Exercise 11 Chondrichthyes and Osteichthyes: Observation and Classification of Specimens

EXERCISE 11 CHONDRICHTHYES AND OSTEICHTHYES: OBSERVATION AND CLASSIFICATION OF SPECIMENS

Structure

11.1 Introduction Objectives 11.2 Materials Required 11.3 General Features and Type Study of Class Chondrichthyes Sphyrna Pristis Torpedo 11.4 General Features and Type Study of Class Actinopterygii Labeo rohita Anguilla Exocoetus 11.5 Terminal Questions 11.1 INTRODUCTION

This laboratory exercise involves the study and observation of jawed fishes which is based on Unit 13 of Block 3 of the Animal Diversity theory course. You will recall that the cartilaginous fishes are known as Chondrichthyes (Gr., chondros , cartilage and ichthyes , fish) Whereas Osteichthyes includes bony fishes. In this exercise you will study some representative members of cartilaginous fishes belonging to Subclass Elasmobranchii, (Gr. elasmos , plate and branchia , gills) and some representative members of rayfinned bony fishes included in Class Actinopterygii .

All fishes are aquatic gnathostomes (with true jaws)having a streamlined body. The paired appendages are pectoral and pelvic fins supported by fin rays. The median fins are one or two dorsal fins, an anal fin and a caudal fin. The exoskeleton is in the form of scales, dermal denticles or horny scutes. The notochord is constricted into vertebrae. Respiration is by gills. Most fishes have a well developed lateral line system composed of sensitive receptors that can sense motion by nearby fishes and prey. The general position of fish in the animal kingdom is shown in the following schematic diagram.

Chondrichthyes and KINGDOM ANIMALIA Osteichthyes: Observation and Classification of

Specimens CHORDATA NON CHORDATA Groups

Protochordata Vertebrata (Craniata)

Superclasses

Agnatha Gnathostomata (without jaws) (Jawed fishes and tetrapods)

Chondrichthyes Osteichthyes Amphibia Reptilia Aves Mammalia Subclasses

Elasmobranchii Holocephali

Fig. 11.1: Schematic diagram depicting the general position of fish in the animal kingdom.

Objectives

After performing the exercise you will be able to:

• identify and give the scientific and common names of the specimens of cartilaginous fishes like Sphyma , Pristis , Torpedo and bony fishes like Labeo, Exocoetus and Anguilla ,

• classify the identified cartilaginous and bony fishes up to the level of orders,

• list characters justifying the classification of the identified genera of cartilaginous and bony fishes, draw their well labelled diagrams and mention special features, if any,

• mention the habit and habitat and geographical location and economic importance, if any of each identified genus of the cartilaginous and bony fishes. 11.2 MATERIALS REQUIRED

1. Museum specimen of the following cartilaginous and bony fishes:

i) Sphyrna

ii) Pristis (sawfish)

iii) Torpedo (electric ray)

iv) Labeo

v) Exocoetus 131

Animal Diversity: vi) Anguilla Laboratory 2. Laboratory Practical file.

3. Pencil, eraser and ruler. 11.3 GENERAL FEATURES AND TYPE STUDY OF CLASS CHONDRICHTHYES

Members of class Chondrichthyes retain their cartilaginous embryonic endoskeleton throughout their life. It is not replaced by bone though calcium salts are sometimes deposited within it in order to strengthen it. The general position of cartilaginous fish is given in Fig. 11.1.Class Chondrichthyes is divided into two subclasses: (i) Elasmobranchii and (ii) Holocephali. We will be studying some representatives of elasmobranchs. Features of Chondricthyes

i) Cartilaginous fishes are mostly marine and predaceous.

ii) They have fusiform or spindleshaped body.

iii) Their fins are both median and paired, all supported by finrays. Pelvic fins bear claspers in males.

iv) Tail is heterocercal.

v) Skin is tough. It contains minute placoid scales (Fig. 11.2) and mucous glands.

vi) Endoskeleton is entirely cartilaginous without any bones.

vii) Mouth is ventral and jaws have teeth.

viii) Sexes are separate, gonads are paired and gonoducts open into cloaca.

ix) These fishes are oviparous or ovoviviparous and fertilization is internal.

x) No swim bladder present.

