BIOS
Marine Invertebrates of Bermuda

Arrow Crab (Stenorhynchus seticornis)

By Joshua Jones
and
James B. Wood (Ed)


Abstract Taxonomy  Habitat  Ecology  Recent Research  Commercial Importance  Bermuda Laws  Personal Interest  References  Links 



Abstract


Stenorhynchus seticornis, or the yellow line arrow crab, is commonly found in shallow water among corals, and in deeper waters up to 180 m. It is part of the family Inachidae which are true crabs, meaning they have their antennae between their eyes. It is abundant in the tropical Atlantic in and around Florida, the Bahamas, and throughout the Caribbean down to parts of South America. These crabs are geographically limited from North Carolina to Argentina. It is commonly found amoung rocks, corals, calcareous algae, over sand, and sometimes in the spines of urchins. S. seticornis, is kept in marine aquaria. High demand and extreme prices have contributed to the endangerment of several groups of marine organisms. While fish and coral species are usually the main target, the popularity of decopod species in aquariums is rapidly increasing..

Taxonomy


Phylum:Arthropoda
  Class:Malacostraca
    Order:Decapoda
      Family:Inachidae


Stenorhynchus seticornis belongs to the phylum Arthropoda. This organism has several characteristics that define it as an arthropod. They have an articulated segmented chitonous exoskeleton, segmented jointed appendages, tagmatization which is the joining of the head and the thorax, a unique brain organization, and a heart with paired ostea. They are part of the subphylum Crustacea which is comprised 22,000 species. Arrow crabs are part of the class Malacastraca which is the largest group of crustacea. They are in the order Decapoda, which all contain ten legs. Inachidae is a family of crabs that contain 700 species known for having a carapace that is longer than it is wide and forms a point at the front end of the crab.

Habitat


Stenorhynchus seticornis is found in shallow water among corals, and in deeper water up to 180 m (Sterrer, 1986). S. seticornis is found in a wide variety of habitats (Humann and Deloach, 1992). It is commonly abundant in the tropical Atlantic in and around Florida, the Bahamas, and throughout the Caribbean down to parts of South America (Humann and Deloach, 1992; George, 1979). Its geographical distribution is limited from North Carolina to Argentina (Cobo, 2002). It moves slowly on algae and corals feeding on crustaceans and small colonial animals (George, 1979). It is commonly found around rocks, corals, calcareous algae, over sand, and rarely among the spines of urchins ( Cobo, 2002; Sterrer, 1986).



Ecology


Stenorhynchus seticornis is a very small species with the carapace rarely exceeding 1 cm in width (George, 1979). It has a characteristic long spiny rostrum and long thin legs (George, 1979). It has a reddish brown carapace and walking legs, and smooth purplish grey claws (Humann and Deloach, 1992). Its joints are bright red with stripes of brown or black diverging obliquely from the median line to the posterior margin (Sterrer, 1986). The antennae on the carapace are much smaller and reduced when compared to the long sensory antennae of lobsters and shrimp (Warner, 1977). The entire surface of the crabs body is covered by an exoskeleton cuticle that is heavily calcified and provides protection (Warner, 1977). Crabs are described as having an open circulatory system, or are specifically known as haemocoelic (Warner, 1977). The nervous system is very compact and centralized when compared with the long ganglionated nerve cord typical in most arthropods (Warner, 1977). In both sexes the reproductive organs are located on the ventral side of the carapace lying above the anterior and lateral lobes of the hepatopancreus (Warner, 1977). Movement is achieved by using its long legged appendages, which allow it to walk slowly and swim (Warner, 1977). The mouthparts, which manipulate food and move it into the mouth, are located just under the anterior portion of the carapace (Warner, 1977). S. seticornis also has chelipeds which are used for catching prey, taunting rivals, and attracting mates (Warner, 1977). Each appendage consists of a chain of jointed articulated segments that are moved by muscles which insert on tendon like appendages (Warner, 1977).

The larval anatomy of Stenorhynchus seticornis is very similar to many other crabs, and the physical characteristics of its larvae have been controversial for more than a century (Yang, 1976). Yang (1976) performed an experiment to distinguish its larval characteristics to distinguish it from those of other crab species. The larval carapace length averaged .75mm (Yang, 1976). He found that the postero- lateral section is simple and inflated while other species it is larger and hemispherical (Yang, 1976). He also found that it contains light brown pigments in addition to red-orange chromatophores (Yang, 1976). Like most brachyuran crabs, daylight cycles and temperature variables are the most important environmental factors determining the breeding period (Cobo, 2002). The breeding period of S. seticornis was not specific to certain times of the year and breeding occured year round (Cobo, 2002). The lifecycle of S. seticornis begins as a planktonic zoea larvae (Yang, 1976). As the larva matures it goes through a series of molts which allows it to grow and slowly reach maturation (Warner, 1977).

Stenorhynchus seticornis has long and odd shaped appendages compared to its body, and it is a very slow moving creature (George, 1979). It lives on algae and coral feeding on crustaceans and small colonial animals (George, 1979). Since S. seticornis is a relatively small animal, it has been seen taking refuge under other marine invertebrates (Hayes et al., 1998; Herrnkind et al., 1976). S. seticornis is commonly found associating with sponges, stony corals, soft corals, gorgonians, anemones, and crinoids (Hayes et al., 1998). S. seticornis was commonly found interacting with anemones near grand Bahama (Herrnkind et al., 1976). S. seticornis was found near edges of anemones and appeared to be using them as protection from predation (Herrnkind et al., 1976). When S. seticornis was in danger of capture, it reacted by retreating into the long spines of a Diadema urchin and became difficult to capture (Hayes et al., 1998). S. seticornis’s predators are common reef fish such as the red grouper and also some species of sea stars (Freitas, 1982).

