Transcript Morphological Characters and Character States : Holothuroidea

Morphological characters and
their states : Holothuroidea
Ahmed S Thandar
School of Biological and Conservation Sciences
University of KwaZulu-Natal, Westville Campus
Durban, South Africa
• Classical/traditional taxonomy has always favoured the use of
morphological characters as they are readily perceived and easiest to
use. At our first workshop we attempted to standardize and define
some of them and utilized their states for preliminary analyses. For
the sake of posterity we must revise and refine these, at this and
subsequent workshops.
• Variations in morphological characters have always been accepted
as indicators of genetic variations and their similarities as indicators
of relationships.
• Thus, over the years, as a result of the correct use of morphological
characters, a more or less natural system of classification has
evolved for most of the higher taxa but this is far from satisfactory.
• When selecting morphological characters, especially for the higher
taxa, we must seek non-adaptive characters as they change very
slowly, unlike adaptive characters which are fast-changing and thus
most likely to fluctuate under environmental pressures. The use of
the latter, I believe, has be-devilled a rational classification amongst
some holothuroids, notably the Dedrochirotida.
•
I will recall some of the morphological characters and their possible
states but will not limit my consideration to the Aspidochirotida since
an appreciation of these throughout the group, will be necessary for
critical appraisement of original descriptions and during examination
and/or re-description of types.
Distinction between orders based on:
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Gross morphology of tentacles
Presence/absence of podia
Presence/absence of introvert and retractor muscles
Gross morphology of calcareous ring
Presence/absence of respiratory trees
peltatodigitate
digitate
peltate
dendritic
pinnate
Distinction between families within the Aspidochirotida:
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Form and arrangement of tentacles
Presence/absence of tentacle ampullae
Form of the calcareous ring
Single/paired gonadal tufts
Presence/absence of Cuvierian tubules
Presence/absence of table deposits
Presence/absence of button deposits
Presence of rosette-derived (120º) and button-derived
(90º) plates
Characters at generic level within the Aspidochirotida
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Tentacle form and number
Presence of modified podia
Form of calcareous ring
Ossicle assemblage of:
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–
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–
–
Labidodemas rugosum
body wall (mid-dorsal & mid-ventral)
dorsal podia and/or papillae
ventral podia (tubefeet/pedicels)
tentacles
gonad
cloaca
longitudinal muscles
cloacal suspensor muscles
Holothuria pervicax
Stichopus herrmanni
Bohadschia marmorata
Actinopyga echinites
Synallactes n. sp.
Characters at specific level:
• Many old descriptions are very brief, hence, in the absence of type
material, a lot of guesswork must have been involved in deciphering
which species a particular taxonomist was describing.
• Therefore, there is need for complete species descriptions. For
these, we need to develop a standardized list of morphological
characters and their possible states.
• Such a list must not be exhaustive as many species present other
characters (special/unique) which also need recording.
Characters at specific level
• Although the most important characters for species distinction are
the ossicles, my task is to review external and internal morphological
characters (excluding ossicles) and their states, to allow us to
standardize and define these.
• Detailed descriptions are indispensable for delineating species,
separating related or sister species, allowing the assemblage of
these into higher taxa and aiding in the determination of
relationships with the use of computer-based software.
External morphological characters
• Body form –
– cylindrical, sub-cylindrical, vermiform, robust/slender, barrelshaped, U-shaped, cigar-shaped, pentagonal/quadrangular in
cross-section, psolid-like, etc., sometimes in combination of
more than one character state
(wherever possible a colour or black & white photograph or drawing
of the entire animal must be given)
External morphological characters
• Size
– indicative of maximum size and/or maturity (mention
must be made whether one is dealing with a
contracted or relaxed specimen)
– measurements must be given for total length, width
of mid-body
– width of anterior and posterior ends, in an
attenuating specimen
(for U-shaped forms it would be ideal to measure
lengths of both the dorsal and ventral surfaces)
External morphological characters
• Colour
– important diagnostic feature for many nonholothuroid taxa
– live colouration more important
– colour description must include that of tentacles
(stalk and branches), podia, papillae,
warts/tubercles, etc.
External morphological characters
• Mouth
– position of mouth (terminal, sub-ventral, ventral, etc)
– presence/absence of a collar (naked/papillose, fused/unfused
papillae)
– presence/absence of valves around mouth.
• Anus
– position of anus (terminal, dorsal, sub-dorsal)
– associated structures (specialised papillae, typical podia, anal
teeth or a mixture of these)
External morphological characters
• Tentacles
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number
arrangement
size variation
type, shape
length of largest relaxed
length of shortest relaxed
colour of stalk and branches
• Podia
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arrangement, dorsal & ventral (scattered, in ambulacra, rows)
abundance
form and rigidity, if any
sucking disc-diameter, colour, etc.
(in some species podia may be all in the form of tube feet/ pedicels, in
others tube feet ventrally, papilliform dorsally, or papilliform throughout)
External morphological characters
• Warts (tubercles) and/or papillae
– size & number
– arrangement
– colour
• Sensory cups and eyes (only in apodids)
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number
form
position
arrangement
External morphological characters
• Consistency of body wall
– soft/flaccid, firm/rigid, gelatinous, etc.
