Functional morphology and ultrastructure of the mouth apparatus in the freshwater mite larvae Limnochares aquatica (L., 1758) (Acariformes, Limnocharidae)

IF 1.7 3区 农林科学 Q2 ENTOMOLOGY Arthropod Structure & Development Pub Date : 2024-01-01 DOI:10.1016/j.asd.2024.101331
Andrey B. Shatrov, Elena V. Soldatenko, Anatoly A. Petrov
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Abstract

The mouth apparatus in larvae of the freshwater mite Limnochares aquatica (L., 1758) (Acariformes, Limnocharidae), belonging to the lower Hydrachnidia, was studied with light microscopy, scanning (SEM) and transmission (TEM) electron microscopy, as well as with confocal laser scanning microscopy (CLSM) to reveal its main morphological and functional characteristics. The gnathosoma, functioning as a mouth organ takes a prognathous position, and inclines to the body axial line at the angle of around 30°. The gnathosoma is composed of segments of the two pairs of anterior appendages and their derivatives – two-segmented chelicerae lying above the infracapitulum – the compound medial portion of the palpal coxae, and five-segmented palps, articulated with the infracapitulum laterally. The palp tibia bears the bifid palpal claw facing downward nearly at right angle. The basal cheliceral segments are free, i.e., are not covered with the integumental fold posteriorly, and do not fuse with each other. Apically, they articulate with the relatively short movable digits composed of the basal portion (lever) and the distal portion (the cheliceral blades) curved upward by their ends. The flexible fixed digits protrude forward from the distal parts of the basal cheliceral segments. The ventral wall of the gnathosoma (mentum) transforms into a very specific papillary area (velum). A papillary area with long slim papillae is formed of a light cuticle and likely acts as a sucker but does not have contractile elements. The hypostome possesses the well developed lateral lips (galea) tightly embracing the distal portions of the chelicerae and hiding the movable digits. The roof of the infracapitulum (the cervix, or epistome) lying beneath the chelicerae, shows a compound structure. Anteriorly it connects with the inner hypostomal walls forming a particular pharyngeal ring framing the narrow mouth opening. We saw no evidence of a labrum. A characteristic valve projects forward from the dorsal surface of the cervix. A crescent-shaped pharynx runs along the bottom of the infracapitulum and is attached but not fused with the cuticle of the papillary area. The dorsal pharyngeal dilators originate on the cervix, sigmoid pieces and the lateral walls of the infracapitulum at their junction with the dorsal walls of the basal cheliceral segments. A pair of sigmoid pieces having small cavities inside serves for termination of the cheliceral elevators originated on the posterior portions of the dorsal walls of the basal cheliceral segments. The organizational pattern of the gnathosoma in larvae of L. aquatica is rather specific and is quite different from those of other aquatic or terrestrial parasitengonin larvae.

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淡水螨幼虫 Limnochares aquatica (L., 1758) (Acariformes, Limnocharidae) 口器的功能形态和超微结构。
研究人员利用光学显微镜、扫描电子显微镜(SEM)、透射电子显微镜(TEM)以及激光共聚焦扫描显微镜(CLSM)对淡水螨(Limnochares aquatica (L., 1758))(螨形目,Limnocharidae)幼虫的口器进行了研究,以揭示其主要形态和功能特征。作为口腔器官的咬合瘤呈前腹状,与身体轴线成 30° 左右的倾斜角。鳃瓣由两对前附肢及其衍生物--位于颌下部上方的两节螯肢--颚跗关节的复合内侧部分和五节颚组成,颚跗关节侧面与颌下关节铰接。颚胫骨上有朝下、几乎成直角的两裂颚爪。基部螯节是游离的,即没有被后部的皮褶覆盖,也没有相互融合。在顶部,它们与相对较短的活动指节相衔接,活动指节由基部(杠杆)和末端向上弯曲的远端(螯叶)组成。灵活的定指从基部螯片的远端向前突出。咬合瘤(mentum)的腹壁转变成一个非常特殊的乳头区(velum)。乳头区有细长的乳头,由浅色角质层形成,可能起吸盘作用,但没有收缩元件。下躯体具有发达的侧唇(galea),紧紧包裹着螯肢的远端,并隐藏着可活动的指头。位于螯肢下方的螯下顶(宫颈或外顶)显示出一种复合结构。它的前部与下体内壁相连,形成一个特殊的咽环,将狭窄的口腔开口框住。我们没有看到唇瓣的迹象。子宫颈背侧有一个特征性的瓣膜向前突出。新月形的咽部沿着下腔底部延伸,与乳头区的角质层相连但不融合。咽部背侧扩张器起源于子宫颈、乙状结肠片和与基部螯片背壁交界处的咽下腔侧壁。一对乙状结肠片内部有小空腔,用于终止基部螯节背壁后部的螯隆起。L. aquatica 幼虫的鳃瓣组织模式相当特殊,与其他水生或陆生寄生虫幼虫的鳃瓣组织模式截然不同。
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来源期刊
CiteScore
3.50
自引率
10.00%
发文量
54
审稿时长
60 days
期刊介绍: Arthropod Structure & Development is a Journal of Arthropod Structural Biology, Development, and Functional Morphology; it considers manuscripts that deal with micro- and neuroanatomy, development, biomechanics, organogenesis in particular under comparative and evolutionary aspects but not merely taxonomic papers. The aim of the journal is to publish papers in the areas of functional and comparative anatomy and development, with an emphasis on the role of cellular organization in organ function. The journal will also publish papers on organogenisis, embryonic and postembryonic development, and organ or tissue regeneration and repair. Manuscripts dealing with comparative and evolutionary aspects of microanatomy and development are encouraged.
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