Heterocarpus sibogae De Man , 1917

Jiang, Guo-Chen, Chan, Tin-Yam & Shih, Tung-Wei, 2014, Morphology of the first zoeal stage of three deep-water pandalid shrimps, Heterocarpus abulbus Yang, Chan & Chu, 2010, H. hayashii Crosnier, 1988 and H. sibogae De Man, 1917 (Crustacea: Decapoda: Caridea), Zootaxa 3768 (4), pp. 428-436 : 432-435

Heterocarpus sibogae De Man, 1917

( Fig. 3 , Table 1 )

Size: CL, mean 0.41 mm (range 0.38–0.43 mm); BL, mean 1.88 mm (range 1.85–1.90 mm); TL, mean 2.28 mm (range 2.25–2.30 mm).

Carapace ( Figs. 3 A, B, D): Dorsoventrally flattened; rostrum slightly curved and slender, longer than antennular peduncle; dorsal anterior and posterior processes present; anteroventral margin bearing strong pterygostomian spine and 1 distinct spine; eyes sessile.

Antennule ( Fig. 3 E): Peduncle unsegmented, slender and bearing 1 small tubercle; exopod unsegmented with 1 spatulate seta and 3 terminal aesthetascs as well as 1 terminal plumose seta; endopod with 1 long plumose seta.

Antenna ( Fig. 3 F): Peduncle unsegmented and with 1 distal spine; endopod unsegmented, with 1 long terminal plumose seta and 1 slender spine; exopod distally 6-segmented, with 11 marginal plumose setae, 1 distolateral seta and inner tubercle.

Mandible ( Fig. 3 G): Palp absent; incisor and molar processes well differentiated; with lacinia mobilis.

Maxillule ( Fig. 3 H): Coxal endite with 7 (2 subterminal+5 terminal) setae; basial endite with 2 strong setae and 3 cuspidate setae; endopod unsegmented, with 2 subterminal setae and 3 terminal setae; exopod absent.

Maxilla ( Fig. 3 I): Coxal endite bilobed with 9+4 setae; basial endite bilobed with 3+4 setae; endopod with 9 (3+2+1+1+2) setae; scaphognathite margin with 5 plumose setae.

First maxilliped ( Fig. 3 J): Coxa with 4 setae; basis with 9 setae; endopod unsegmented with 3, 1, 2, 4 (1 subterminal+3 terminal) setae; exopod unsegmented with 4 long plumose natatory setae.

Second maxilliped ( Fig. 3 K): Coxa with 1 seta; basis with 6 setae; endopod 4-segmented with 2, 1, 2, 4 (1 subterminal+3 terminal) setae; exopod unsegmented with 5 long plumose natatory setae.

Third maxilliped ( Fig. 3 L): Coxa without setae; basis with 4 setae; endopod 4-segmented with 2, 1, 2, 4 (1 subterminal+3 terminal) setae; exopod unsegmented with 5 long plumose natatory setae.

Pereiopods: Absent.

Abdomen ( Fig. 3 A, C): With 5 somites and without setae or spines.

Pleopods: Absent.

Uropods: Absent.

Telson ( Fig. 3 A): Subtriangular, posterior border with 7+7 setae, outermost 2 pairs only plumose on inner margin; bases of each seta except outermost one with row of minute spinules.

H. abulbus H. hayashii H. sibogae H. ensifer The morphology of larvae have been known in nine pandalid genera ( Atlantopandalus, Pike & Williamson 1964 [Z1, Z7; Z = Zoea]; Austropandalus, Thatje & Bacardit 2000 [Z1–Z5]; Chlorotocus, Heegaard 1969 [Z1]; Dichelopandalus, Lebour 1940 , Pike & Williamson 1964 [Z1–Z6], Pandalina, Lebour 1940 , Pike & Williamson 1964 [Z1–Z7, P = Post-larva]; Pandalus, Lebour 1940 , Pike & Williamson 1964 [Z1–Z6]; Stylopandalus, Lebour 1940 [Z1–Z9, P]; Plesionika, Landeira et al. 2009 [Z1–Z5]; Heterocarpus, Iwata et al. 1986 , Landeira et al. 2010 [Z1–Z5]). Common characters of pandalid larvae are: eye peduncle narrowed at base; carapace with two dorsal protuberances and anteroventral margin bearing spines, antennule with peduncle strongly concave and exopod bearing spatulate seta; antennal exopod segmented; rostrum well-developed since early stages (also see Thatje & Bacardit 2000, Landeira et al. 2010). For the first zoeal stage, however, there are no clear difference found amongst different pandalid genera.

