Amboherpia dolicopharyngeata, Gil-Mansilla, Esther, García-Álvarez, Óscar & Urgorri, Victoriano, 2008

Gil-Mansilla, Esther, García-Álvarez, Óscar & Urgorri, Victoriano, 2008, New Acanthomeniidae (Solenogastres, Cavibelonia) from the abyssal Angola Basin *, Zootaxa 1866, pp. 175-186 : 176-181

Amboherpia dolicopharyngeata new species

Body to 2.6–4.5 mm x 0.4–0.8 mm, posterior region 0.1 mm thinner. Thin cuticle (8 μm), without epidermal papillae, with different types of sclerites in one layer: straight and curved acicular hollow sclerites; rimmed and unrimmed solid scales; blade­shaped scales on both sides of the pedal groove. Common atrio­buccal cavity. Pedal groove with a small fold that does not reach the pallial cavity. Monoserial radula with two dorsolateral hollow denticles. Ventrolateral foregut glandular organs type A (according to Salvini­Plawen 1978) or type Acanthomenia (according to Handl & Todt 2005). Midgut without constrictions. With a pair of seminal vesicles. Single opening of the spawning duct. Without respiratory folds. Without copulatory stylets. With a dorsoterminal sense organ.

Types: Holotype and paratypes 1–6 (cut in serial sections) and paratypes 7–12 and 15 are deposited in the Zoologische Staatssammlung München (ZSM Mol 20070743). Paratypes 13 and 14 were used to get the radula, therefore the specimens were destroyed.

Type locality: Abyssal Angola Basin (SW Africa) (station 350 – Me48/1 DIVA 1; 16°14'18'' S 05°26'48'' E – 16°14'54'' S 05° 26'42'' E; 5389 m depth).

Other localities: Abyssal Angola Basin (SW Africa): Paratypes 1, 2 and 15 (station 340 – Me48/1 DIVA 1; 18°18'18'' S 04° 41'18'' E – 18°19'24'' S 04°41'54'' E; 5395 m depth); Paratypes 3–5 (station 344 – Me48/1 DIVA 1; 17° 06'12'' S 04°41'42'' E – 17°07'30'' S 04°42'18'' E; 5415 m depth); Paratypes 6–14 (station 348 – Me48/1 DIVA 1; 16°18'6'' S 05° 27'12'' E – 16°19'18'' S 05°27'12'' E; 5390 m depth).

Etymology: Greek: dolico, long; Greek: pharynx, throat; latin: – atus, provided with; with reference to its long pharynx.

Description:

Habitus: 2.6–4.5 mm long and 0.3–0.8 mm thick specimens, posterior region 0.1 mm thinner. Round body in cross section, no lumps or keels. Sclerites present oblique insertion into the cuticle and protrude from it. Marked pedal groove. Specimens, observed after fixation and preserved in 70º ethanol, are white (figure 1A).

Mantle: Thin cuticle (8 μm) without epidermal papillae. Different types of sclerites in one layer (figure 1B): curved hollow acicular sclerites with elliptical section (60­220 μm x 4­5 μm); rectilinear hollow acicular sclerites (50­140 μm x 4­5 μm), in which the hollow represents a 28­45 % of the its length; unrimmed solid scale­shaped sclerites, with pointed distal end and wider proximal end (maximal width 75­95 μm x 12­15 μm); rimmed solid scale­shaped sclerites with a sharp distal end and a round and wider proximal end (maximal width 75­95 μm x 8­10 μm); blade­shaped sclerites (60 μm x 15 μm) present on both sides of the pedal groove.

Pedal groove and pallial cavity: The pedal groove originates in a pedal pit (85 µm x 50 µm x 30 µm) with numerous long cilia and a large opening to the outside (figure 1C, 1D). The pedal groove has a small ciliated fold that does not get into the pallial cavity. It ends before a pouch (figure 1E, 3D) that contains prepallial spicules (there are at least 10). The anterior region of this pouch is unpaired, with musculature and glands. Its posterior region presents two lobes. The pallial cavity has a small size, lacks respiratory folds and opens in the ventral side (figure 1E). Its epithelium is ciliate and presents glandular cells. The anus opens into the dorsoanterior region of the pallial cavity, whereas the spawning duct opens in the anteroventral side of this cavity (figure 1E).

