How does one tell the difference between the Caridean (true
shrimp) and the Penaeids (prawns)? The quickest method is to
simply examine the second abdominal segment. If segment two
overlaps both segments one and three, then you have a Caridean
(shrimp). If segment two overlaps only segment three, then you
have a Penaeid (prawn).
Caridoid facies :
The morphological characteristics that adapt a true shrimp to swimming is known as the Caridoid facies. Carid
(latin) means shrimp with the suffix oid
meaning "-like" and facies
refers to the general appearance. The crustaceans that most fully
exhibit the caridoid facies are those species found in the
Malacostracan super order Eucarida (Eu
, "true", Carrid
The components of the caridoid facies involve hydrodynamic
adaptations that make shrimp highly streamlined and suited for
swimming. The paddle like pleopods power forward swimming and in
some caridoids, oar like outer branches of the thoracid legs (exopods)
also aide in forward swimming. The backward tail flipping
(retrograde escape response) of a frightened or startled shrimp is
another form of swimming to which several caridoid features are
involved. Propulsion is provided by rapid flexing of the abdomen
which pushes forward the tail fan uropods propelling the shrimp swiftly
In true shrimp, a cuticular cover, the carapace,
extends over and covers the thoracid segments that streamlines the
shrimp. The dorsal midline of the cephalothorax is often produced
into a dorsal carina (keel) that looks and acts much like the keel of a
ship, but in shrimp, the "keel" is upside down yet serves the same
function by providing stability as the shrimp moves through the water.
An extension of the dorsal carina is the rostrum, a sword like
blade that presumably functions as another aide in stability. The
flat antennal scales (exopods of the second antennae) spread and tilt
during swimming, acting as both rudders and brakes. The uropods
of the tail fan are also important steering devices during backward
Stalked eyes and biramous antennule (first
antenna) are adaptations of mobile shrimp. The compound eye
located on a movable stalk can detect movement and form images over a
wide field of vision. The area that they can cover with such
stalked eyes became quite apparent during my efforts to catch live
specimens as I quickly became aware of the fact that there is no such
thing as sneaking up behind a shrimp. The outer branch of the
antennule caaries the aesthetascs which are sensitive to dissolved
compounds in the water, a sense of "smell" if you will. The long
antennae carries a variety of tactile or touch receptors as well as
chemoreceptors sensitive to higher concentrations of chemical stimuli
able to sweep all around the shrimp in order to detect and recognize
nearby objects. This ability to reach out and touch can be
observed with captive shrimp that have grown accustomed to hand
feeding. But before approaching the hand that literally feeds
them, they will first sweep their antennae over your hand or fingers as
their means to taste and touch test before approaching closer.
This ability also ensures their safety in the wild as it gives
them a means to detect non-moving hazards that their motion sensitive
eyes can not detect.
The caridoid form is considered to be
a very successful one within the marine habitats but in terms of
numbers of species, the carideans are by far the most successful.
Such high biological diversity reflects their much wider range of
habitats in comparison with other caridoid groups. There can be
little doubt that the caridoid body plan, having been modified in a
variety of ways, has been the basis from which extensive invasion and
diversification in the benthic environment has occurred.
Glossary of common terms used in taxonomy: cf :
(example - Genus name cf
species name) - denotes a case where the identity is in doubt, but the organism is similar to a
known species in the opinion of whoever "cf-ed" them. Sometimes these end up
being assigned to the names species, sometimes they end up being new species.
cf = confer (Latin), = compare (English). nov:
New as in a new species. aff. (affine):
with affinity to. species complex:
A group of species which satisfy the
biological definition of species, that is, they are reproductively isolated from
each other, but they are not morphologically distinguishable or at
least are not readily or reliably distinguishable on a morphological basis.
Glossary of descriptive terms with notes on form and function :
Abdomen: (Fig.1) The tail, consisting of six
body segments and the telson/uropods.
Carina: The ridge flanking the rostrum,
sometimes nearly reaching the end of the carapace.
Sulcus: The groove flanking the rostrum to
the adrostral carina, sometimes nearly reaching the end of the
Antenna (Antennae): (Fig.1) Long, paired, usually flagellate appendage
projecting from the front of the cephalothorax.
Carina: The ridge extending posteriorly
along dorsal extremity of antennal region, often continuous with antennal
Antennal Flagellum (Antennal Flagella): (Fig.1) Multiarticulate, whip-like terminal part of the
Antennal Peduncle: Three basal segments of the antenna, from which the
Antennal Region: Area on the lateral face of the carapace posterior
to and encompassing the antennal spine.
Spine: Spine situated on the anterior
margin of the carapace just ventral to the orbital
Antennular Flagellum (Anmnnular Flagella). Multiarticulate paired filaments (sometimes
flattened and lamellate) of the antennule.
