Key to BC Dendrobranchiata Karl P. Kuchnow

Taxonomy

Family:

Benthesicymidae Bentheogennema borealis Northern Blunt-Tailed Shrimp Bentheogennema burkenroadi Burkenroad’s Blunt-Tailed Shrimp

Sergestidae Sergestes similis Pacific Sergestid Sergia tenuiremis Ocean Sergestid Sergia japonica Prawn

BACKGROUND

The Dendrobranchiata are a group of prawns that closely resemble the caridean shrimp. Globally, there are approximately 450 species of Dendrobranchiata. Until recently, all dendrobranchiates were included in two families: the Penaeidae and the Sergestidae. Recent revision has split what once were subfamilies into families in their own right. The interested reader should consult the authoritative work by Pérez Farfante and Kensley (1997) for a detailed consideration of the group. Globally, this group includes several economically important species (Brusca and Brusca 1990), including the Giant Tiger Prawn (Penaeus monodon) and the Chinese Prawn (Fenneropenaeus chinensis). While none of the five species of Dendrobranchiata prawns found in BC waters are important to commercial or recreational fisheries (Tavares and Martins 2010), these prawns may be caught as by-catch during other fisheries. The Dendrobranchiata are a group of deep-water, marine prawns. All species found in BC waters generally occur in water deeper then 100-500m (Butler 1980). These prawns may be either pelagic or benthic (Brusca and Brusca 1990). The fact that only five species of dendrobranchs are found in BC waters may be a reflection of limited sampling, and additional species may be present. The Dendrobranchiata have an overall shrimp-like body plan and are similar in appearance to the Caridea. Five pairs of legs originate from the carapace, the first three of which are chelate (Brusca and Brusca 1990; Tavares and Martins 2010). They are most easily differentiated from the Caridea by the morphology of the second abdominal pleuron (segment). When viewed from the side, the second pleuron of a Dendrobranchiata prawn overlaps only the third pleuron. In contrast, in the Caridea the second pleuron overlaps both the first and third pleurons (Brusca and Brusca 1990; Tavares and Martins 2010). Species of the family Benthesicymidae occur on the continental slopes and in the offshore water column. These species are poorly known, and may be more common than their records indicate. The exoskeleton is thin and membranous. Many species are coloured orange to dark red. Although features of the telson and carapace may be characteristic of certain species, the soft exoskeleton often is torn or twisted during collection. Mid-water benthesicymids undergo vertical migrations. They feed primarily on copepods, ostracods, and other small crustaceans. The Sergestidae are a widespread family of pelagic shrimp. Two colour patterns are common among the species: partly pigmented, with red pigment in the anterior body and translucent appendages and abdomen with small pigment spots; and solid bright red. Usually, the partly pigmented species occur at shallower depths than the bright red species, which often live at depths of 500m or more. Many species undergo daily vertical migrations, and occur at lesser depths during the night than by day. Sergestids have extremely long antennal flagella. The Dendrobranchiata have separate sexes and reproduce externally. Courtship and mating can last from 30 minutes to three hours (Tavares and Martins 2010). They do not carry their eggs/embryos underneath the abdomen; instead they release their fertilized eggs into the water column where they drift until the larvae are ready to settle (Brusca and Brusca 1990; Tavares and Martins 2010). This is unique among the decapods, hence the presence of eggs on the underside of a shrimp indicates that the individual must be a caridean. However, the absence of eggs attached to the underside of the abdomen is not proof that a specimen is a member of the Dendrobranchiata, as the individual might be a male caridean shrimp or a female caridean that is not gravid.

