# Geosesarma dennerle

Geosesarma dennerle is a species of small land-living crabs found on Java, Indonesia.
It is popular in the aquarium trade, where G. dennerle, in particular, is often simply called Vampire Crab. Crabs called "Geosesarma bicolor Krakatau Vampirkrabbe" are probably also G. dennerle.
The species is named after the aquarium supply company Dennerle, which supported one of the describing authors' (Christian Lukhaup) study in Java.
The coloration of G. dennerle can be very similar to G. bicolor. The describing paper mentions chelipeds, male abdominal and G1 structures as distinguishing features.

## Description

Geosesarma dennerle is a member of the phylum Arthropoda, and subphylum Crustacea. This species resides in the genus Geosesarma de Man, which comprises 67 recognized species, commonly found in Southeast Asia. These crabs are generally from 1.5 to 2 inches (38 to 51 mm) in size. The crab features a two-colored carapace, being predominantly purple with a patch of cream/yellow on its back. Dennerle also possesses bright yellow eyes and vibrant violet claws.
As a member of the order Decapoda, this crab has 5 pairs of segmented limbs. Unlike some species of crab that have specialized claws, dennerle does not have swollen chellae. The carapace is described as square-esque in shape, with well defined regions of the shell, and the abdomen being broad. The ambulatory legs of this crab are generally long and thin, with broad segments. Dennerle often have tubercles along its dorsal carapace, providing some texture to the otherwise smooth shell.
G. dennerle are similar to other species of crabs with the occurrence of sexual dimorphism. The sex of Geosesarma species can be identified by observation of abdominal flaps. The males have narrow and pointed abdominal flaps, while the females possess wider flaps which are ovular in shape. Males are also noted to be slightly larger than females.

## Ecology

G. dennerle is endemic to Central Java.
As the prefix "geo-" suggests, G. dennerle is a terrestrial crab. It is common to find dennerle hiding in burrows in areas composed of muddy creek valleys, with rocks and dense vegetation. The diet of dennerle is greatly composed of insects and plant matter. The high endemism of species within the Geosesarma genus, means there is not a great amount of geographic distribution.

## Reproduction

Sexual reproduction in Geosesarma dennerle is similar to that of the majority of other species of crabs. Little has been observed towards specific variations in this species reproduction method in comparison to other species in the Geosesarma genus.
Members of the Geosesarma genus commonly produce large eggs, averaging between 1.2 and 1.8 mm in diameter. Members of Geosesarma become sexually mature around 6 months of age, with breeding consisting of the male mounting the female to fertilize eggs. This species has direct development offspring: fully formed miniature versions of the adults hatch from the eggs. The female will carry around 20–80 fertilized eggs for about a month before hatching occurs. These newly hatched offspring are often independent, and will disperse from the point where they hatch.

## Geosesarma dennerle in captivity

Vampire Crabs have become extremely popular in the exotic animal hobby over recent years. However, there is a lot of misconception about how to best keep them. They are often mistaken for aquatic crabs and kept in unsuitable conditions with excessive amounts of water, which leads to shortened life spans. The ideal captive environment for Geosesarma dennerle and all other Geosesarma species is one that consists of 80% land and 20% water. With natural soil and dense planting making up the majority of the terrestrial area. As these species live in the ground, primarily in burrows, soil is vital for their well-being, stress reduction and breeding.
While they also require water to survive, it is primarily used for molting and hydration. Both of which can easily be met with a small water volume, enough to cover their entire body completely will suffice. However it is advised to have a depth of at least double their body height to account for any evaporation. Without access to water Geosesarma dennerle will dry out and perish.
It is also important to never mix any other species of Geosesarma together. While they are a semi-social species of crab, they are extremely aggressive towards other species and will almost always kill other species present in their territory.
Environmental Parameters for keeping Geosesarma dennerle in captivity
Water temperature: 22–25 °C (71–78 °F)
Air Temperature: 22–28 °C (71–82 °F)
Humidity: Above 75%
PH: Between 7.5 and 8.0
KH (carbonate hardness): Between 0 and 10
GH (general hardness) Between 4 and 16
Ammonia: 0
Nitrite: 0
Nitrate: Lower than 20 ppm