Brachiomya stigmatica

Brachiomya stigmatica
Brachiomya stigmatica (holotype, from Pilsbry 1921: p. 325, Fig. 7)
Systematics
Superordinate : Imparidentia Order : Superfamily : Galeommatoidea Family : Lentil mussels (Montacutidae) Genre : Brachiomya Type : Brachiomya stigmatica
Scientific name of the  genus
Brachiomya
Jespersen , Lützen & Nielsen , 2004
Scientific name of the  species
Brachiomya stigmatica
( Pilsbry , 1921)

Inner skeleton without spines of Brissus latecarinatus

Brachiomya stigmatica is a mussel species from the lentil mussel family(Montacutidae). The species lives commensally with the sea ​​urchin species Brissus latecarinatus . It is the type and only species of the genus Brachiomya Jespersen, Lützen & Nielsen, 2004.

features

The housings, which have the same flaps, are transversely ovoid in outline. The housings are max. eight millimeters long, but most specimens are no larger than three millimeters (holotype: 5.3 mm long, 3.5 mm high and 1.8 mm thick). The width to height ratio is about 1.4 to 1.5. The cases are slightly unequal, the vertebrae sit a little in front of the middle of the case length. The dorsal margin is curved, the ventral margin is almost straight. The front end is slightly more rounded than the rear end.

The ligament sits externally in a pit behind the vertebrae. The right valve has a small, protruding, triangular pseudocardinal tooth below the vertebra. The left valve has a low, lamellar tooth in front of the vertebra. The Prodissoconch II measures 225 µm in diameter. The shell is thin and fragile, almost glass-like and translucent. The glossy surface is smooth apart from fine strips of growth. A reddish-brown stripe runs from the vertebra to the rear of the ventral margin. Most of the time, however, the stripe is lost before the edge of the case.

When the animal is undisturbed, the lobed, extended coat covers almost the entire housing, with the exception of the vertebral area. At the front end it is pulled out to a large inlet siphon. At the rear end it forms a smaller discharge siphon. The edge of the mantle is provided with numerous slender, spatulate-shaped tentacles at the end. At the front end, the jacket is extended like a hood and protrudes far beyond the housing. This structure acts as an inflow siphon above the foot, which is, however, significantly longer and protrudes under the hood-shaped mantle flap. The outflow siphon at the rear end is a narrow opening in the rear area of ​​the jacket. The dorsal edge of the outflow siphon is drawn out into a 1.5 mm long pointed tentacle. The lobes of the middle part of the mantle, which are externally around the housing, are covered on both sides with 15 to 16 spatulate-shaped tentacles that move continuously in the living animal and with very small papillae. The tentacles can no longer be fully retracted into the housing. The foot, which is rounded and pointed at the front, is very flexible and can also be stretched twice the length of the case. The gills only have the inner gill leaf with a well-developed longitudinal pit for transporting the food particles. The lamellae of the gills are connected to one another by a few intermediate bridges. The mouth lobes (labial palps) are moderately long and have four or five longitudinal pits on the inside. The sexual organs take up about two-fifths of the space of the viscera, especially the rear area above the foot. The pair of lateral lobes of the genital organs extend forward and partially enclose the digestive glands. The openings of the sex glands are located on small papillae in the upper mantle cavity. There are no sperm pockets to hold sperm packets. Of six specimens examined, one specimen was a male, another was a hermaphrodite with large oocytes and spermiogenesis in the tests, and four were females, one of which was previously a male. According to these observations, animals are either proterogyne or alternative hermaphrodites. The maximum diameter of the oocytes was 125 µm. None of the four female specimens "incubated" eggs or embryos in the mantle cavity.

Similar species

The genus and species differs from other genera of the lentil mussels (Montacutidae) by the large folds of the mantle, which lie over the outside of the housing and are covered with numerous, long spatula-shaped tentacles at the end.

Geographical distribution, habitat and way of life

The species was originally described from the waters off Hawaii . Since then it has also been detected off Japan , in the waters of the Philippines and Thailand. It lives with byssus attached in the ambulacra , or more often in the periproct of the irregular sea urchin Brissus latecarinatus . The hosts themselves are about seven to eight centimeters tall. The species is associated with the same host in all previously known locations. Brissus latecarinatus lives in Thailand in the upper 10 to 15 cm of coarse, clean sand from below the low water line to a water depth of a few meters. This species is not only host to Brachiomya stigmatica there , but also to Scintillona brissae Morton & Scott, 1989 (family Galeommatidae ) and Montacutella echinophila Jespersen, Lützen & Nielsen, 2004 (family Montacutidae).

Taxonomy

The Arttaxon was first described in 1921 by Henry Augustus Pilsbry as Solecardia stigmatica Pilsbry, in 1921. In 2004, Åse Jespersen, Jørgen Lützen and Claus Nielsen established the genus Brachiomya for this species . Genus and species names are accepted by the MolluscaBase as valid taxa. The genus name is derived from the Greek brachion = arm and mya - a suffix of many types of mussels. It alludes to the arm-like tentacles on the edge of the coat.

supporting documents

literature

• Åse Jespersen, Jørgen Lützen, Claus Nielsen: On three species and two new genera (Montacutella and Brachiomya) of galeommatoid bivalves from the irregular Sea Urchin Brissus latecarinatus with emphasis on their reproduction. Zoologischer Anzeiger, 243: 3-19, 2004 doi : 10.1016 / j.jcz.2004.04.001

Individual evidence

1. ^ ^{A b} Henry Augustus Pilsbry: Marine Mollusks of Hawaii, VIII-XIII. Proceedings of the Academy of Natural Sciences of Philadelphia, 72: 296-328, Philadelphia, Pennsylvania 1921 Online at www.biodiversitylibrary.org
2. ↑ MolluscaBase: Brachiomya stigmatica (Pilsbry, 1921)

Web links

Commons : Brachiomya  - collection of images, videos and audio files