Antennular Peduncle: Three basal segments of the antennule, from which
the flagella arise.
Antennule: Short, paired, usually flagellate appendages
projecting from the front end of the
Anterior: The front or frontal area.
Anterolateral Carina: Longitudinal ridge extending along the anterior part
of the carapace, ventral to the gastro-orbital
Arthrobranchia (Arthrobranchiae): Branchia (gill) attached to the joint area between
the body and the first podomere of the leg.
Article: Any one of the subdivisions of an appendage
Articular Membrane: Uncalcified integument at a joint, permitting
movement of the exoskeleton, as between the segments of a
Basial Spine: Spine projecting from a thoracic
Biunguiculate: Having two of or being forked.
Branchia (Branchiae): Respiratory organ (gill) associated with an
appendage or with the body wall.
Branchial Region: Area of the carapace overlying the branchial cavity
Branchiocardiac Carina. Ridge extending along the posterodorsal limit of
Branchiocardiac Sulcus: Groove extending along the dorsal limit of the
branchiostegite, running parallel to the branchiocardiac
Branchiostegal Carina: Longitudinal ridge extending along the
anteroventral part of the carapace, usually continuous with the branchiostegal
Branchiostegal-Hepatic Carina: Longitudinal ridge consisting of the fusion of the
branchiostegal and hepatic carinae.
Spine: Short spine on or near the anterior
margin of the carapace ventral to the antennal spine and dorsal to the
anteroventral angle of the carapace.
Sulcus: Groove often accompanying the
branchiostegal carina, located on the anteroventral part of the
Branchiostegite: Expanded ventrolateral part of the carapace covering
"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): A ridge or keel of the
Cephalothorax: Anterior part of the body consisting of the fused
cephalon (head) and thorax, bearing all the appendages except the pleopods and
Transverse ridge starting at the top of the carapace and extending down and
toward the front of the carapace.
Cervical Sulcus: Transverse groove starting at the top of the
carapace and extending down and toward the front of the
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
Appendage ending in a chela (claw).
Cheliped: Any chela (claw)-bearing thoracopod; typically refers to first
pair(s) of pereopods. (See below Photos)
(Cicatrices): Longitudinally disposed
ridge often present on the lateral part of the sixth abdominal
Cincinnuli (Cincinnulus): Minute interlocking processes projecting from the
dorsomesial margins of the petasmal endopods.
Cornea: Faceted, usually pigmented portion of the
Coxa (Coxae): First
or proximal podomere of a typically seven-segmented
Coxal Spine: Spine
projecting from the coxa of a thoracic
Terminal podomere of a typically seven-segmented
Dendrobranchiate Gill: One in which the paired primary branches are
subdivided, sometimes highly so.
Discoidal: Cleavage or furrow.
Distal Fold: Distal pleat in the dorsolateral lobule of the
Distolateral Projection: Distolateral, ventrally inclined projection or spur
of the basis of the endopod of the male second
Distomedian Projection: Distal, relatively narrow extension of the
dorsomedian lobule of the petasma.
Carina: Longitudinal ridge on the
dorsolateral region of the carapace running dorsal to the orbital
Dorsolateral Lobule: Dorsal part of the lateral lobe of the
Dorsolateral Sulcus: Longitudinal groove sometimes present close to the
dorsomedian line of the sixth abdominal somite.
Carina: Ridge extending along the
middorsal line of the abdominal somites.
Lobule: Part of the median lobe of the
ramus of a biramous appendage, especially one arising from the basis or from the
protopodite of the pleopod.
Endite: Lobe of several proximal podomeres of various
Epigastric Tooth: Tooth on the carapace situated above the gastric
region behind the first (posteriormost) rostral
exite of the coxa of a thoracic appendage, sometimes branchial in
Transverse plate anterior to mouth area.
Exopod: Lateral ramus of a biramous appendage, arising from
the basis, or from the protopodite.
Exuviae: The shed exoskeleton or molt.
Eyestalk: Peduncle or unfaceted part of the eye supporting
Flagellum (Flagella): Multiarticulate, usually whip-like terminal part of
the antennule or antenna.
Frontal Region: Anterior area of the carapace lying between the
orbits and bounded posteriorly by the gastric region.
Region: Principal median area of the
carapace bounded anteriorly by the frontal and orbital regions, and posteriorly
by the cardiac region, and laterally by the branchial and hepatic
Gastrofrontal Carina: Short longitudinal ridge extending posteriorly from
the ventral extremity of the orbital region.
Sulcus: Short longitudinal depression
accompanying the gastrofrontal carina dorsally.
Gland: Digestive gland associated with the
midgut, within the cephalothorax.
Carina: Short longitudinal ridge extending
(often curving) anterodorsally from the cervical sulcus towards the orbital
external reproductive structures.
Glabrous: Smooth, glossy.