• Texture of body wall
– smooth, rough
• Thickness of body wall
– dimension
(must state whether relaxed/contracted specimen)
Internal morphological characters
• Calcareous ring
– very important, preserved also in fossils
– adult material better as ring can change with growth
– generally five radial plates alternating with five
interradial plates (in apodids and malpadids, plates
may exceed 10)
– while type of ring is indicative of order or family,
form and size of individual plates may offer good
generic, subgeneric or specific characters
Internal morphological characters
Calcareous ring – Aspidochirotida
• radial plates usually larger than interradial
Labidodemas rugosum
plates. Must record:
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shape
proportion -length vs breadth
Stichopus herrmanni
height in relation to interradial plates
peculiar scrupturings, if any
anterior and posterior configurations, eg.
notches, concavities
– presence / absence of postero-median
projections
– variations, if any, between dorsal radial plates
Holothuria discrepans
Holothuria squamifera
Actinopyga echinites
Bohadschia marmorata
as opposed to ventral ones
Synallactes n. sp.
Internal morphological characters
• interradial plates usually smaller than radial plates.
Must record
– form
– size in relation to the radial plates
– anterior an posterior configurations
( necessary to illustrate CR as description of one author may vary from
that of another)
A
Internal morphological characters
Calcareous ring - Dendrochirotida
B
• simple, ribbon-like, without posterior prolongations as in
some cucumariids , eg. Aslia (A)
• Simple, thick, without posterior prolongations, as in most
C
cucumariids, eg. Pentacta (B)
• ring with paired, posterior prolongations as in the 10tentacled phyllophorids. Such ring always referred to as
complex/tubular or both. Basically three types:
– plates compact, separate or only basally united, hardly forming a tube
but with usually long, subdivided posterior processes, as in
Sclerothyoninae (C)
– plates compact, fused/unfused, forming only a short tube with short
posterior processes that are either subdivided or entire as in
Sclerodactylinae (D)
– plates elongated, fused, compact or broken into a mosaic, forming a
long tube with usually sub-divided posterior processes, as in the
Thyoninae (E)
D
E
Internal morphological characters
• In the “supergenus” Thyone, the tubular ring is variable –
generally of three types, demonstrating some geographic
variation, with radial plates bifurcating either:
– beyond posterior border of interradial plates or
– before posterior border of interradial plates or
– at posterior border of interradial plates
Internal morphological characters
• The polytentaculate phyllophorids do not seem to be a
natural group as they exhibit all forms of calcareous rings.
Even in just one subfamily, the Cladolabinae, we find all
forms of calcareous rings, except that which is tubular.
This
must
be
borne
in
mind
when
determining
phylogynies.
Cladolabes aciculus
Actinocucumis
typicus
Afrocucumis africana
Ohshimella
ehrenbergii
Internal morphological characters
• Tentacle ampullae
– although their presence/absence is important at higher
level, their size and shape may be important at specific
level but some caution needs to be exercised
• Water vascular ring
– position in relation to the calcareous ring
• Polian vesicles
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number
position
length
shape (some caution also needs to be exercised here)
Internal morphological characters
• Stone canal(s)
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number
position
length
form
free/attached
OVAL
Holothuria n. sp.
GLOBULAR
FILAMENTOUS
H. difficilis
H. hilla
• Madreporite
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internal/external
free/attached
degree of calcification
form (elongate, kidneyshaped, lobed, globular,
coral-like, etc.)
H. pardalis
H. scabra
Neostichopus grammatus
H. pervicax
H. parva
Mesothuria parva
Internal morphological characters
• Respiratory trees
– nearly always paired, profusely
branched, one usually longer
– either arise from cloaca independently
or together
Psolidothuria octodactyla
– in some psolids and dactylochirotids
may be very simple, often asymmetrical,
with scant saccular/filiform end-branches
– sometimes branchings very complicated
with well-branched supplementary
trunks giving impression of four trees, as
in Massinium.
Massinium arthroprocessum
Internal morphological characters
• Gonad
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form of branchings (dichotomous, irregular, etc.)
maturity
gametes, hermaphrodity
brood pouches, if any
• Longitudinal muscles
– usually paired in aspidochirotids, singular in dendrochirotids and
some others
– in molpadids either paired/singular
• Retractor muscles
– sites of origin and insertion
– ventral ones usually arise more anteriorly
– divide/undivide before insertion
Internal morphological characters
• Cuvierian tubules
– presence or absence
– expellable or non-expellable
– adhesivity or non-adhesivity
– appearance (long,thin; short, thick; short, thin; etc.)
– structure of proximal and distal ends
– number of attachment sites
• Ciliary funnels
– shape/form
– solitary, or in clusters
– sessile, stalked
Chiridota
(illustrations necessary as shape difficult to describe)
Polycheira
Acknowledgements
• Clark, A.M. & Rowe, F.W.E. (1971) Monograph of shallow- water Indo-West Pacific
echinoderms. British Museum (Natural History), London, 238 pp
• Rowe, F.W.E. & Richmond, M.D. (1997) Echinodermata. In Richmond, M.D. (Ed.) A
guide to the seashores of eastern Africa and the Western Indian Ocean Islands. Sida,
1997:290-320
• Thandar, A.S. (1987a) The southern African stichopodid holothurians, with notes on
the changes in spicule composition with age in the endemic Neostichopus grammatus
(H.L. Clark). South African Journal of Zoology, 22, 278-286.
• Thandar, A.S. (1989c) The sclerodactylid holothurians of southern Africa, with the
erection of one new subfamily and two new genera (Echinodermata : Holothuroidea).
South African Journal of Zoology, 24, 290-304.
• Thandar, A.S. (1990) The phyllophorid holothurians of southern Africa with the
erection of a new genus. South African Journal of Zoology, 25, 207-223.
• Thandar, A.S. (1991) The cucumariid holothurians of southern Africa with the erection
of a new genus. South African Journal of Zoology, 26, 115-139.