SPECIAL ICHTHYOLOGY - R. S. Pentyliuk - 2011

1. ORIGIN AND EVOLUTION OF CYCLOSTOMES AND FISHES. SYSTEMATICS OF MODERN CYCLOSTOMES AND FISHES. SUBPHYLUM CRANIATA. INFRAPHYLUM AGNATHA. CLASS CYCLOSTOMATA

1.3. Subphylum Craniata. Infraphylum Agnatha. Class Cyclostomata

1.3.2. Subclass Myxini (Hagfishes)

Unlike lampreys, hagfishes are much less studied, although their number of genera and species is comparable to that of lampreys. Hagfishes are exclusively marine animals; they not only fail to enter rivers but are also absent from low-salinity environments, perishing when salinity drops to 25%.

The Mouth of hagfishes lacks a suctorial disc, but is instead surrounded by two pairs of barbels. In A number of species, the gill pouch apertures open not directly to the outside, but into a common duct whose exit pore is located considerably further back. The olfactory sac, connected to the nasal opening, communicates with the pharyngeal cavity, allowing hagfishes to breathe by drawing in Water through the Nose as well. The eyes of hagfishes are underdeveloped and hidden beneath the Skin, so they rely primarily on Touch and smell to navigate their environment.

Unlike lampreys, The Development of hagfishes is direct. They lay only 20–30 relatively large (over 2 cm) yolk-rich eggs, which eventually hatch into young hagfishes. Adult hagfishes do not die after spawning. Widely distributed across various seas in temperate and subtropical zones, hagfishes are primarily benthic, found at depths ranging from 100 to 500 m, although they can occasionally ascend near the surface or descend to depths exceeding one kilometer.

Hagfishes are predatory; carrion forms a significant part of their diet, along with small invertebrates such as polychaete worms. However, hagfishes also attack living Fishes, both weakened and healthy ones, causing considerable damage to fisheries by consuming a large quantity of fish trapped in nets.

Hagfishes possess more salivary Enzymes than lampreys, and rather than merely sucking the Blood of their victim by attaching externally, a hagfish will find a suitable host, bite a hole into its body, and gradually burrow deeper and deeper, ultimately leaving behind literally «skin and bones» after its meal. The size of various hagfish species ranges from 20–30 cm up to 1 m.