Fig. 11.2: Small placoid scales are conical tooth-like structures are characteristic of cartilaginous fishes, the Chondrichthyes. 132

Sub-class Elasmobranchii Chondrichthyes and Osteichthyes: Observation and Elasmobranchs have five to seven separate gill openings on each side; Classification of operculum or gillcover is absent, dorsal fin(s) and spines, if present, are rigid; Specimens males usually possess modified pelvic fins with claspers; dermal placoid scales often present; palatoquadrate (upper jaw) not fused to cranium (suspension amphistylic or hyostylic); branchial basket mostly behind the neurocranium; both upper and lower jaws have rows of sharp teeth which are replaced relatively rapidly; some ribs usually present; spiracle opening (remains of hyoidean gill slit) usually.

Elasmobranchs are typically predaceous fishes that rely more on smell than on sight for obtaining their food (the olfactory capsules are relatively large and the eyes are relatively small).

In the present laboratory exercise you will study the specimens of three elasmobranchsSphyrna, Pristis and Torpedo. 11.3.1 Sphyrna

Sphyrna (Fig. 11.3) is commonly known as hammerhead shark .

Examine the specimen and note the following features: i) Body is elongated measuring about .09 to 6 metres in length and divided into head, trunk and tail: Colour of the body is grayish dorsally whereas ventrally it is yellowish. ii) From the front head is flattened and expanded sideways into two prominent lateral lobes hence, it looks like a hammer. iii) Eyes are found at the tips of lateral lobes and provided with 3 eyelids (the third eyelid is a nictitating membrane that protects the eye in the water). iv) Mouth is crescentric and ventral, at the base of lateral lobes, nostril is located ventrally. v) There are five pairs of lateral gill slits. Spiracles are absent. vi) Trunk part of the body has median as well as paired fins. There are two dorsal median fins, caudal and anal fins. vii) Pectoral and pelvic fins are paired. viii) Viviparous, produces about 40 young. ix) Sphyrna is caught for its oil and for its fins that are considered a delicacy in shark fin soup.

Habit and Habitat It is common marine shark living in deep waters. Hammerhead shark is ferocious and voracious feeder and it feeds on small fishes , crabs, lobsters etc. It is a swift swimmer and because of its panoramic vision catches its prey swiftly

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Animal Diversity: Geographical distribution: Found in topical and subtopical seas and coastal Laboratory warm waters of Pacific Ocean.

Fig. 11.3: Sphyrna, in its natural habitat. Classification and its Justification Kingdom Animalia Animals, multicellular organisms with cells that lack a cell wall, many capable of movement or movement of some of their body parts or capable of movement at some time of their life cycle; heterotrophic nutrition.

Phylum Chordata Dorsal tubular nerve cord, notochord and paired gillslits are present.

Group Vertebrata Notochord is replaced by vertebral column; two pairs of appendages; circulatory system closed; hepatic portal system present; bloodcontaining R.B.Cs.

Superclass Gnathostomata Jaws and paired appendages are present . Class Chondrichthyes Cold blooded vertebrates, gills for respiration, fins for locomotion; streamlined body covered with scales. Cartilaginous endoskeleton; skin has tough but minute placoid scales. 134

Subclass Elasmobrachii Plategilled fishes. 57 separate gill Chondrichthyes and Osteichthyes: openings on each side in sharks and Observation and ventral in rays; Dorsal fin and spines if Classification of present are rigid; anal fin present in Specimens most sharks; spiracles present; upper jaw not fused with cranium; both lower and upper jaws have sharp teeth; lateral line system well developed.