Digestive system: The narrow mouth opens into the dorsoposterior region of the common atrio­buccal cavity. It continues by a long and protruding pharynx, provided with glandular epithelium. The pharynx presents two regions: one anterior narrow region (150 μm x 45 μm) and one posterior region, longer and wider (400 μm x 85 μm) (figure 1C). The radular apparatus consists of a monoserial radula with 6­7 tooth rows, a radular support of very large and vacuolized cells and a short radular sheath, in which 1 or 2 teeth can be observed. Without a differentiated radular sac. Each tooth is 23 μm high and presents a rectangular base (15 μm wide, 11 μm high) without lateral protuberances and two dorsolateral denticles, whose distal ends are separated 20 μm. The denticles are hollow internally and their transversal section is circular. The hollow of each denticle originates from the tooth base, where it opens to the outside and continues along the denticle interior to its distal end (figure 2D). The ventrolateral foregut glandular organs consist of two large ducts encircled by musculature and open into the pharynx at the radula level. At the posterior region of each duct there are bundles of glandular cells that pour their secretions into the ducts (figure 1C, 2A, 2B). They are subepithelial (type A according to Salvini­Plawen 1978) or exoepithelial glandular organs with extraepithelial glandular cells (type Acanthomenia according to Handl & Todt 2005). The pharynx continues with a short oesophagus with glandular unicellular cells; this oesophagus begins in the dorsoposterior region of the pharynx, continues to the anterior region and opens into the midgut (figure 1C). The midgut presents a dorsoanterior caecum situated above the posterior region of the pharynx. The epitelium of the midgut is thin, without folds or constrictions. Some nematocysts may be observed inside the midgut. The posterior region of the midgut becomes a narrow ciliated rectum. The anus is situated in the dorsoanterior region of the pallial cavity (figure 1E).

Nervous system and sense organs: The cerebral ganglion (80 μm x 100 μm x 60 μm) presents a trapezoidal transverse section and is situated above the anterior region of the pharynx. On each side of this ganglion, there are two small lateral ganglia. Each ventral ganglion (90 μm x 100 μm x 40 μm) is situated above the dorsal region of the pedal pit and they join by a commissure. A very developed supra­rectal commissure can be observed above the rectum. The atrial sense organ is ciliated in its back part and presents 7–10 simple papillae. There is a dorsoterminal sense organ in the dorsoposterior region of the body, above the pallial cavity (figure 1C, 1D, 1E).

Circulatory system: The pericardium (200 μm x 60 μm x 40 μm) contains a tubular heart in its interior, free in most of its length, which joins in its front and back ends to the dorsal wall of the pericardium. Blood cells (8­12 μm diameter) are round and nucleated.

Reproductive system: Gonads are long, tubular and are placed above the dorsal region of the midgut. The spermatogonia can be observed in the anterior region of the gonads. Some ova (30–45 μm diameter) can be observed in the middle area of the gonad, the posterior region is full of large spermatozoids (8.5 μm long) with a thick flagellum. The gonads continue along a pair of short gonopericardioducts, whose end part is fused and full with spermatozoids. They open into the anterior region of the pericardium, which contains spermatozoids inside. The posterior region of the pericardium narrows and continues in a wide bag, from which each pericardioduct starts. Two large seminal vesicles, which are full of spermatozoids (figure 1E, 3B), come out into the proximal region of each pericardioduct. The anterior region of the the pericardioducts are narrow, but they widen in their posterior region, before they open into the spawning duct. The spawning duct epithelium presents many secretory cells with different contents. The anterior region of the spawning duct is paired in 1/5 of its total length (figure 3A); its end region (1/4 of the posterior region of the duct) is separated from the rest of the duct by a very developed muscular sphincter (figure 3C) and has no secretory cells. The spawning duct narrows and finishes through a unpaired opening into the anteroventral region of the pallial cavity. It presents no copulatory stylets.

Discussion:

Amboherpia dolicopharyngeata n. sp. is included in the order Cavibelonia Salvini­Plawen, 1978 because it presents hollow acicular sclerites and is classified in the family Acanthomeniidae Salvini­Plawen, 1978 , as it has a thin cuticle, a monoserial radula and a pair of ventrolateral foregut glandular organs type A (according to Salvini­Plawen 1978) or type Acanthomenia (according to Handl & Todt 2005). The new species is classified within the genus Amboherpia due to the presence of a common atrio­buccal cavity, a monoserial radula with a pair of denticles and the lack of respiratory folds ( Handl & Salvini­Plawen, 2002). So far, the genus Amboherpia has been represented by one species, Amboherpia heterotecta ( Handl & Salvini­Plawen 2002) . There are several significant differences between Amboherpia dolicopharyngeata n. sp. and Amboherpia heterotecta (table 1). The hollow acicular sclerites of Amboherpia dolicopharyngeata n. sp. are more curved, and it presents unrimmed solid scale­shaped sclerites. The pharynx is narrow in its anterior region, wide in its posterior region and twice as long as the pharynx of Amboherpia heterotecta ( Handl & Salvini­Plawen 2002) . It has no preradular muscular sphincter, but presents an oesophagus. The radular teeth in Amboherpia dolicopharyngeata n. sp. lack lateral protuberance on the base and the denticle hollows are not U­shaped. The ventrolateral foregut glandular organs of Amboherpia dolicopharyngeata n. sp. have a glandular association situated at the posterior region of each duct and each of them opens laterally into the pharynx at the level of the anterior region of the radula, whereas in Amboherpia heterotecta they present several glandular associations and the ducts open into the ventral region of the pharynx, in the preradular region, just before the beginning of the radula. The paired part of the spawning duct in Amboherpia dolicopharyngeata n. sp. is just 1/5 of its length, while it represents 1/ 3 in Amboherpia heterotecta . Finally, the posterior region of the spawning duct in Amboherpia dolicopharyngeata n. sp has a muscular sphincter that Amboherpia heterotecta does not present.