Hepatic Carina: Longitudinally or obliquely disposed ridge of
variable length lying ventral to the hepatic region, sometimes extending almost
to the anterior margin of the carapace.
Region: Paired anterolateral areas of the
carapace bounded anteriorly by the antennal region, posteriorly by the branchial
region, and mesially by the gastric region.
Spine: Lateral spine situated near the
anterior margin of the hepatic region of the carapace.
Sulcus: Groove ventral to the hepatic
region extending posteriorly, sometimes from near the anterior margin of the
Incisor Process: Cutting process, often toothed or cusped, of the
The act of placing or introducing sperm onto or into the thelycum or seminal
receptacles of the female
Integument: Outer covering or
Ischial Spine: Spine projecting from the ischium or third segment
of the thoracic appendage.
Ischium (Ischia): Third podomere from the proximal end of a typically
Labrum: Upper lip or unpaired structure arising anterior to
the mouth and often covering it.
Lateral Lobe: One of the paired lateral parts, often folded, of
Longitudinal Suture: Fine longitudinal line extending posteriorly just
above the base of the antennal spine.
One of the heavily calcified jaws lying anterior to (beneath, in
ventral view) other mouth-parts. Each mandible is a stout, muscle
filled structure and comes in several variations. It may carry
both an incisor process for biting and cutting and a molar process for
crushing and grinding food. Often present is a small, segmented
palp (mandibular palp) equipped with setae which may function in
cleaning the mouthparts. The various combinations of palp,
incisor process and molar process are important features in the
taxonomy and classification of the caridean shrimp.
Palp: Segmented endopods attached
laterally to the masticatory part of the mandible.
Maxillae: Posterior to the mandibles are two pairs of maxillae which play a role in food handling.
1st maxilla (maxillule) :
The second mouthpart and fifth cephalic appendage.
Paired mouthpart appendages of the fourth and fifth cephalic somites.
The lateral blade of the maxilla (scaphognathite) extends back
into the gill chamber, also known as the gill bailer.
Maxillipeds: One of a pair of three sets of thoracic appendages,
arising posterior to the primary mouthparts. The two anterior pairs are often
modified for feeding, while the third pair is often pediform, resembling the
One of the paired dorsal parts, often folded, of the
Median Sulcus: Dorsomedian groove on the
Fourth segment from the proximal end of a typically seven-segmented
Mesial Tubercle: A conical to low, rounded protuberance on the
surface of the optic calathus.
Ocular Plate: Median cephalic plate bearing the eyestalks
Scale-like structure located on the basal segment of
Terminal article of the eyestalk supporting, often embracing, the cornea of the
Anterior border of the carapace, often contiguous to the
Paired areas on the carapace just posterior to the
Spine projecting from the ventral extremity of the orbital
Orbito-Antennal Sulcus: Longitudinal or oblique depression between the
orbital margin and the hepatic spine.
Palm: Portion of the chela proximal to the propodal
Paragnaths: A pair of ventral projections of the cephalic cuticle just posterior and medial
to the mandibles.
One of the five posterior paired appendages or legs of the
cephalothorax. These limbs have the typical coxal and basal
segments of a biramous crustacean limb and a sticklike endopod of five
segments: ischium, merus, carpus, propodus and dactylus (dactyl).
The first two pairs of caridean pereopods are equiped with chelae
(claws). The chelae are used for food searching and handling,
aggression and defense and grooming. In many caridean species one
of the two pairs is stout and robust while the other pair is slender
and delicate with the chelae carrying tufts of setae which can be used
for grooming. The posterior (or last) three pairs of pereopods are the
walking legs, allowing the shrimp to step in all directions as well as
supporting the body when at rest. There is considerable variation
in the length and thickness of the walking legs amongst the species and
usually correlate with the general body robustness and exoskeleton
Petasma (Petasmata): The male genital structure consisting of the much
enlarged and coupled endopods of the first pair of pleopods.
Open: The lateral lobes are quite
flexible, partially or entirely extended laterally, with the ventral costae not
or barely turned ventrally.
Petasma, Semi-Open: The lateral lobes are flexible but folded, with the
ventral costae distinctly turned ventromesially, delimiting relatively ample
space extending from proximal to distal ends.
Semi-Closed: The lateral lobes are rather
flexible, markedly folded, supported by strong ribs, with the ventral costae
approaching rather closely, delimiting a moderately large space, narrowly open
distally where usually overlapped by well-developed distomedian
Petasma, Closed: The lateral lobes are heavily sclerotized,
sometimes making the structure virtually rigid, with the ventral costae situated
ventromesially, almost abutting, and delimiting a small, sometimes extremely so,
space; lateral lobe is usually produced distally into lateral spouts or
Phyllobranchiate Gill: A gill in which the branches are plate-like,
usually occurring in paired series along the gill
Pleopod: One of the
biramous paired appendages typically arising ventrally from each of the anterior
five abdominal segments. They are primarily swimming
Pleurobranchia (Pleurobranchiae): Gill attached to the body wall (pleural membrane),
dorsal to the articulation of the appendage.