Superorder Galeopmorphi Usually 2 dorsal fins with or without spines; 5 gill slits present;anal fin present; caudal fin heterocercal to diphycercal; spiracles may or may not be present.

Order Carcharhiniformes 2 dorsal fins without spines; eyes dorsal or dorsolateral with nictitating membrane; spiracles absent; pectoral fins behind 5 gill slits; Genus Sphyrna Common Hammerheadshark Name 11.3.2 Pristis

Pristis is commonly known as sawfish (Fig. 11.4).

Examine the specimen and note the following features: i) These are also hypotrematic elasmobranchs; the body is shark like with flattenedunderside.. ii) The sawfish may attain a length of 3 to 6 metres. iii) Rostrum or snout is an elongated bladelike structure armed on either lateral side with a row of sharp toothlike scales (denticles), which make it a formidable weapon for defense as well as food capture. iv) Spiracles are present behind the eyes. v) Dorsal fins are large with the first dorsal fin being opposite to the pelvic fin. vi) Tail is well developed and terminates in heterocercal caudal fin.

Features of Special Interest

As the sawfish swims through groups of small fishes, it swings the saw from side to side, thus disabling many of them and eating them at leisure.

Economic Importance

This fish is invaluable for liver oil of high vitamin value and for skin which is used for making scale boards.

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Animal Diversity: Laboratory

(a)

(b)

Fig. 11.4: Pristis (sawfish). a) Museum specimen, b) In its natural habitat.

Habit and Habitat The fish is predaceous with food chiefly comprising small fishes, flesh of whales and other marine animals. Geographical Distribution: This fish is marine and is found in Mediterranean and Atlantic Oceans particularly in America, West Indies, China and Gulf of Mexico. There are 2 species in India, P. cuspidata and P. microdon . Classification and its Justification Kingdom Animalia Animals, multicellular organisms with cells that lack a cell wall, many capable of movement or movement of some of their body parts or capable of movement at some time of their life cycle; heterotrophic nutrition. Phylum Chordata Dorsal tubular nerve cord, notochord 136 and paired gill slits are present.

Group Vertebrata Notochord is replaced by vertebral Chondrichthyes and Osteichthyes: column; two pairs of appendages; Observation and circulatory system closed; hepatic portal Classification of system present; blood containing Specimens R.B.Cs. Superclass Gnathostomata Jaws and paired appendages are present. Class Chondrichthyes Cold blooded vertebrates, gills for respiration, fins for locomotion; streamlined body covered with scales. Cartilaginous endoskeleton; skin has tough but minute placoid scales. Subclass Elasmobrachii Plategilled fishes. 57 separate gill openings on each side in sharks and ventral in rays; Dorsal fin and spines if present are rigid; anal fin present in most sharks; spiracles present; upper jaw not fused with cranium; both lower and upper jaws have sharp teeth; lateral line system well developed.

Superorder Batoidea All rays and skates. Body dorsoventrally flattened, trunk and tail muscles reduced; 5 gill openings ventral; spiracles present: anterior edge of pectoral fin greatly enlarged and attached to side of head beyond the gill openings. Differ from all other sharks by not having a free upper eyelid.

Order Pristiformes Body flattened on the underside and snout or rostrum long and lined on both sides by sharp transverse denticles; two dorsal and a caudal fin Genus Pristis Common Sawfish Name 11.3.3 Torpedo

Torpedo (Fig. 11.5) is commonly known as electric-ray.

Examine the specimen and note the following features: i) Body is circular and dorsoventrally flattened with enormous pectoral fins joined to the head and trunk forming a circular body disc. ii) The semicircular anterior margin of the disc is supported in the centre by a branched prenasal rostrum and laterally by the branched preorbital cartilage.

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Animal Diversity: iii) Skin is smooth. Laboratory iv) Mouth is transverse and ventral.

v) Quandrangular nasofrontal lobe is present.

vi) A pair of large electric organs, one on either side in between the pectoral fins and head are present.

vii) A pair of large spiracles with valves are situated dorsally on the head.

viii) Five pairs of gill slits are present on the flat ventral surface of the head.

ix) Tail is slender with a dorsal and a caudal fin.

x) They are modern derivatives of sharks and specialized for bottom dwelling.

