Hyalogyrina grasslei Warén & Bouchet, 1993
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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/03DC2538-0379-BF0B-FF7A-3D45B44A3F95 |
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treatment provided by |
Felipe |
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scientific name |
Hyalogyrina grasslei Warén & Bouchet, 1993 |
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Hyalogyrina grasslei Warén & Bouchet, 1993 View in CoL ( Figures 14 View Fig , 15 View Fig , 16 View Fig and 17 View Fig )
External morphology
The epithelium of the head region is covered by a microvillous border with interspersed ciliary tufts. The snout is tapered but slightly bilobate, the mouth opening is quite small. Between the cephalic tentacles there are two short, ciliated knobs ( Fig. 14a,b View Fig ). Another small process—probably a copulatory organ (see below)—is situated at the basis of the right cephalic tentacle close to the openings of receptaculum and gonoduct. A seminal groove could not be detected. In the anterior part of the right mantle cavity there is another small (about 0.2 mm), ciliated tentacle.
Pedal structures
The foot is folded due to preservation. The single pedal gland opens via a wide pore at the anterior border of the foot, but its posterior portion is difficult to distinguish from the surrounding connective tissue. In the center of the foot there is a densely packed group of large (diameter 80 μm) and transparent calcium cells, each provided with a large (diameter 13 μm) nucleus ( Fig. 15g View Fig ). The remaining foot mass shows large haemocoelic spaces with interspersed collagen and muscle fibers; parenchymous cells are rare.
Shell muscle, haemocoel, and mantle cavity
The conditions of the shell (columellar) muscle and of the haemocoel resemble those in Xenoskenea pellucida and Hyalogyrina depressa .
The entire mantle roof includes large blood sinuses, which are separated from each other by fine fibers of muscle or collagen. The mantle cavity itself is quite large and shows (from left to right) the following structures ( Figs. 14a,b View Fig ; 15a View Fig ). On the very left, the osphradium forms a round, elevated structure underlain by the osphradial ganglion. Whereas distinct hypobranchial and pallial glands are lacking, the anterior part of the mantle roof is glandular. The single, prominent, bipectinate gill has 19 dorsal and 16 ventral alternating leaflets, which lack a skeleton but are densely ciliated except for flat, interspersed non-ciliated cells, which dominate the distalmost parts of the leaflets ( Fig. 15b,c View Fig ). The gill reaches from the left posterior portion of the mantle roof to the posterior mediodorsal region. Afferent and efferent sinuses are well visible in the sections. At the very left pallial roof the single large, elongated kidney is situated behind the gill, followed by the pericardium with the heart. The right pallial roof is occupied by several loops of the rectum. To the very right there are the openings of the receptaculum and the gonoduct.
Excretory organ, heart and circulatory system
The efferent gill sinus runs backwards and becomes the afferent sinus of the kidney, the ventral (pallial) wall of the latter shows many blood sinuses. The narrow nephropore lies adjacent to the posterior edge of the gill. Whereas the main portion of the kidney shows the typical epithelium with small, round concrements, which are also present in the lumen, the right posterior part of the kidney is glandular ( Fig. 15d,e View Fig ). Posteriorly a ciliated renopericardial duct connects the kidney with the pericardium. Leaving the kidney posteriorly the sinus enters the auricle and ventricle of the monotocardian heart, which is situated behind the kidney. Again the head aorta runs forwards along the median mantle floor.
Genital system ( Fig. 16 View Fig )
Hyalogyrina grasslei is a simultaneous hermaphrodite. The tubular hermaphroditic gonad is composed by two main branches, an anterior and a posterior one, which split into a fan-like structure ( Fig. 16a View Fig ). Spermiogenesis takes place in the outer parts, oogenesis in the inner parts of the tubes ( Fig. 16c View Fig ); both types of germ cells show all stages of development. The fused portion of the two main branches becomes the hermaphroditic duct, which is not glandular but densely filled with sperm for a length of about 250 μm, and is meandering later on. Connected with the latter portion of the hermaphroditic gland there is a prominent blind sac ( Fig. 16a,c View Fig : bs1), which runs backwards for about 200 μm.
