Heiner Iben, Kristensen Reinhardt Møbjerg
Invertebrate Department, Zoological Museum, Natural History Museum of Denmark, Universitetsparken 15, Copenhagen, DK-2100, Denmark.
J Morphol. 2009 Feb;270(2):129-53. doi: 10.1002/jmor.10671.
A new species of Loricifera, Urnaloricus gadi nov. gen. et nov. sp., is described from the Faroe Bank, located Southwest of the Faroe Islands, North Atlantic. The new species does not fit into any known families of Loricifera and therefore it is grouped into a new family Urnaloricidae nov. fam. The new species is characterized by having a very complicated life cycle that involves a large cyst-like mega-larva, two reduced larval instars and the Higgins-larvae eating their maternal stage from within. An adult stage is missing. This form of reproduction is called viviparous pedogenesis and normally is found only in nematodes and insects. In the life cycle of Urnaloricidae nov. fam., there are two types of free-living larval stages: a Higgins-larva and a mega-larva. The latter is found in two different forms, a pre- and a cyst-forming mega-larva. Additionally, there are two reduced life history stages, the reduced larval stage (probably a postlarva) and the ghost-larval stage inside the cyst-forming mega-larva. The external morphology of the two forms of mega-larvae is much reduced, e.g., the introvert has only a few rows of scalids when compared with the Higgins-larva. The pre mega-larva is free-living and can sometimes be covered with coccoliths. Internally, a large ovary with a few oocytes, a digestive system, and an internal armature with retracted scalids are present. The pre mega-larva presumably molts into a cyst-forming mega-larva and thereby the ovary is now seen inside the cyst-forming mega-larva. The cyst-forming mega-larva has the same structures as in the pre mega-larva though here the scalids are protruded and there is a gonopore. Inside the cyst-forming mega-larva the ovary produces more oocytes and begins to fill out the entire lumen. At this stage the cyst-forming mega-larva molts first to the presumed postlarval stage, and then this stage molts to a ghost-larva. Hence, the ovary now matures inside the ghost-larva, which is surrounded by both the cuticle of the reduced postlarval stage and the cuticle of the cyst-forming mega-larva. The oocytes mature into eggs, and then into embryos and finally into Higgins-larvae while reabsorbing all the tissue of their maternal stage, the ghost-larva. During this maturation the cuticle of the cyst-forming mega-larva starts to harden and become cyst-like. The fully developed Higgins-larvae emerge through the gonopore of the cyst-forming mega-larva by penetrating the thin cuticles of the ghost-larva and the postlarva. The embryos have holoblastic radial cleavage and later a fluid-filled blastocoel is formed. The eggshells are extremely elastic; hence, they can become very elongated as the embryos mature into Higgins-larvae.
一种新的铠甲动物门物种，即Urnaloricus gadi，新属及新种，是从位于北大西洋法罗群岛西南的法罗浅滩发现并描述的。该新物种不属于任何已知的铠甲动物门科，因此被归入一个新科Urnaloricidae，新科。该新物种的特点是具有非常复杂的生命周期，包括一个大型囊状巨型幼虫、两个发育不全的幼虫龄期，以及希金斯幼虫从内部吃掉其母体阶段。缺少成虫阶段。这种繁殖形式被称为胎生幼体生殖，通常仅在线虫和昆虫中发现。在新科Urnaloricidae的生命周期中，有两种自由生活的幼虫阶段：希金斯幼虫和巨型幼虫。后者有两种不同形态，即前期巨型幼虫和形成囊状的巨型幼虫。此外，还有两个发育不全的生活史阶段，即发育不全的幼虫阶段（可能是后期幼虫）和在形成囊状的巨型幼虫内部的幽灵幼虫阶段。两种巨型幼虫形态的外部形态大大简化，例如，与希金斯幼虫相比，吻部只有几排鳞片。前期巨型幼虫是自由生活的，有时会被颗石藻覆盖。内部有一个带有少数卵母细胞的大卵巢、一个消化系统，以及带有缩回鳞片的内部骨架。前期巨型幼虫大概会蜕变成形成囊状的巨型幼虫，此时卵巢可见于形成囊状的巨型幼虫内部。形成囊状的巨型幼虫具有与前期巨型幼虫相同的结构，不过这里鳞片突出且有一个生殖孔。在形成囊状的巨型幼虫内部，卵巢产生更多卵母细胞并开始充满整个内腔。在此阶段，形成囊状的巨型幼虫首先蜕变成假定的后期幼虫阶段，然后这个阶段再蜕变成幽灵幼虫。因此，卵巢现在在幽灵幼虫内部成熟，幽灵幼虫被发育不全的后期幼虫阶段的角质层和形成囊状的巨型幼虫的角质层所包围。卵母细胞发育成卵，然后发育成胚胎，最后发育成希金斯幼虫，同时吸收其母体阶段幽灵幼虫的所有组织。在这个成熟过程中，形成囊状巨型幼虫的角质层开始硬化并变成囊状。完全发育的希金斯幼虫通过穿透幽灵幼虫和后期幼虫的薄角质层，从形成囊状的巨型幼虫的生殖孔中出来。胚胎进行全裂辐射卵裂，随后形成一个充满液体的囊胚腔。卵壳极具弹性；因此，随着胚胎发育成希金斯幼虫，它们会变得非常细长。