Features of Special Interest

Some dorsal muscles are modified into a powerful electric organ on either side between the eye and pectoral fin. They are capable of giving a powerful electric shock (about 200volts) to stun their prey and enemies. Therefore, these organs are excellent for predation and defense purposes.

(a) (b) Fig. 11.5: Torpedo (electric ray). a) Californian electric ray. b) Museum specimen of electric ray.

Habit and Habitat

The electric rays conceal themselves in the sand rather than retreating. These fishes often eat bony fishes as large as is possible for them to swallow.

Geographical Distribution : Torpedo is found in Mediterranean and Red Sea, Atlantic and Pacific Oceans. T. marmorata is found in Indian Ocean.

Classification and its Justification

Kingdom Animalia Animals, multicellular organisms with cells

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that lack a cell wall, many capable of Chondrichthyes and Osteichthyes: movement or movement of some of their Observation and body parts or capable of movement at Classification of some time of their life cycle; heterotrophic Specimens nutrition. Phylum Chordata Dorsal tubular nerve cord, notochord and paired gillslits are present. Group Vertebrata Notochord is replaced by vertebral column; two pairs of appendages; circulatory system closed; hepatic portal system present; blood containing R.B.Cs. Superclass Gnathostomata Jaws and paired appendages are present. Class Chondrichthyes Cold blooded vertebrates, gills for respiration, fins for locomotion; streamlined body covered with scales. Cartilaginous endoskeleton; skin has tough but minute placoid scales. Subclass Elasmobrachii Plategilled fishes. 57 separate gill openings on each side in sharks and ventral in rays; Dorsal fin and spines if present are rigid; anal fin present in most sharks; spiracles present; upper jaw not fused with cranium; both lower and upper jaws have sharp teeth; lateral line system well developed. Superorder Batoidea All rays and skates. Body dorsoventrally flattened, trunk and tail muscles reduced; 5 gill openings ventral; spiracles present: anterior edge of pectoral fin greatly enlarged and attached to side of head beyond the gill openings. Differ from all other sharks by not having a free upper eyelid. Order Torpidiniformes Have unique electric organs on head which are capable of giving shocks from 2 220 volts depending on the species; sluggish bottom dwellers; body disc like with stout tail; no dermal denticles. Genus Torpedo Common Electric ray Name 11.4 GENERAL FEATURES AND TYPE STUDY OFCLASS ACTINOPTERYGII

In the modern bony fishes belonging to Class Actinopterygii, the endoskeleton is bony and skin with mucous glands. The body is either naked or with an 139

Animal Diversity: exoskeleton of scales; the scales may be cycloid or ctenoid. The gill arches or Laboratory branchial arches are 4 or 5 in number and the gill openings are covered with

an operculum on each side supported by bones. The jaws are well formed ensheathed with membrane bones. Air bladder (or swim bladder) is usually present. The tail is diphycercal or homocercal. The mouth is usually terminal. The bases of the pectoral fin are not fleshy. The pectoral fins are supported by bony dermal fin rays or lepidotrichia, attached to the girdle directly. The jaw suspension is hyostylic. The internal nares are absent. Nervous system consists of a brain with small semicircular canals. Sexes are separate (sex reversal in some), gonads paired; fertilisation usually external; larval forms may differ greatly from adults.

Modern bony fishes are very widely diversified. They have conquered both fresh water and marine environment. They show a high degree of adaptive radiation. In the fresh water, the fishes are adapted to fast flowing streams in the hills, rivers, ponds, and lakes. In the marine medium they are present in the shore region, oceanic region and in the deep seas. Some of the bony fishes exhibit the phenomenon of migration for breeding purpose; from rivers to sea e.g. Anguilla (eel) (catadromous migration) and from sea to rivers e.g. Salmo (anadromous migration). This is of immense interest to ichthyologists. Some bony fishes exhibit parental care in many ways. Thus, an indepth study of bony fishes is of great value to the students who are interested in the study of fishes.

