Alexandromenia avempacensis Pedrouzo and Cobo, 2014
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publication ID |
https://doi.org/ 10.1080/00222933.2014.959576 |
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publication LSID |
lsid:zoobank.org:pub:EA987A53-FF5D-463F-A072-0EA99BCDA129 |
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persistent identifier |
https://treatment.plazi.org/id/2CC9BAA4-D457-48E0-BD4B-4402A27C08A6 |
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taxon LSID |
lsid:zoobank.org:act:2CC9BAA4-D457-48E0-BD4B-4402A27C08A6 |
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treatment provided by |
Felipe |
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scientific name |
Alexandromenia avempacensis Pedrouzo and Cobo |
| status |
sp. nov. |
Alexandromenia avempacensis Pedrouzo and Cobo View in CoL sp. nov.
( Figures 3–5 View Figure 3 View Figure 4 View Figure 5 )
Type material
Holotype. MNCN 15.02 About MNCN .100. One adult specimen cut in serial sections (24 slides) at 5 µm; two sclerites slides. Internal anatomy manually reconstructed ( Figure 4A, B View Figure 4 ).
Type locality
Seamount Avempace (Alborán Sea) (DEEPER 0409–BT04) 36°21.1′ N, 03°58.6′ W, 349 m / 36°21.1′ N, 03°58.1′ W, 365 m ( Table 1).
Etymology
The name was chosen with regard to the seamount Avempace, where the holotype was collected.
Diagnosis
Long and slender; maximum body length at least 17.18 mm. Body surface velvety. Thick cuticle with epidermal papillae. Main body sclerites hollow acicular, either straight or curved, and slender blade-shaped scales. Pedal groove with 3 folds along its whole length. Atrial papillae digitiform. Two types of preradular pharyngeal glands. Ventrolateral foregut glands with one main duct and two ramifications and monoserial radula, teeth with five denticles: a single central denticle with paired tips, flanked by a pair of small and a pair of large denticles. With chondroid cells between the sheath and the radular sac. Long pharynx. Long and narrow oesophagus. Very long anterodorsal intestinal caecum. One pair of large seminal receptacles. Secondary genital opening unpaired in the ventroanterior region of the pallial cavity, with a muscular sphincter. With few respiratory folds. Dorsoterminal sense organ in dorsal position.
Description
Habitus. Specimen 17.18 mm long and 0.9 mm thick in its medial body region; wider in its anterior body (1.02 mm) and narrow in its posterior body (0.71 mm) ( Figure 3A View Figure 3 ). Radial sclerites protrude somewhat from the body surface, giving the animal a velvety shine. Pedal pit and groove very marked externally ( Figure 3B View Figure 3 ). Whiteyellowish colour in 70% ethanol.
Mantle. Cuticle 50–70 µm thick, with stalked epidermal papillae. With three types of sclerites arranged in several layers: hollow acicular of two types, either straight or curved, (80–205 µm long and 5–10 µm wide) ( Figure 3C View Figure 3 ) and blade-shaped scales (110 µm long and 5 µm wide). No scales of the pedal groove were observed.
Pedal groove and pallial cavity. Wide pedal pit (110–150 µm long, 200 µm high and 260 µm wide). Pedal groove with three folds that do not reach into the pallial cavity: large central fold with a smaller lateral fold on each side. Subterminal pallial cavity with six radial respiratory folds ( Figure 5F View Figure 5 ). The spawning duct opens into the ventroanterior region of the cavity, whereas the rectum opens into the dorsoanterior region. No accessory reproductive structures were observed.
Digestive system. Mouth opening in the posterior area of the atrium. Pharynx narrow along its whole length. It is surrounded by numerous spherical pharyngeal gland cells with a long and narrow stalk, and by a thin layer of longitudinal and circular musculature, less clear in the medial area. The ventrolateral foregut glands are branched ducts with terminal groups of glandular cells, type D ( Salvini-Plawen 1978) or Amphimenia-type ( Handl and Todt 2005). Each glandular organ opens laterally via a cone-shaped papilla into the preradular region of the pharynx ( Figure 5B View Figure 5 ). The main duct of each glandular organ extends laterodorsally to the pharynx with many curvatures and bears two ramifications, a short dorsal and a longer ventral one. Radula with a muscular sheath and a ventral sac, between which a set of chondroid cells serve as a support. Monoserial radula with 8 rows of trapezoidal teeth (21–30 µm wide and high). Each tooth has five denticles: a pair of large lateral denticles (10–11 µm high), a pair of smaller intermediate denticles (6–8 µm high) and a single central denticle (4–6 µm high) with two distal tips ( Figures 3D View Figure 3 , 5C, D, E View Figure 5 ). The long and narrow oesophagus opens ventroanteriorly into the midgut. Very long, tube-shaped dorsoanterior midgut caecum that reaches the anterior part of the atrium. The midgut lacks constrictions. The rectum, with triangular outline in cross section, extends under the pericardium. Narrow anus of circular cross section.
