| Fritillaria | |
|---|---|
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Subphylum: | Tunicata |
| Class: | Appendicularia |
| Order: | Copelata |
| Family: | Fritillariidae |
| Subfamily: | Fritillariinae |
| Genus: | Fritillaria Fol, 1872 |
| Species [1] | |
Fritillaria is a genus of larvacean tunicates belonging to the family Fritillariidae.
Fritillaria differs from other larvaceans like the well-studied Oikopleura by having an elongated trunk region, divided into three distinct sections.
Only the anterior section, comprising the mouth, pharynx and cerebral ganglion, is covered in oikoplastic epithelium. [2] It features a dorsal projection of epithelium, comprising many cellulose-secreting oikoplasts.
The middle section, connected to the front by the oesophagus, comprises the gut and anus, and connects to the tail. In the larva, it is covered by the epithelium, before the latter retracts to the anterior lobe and differentiates into oikoplasts.
The posterior section houses the gonads, growing inside an extension of the trunk.
The latter two sections are devoid of epidermis, instead replaced by a thin cuticular layer secreted by the epithelium during the larval stage.
Like other larvaceans, Fritillaria secretes a house made of mucopolysaccharides and cellulose, helping catch food particles for filter-feeding. However, Fritillaria's house does not fully cover the animal, instead only expanding on the anterior side. Also, instead of being discarded when clogged like in other larvacean genera, it is here regularly inflated and deflated, helping cleaning off clogged particles.[ citation needed ]
Fritillaria is a widespread genus of larvaceans. Unusually for larvaceans, F. rex has been reported to occur deep into the bathypelagic zone in Monterey Bay. [3]
The thyroid, or thyroid gland, is an endocrine gland in vertebrates. In humans, it is in the neck and consists of two connected lobes. The lower two thirds of the lobes are connected by a thin band of tissue called the isthmus (pl.: isthmi). The thyroid gland is a butterfly-shaped gland located in the neck below the Adam's apple. Microscopically, the functional unit of the thyroid gland is the spherical thyroid follicle, lined with follicular cells (thyrocytes), and occasional parafollicular cells that surround a lumen containing colloid. The thyroid gland secretes three hormones: the two thyroid hormones – triiodothyronine (T3) and thyroxine (T4) – and a peptide hormone, calcitonin. The thyroid hormones influence the metabolic rate and protein synthesis and growth and development in children. Calcitonin plays a role in calcium homeostasis. Secretion of the two thyroid hormones is regulated by thyroid-stimulating hormone (TSH), which is secreted from the anterior pituitary gland. TSH is regulated by thyrotropin-releasing hormone (TRH), which is produced by the hypothalamus.
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Fritillariidae is a family of tunicates belonging to the order Copelata.
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