Corynascidia suhmi Herdman, 1882

Sanamyan, K. E. & Sanamyan, N. P., 2005, Deep-water ascidians from the North Atlantic (RV Academic Keldysh, cruise 46 and 49), Journal of Natural History 39 (22), pp. 2005-2021 : 2006-2008

Corynascidia suhmi Herdman, 1882

( Figure 1 ) Corynascidia suhmi Herdman 1882, p 186 ; Hartmeyer 1924, p 19; Kott 1969, p 87; Millar

1988, p 1429; Monniot and Monniot 1994, p 22; Sanamyan and Sanamyan 2002, p 335. Corynascidia hartmeyeri Monniot and Monniot 1994, p 23 .v

Material examined

Submersible MIR-2; st. 4540, 4313 m, two specimens.

Description

Specimens, about 12 cm long, are in excellent condition. The test, as in all Corynascidia species , is thin, soft and transparent, and slightly thicker on the peduncle and on the top of the body. The peduncle is shorter than the body and distinctly demarcated from it. The apertures are on the short siphons on the side of the body. Body muscles and the position of the gut loop in the upper (distal) corner of the body ( Figure 1C ) are identical with the description of specimens of C. suhmi Herdman, 1882 from the South Orkney Trench ( Sanamyan and Sanamyan 2002). Some details of the inner anatomy, however, are different. The inner surface of the atrial siphon has minute papillae visible only after staining. The tentacles are long and numerous, 150 or more. The prepharyngeal band is composed of two thick lamellae. The anterior lamella curves immediately behind the dorsal tubercle where it becomes higher and thicker, forming a small triangular papilla. The posterior lamella makes a thick-walled narrow V behind the dorsal tubercle. The dorsal lamina has a line of long dorsal languets. In one specimen 24–27 transverse rows of about 42–47 spiral infundibula, each with 1.5 to three coils are on each side of the branchial sac; another specimen has 32–36 transverse rows of about 47 spirals. Each spiral is crossed by two, three, or seldom more, thin radial vessels. About 60–63 entire inner longitudinal vessels are present on each side of the branchial sac, they are on long papillae arising from the transverse vessels.

The gut loop ( Figure 1A ) is distinctly displaced to the right side of the body. The welldefined small stomach is clearly demarcated from the intestine and oesophagus and has distinct longitudinal ridges. The long rectum ends with an anus of a characteristic shape, its two anterior lobes fringed with long finger-shaped lobes. The testis follicles spread around the proximal end of the tubular ovary in the gut loop. The gonoducts run together along the rectum, their openings close together near the anus.

Remarks

The genus Corynascidia contains eight nominal species (four sessile and four stalked). Six are known from the southern hemisphere, one was recorded in the Bering Sea and one in the North Atlantic (61 ° 50 9 N, 56 ° 27 9 W). The North Atlantic specimens, initially identified by Hartmeyer (1924) as C. suhmi Herdman, 1882 , were considered a distinct species, C. hartmeyeri Monniot and Monniot, 1994 , characterized by its plain-edged dorsal lamina. In almost all features, except the dorsal lamina, the present specimens conform to the description of C. hartmeyeri , and the geographic region is the same. The figure reproduced by Monniot and Monniot (1994) shows only the upper portion of the dorsal lamina which appears to be of about the same height as the prepharyngeal band. The structure resembling a low thick-walled lamina just behind the dorsal tubercle, as in the present specimens ( Figure 1D ), and in some other species ( C. lambertae Sanamyan and Sanamyan, 2002 and especially C. vinogradovae Sanamyan, 1998 ), tends to confirm the view that other features, such as the dorsal languets would be similar in the specimens assigned to C. hartmeyeri . The plain dorsal lamina is so unusual for Corynascidia , all other species having dorsal languets, that there is some doubt that the feature was correctly observed or interpreted.

The characteristic shape of the anus with the margin fringed with the long papillae is a second feature distinguishing the present specimens from C. hartmeyeri , which has ‘‘large anus without lobes’’ ( Monniot and Monniot 1994, p 24). We observed a similar lobed and papillated anus on perfectly preserved species of C. suhmi , C. vinogradovae and C. herdmani (see Sanamyan 1998; Sanamyan and Sanamyan 2002), although the original description of C. herdmani states that the anus is smooth ( Ritter 1913). However, if the terminal portion of the rectum is contracted, the anal border appears to be smooth (as in C. lambertae ). Thus, there seems to be no justification for keeping C. hartmeyeri as a separate species.

The present specimens differ from the southern specimens of C. suhmi in the number of transverse rows of stigmata. However, rows appear to be added with the growth of the specimens and two of the present specimens show relatively large variations (24–27 and 32–36 rows in the specimens of about the same size, and the number reported for C. suhmi by Sanamyan and Sanamyan 2002 was about 60 rows). Differences in number of branchial spirals and internal longitudinal vessels or papillae could be more significant, although more data are needed to confirm this. Herdman’s original figure of C. suhmi shows about two internal longitudinal vessels for one spiral ( Herdman 1882, Plate 25, Figure 6 ). This number was confirmed by Sanamyan and Sanamyan (2002) in specimens from the South Orkney Trench. The present specimens (as well as in C. hartmeyeri type specimens), have about three papillae per two stigmata. There is also a difference in the shape of the prepharyngeal band, posterior lamella of which makes a narrow V behind the dorsal tubercle in the present species—a structure apparently not present in southern specimens of C. suhmi , but again, this needs to be confirmed in more material. A similar structure was reported for C. lambertae .

The two remaining pedunculate Corynascidia species ( C. herdmani and C. lambertae ) have a different orientation of the body, and the position of the gut loop, the siphons being more or less on the sides of the top of the body and the gut loop orientated vertically with the pole directed down. This appears to be a stable specific feature and is not affected by the size of the specimen, C. lambertae being a relatively small (4 cm) species, while known specimens of C. herdmani are from 9 to 20 cm long.

Figures

Figure 1. Corynascidia suhmi Herdman, 1882. (A) Gut loop and inner surface of the atrial siphon; (B) anal margin; (C) body including top of the stalk removed from the test; (D) internal view of antero-dorsal mid line (branchial tentacles, prepharyngeal groove, dorsal tubercle and anterior part of dorsal lamina).

Figure 6. Styela calva Monniot, Monniot and Millar, 1976. Specimen opened along ventral mid line; branchial sac removed.