The hermaphroditic duct opens into the glandular part of the gonoduct; it can be divided in several portions on account of distinct mucous cell types. Along the most proximal portion the glandular cells are cuboidal and contain granules which stain heavily. At the line of the posterior end of the mantle cavity the (still closed) lumen of right/left anterior pedal nerve, 7/7’ = right/left ventral pedal nerve, 9 = buccal commissure, 10 = supraoesophageal connective, 11 = supraoesophageal-osphradial connective, 14’ = left mantle nerve. Supplementary plate 3 offers an interactive 3D model of Hyalogyrina grasslei that can be accessed by clicking into Fig. 14 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.)
the gonoduct splits into a ciliated seminal portion (vas efferens) and a thick, glandular oviduct. Both ducts remain associated, however ( Fig. 16f View Fig ). There is a second, narrow, ciliated blind sac ( Fig. 16g View Fig : bs2) again leading backwards, but this also has a very narrow connection to the distal part of the vas deferens. The thick oviduct shows several prominent mucous cells. The distalmost part of the gonoduct still shows the oviduct and the vas deferens in close association, but there are separate openings for sperm and eggs.
Anterior to the female opening there is the opening of a prominent receptaculum seminis, which runs backwards adjacent to the oviduct nearly to the line of the second blind sac. Its epithelium is densely ciliated ( Fig. 16b,d View Fig ) and underlain by a muscular layer, the lumen is filled with sperm ( Fig. 16d,h View Fig ).
As outlined above, there is no seminal groove and only a small copulatory organ at the basis of the right cephalic tentacle.
Alimentary tract ( Fig. 17 View Fig )
The whole buccal apparatus is structured nearly identically to that in Xenoskenea pellucida and Hyalogyrina depressa (see above). Here we recognized a specific paired retractor muscle from the anterior lateral buccal wall to the posterior wall of the head, with an enclosed nerve that originates from the buccal ganglion.
The conditions of the oesophagus and stomach also strongly resemble those in Xenoskenea . We recognized five teeth of the gastric shield ( Fig. 17f View Fig ), and the two digestive glands have a common opening into the stomach. The very short intestine starts at the anterior wall of the stomach. The rectum passes beneath the heart, runs forwards to the left, then makes three loops in the pallial roof. The anal opening ciliary sorting area of stomach, dfc = dorsal food channel, dg = digestive gland, ex = external milieu, gd = gonoduct, gs = gastric shield, gt = spines of gastric tooth, hao = head aorta, i = intestine, j = jaw, mc = mantle cavity, oe = oesophagus, ph = pharynx, poe = posterior oesophagus, r = radula, re = rectum, rm = radular musculature, sg/sg’ = right/left salivary gland, st = stomach, x = degraded food
( Fig. 17g View Fig ) is situated in the anterior right mantle cavity close to the male opening and shows a free end of the rectal tube.
Nervous system and sensory organs
The nervous system is nearly identical to those in Xenoskenea pellucida and Hyalogyrina depressa (see, e.g., Fig. 14c,d View Fig ).
The cephalic tentacles with their bifid tentacular nerves are densely ciliated, except in the outer lateral portions. Eyes are entirely lacking; the small statocysts again contain single statoliths.
Available data from other sources
Warén and Bouchet (1993) described the shell (op.cit.: figs. 39D–G) as small (max. 2.6 mm), very thin, and colourless, and the smooth protoconch as indistinct with 0.6 to 0.7 whorls (fig. 42E). The operculum is multispiral. The short radula is rhipidoglossate with the formula n 3 1 3 n (op.cit.: SEM figs. 40B, C, E); about 20 marginal teeth are present. Concerning external morphology (SEM figs. 41B– D), the animal has a long, tapered snout; eyes are lacking. Three short, flat tentacle-like structures with ciliated edges are situated between the smooth cephalic tentacles with lateral ciliation. A copulatory organ could not be observed even by SEM; the pallial margin is very thick. The foot is bifurcated anteriorly, whereas the posterior end is truncated; epipodial tentacles are lacking. A prominent, bipectinate gill with about 15 leaflets occupies most of the mantle cavity.
The discrepancy concerning the copulatory organ remains obscure: even the SEM photos provided by Warén and Bouchet (1993) do not show any trace of it, whereas our sections revealed it beyond doubt. Since species identity appears certain (we examined paratype material), the only explanation might be that the specimens examined in the two studies differed in sexual maturity.
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.