For a complete classification you must refer to Unit 13 in the theory course of Animal Diversity. Class Actinopterygii can further be divided into three subclasses (1) Cladista, (2). Chondrstei and (3).Neopterygii.In this exercise we will now study some representative members of modern bony fishes that are grouped in Division Teleosti under subclass Neopterygii. 11.4.1 Labeo rohita

Characters

i) Labeo rohita (Fig. 11.6) is commonly called ‘Rohu’ in Hindi.

ii) Body laterally compressed, fusiform, attains maximum length of one meter.

iii) It is blackish grey on the back and silvery white below.

iv) The body is covered with overlapping cycloid scales.

v) Head prominent with a blunt, oblong and depressed snout and is covered with small tubercles.

vi) Mouth subterminal, directed downwards and surrounded by thick lips.

vii) Upper lip with a pair of short barbels and lower lip fringed. Jaws without teeth.

viii) Dorsal fin large and placed about the middle of the body.

ix) Pectoral fin without spinous rays.

140 x) Tail small and homocercal.

xi) Air bladder connected to the oesophagus (physostomous) and divided Chondrichthyes and Osteichthyes: into an anterior and a posterior chamber. Observation and Classification of xii) Weberian apparatus joins the air bladder with the internal ear. Specimens xiii) Lateral line canal passes through the scales.

Fig. 11.6: Labeo rohita (Rohu). (From wikipedia)

Habit and habitat

Lives in rivers, ponds and lakes; used in pisciculture; column feeder; feeds on flora and fauna in deep waters. It is an edible fish.

Geographical Distribution : Widely distributed Indian carp. Found in tropical and subtropical regions.

Classification and its Justification

Kingdom Animalia Animals, multicellular organisms with cells that lack a cell wall, many capable of movement or movement of some of their body parts or capable of movement at some time of their life cycle; heterotrophic nutrition.

Phylum Chordata Dorsal tubular nerve cord, notochord and paired gillslits are present.

Group Vertebrata Notochord is replaced by vertebral column; two pairs of appendages; circulatory system closed; hepatic portal system present; Blood containing R.B.Cs.

Superclass Gnathostomata Jaws and paired appendages are present.

Class Actinopterygii Endoskeleton ossified, single external gill opening on either side covered by operculum. Paired fins are supported by fin rays; limb musculature within body; swim bladder if present; mainly hydrostatic organ.

Subclass Neopterygii Skeleton bony; caudal fin homocercal; 141

Animal Diversity: scales cycloid, ctenoid or absent or rarely Laboratory ganoid; fin ray number equal to their

support in dorsal and anal fin.

Superorder Ostariophysi mostly freshwater; modification of first four vertebrae forming Webarian apparatus for amplifying sound transmission Swim bladder present, divided into two chambers.Pelvic fin if present abdominal.

Order Cypriniformes Air bladder physostomous; tail homocercal, operculum supported by bones. Mouth toothless; upper jaw protrusible; Scales cycloid, barbels reduced, commonly called as carps.

Genus Labeo

Species rohita

Common Rohu Name 11.4.2 Anguilla

Characters

i) Anguilla (Fig. 11.7) is commonly called as eel.

ii) The body is elongated and cylindrical in shape.

iii) Skin is brownish on the dorsal side and yellowish below.

iv) Skin with rudimentary scales arranged in oblique rows at right angles to one another.Cutaneous respiration is well marked.

Fig. 11.7: Anguilla (Eel).

v) Fins are soft; pectoral fins are short; pelvic fins absent.

vi) Dorsal and anal fins are elongated and continuous with caudal fin.

vii) Tail is long and cylindrical.

viii) It exhibits catadromous migration (lives in freshwater and migrates to 142 saltwater to spawn).

