FAO Species Identification Guide for Fishery Purposes Western

726 Cephalopods
it may be necessary to check internal anatomical features to determine sex. To examine the contents of
the mantle cavity, a median longitudinal incision needs to be made through the mantle on the ventral side
of the animal. The internal features of males and females are shown in Figure 5. Mature females can readily
be distinguished from males by the presence of a pair of leaf-shaped creamy yellow nidamental glands
(Fig. 5b). Eggs may also be seen in the ovary, below and posterior to the nidamental glands. In immature
females, the nidamental glands may be greatly reduced in size or visible only as two short slits. The shape
of the male and female genital openings on the left side of the mantle cavity also differs slightly between
the sexes (Fig. 5a, b). Any body patterning, such as transverse wavy lines or bands on the dorsal side of
the mantle, is usually more pronounced in males and may be faint or absent in females.
The number and size of the tentacular club suckers are important traits. If the tentacles are retracted,
they can readily be extracted in fresh animals by gently probing inside the pouches between arms III and
IV on either side of the buccal mass (Fig. 1). Extraction of the club may be more difficult in preserved
specimens and dissection may be necessary. The number of club suckers given for each species, and used
in the keys, refers to the number of suckers in transverse rows. This is determined by counting the number
of suckers that are intersected in an oblique line midway along the tentacular club as shown in Fig. 3a.
Other important features of the tentacular club include:
1. The relative sizes of the suckers: they may vary in size (Fig. 3a, c), or be of similar size (Fig. 3b);
2. The protective membranes may be joined at the posterior end of the sucker-bearing face of the club
(Fig. 3a, c), or not joined (Fig. 3b);
3. The swimming keel may extend beyond the sucker-bearing face of the club (Fig. 3c), or may be
equivalent in length to the sucker-bearing face;
4. The sucker-bearing face may be joined to the tentacle stalk (Fig. 3b), or may be separated from it
by a membrane (Fig. 3c).
Suckers are described as normal or normal-sized if they do not differ obviously in size from other suckers.
As for club suckers, arm sucker “rows” refer to suckers positioned in transverse rows, that is, positioned
in oblique lines approximately perpendicular to the longitudinal axis of the arm. “Series” refers to suckers
positioned approximately parallel to the longitudinal axis of the arm. Biserial suckers are those arranged
in 2 series, tetraserial are those arranged in 4 series.
The cuttlebone (Fig. 4) can easily be removed from a fresh animal by
making a median longitudinal incision along the length of the mantle,
and two shorter incisions at the anterior end of the mantle as shown in
Fig. 6. The skin can then be peeled open to reveal the cuttlebone below.
Aside from its shape, important features of the cuttlebone include:
1. The width of the outer cone: it may broaden posteriorly
(Fig. 4a, b), or be of approximately uniform width along the length
of the cuttlebone (Fig. 7);
2. The inner cone may be narrow throughout (Fig. 7), or broaden
posteriorly (Fig. 4a, b);
3. The inner cone may be thickened posteriorly, and/or form a raised
ledge (Fig. 4b);
4. The median sulcus (or furrow) may be wide, or narrow;
5. The shape of the striae: while the striae may vary in shape within
species along the length of the cuttlebone, the shape of the
anteriormost striae (where the striated zone joins the last loculus)
is rather uniform and used for diagnoses. However, in some
cases, the distinction between “anterior striae inverted U-shape”,
and “anterior striae inverted V-shape” is not clear-cut, so identification
should be confirmed following examination of other characters.
The anterior extent of the striated zone may vary with the
size of the animal, so may differ in some cases from that shown
in illustrations.
No other internal features, requiring dissection of animals, are included
in the following key. Reference should be made to Figures 1 to 4 and the
“Glossary of Technical Terms” (pages 692 to 698).
suggested
incision for
dissection
Fig. 6 cuttlefish in dorsal view