Hyalogyrina depressa Hasegawa, 1997
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publication ID |
https://doi.org/ 10.1007/s13127-011-0048-0 |
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persistent identifier |
https://treatment.plazi.org/id/03DC2538-0361-BF00-FF7A-391DB6C6394A |
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treatment provided by |
Felipe |
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scientific name |
Hyalogyrina depressa Hasegawa, 1997 |
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Hyalogyrina depressa Hasegawa, 1997 View in CoL
( Figures 7 View Fig , 8 View Fig , 9, 10, 11 View Fig , 12 and 13 View Fig )
External morphology
The head bears a conical snout with two anterior bulges. The right side of the head and the neck region are densely ciliated, the neck also shows a glandular epithelium. The cephalic tentacles are dorsoventrally flattened. A small (300 μm long), conical pallial tentacle is visible at the right opening of the mantle cavity. This tentacle is densely ciliated ( Fig. 8a View Fig ) and equipped with prominent longitudinal muscle fibers. Eyes and epipodial tentacles are lacking; the mantle margin is smooth and ciliated.
Foot and shell muscles
In the contracted animals the foot is transversely folded like a pocket knife ( Fig. 7a,b View Fig ). The anterior foot is deeply bilobed, the posterior end is rounded. The epithelium of the foot’ s sole consists of highly cylindrical, densely ciliated cells interspersed with poorly stained mucous cells. The back of the foot lacks cilia, however. The anterior foot gland forms an irregular mass in the dorsal half of the propodium. Two lobes of this mass fill the anterior foot lappets, another two lobes extend laterally, and one lobe runs backwards ventrally. The central duct (diameter 25 μm) opens at the anterior median edge of the foot sole. The cells are large (20 μm× 36 μm) and have irregularly shaped, basal nuclei ( Fig. 7e View Fig ).
The much smaller, posterior foot gland contains weakly stained mucous cells and opens via a short duct in the center of the foot sole. The posterior gland forms a flat mass and is somewhat embedded in the connective tissue of the foot.
In the central portion of the foot there is an accumulation of very large (diameter 60–95 μm), clear, oval to deformed calcium cells with large (diameter 15 μm), round nuclei. Whereas the cytoplasm of these cells is restricted to narrow strings, the main volume of the cells is mainly occupied by large vacuoles containing fine concrements ( Fig. 7d View Fig ), which show negative contrast in phase contrast microscopy. Otherwise the foot mass contains muscle and collagen fibers as usual, haemolymph spaces and parenchymous cells.
There is a single columellar muscle, which adheres ventrally at the shell ( Fig. 9a,b).
Mantle cavity ( Fig. 7a–c View Fig )
The mantle cavity occupies about one third of the volume of the last shell whorl. The anterior part of the mantle cavity is occupied by the gill. On the left side, about 200 μm behind the edge, the osphradium forms a thickened ridge. More posterior and to the left the single kidney is situated in front of the monotocardian heart. The posterior, central and right mantle roof is occupied by several rectal loops, followed towards posterior right by the receptaculum seminis and the gonoduct with the gonopore. The posterior wall of the mantle cavity is formed by the bursa copulatrix, the anterior portion of the digestive gland, and to the left by the stomach.
The whole mantle roof is underlain by wide blood sinuses, in particular near the anterior mantle edge. On the inner side of the mantle roof there are various glands with propodium, pt = pallial tentacle, r = radula, re = rectum, rs = receptaculum seminis, st = stomach, v = heart ventricle. Supplementary plate 2 offers an interactive 3D model of Hyalogyrina depressa that can be accessed by clicking into Fig. 7 View Fig (Adobe Reader version 7 or higher required). Rotate model: drag with left mouse button pressed; shift model: same action+ctrl; zoom: use mouse wheel (or change default action for left mouse button). Select or deselect (or change transparency of) components in the model tree, switch between prefab views, or change surface visualization (e.g. lighting, render mode, crop, etc.)
various types of mucous cells: the right pallial gland consists of cells with an empty or bubble-like structure, and occasional dark, apical granules dominate ( Fig. 7a View Fig : pg; 8a: mg1). On the left side another pallial gland has mucous cells showing metachromatic content ( Fig. 7b View Fig : pg’; 8b: mg2). In the central pallial roof and occasionally also laterally there are mucous cells which appear empty in the sections ( Fig. 8c View Fig : mg3).
The bipectinate gill shows about 20 alternating lamellae, which have ciliary tracts and regions with very flat (respiratory) epithelia ( Fig. 8d View Fig ). Beneath the efferent blood sinus, the efferent gill axis has a thick muscle which runs into the left mantle, but on the right (afferent) side no distinct retractor is present.
Excretory organ, heart and circulatory system ( Fig. 9)
The rectal sinus runs along the rectum forwards to the right and enters the afferent axis of the gill. After passing the leaflets the efferent gill sinus collects the haemolymph and also receives a mantle sinus, thus becoming the afferent sinus of the kidney. After passing the kidney walls the efferent kidney sinus opens into the auricle, followed by the ventricle ( Fig. 9b,c). The head aorta runs forwards along the median mantle floor.