Habit and Habitat Chondrichthyes and Osteichthyes: Common in tropical and temperate regions of the world except eastern Pacific Observation and Classification of and southern Atlantic. Specimens Geographical Distribution : Anguilla is found in Gangetic estuaries, the Bay of Bengal, the India Pacific region to the seas of China and beyond. It lives in freshwaters in Europe and when mature migrates to Sargossa sea for breeding.

Classification and its Justification

Phylum Chordata Dorsal tubular nerve cord, notochord and paired gillslits are present.

Group Vertebrata Notochord is replaced by vertebral column; two pairs of appendages; circulatory system closed; hepatic portal system present; blood containing R.B.Cs.

Superclass Gnathostomata Jaws and paired appendages are present.

Subclass Neopterygii Skeleton bony; caudal fin homocercal; scales cycloid, ctenoid or absent or rarely ganoid; fin ray number equal to their support in dorsal and anal fin.

Subdivision Elopomorpha Leptocephalus (leaf like) larva entirely different from the adult; swim bladder not connected to ear.

Order Anguilliformes Body elongated, paired fins reduced. Skin with reduced scales. Anal and dorsal fins confluent with caudal fin. Pelvic fin and girdle absent

Genus Anguilla

Common Eel Name 143

Animal Diversity: 11.4.3 Exocoetus Laboratory Characters

i) Exocoetus (Fig. 11.8 ) is commonly known as flying fish, because it can leap through air.

ii) Body elongated, laterally compressed, body silvery yellow and bluish above.

iii) Cycloid scales are present on the body.

iv) Eyes large; head covered with scales.

v) Mouth wide, terminal; both jaws are toothed and teeth of equal size.

vi) Dorsal and anal fins are short and opposite to each other near the tail regi on.

vii) Pectoral fins are large and help the fish to glide in the air.

viii) Tail homocercal; caudal fin large and bifid, the ventral lobe of the caudal fin is longer.

Fig. 11.8: Exocoetus (Flying fish).

Habit and Habitat

Marine fish that can leap in the air.

Geographical Distribution : Found in tropical and warm parts of Atlantic and Indian Oceans.

Classification and its Justification

Phylum Chordata Dorsal tubular nerve cord, notochord and paired gillslits are present. 144

Group Vertebrata Notochord is replaced by vertebral column; Chondrichthyes and Osteichthyes: two pairs of appendages; circulatory Observation and system closed; hepatic portal system Classification of present; blood containing R.B.Cs. Specimens

Superclass Gnathostomata Jaws and paired appendages are present.

Subclass Neopterygii Skeleton bony; caudal fin homocercal; scales cycloid, ctenoid or absent or rarely ganoid; fin ray number equal to their support in dorsal and anal fin.

Superorder Acanthopterygii Fins supplied with sharp inflexible spines or rays; mouth highly protrusible.

Series Atherinomorpha Small surface feeding fishes; pectoral fin placed high on the body, pelvic fin abdominal.

Order Beloniformes Dorsal fin near the tail region and opposite to anal fin; fins soft and scales cycloid; fixed nonprotrusible upper jaw

Genus Exocoetus

Common Flying fish Name 11.5 TERMINAL QUESTIONS

1. What are the common names of the following?

i) Sphyrna . ii) Pristis . iii) Torpedo . iv) Exocoetus . v) Anguilla .

2. Explain why the Sphyrna is said to be viviparous.

. .

3. What is the significance of the rostrum of Pristis ?

. .

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Animal Diversity: 4. What is significant about Torpedo ? Laboratory .

.....

5. Give one example each of the bony fishes showing catadromous and anadromous migration.

......

6. Write three important characteristics of bony fishes.

......

7. Describe the habit, habitat, size and feeding behaviours of Labeo , Anguilla , and Exocoetus .

i) Labeo ...... ii) Anguilla ...... iii) Exocoetus ......

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