Recent Research


There has been a lot of research regarding marine ornamental management and aquaculture to provide a feasible and viable resource of ornamental decapods to deter the aquarium industry from live collections on reef habitats (Calado, 2003; Bolker et al., 2002; Rhyne et al., 2005; Lin and Shi, 2002). This is important research because of the fragile ecosystems that the decapod species are being taken from (Personal observation). There have also been recent studies on the fecundity of Stenorhynchus seticornis of the coast off Brazil in South America (Cobo and Okimori, 2003).



Commercial Importance


Stenorhynchus seticornis, the arrow crab, is commonly kept in marine aquaria (Walls, 1982). This could be a potential problem because 90% of the species sold for the aquarium trade are being collected on coral reefs (Calado, 2003). High demand and extreme prices have contributed to the endangerment of several groups of marine organisms (Calado, 2003). While fish and coral species are the main target, decapod species are rapidly becoming popular with hobbyists (Calado, 2003; Bolker et al., 2002). The marine ornamental industry relies heavily on live collection from coral reefs, and that combined with destructive harvesting techniques have increased anthropogenic pressure on many fragile ecosystems (Rhyne et al., 2005). Aquaculture is a viable long-term alternative to wild collection, allowing the aquarium trade's future to become independent from natural resources (Rhyne et al., 2005; Lin and Shi, 2002).



Bermuda Laws


There are currently no Bermuda laws governing the Stenorhynchus seticornis. However, as is the case with all organisms that thrive in the Marine Protected Areas of Bermuda, collection of the S. seticornis is not allowed in protected areas.

Personal Interest


I first had interest in Stenorhynchus seticornis from a trip to Belize when I was younger and learning to dive. I found several of these on the reef in small cracks and crevices. The dive master encouraged me to catch one, and I did. As I held it in my hand I couldn’t help but think what a unique and odd looking creature it was. Since then I have made multiple dives where I have found S. seticornis, and every time they intrigue me a little more. This web project was the perfect chance to explore more about this incredible creature and what affects its everyday life. As a result of their beauty I am concerned with the harvesting techniques that are being used. I think that if S. seticornis is going to become a common species in marine ornamental aquaria, protective measure on collection and an increase in aquaculture will be required.



References

Bolker, B., St. Mary, C.M., Osenberg, C.W., Schmitt, R.J., Holbrook, S.J., 2002. Management at a different scale: Marine ornamentals and local provesses. Bul. of Mar. Sci. Vol 70(2): pp. 733-748.

Cobo, V. J., 2002. Breeding period of the Arrow Crab Stenorhynchus seticornis from Couves Island, south-eastern Brazilian coast. J. of the Mar. Bio. Ass. of the U.K. Vol 82 (6): pp.1031-1032.

Cobo, V.J. and Okimori, C.M., 2003. Fecundity of the arrow crab Stenorhynchus seticornis in the southern Brazilian coast. J. of the Mar. Bio. Ass. of the U.K. Vol. 83(5): pp. 979-980.

Freitas, J., 1989. Predation on Stenorhynchus seticornis (Crustacea, Majidae) by Diplasterias brandtii (Asteroidea) and Epinephelus morio (Teleostei). CIENC. CULT: Vol. 34, pp. 1056-1058.

George, D., George, J., 1979, Marine Life, Lionel Leventhal Ltd. NY: pp. 80.

Hayes, F.E., Joseph, V.L., Gurley, H.S. and Wong, B.Y.Y.,1998. Selection by two decapod crabs (Percnon gibbesi and Stenorhynchus seticornis) associating with an urchin (Diadema antillarum) at Tobago, West Indies. Bul. of Mar. Sci. 63(1) : pp. 241-247.

Herrnkind, W., Stanton, G., and Conklin, E., 1976. Initial characterization of the commensal complex associated with the anemone Lebrunia danae, at Grand Bahama. Bul. of Mar. Sci. 26(1): pp. 65-71.

Humann, P and Deloach, N., 1992. Reef Creature Identification. New World Publications inc. FL.

Lin, J. and Shi, P., 2002. Effects of broodstock diet on reproductive performance of the golden banded coral shrimp Stenopus scutellatus, J. World Aquac. Soc. ,Vol. 33 pp. 383–386.

Sterrer, W., 1986. Marine Fauna and Flora of Bermuda: A Systematic Guide to the Identification of Marine Organisms. Wiley-Interscience Publication.

Wall, J.G., 1982. Encyclopedia of Marine Invertabrates. T.F.H. Publications Inc. NJ: pp. 638.

Warner, G.F., 1977. The Biology of Crabs. Elek Science London. UK

Yang, W.T., 1976. Studies on the western Atlantic arrow crab genus Stenorhynchus (Decapod brachyuran, majidae) I. larval characters of two species and comparison with other larvae of inachinae. Crustaceana Vol. 31(2) pp157-177.



Links

Youtube video showing Arrow Crab feeding
Arrow Crabs on Wikipedia
Aqua Hobby pictures and captive care information
Youtube video showing locomotion