Hesiocaeca methanicola Desbruyeres & Toulmond, 1998
The prostomium is wider than it is long, trapezoid in shape and bilobated anteriorly. There is a facial fold, a feature that connects the anterio-ventral side of the prostomium to the dorsal part of the mouth, which is visible only in specimens with an invaginated pharynx. The palps are biarticulated, and the palpophore is ovoid, flattened and slightly longer than it is wide. The palpostyle is conical and shorter than the palpophore. There are three antennae: paired antennae that are ciliated, conical and five times longer than wide basally and ca. same length as the palpostyle. The median antenna is very short and hardly visible, inserted on the dorsal posterior part of the prostomium. Median antenna furrows are absent. Eyes are absent. Nuchal organs are not visible. The prostomium has an entire posterior end. The prostomium and palpophores are densely covered with small tufts of short cilia. Papillose peristominal membrane and lip glands are absent. There is an eversible pharynx with a folded aperture and with three to four paired conical papillae that are located more deeply.
The noto- and neuropodial lobes and setae are absent on segments 1 and 2. Anterior dorsal cirri are present on segments 1 and 2 with cirrophores that are elevated and not fused. The ventral cirri and enlarged on segments 1 and 2. The following parapodia are subbiramous with a reduced notopodia bearing long and weakly segmented dorsal cirri, and two - three aciculae with slightly curved tip but without extending setae. Ther is a slight segmentation of the dorsal cirri, which is more visible and longer than wide distally. There are enlarged dorsal cirri in segments 1-5 or 1-4, which are irregular in length. The length of the posterior dorsal cirri is irregular, with some being very short and other being very long. This is likely to be linked to a regeneration process. The segments posterior to segment 2 have ventral cirri that are smaller than the parapodia and without a cirriphore. There are ciliated bands on the dorsal part of the segments.
The neuropodium are well developed, with a postsetal lobe that is rounded at the apex. There are four aciculae with slightly curved tips and a spreading fascicle of numerous (>90) compounded setae with long needle-shaped, serrated blades, varying in length. In the lower fascicle there are ca. 60 falcigers with shorter serrated blades that end with a terminal hood.
The anal cirri are ventral and well developed, but shorter than the anterior dorsal cirri. There are no pygidial papillae, and the anus is dorsal.
(Desbruyeres & Toulmond, 1998)
Ecology and Distribution
Types were found on the surface of ice-like methane hydrate mounds in the Gulf of Mexico at 538 m depth (27°44.77`N, 91°13.33`W) (Desbruyeres & Toulmond, 1998).