Pneumodermopsis (Crucibranchaea) macrochira Meisenheimer, 1905c
(See the Pneumodermopsis sp. 1.mov and Pneumodermopsis sp. 2.mov movies of an unidentified specimen of this genus probably P. macrochira)
Overview
This is a small naked pelagic snail up to 0.8 cm long, with a mainly transparent body, the visceral mass is seen through the body wall. The skin has purple and grayish chromatophores. There is no median sucker arm but there are two lateral ones each with up to 55 suckers, the top ones are larger than the others. A posterior gill is present. The posterior footlobe is long. It is a good swimmer that hunts shelled pteropods as food. It lives in all oceans (Pneumodermopsis macrochira 2).
Taxonomic Description
The body is almost colourless, but purple-gray chromatophores may occur on head and foot. The visceral mass fills the whole body. The posterior gill is composed of four crests radiating from the body pole. The lateral gill was found by some authors (Pruvot-Fol, 1942; Lalli, 1970) but not seen by others (Bonnevie, 1913; Tesch, 1950). The median footlobe is relatively long and pointed, while a median tubercle is present. The most typical character for the species is the sucker arms on which Meisenheimer (1905a) nearly based his entire description. Two very distinct lateral arms are present at the top of each is a terminal sucker which is larger than all the other suckers, though similar in structure (Pneumodermopsis macrochira). In total, 55 suckers or somewhat less are found on each arm being arranged in two or three rows. In these rows groups are sometimes recognised, viz. a proximal group of about 30 suckers and a distal group of about 20 behind the single large distal sucker (Pneumodermopsis macrochira drawing). Whether these groups and rows occur without variation has not been determined. The median sucker arm is completely reduced and only represented by five relatively long-stalked suckers. Tesch (1950) reported only four sessile suckers and this may be an exception. Bonnevie (1913) stated, however, that the median suckers can be divided into a group of three larger and one of two smaller suckers. The Pneumodermopsis macrochira radula formula is 6-1-6 or 7-1-7. The median plates are tricuspoid, the central cusp is the smallest. The first laterals have a basal cusp projecting towards the middle of the radula. There are about 16 transverse rows of teeth. The jaw resembles that of Pneumoderma paucidens. The hook sacs are shallow, bearing 16 to 20 rather short hooks.
Maximum body length is 8 mm.
Juveniles
A special description is not available.
Reproduction
This species is a protandric hermaphrodite.
Ecology
This species is a carnivore.
Distribution
This species is widely spread, though only a discontinuous distribution is known. Greater concentrations of animals are found in the N-Atlantic Ocean, Agulhas current, EN-Pacific and Tasman Sea, see Pneumodermopsis macrochira map. The pattern shows an avoidance of equatorial and tropical waters and a greater tolerance for colder areas. Morphological differences between specimens from the Atlantic and E-Pacific are known and they are reflected in the differences in the descriptions given by Pruvot-Fol and Lalli, and by Bonnevie and Tesch.
Types
Pneumodermopsis macrochira Meisenheimer, 1905: 47 + fig.
Syntypes: two spec. not present in HMEB.
Type locality: 28°29'S 6°14'E, 29°6'S 89°39'E, Coll.: CVDE, stat. 86 and 173.