Desmopterus papilio Chun, 1889
Overview
This is a completely shell-less pteropod, very small in size as the swimming disc diameter is only 0.4 cm. The wings are disc-shaped and transparent except for a few muscle fibres. The visceral mass forms an opaque appendix curved around the swimming disc. Besides the median lobe the disc has two long tentacles. There is no separate proboscis. It is an elegant swimmer and mucus feeder feeding on microplankton. It lives in the warm waters of all oceans (Desmopterus papilio 2, Desmopterus papilio bod, Desmopterus papilio total).
Taxonomic Description
Shell, pseudoconch and mantle cavity are absent. The anterior part of the rounded cylindrical body is large, the posterior part is small and only its extreme end shows some coiling (Desmopterus papilio). The head parts are curved ventrally in a right angle to the plane of the swimming plate (Desmopterus papilio 1). Integument with small reddish gland cells. At the posterior body pole a glandular, ciliated fold is present. The swimming plate, composed of five lobes(# Desmopterus papiliowing), represents the wing (Desmopterus papilio photo, Desmopterus papilio detail). This epipodium is thus well developed, while the protopodium (the footlobes) is nearly absent or reduced into a fold hidden between head and swimming plate. The remainder of the foot is a cutaneous fold below the mouth. Buccal appendages are also lacking and the tentacles are small with rudimentary eyes. Two incisions in the swimming plate border separate off a square-shaped median part. The two wing tentacles are implanted between the lateral lobes of the wings (Desmopterus papilio tentacle), are reddish, flattened and long in living specimens. The mantle gland is rudimentary. The Desmopterus papilio radula with the formula 1-1-1 is composed of up to 30 transverse rows of teeth. This species shows strongly pronounced protandry. The penis is of the normal thecosomatous type.
The body length varies between 0.5 and 2.0 mm, while the swimming plate measures 2 to 4 mm in diameter.
Juveniles
A special description is not available.
Reproduction
This species is a protandric hermaphrodite.
Ecology
This species is phytophagous and epipelagic.
Distribution
Tesch (1949) believed that Desmopterus is in principle an Atlantic genus but it should be considered an Indian Ocean genus. The present species occurs in all faunal centres of the Indian Ocean including the Red Sea. It penetrates the Pacific Ocean and occurs in the entire warmer Atlantic Ocean. Though it penetrates from the Indian Ocean into the Red Sea, it does not normally penetrate most of the Mediterranean and Caribbean waters. Avoidance of upwelling or central waters is not shown in this species, see the Desmopterus papilio map. The incidental records (a.o. Bianco, 1903) in the Mediterranean may be due to long distance transport.
Types
Desmopterus papilio Chun, 1889: 540, pl. 3, figs. 11-14.
Syntypes not found though at least 11 spec. were reported.
Type locality: off Orotava (Tenerife Is.) surface.