparation. Catenae appear restricted to the malleo-virgate (e.g. Proales ( Figs 6 , 7 ), Proalinopsis ( De Smet 1996, Pl.4, Fig. 4 )), Halolepadella ( De Smet 2015, Fig. 25)) and malleate trophi types (e.g. Mytilina ( Fig. 7 C, D), Proalides ).

The term uncinal transverse process is used to denote the protuberance inserted transversally at the outer margin of the major tooth of the unci ( Figs 6 C, 7B: tp) in malleate and malleo-virgate trophi ( Proalides , Proales , Proalinopsis , Wulfertia , Halolepadella ). The process is generally located at 1/3 from the base of the uncus to the middle of the tooth margin. SEM preparations ( Fig. 6 C: l) show that it is a juncture for a ligament interconnecting unci and rami.

Figures

FIGURE 4. Flabella, rami apophyses and transversal sclerites, SEM photographs. A. Cephalodella theodora, complete set of trophi, inner view; B. C. theodora, flabellum; C. C. gibba, ventro-frontal, flabella; D. Cephalodella sp. 1, flabellum; E. C. megalocephala, complete set, lateral right; F. C. megalocephala, flabellum; G. Cephalodella sp. 2, subdistal lateral ramus apophysis; H. C. theodora, apical rami apophyses; I. Notommata glyphura, transversal sclerites; J. N. copeus, transversal sclerite, right; K. N. copeus, transversal sclerite, left. aa: apical ramus apophysis; f: flabellum; la: subdistal lateral ramus apophysis; mt: medial rami teeth; p: pecten; su: subuncus consisting of field of knobbed protuberances; u: uncus. Scale bars: A − E, I − H: 10 µm, F: 1 µm.

FIGURE 5. Proales gammaricola n. sp., female. A. Live animal, lateral; B. habitus, dorsal; C. habitus, lateral; D. ultimate foot pseudosegment and toe, left, lateral; E. ultimate foot pseudosegment and toes, dorsal; F. trophi elements, incus ventral, mallei outer view. Scale bars: 10 µm.

FIGURE 6. Proales gammaricola n. sp., SEM photographs of trophi. A. complete set, incus ventral, left manubrium outer view; B. ibidem, detail; C. detail rami (ventral) and unci (outer view); D. complete set, lateral; E. incus, dorsal. c: catenae; l: ligament; tp: transverse uncinal process. Scale bars: 10 µm.

FIGURE 7. Catenae, SEM photographs. A. Proales halophila, dorsal; B. P. similis, ventral; C. Mytilina bicarinata, ventral; D. Mytilina sp., detail rami tips and catenae, dorsal. c: catena; m: manubrium; r: ramus; u: uncus; tp transverse uncinal process. Scale bars: A, B, D: 5 µm; C: 10 µm.