ANATOMY

Figure 1: Dendrobranch morphology (adapted from Butler, 1980) GLOSSARY OF TERMS

Abdomen: tail, consisting of six segments (A1-A6) and the telson/uropods

Antennal spine: spine positioned on the anterior margin of the carapace just ventral to the orbital margin

Branchiostegal spine: spine at or near the anterolateral margin of the carapace

Carapace: "head shield" cuticular structure arising from the posterior margin of the cephalon, extending anteriorly and posteriorly, and covering the cephalothoracic somites of the body

Carina (Carinae): ridge or keel of the exoskeleton

Cephalothorax: anterior part of the body consisting of the fused cephalon (head) and thorax, bearing all the appendages except the pleopods and the uropods

Cervical Sulcus: transverse groove starting at the top of the carapace and extending toward the front of the carapace

Chela (Chelae): pincer formed by the two distal podomeres of a pereopod in which the movable finger (dactyl) opposes a fixed finger formed by a distal extension of the propodus

Chelate: appendage ending in a chela (claw)

Cheliped: any chela (claw)-bearing thoracopod; typically refers to first pair(s) of pereopods

Cornea: faceted, usually pigmented portion of the eye

Dactyl: terminal podomere of a typically seven-segmented appendage

Endopod: mesia (inner) ramus of a biramous appendage

Exopod: lateral (outer) ramus of a biramous appendage

Eyestalk: peduncle or unfaceted part of the eye supporting the cornea

Hepatic spine: lateral spine situated near the anterior margin of the hepatic region of the carapace

Orbital spine: spine projecting from the ventral extremity of the orbital margin

Pereopod: one of the five posterior paired appendages or legs of the cephalothorax (P1-P5)

Postcervical sulcus: subvertical carapace groove located posterior to the cervical sulcus

Postorbital spine: spine situated near the orbital margin posterior to the antennal spine

Rostrum: anteromedian projection of the carapace between the eyes

Sulcus (Sulci): groove

Telson: terminal unit of the abdomen bearing the anus

Uropod: paired, biramous appendage attached to the sixth abdominal segment, usually combining with the telson to form the tail fan

THE KEY

This online taxonomic key is not intended to be a typical dichotomous key. The intent is to present well defined traits that can be easily scored, and in combination used to arrive at a correct species designation. Species included in the key are those found in the waters of British Columbia. Several of the species treated here show a great deal of similarity to each other including the two species of Bentheogennema, as well as the two species of Sergia. Descriptions, as well as diagrams and illustrations used in the online key, for the most part, follow those of Butler (1980) and Wicksten (2009). Those interested in more complete descriptions or the more traditional dichotomous keys are referred to these works. REFERENCES

Baldwin, A. 2010. Checklist of the shrimps, crabs, lobsters and crayfish of British Columbia 2010 (order Decapoda). In: E-Fauna BC: Electronic Atlas of the Fauna of British Columbia, B. Klinkenberg (Ed.). Accessed January 6, 2011. http://www.geog.ubc.ca/biodiversity/efauna/documents/DecapodsofBCBaldwin2011.pdf

Brusca, R.C. and G.J. Brusca. 1990. The Crustaceans. In: Invertebrates. Sunderland, Sinauer Associates, 618-658.

Butler, T.H. 1980. Shrimps of the Pacific coast of Canada. Department of Fisheries and Oceans Canada, Ottawa, 280 pp.

Perez Farfante, I. and B.F. Kensley. 1997. Penaeoid and sergestoid shrimps and prawns of the world. Keys and diagnoses for the families and genera. Mém. Mus. Nat. Hist., Paris, 175: 1-233.

Tavares, C. and J.W. Martins. 2010. Suborder Dendrobranchiata. In: Treatise on Zoology – Anatomy, Taxonomy, Biology – The Crustacea, Decapoda, Volume 9 Part A Eucarida: Euphausiacea, Amphionidacea, and Decapoda (partim). F.R. Schram and J.C. von Vaupel Klein (Eds.). Leiden, Koninklijke Brill NV, 99-164.

Vereshchaka, A.L. 2000. Revision of the genus Sergia (Decapoda: Dendrobranchiata: Sergestidae): taxonomy and distribution. Galathea Report: Scientific Results of the Danish Deep-Sea Expedition Round the World 1950-52, 18. 69-207.

Wicksten, M.K. 2009. Decapod Crustacea of the Californian and Oregonian Zoogeographic Provinces. UC San Diego Scripps Institution of Oceanography Library, Scripps Institution of Oceanography. http://escholarship.org/uc/item/7sk9t2dz