The monotocardian heart is situated in the left posterior mantle cavity. The kidney forms a boomerang-shaped organ in the posterior mantle roof and shows a distinct nephropore ( Fig. 8e View Fig : arrowhead). It is connected with the pericardium by a ciliated renopericardial duct.
Genital system ( Figs. 10, 11 View Fig )
The true hermaphroditic gland occupies the right half of the visceral body ( Fig. 10a). The right portion has a homogenous lumen, from which several lobes expand to the left ( Fig. 10b,c). The inner portion of these lobes produces the eggs, which become more mature from left to right and from posterior to anterior ( Fig. 11f View Fig ). Spermiogenesis takes place towards the central parts in the portions of the hermaphroditic gland which lie adjacent to the external epithelium of the visceral sac ( Fig. 11f View Fig ). Mature sperm (only one type is present) have filiform heads and long flagella, and are orientated centrifugally ( Fig. 11g View Fig ).
The hermaphroditic duct emerges on the median side of the gonad and runs to the right, where it widens to form a vesicula seminalis containing autosperm with their heads orientated forwards ( Fig. 11d View Fig ). From the proximal part of the gonoduct a prominent blind sac (ca. 350×100× 40 μm) emerges ventrally ( Figs. 10a,b; 21c View Fig : vs). Its dorsal epithelium consists of thick (up to 22 μm) glandular cells with heavily stained cytoplasms, whereas the ventral epithelium is densely ciliated. The gonoduct as a whole forms an Sshaped loop towards ventral, then anteriorly left, and finally runs in a curve to ventral right towards the genital atrium. It consists of three histologically distinct regions ( Fig. 10d: gd1/2/3), as follows. (1) The glandular proximal part shows many dark granules of various sizes, further structures are poorly preserved ( Fig. 10d: gd1). From here a prominent sinuses and gill muscle. (d) Circulatory system and kidney (pericardium transparent), left side view. Labels: a = auricle, ags = afferent gill sinus, ao = aorta, cm = columellar muscle, egs = efferent gill sinus, gi = gill, gm = gill muscle (retractor), hm = head muscle (retractor), k = kidney, pc = pericardium, rs = rectal sinus, v = heart ventricle
(350 μm×100 μm×40 μm) blind sac emerges ( Figs. 10d; 11a View Fig : bs1). Its epithelium shows mucous cells with dark cytoplasm and pale nuclei, as well as clear granula or vesicles; the ventral epithelium is densely ciliated. (2) The proximal part is continued by the central part of the gonoduct consisting of long, ciliary cells filled with large, dark vesicles ( Figs. 10d; 11a,c View Fig : gd2). At the distal end of the central part another glandular blind sac (440 μm× 95 μm×30 μm) is formed, somewhat surrounding the gonoduct ( Figs. 10d; 11a View Fig : bs2). This gland consists of many lobes with lightish, homogeneous lumina; the lumen opens via a ciliary duct into the gonoduct. (3) The distalmost part of the gonoduct is again formed by long cells with granules, but the latter show metachromic staining ( Fig. 11a View Fig : gd3). The duct finally enters the genital atrium, from which the following two further structures arise.
(A) The bursa copulatrix is embedded in the proximal and median gonoduct ( Fig. 10b,c). It is a bean-shaped structure (50 μm×160 μm×50 μm) with a ciliated epithelium. Its large lumen shows organic particles that could not be identified unequivocally, but probably are degraded allosperm ( Fig. 11e View Fig ). A narrow, ciliated duct connects the bursa with the genital atrium.
(B) The receptaculum seminis (160 μm×80 μm×70 μm) is situated to the right of the bursa and also lies adjacent to the gonoduct ( Fig. 10a–c: rs). It is filled with densely packed allosperm ( Fig. 11c View Fig ). The ciliated duct runs along the gonoduct and again opens into the genital atrium.
The genital atrium itself opens via a short duct into the posterior right mantle cavity. A copulatory organ is not present.
Alimentary tract ( Fig. 12)
The small and narrow mouth opening is flanked by lateral oral lappets. Behind the mouth opening two triangular jaw gonoduct (arrow marks position of blind sac 2 along ridge). Labels: b = bursa, bs1/2 = blind sac 1/2, g = gonad, ga = genital atrium, gd = gonoduct, gd1/2/3 = proximal/median/distal portion of gonoduct, rs = receptaculum seminalis, vs = ventral sac plates are situated laterodorsally, consisting of tooth-like elements flanking the oral cavity, which is of inverted Yshape ( Fig. 12d). The radula is supported by a purely muscular odontophore; true cartilages are lacking. The radula sheath makes a sharp loop downwards, its blind end consists of numerous odontoblasts ( Fig. 12e).
The pharynx continues dorsally into the anterior oesophagus, which shows several densely ciliated, longitudinal folds ( Fig. 12f). It is flanked by the paired, large (200 μm × 80 μm × 40 μm) salivary glands, which possess many small lobes. The salivary ducts show many loops (due to the contracted condition), their glandular epithelia are heavily stained, whereas the posterior parts show large, pale cells with very large nuclei ( Fig. 12g). Effects of torsion are minimal; the posterior part is a simple, narrow (diameter 55 μm) tube that runs backwards and enters the stomach between the openings of the two digestive glands ( Fig. 12i).