Nervous system and sense organs. Large cerebral ganglion (85 µm long, 90 µm high and 240 µm wide) of oval cross section, located dorsally to the anterior part of the pharynx and ventrally to the anterior part of the dorsal caecum. It has two small lateral ganglia. Buccal ganglia located near the outlet of the lateral glandular organs. Large pedal ganglia (50 µm wide, 305 µm long) connected by a narrow commissure. Suprarectal commissure located under the terminal segment of the pericardium, where the pericardioducts come up. Atrial sense organ with numerous digitiform papillae, narrow and long ( Figure 5A View Figure 5 ). Dorsoterminal sense organ located in a cleft of the cuticle, dorsal to the posterior part of the pallial cavity.
Gonopericardial system. Paired gonad located dorsally of the digestive tract reaching into the anterior part of the body. Spermatozoa and oocytes were observed in the posterior part of the body. Gonads taper as a pair of gonopericardioducts that continue into a very voluminous pericardium (710 µm long, 280 µm high and 50 µm wide). Tubular heart 25–45 µm long. Two types of blood cells were found: round erythrocytes with a distinct central nucleus and oval granulocytes without a clear nucleus. The posterior part of the pericardium gives off the pericardioducts, which bend and continue anteriorly until connecting with the spawning ducts. Both spawning ducts stretch anteriorly and form large seminal receptacles. The spawning ducts unite in their medial area in a single duct that opens through a muscular sphincter into the ventroanterior region of the pallial cavity.
Taxonomic remarks
The shape of the outlet of the foregut glandular organs as well as the presence of a monoserial radula, respiratory folds and a dorsoterminal sense organ, place this species within the genus Alexandromenia . Of the nine species that make up this genus, four are known from the extended geographical area of Alexandromenia avempacensis sp. nov.: Alexandromenia crassa Odhner, 1921 , from Bergen ( Norway), 100–200 m depth; A. pilosa Handl and Salvini-Plawen, 2002 , from Trondheimsfjord ( Norway), 180–240 m; A. grimaldii Leloup, 1946 , from the Azores Islands, 1250 m and A. gulaglandulata Salvini-Plawen, 2008 , from the West European Basin, 1050 m ( García-Álvarez and Salvini-Plawen 2007; Salvini-Plawen 2008). These species are quite distant biogeographically and bathymetrically and show clear morphological differences from A. avempacensis sp. nov. A. crassa has more pedal and respiratory folds (nine and 10 respectively) and radula teeth with a greater number of medial denticles (seven to eight small denticles) ( Odhner 1921). Alexandromenia pilosa has more pedal and respiratory folds (three to five and 15 respectively); radula teeth with only four denticles and a central denticle is lacking. In addition, this species has a shorter bilobed midgut caecum and the spawning duct is lacking a papilla ( Handl and Salvini-Plawen 2002). Alexandromenia grimaldii has more pedal and respiratory folds (three to seven and 17 respectively). The radula teeth are U-shaped, that is, with two large lateral denticles each accompanied by a mediodistal small denticle. The dorsoanterior caecum of the midgut is short in this species ( Leloup 1946; Salvini-Plawen 1972). Alexandromenia gulaglandulata has more pedal folds (18 in the anterior part, which decrease to four in the opening of the pallial cavity), a greater number of respiratory folds (16), radula teeth with only two denticles, a much shorter anterodorsal caecum of the midgut, and the spawning duct of this species is surrounded by a dense mass of glands ( Salvini-Plawen 2008).
Habitat and associated fauna
The holotype was collected at 349–365 m depth in the area surrounding the seamount Avempace (Alborán Sea) at 349–365 m depth, on a seafloor covered by bioclastic gravel, where the crinoid Leptometra phalangium is the most abundant species, followed by the bivalve Limopsis aurita (Brocchi) and the polychaete Hyalinoecia tubicola (Müller) . No cnidocysts were found in the midgut of the specimen.
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