Culeolus suhmi Herdman, 1881

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 : 2015-2020

Culeolus suhmi Herdman, 1881

( Figure 8 )

Culeolus suhmi Herdman 1881, p 86 ; Sanamyan and Sanamyan 2002, p 350 (synonymy).

Material examined

St. 4226, 3600–3630 m, four specimens; st. 4234, 3162– 3136 m, two specimens; st. 4254, 3796– 3780 m, four specimens; st. 4569, 3182– 3152 m, three specimens.

Remarks

Most specimens are small, body length 1–3.5 cm. They do not differ significantly from the larger specimens from the central Atlantic ( Sanamyan and Sanamyan 2002). The main distinguishing features of the species are the complete ring of papillae encircling the posterior end of the body, and the presence of usually two gonads on each side. The presence of three gonads on the right previously was suggested to be an abnormality ( Sanamyan and Sanamyan 2002), but it may be a normal variation since one of the dissected specimens of the present material also has three gonads on the right side. Two of them are in one line suggesting that one gonad has divided into two ( Figure 8B ).

The genus Culeolus comprises about 20 species, many of which are widely distributed in the deep waters of all oceans and many are common, but only one species, C. suhmi , was recorded in the North Atlantic. This species has also been recorded in the central Atlantic and in the Indian Ocean; the depth range is 2695–5312 m.

Pyurella hernia Monniot and Monniot, 1973

( Figures 9 , 10 )

Pyurella hernia Monniot and Monniot 1973, p 447 .

Microcosmus hernius: Monniot 1974, p 1346 .

Material examined

St. 4569, 3182– 3152 m, one specimen.

Description

The body of the single examined specimen is oval, slightly depressed dorso-ventrally, not attached, 7 mm in height and 9 mm wide. Fine test hairs are sparse and present mainly on the ventral half of the body. Globigerina shells are attached to the test, but foreign particles are relatively sparse and do not form a solid layer as in many other deep-water species. The areas of the test which are free from adherent matter are thin and semitransparent. Apertures are on sessile four-lobed siphons on the upper surface of the body; the distance between the siphons is not large, but they are not in contact with each other. Minute, 0.050 –0.055 mm long and 0.013 –0.014 mm wide, siphonal spines are crowded on the test inside and around the siphons ( Figure 9E ).

The musculature is characteristic of the Pyuridae , consisting of numerous evenly spaced longitudinal bands radiating from the siphons and numerous similarly spaced circular siphonal muscles, and, on the lower half of the body, transverse bands encircling the body. The branchial velum is not high, but is unusually thick and muscular. A circle of small simple papillae is on the outer side of the branchial velum; papillae arise from the base of the velum and, occasionally, from the inner surface of the branchial siphon. Atrial tentacles are of the same structure as the simple papillae on the branchial velum, they are short, clavate and equally spaced on the margin of the atrial velum. The atrial velum is higher dorsally and makes a perfect circle. There are about 20 large and a number of small branchial tentacles of at least three orders, with closely set branches of the first order, and short branches of the second order. The prepharyngeal band consists of two lamellae and makes deep undulations but does not form a dorsal V enclosing a peritubercular area. The dorsal tubercle has a simple transverse slit, the ganglion is just posterior, halfway between the siphons. The dorsal lamina has a plain edge. Five high, well-marked folds are on each side of the branchial sac. Only one longitudinal vessel is between the folds: E1(9)1(10)1(10)1(10)1(11)1DL1(11)1(10)1(10)1(10)1(11)E.

Five primary transverse branchial vessels divide the branchial sac into six transverse double rows of longitudinal stigmata between the folds and six infundibulae of curved and coiled stigmata in the folds. Each double row is crossed by a thinner secondary transverse vessel. Straight short and longitudinal stigmata are between the folds, but in folds they curve around projecting cones or infundibulae.