The posterior stomach (diameter 500 μm) is equipped with a large but thin gastric shield with tooth, followed more anteriorly by ciliated areas with high prismatic cells ( Fig. 12h). Again a small caecum is present at the ventral side of the stomach ( Fig. 12h: ca).
The anterior digestive gland occupies the visceral body to the right of the stomach, whereas the posterior gland fills the visceral sac. Both consist of a spreading duct system reaching into irregularly shaped diverticles ( Fig. 12i). The epithelium of the digestive glands shows lightish cells with round nuclei and a compact cytoplasm in the apical portion ( Fig. 12i).
The short and ciliated intestinal tube (diameter 80 μm) emerges from the stomach on the right side, runs forwards and then upwards entering the mantle roof. The rectal portion shows several narrow loops in the mantle roof ( Figs. 7c View Fig ; 12c). The anal opening is situated in the posterior right mantle cavity.
Stomach and intestine contain remnants of detritus, including diatom tests.
Nervous system ( Fig. 13a,b View Fig )
The cerebral ganglia are situated at the basis of the cephalic tentacles. They are compressed dorsoventrally and connected by a short commissure. The tentacle nerve bifurcates shortly after emergence ( Fig. 13a,b View Fig : nerve 2). The pleural ganglia are fused with the cerebral ganglia (epiathroid condition); these cerebropleural ganglia are connected to the pedal ganglia by two connectives (n3, n4). The pedal ganglia are connected by a short commissure; one pair of pedal nerves runs forwards (n6), another pair (n7) backwards into the foot. The buccal ganglia with their thin and quite long commissure (n9) are situated at the line of the opening of the salivary glands, and are connected to the cerebral ganglia (n8).
stomach (arrowheads: gastric shield). (i) Longitudinal section of posterior oesophagus at line of digestive gland openings, anterior is at right (arrowhead: dense cytoplasm of apical epithelium of digestive gland). Labels: adg = anterior digestive gland, asg = anterior part of salivary gland, ca = stomach caecum, ci = ciliary border, csa = ciliary sorting area of stomach, gs = gastric shield, hao = head aorta, hec = head epidermis, j = jaw, mc = mantle cavity, mt = mouth tube, od = odontoblasts, oe = oesophagus, pdg = posterior digestive gland, ph = pharynx, psg = posterior part of salivary gland, r = radula, re = rectum, sg/sg’ = right/left salivary gland, st = stomach
From the right pleural ganglion a connective (n10) crosses above the oesophagus to the left side and reaches the supraoesophageal ganglion, which is situated above the left pleural ganglion. From the latter a short nerve (n11) connects to the osphradial ganglion in the left mantle roof. A left zygoneurosis ( Fig. 13b View Fig : arrowhead) connects the left pleural with the supraoesophageal ganglion. Posteriorly a mantle nerve (n12) and the posterior portion of the visceral loop (n14’) emerge from the left pleural ganglion.
From the left pleural ganglion another connective (n13) crosses below the oesophagus to the right and reaches the suboesophageal ganglion at the line of the right pedal ganglion. Again a mantle nerve (n12) and the posterior part
P/P’ = right/left pedal ganglion, Pl/Pl’ = right/left pleural ganglion, Sb = suboesophageal ganglion, Sp = supraoesophageal ganglion, st/st’ = right/left statocyst; 1 = cerebral commissure, 2/2’ = right/ left tentacle nerve, 3/3’ = right/left cerebropedal connective, 4/4’ = right/left pleuropedal connective, 5 = pedal commissure, 6/6’ = right/left anterior pedal nerve, 7/7’ = right/left ventral pedal nerve, 8/8’ = right/left cerebrobuccal connective, 9 = buccal commissure, 10 = supraoesophageal connective, 11 = supraoesophageal-osphradial connective, 12 = visceral loop, 13 = suboesophageal connective, 14/14’ = right/left mantle nerve of the visceral loop (n14) emerge posteriorly. A visceral ganglion could not be detected.
Sensory organs ( Fig. 13c,d View Fig )
Eyes and epipodial tentacles are entirely lacking; the cephalic tentacles are smooth ( Fig. 13d View Fig ). Each of the two bean-shaped statocysts (30 μm×20 μm ×10 μm), which are situated at the postero-dorsal sides of the pedal ganglia, contains a small (diameter 12 μm), round statolith ( Fig. 13c View Fig ). The osphradial epithelium is higher than that of the surrounding mantle roof; histological details could not be detected ( Fig. 13d View Fig ).
Data from other sources
Hasegawa (1997) gave SEM images of the depressed, smooth shell (op.cit.: fig. 29A–C), the hyperstrophic granular to smooth protoconch (fig. 29D, E) forming an anastrophic apex, of the round, multispiral operculum (fig. 29F), the rhipidoglossate radula (fig. 29G, H) with the formula n-1-1-1-n, and of a jaw plate (fig. 29I) consisting of tooth-like elements. He also provided SEM photos of the head-foot (fig. 30A, B) and the gill leaflets (fig. 30C).
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