Pleurite : One of the lateral flaps on each
of the anterior five abdominal segments.
(Podobranchiae): Gill borne on the basal
segment (coxa) of a thoracic appendage.
Podomere: Any one of the segments of an appendage, such as a
segment of a pereopod or maxilliped.
Postantennal Spine: Spine located on the anterolateral area of the
carapace (on the posterior part of the antennal
Postcervical Spine: Spine located immediately posterior to the cervical
Postcervical Sulcus: Subvertical carapace groove located posterior to
the cervical sulcus.
Posterior: The polar opposite of Anterior (front) or the back end.
Posterior Process: Posterior part of an elongate median protuberance
projecting caudally onto the last (XIV) thoracic
Posterior Protuberance: Conspicuous elevation arising from the
posteromedian part of the last (XIV) thoracic
Posthepatic Carina: Ridge posterior to the hepatic carina, extending
onto the lower branchiostegite.
Postocular Sulcus: A small groove situated near the dorsal extremity
of the orbital margin.
Postorbital Spine: Spine situated near the orbital margin posterior to
the antennal spine.
Postrostral Carina: Dorsomedian ridge extending posteriorly from the
base of the rostrum, sometimes nearly reaching the posterior margin of the
Propodus (Propodi): Sixth or penultimate segment of a typically
Prosartema: Variable in shape, thin, sometimes scale-like
process arising from the mesial base of the first antennular segment, and
Protocephalon: Anteriormost part of the body bearing
Pterygostomian Carina: Ridge running posterior to pterygostomian spine on
anteroventral part of carapace.
Pterygostomian Region: Anteroventral area of the
Pterygostomian Spine: Marginal spine arising from the anteroventral angle
or border of the carapace.
Ramus (Rami): A branch of an exopod or
Rostrum (Rostra): Anteromedian projection of the carapace between the
eyes. (See below Photos)
Laterally rigid lamellate exopod of the antenna; the antennal
Segment: Division of
Seminal Receptacles: Unpaired or paired bulbous or tubular sacs
associated with the thelycum for the storage of spermatophores or
Unpaired Receptacles: Noninvaginated, opening either through an exposed
median longitudinal slit flanked by lateral plates of sternite XIV, or opening
anterior to a single plate.
Paired Receptacles: Invaginated into the cephalothoracic cavity,
opening through well protected slits usually on anterior border of sternite XIV,
or on anterior part of XIII.
Somite: Each of the main divisions of the
sperm-carrying, variously complex mass, issuing from the male petasma during
Sensory organ of awareness of rotation and position located at the base of the
Ventral part of a thoracic or abdominal
surface of the cephalothorax or abdomen.
Stylocerite: Pointed scale arising from the lateral base of the
first segment of the antennular peduncle.
Sulcus: Groove located well ventral to the
hepatic region of the carapace and the hepatic
Groove located ventral to the lateral carina of the
Submarginal Carina: An almost longitudinal ridge extending between the
rigid and the membranous part of the
Subrostral Sulcus: A longitudinal elongate groove extending along the
dorsal limit of the orbital region.
Sulcus (Sulci): Groove.
Spine: Spine arising from the edge of the
cervical carina dorsal to the hepatic spine.
Spine: Spine located posterior to the
orbital margin of the carapace.
Suture: Either transverse or longitudinal, weakly
sclerotized line or seam on the carapace.
Telson: Terminal unit of the abdomen bearing the
Arched dorsal part of each of the anterior five abdominal
Thelycum (Thelyca): The female genitalia consisting of modifications of
the posterior two, or sometimes three, thoracic sternites (XII–XIV) serving for
the storage or transfer of the sperm, usually in spermatophores, and often
shielding seminal receptacles.
Thelycum, Open: One in which the seminal receptacles are
One in which the seminal receptacles are present.
Ridge: Highly sclerotized, rib-like
transverse structure across posterior margin of sternite
Fine, short vertical line extending dorsally from the ventral margin of the
Trichobranchiate Gill: A gill in which the branches are fingerlike and
project from a central axis.
Uropod: Paired, biramous appendage attached to the sixth
abdominal segment, usually combining with the telson to form a
Ridge extending along the ventropiesial margin of the ventrolateral lobule of
Ventral Surface: The side closest to the ground or the "under-side".
Ventrolateral Lobule: Ventral part of the lateral lobe of the
Ventromedian Lobule: Lateral part of
the median lobe of the petasma.
References: Bauer, Raymond T. Remarkable shrimps : adaptations and natural
history of the Carideans. University of Oklahoma Press, Norman,