The gut forms a narrow, straight horizontal loop. The stomach is the same diameter as the intestine; the liver pouches are relatively flat and not much branched, projecting from around the stomach. A characteristic flattened pouch or diverticulum projects from the ventral side of the intestine about halfway up the ascending limb of the gut loop. The anus has a thick, slightly wrinkled margin. One straight gonad is on the right of the kidney across the postero-ventral corner of the body. Five or six large round male follicles overlie the proximal half of the ovarian tube, which contains a few small oocytes. The oviduct is thick and not very long, the male opening is on a short papilla in the middle of the oviduct. No traces of a left gonad were detected, even after staining.

A sheet of thin tissue that may be a damaged renal sac or hypertrophied heart lies along the ventral side of the gonad, near the endostyle. Endocarps are not present.

Remarks

Pyurella hernia is the type of the monotypic genus Pyurella Monniot and Monniot, 1973 . The original description of this species is based on two mature and two immature specimens from near the Azores Islands, at 1200 m and 1700–1776 m ( Monniot and Monniot 1973). Monniot (1974) recorded another specimen from the same region but from a shallower depth (220 m), this specimen had a gonad on each side and based on this feature the species was transferred to the genus Microcosmus .

The present specimen differs significantly from the specimen described by Monniot and Monniot (1973) in the structure of the branchial sac in that they did not detect branchial infundibulae and spiral stigmata, which are conspicuous in the present specimen. However, other, reliable and unique characters are present in both, namely the unusual large pouch on the intestine, a ring of simple papillae inside the ring of the branchial tentacles, the number of branchial folds, the presence of only one gonad on the right side and the structure of the gonad with few large male follicles. Despite the differences in the branchial sac it appears that the specimens are conspecific.

The taxonomic position of this species is problematic. Although the spiral stigmata occur in some pyurid genera, the presence of two stigmata on the top of infundibula is a feature more characteristic for the Molgulidae ( Monniot 1965) . Unfortunately it is not possible to determine in the present specimen whether the organ between the gonad and endostyle is a molgulid renal sac or a hypertrophied heart characteristic for some pyurid genera (but not for Microcosmus ). Presence of the siphonal spines suggests that the species was correctly assigned to Pyuridae , but we believe it is more accurately placed in Pyurella , the genus originally created for this species, rather than in Microcosmus . In general, the spiral stigmata are not characteristic for Microcosmus , only young specimens of some Microcosmus species may have them ( Monniot 1965). In the present species we see the opposite condition: smaller specimens described by Monniot and Monniot (1973) and Monniot (1974) have no spirals, while the present specimen, which is larger, has very distinct spirals. Also, as it appears from the present material, the absence of the left gonad is not an anomaly.

It is possible that Pyurella is identical to Anomopera Hartmeyer, 1923 , an imperfectly known genus assigned by its author to the Molgulidae and containing a single species A. ingolfiana Hartmeyer, 1923 . But the single known specimen of A. ingolfiana has a different gut (including a stomach clearly demarcated from the oesophagus and intestine), and only four branchial folds (see Hartmeyer 1923, Plate 1, Figures 2–4 ), that clearly distinguish it from the present species.

Figures

Figure 2. Cnemidocarpa bythia (Herdman, 1881). Specimen opened along ventral mid line, branchial sac removed.

Figure 3. Cnemidocarpa bythia (Herdman, 1881). External view.

Figure 4. Polycarpa albatrossi (Van Name, 1912). (A) Specimen opened along ventral mid line; branchial sac removed; (B) gonad, top and lateral view; (C) gonad of another specimen.

Figure 8. Culeolus suhmi Herdman, 1881. (A) Intact specimen (whole stalk not shown); (B) specimen opened along ventral mid line; branchial sac removed to show gut, gonads and muscles.

Figure 9. Pyurella hernia Monniot and Monniot, 1973. (A) Specimen opened along ventral mid line; branchial sac removed; (B, C) details of the branchial sac; (D) branchial tentacles; (E) siphonal spines.

Figure 10. Pyurella hernia Monniot and Monniot, 1973. External view.