Agnezia orthenteron ( Redikorzev, 1941 )

Sanamyan, Karen & Sanamyan, Nadya, 2012, Deep-water Ascidiacea from the Sea of Japan, Zootaxa 3245, pp. 63-68 : 64

Agnezia orthenteron ( Redikorzev, 1941)

( Figure 1 )

Agnesia orthenteron Redikorzev, 1941: 199 . Nishikawa, 1991: 60.

Material examined. St. A6-8(1), 2545–2555m, 1 specimen; St. A6-8(2), 2545–2555m, 2 specimens; St. A6-7, 2511– 2534m, 2 specimens; St. B5-8, 2609– 2655m, 1 specimen.

Description. The specimens are oval in outline and laterally flattened. The largest is about 15mm diameter. The test is colourless, clear and transparent. Few fine test processes may present on the posterior end of the body along with sparse spicules of sponges attached to them, otherwise the surface of the test is smooth. Most specimens have epibionts (probably bryozoans) on the test around siphons.

Siphons short, the branchial is terminal and the atrial one third down along mid dorsal line of the body. Body wall, as in most species of the genus, is very thin and transparent ( Fig. 1 A). Muscles almost equally developed on both sides of the body. Thick circular muscle fibers are on the body wall around the atrial siphon, and circular muscles on the branchial siphon are limited to the wall of the siphon and do not extend beyond the branchial velum. Eight to ten thin short radial muscles radiating from the branchial siphon, the same number of longer and thicker muscles radiate from the atrial siphon. No muscles crossing intersiphonal area. Rather long parallel transverse muscles form a band on each side of the endostyle and cross the dorsal surface posterior to the atrial siphon.

Numerous branchial tentacles of different lengths are arranged in several cycles and situated halfway between the branchial aperture and strong muscular branchial velum. Prepharyngeal band runs close to the velum without any noticeable undulations and makes a prominent dorsal V around the long ganglion. The dorsal tubercle was not detected.

Each side of the branchial sac has six double rows of ten or eleven spiral stigmata ( Fig. 1 B). The stigmata are not interrupted, mostly with four coils, and form perfectly rectangular meshes, although several polygonal figures are also present. Typically four, occasionally more radial parastigmatic vessels present on each mesh. Double rows of stigmata are separated by five transverse vessels. Each vessel has 10 or 11 simple papillae on the right side of the body and 9 or 10 on the left, and a dorsal languet displaced slightly to the left from mid-dorsal line.

The gut forms slightly curved loop at posterior part of the left side of the body. The gonads consisting of ramified testis and the ovary are in the gut loop and male and female ducts run along the rectum to open together near the anus.

Remarks. So far the species was known from only one specimen described from the Sea of Japan, 2090m. The present specimens come from similar depths and correspond well to the original description. According to Redikorzev (1941) the species has 5 transverse vessels and the space between transverse vessels and above the first and the last vessel is divided into six "fields" making seven "rows". This sentence is hard to understand, but the whole detailed description suggests that the branchial sac of Redikorzev's specimen had six double rows separated by five transverse vessels (see also Nishikawa, 1991), and thus the branchial sac has the same structure as in the present material. Redikorzev (1941) recorded nine papillae on each transverse vessel and the newly recorded specimens are larger and have nine to 11 papillae. Gut loop is not straight and J-shaped as figured by Redikorzev, but slightly curved along postero-dorsal corner of the body, but the difference is not enough to doubt conspecificity the present specimens with A. orthenteron .

The species is known only from the Sea of Japan, from 2090 to 2655 m.

Figures

FIGURE 1. Agnesia orthenteron. A, body with tunic removed from left and right side; B branchial sac.