With respect to the genus Heterocarpus , the first zoeae of only two species were known, namely H. ensifer ( Landeira et al. 2010) and H. sibogae ( Iwata et al. 1986) . However, the description of H. sibogae is rather brief and the present work re-describes the first zoea of this species in details. With the addition of H. abulbus and H. hayashii , the first zoeae of four species in this genus are now known. All of them share the common characters of anteroventral margin of carapace bearing spines, carapace with dorsomedian tubercles on anterior and posterior parts, and antennule with spatulate seta. On the other hand, the first zoeae of these four species can be readily distinguished by the following characters (also see Table 1 ):

(1) Spines on anteroventral margin of carapace: Other than the pterygostomian spine, H. sibogae differs from the other three species in bearing only one additional spine at the anteroventral margin of carapace (vs. 2 spines in others). Heterocarpus abulbus can also be separated from H. ensifer and H. hayashii in the one of the two additional spines at the anteroventral carapace being rather weak (both spines very distinct in H. ensifer and H. hayashii ).

(2) Body size and rostral length: The size of the zoea is much larger for H. abulbus (body length 2.44 mm) as compared to the other three species (body lengths 1.93 mm, 1.89 mm, 1.88 mm in H. ensifer , H. hayashii and H. sibogae , respectively). The rostrum of H. ensifer is distinctly shorter than the other three species in only extending to the middle of the antennular peduncle (vs. reaching or overreaching distal margin of antennular peduncle).

(3) Appendage setation: The endopod of maxillule has three subterminal setae in H. ensifer , whilst the other three species have only two subterminal setae. Heterocarpus abulbus can be further separated from H. hayashii and H. sibogae in having two instead of one seta on the coxa of the second maxilliped. Moreoever, H. sibogae has a somewhat different endopod setation at the second maxilliped (2, 1, 2, 4 vs. 3, 1, 2, 4– 5 in the other three species, see Table 1 ).

As in adults, the first zoeae of H. ensifer , H. hayashii and H. sibogae are more similar than with H. abulbus , which belongs to a different species group than the former three. On the other hand, although adults of H. ensifer , H. hayashii and H. sibogae are rather similar, distinct differences are already present amongst the zoeae of these closely related species. All these suggested that larval characters can provide important insights to the understanding of the taxonomy and phylogenetic relationships amongst Heterocarpus shrimps.

Figures

FIGURE 3. First zoea of Heterocarpus sibogae De Man, 1917; A) dorsal view; B) carapace lateral view; C) abdomen lateral view; D) anteroventral margin of carapace; E) antennule; F) antenna; G) mandible; H) maxillule; I) maxilla; J) first maxilliped; K) second maxilliped; L) third maxilliped.

Tables

TABLE 1. Characteristics of the first zoeae in four species of Heterocarpus. a, aesthetascs; b, basal spines; c, cuspidate setae; d, distolateral setae; p, plumose setae; s, spatulate setae; t, strong setae; v, slender spines.

	(present study)	(present study)	(present study)	(Landeira et al. 2010)
Carapace
Length (mm)	0.53–0.58	0.38–0.45	0.38–0.43	about 0.42
Anteroventral spines Antennule	2	2	1	2
Peduncle Endopod Exopod setation Antenna (setation)	1 small tubercle long plumose seta 3a+1p+1s	1 small tubercle long plumose seta 3a+1p+1s	1 small tubercle long plumose seta 3a+1p+1s	2 small tubercles long plumose seta 3a+1p+1s
Peduncle Endopod Exopod Maxillule (setation)	1b 1p+1v 11p+1d	1b 1p+1v 11p+1d	1b 1p+1v 11p+1d	1b 1p+1v 11p+1d
Coxal endite Basial endite Endopod Exopod Maxilla (setation)	7 2t+3c 5 0	7 2t+3c 5 0	7 2t+3c 5 0	7 2t+3c 6 0
Coxal endite Basial endite Endopod Scaphognathite 1 Maxilliped (setation)	8+3 3+4 3,2,1,1,2 5p	8+3 4+4 3,2,1,1,2 5p	9+4 3+4 3,2,1,1,2 5p	9+4 5+5 3,2,1,1,2 5p
Coxal Basis Endopod Exopod 2 Maxilliped (setation)	5 11 3,1,2,4 4p	4 10 3,1,2,4 4p	4 9 3,1,2,4 4p	7 12 3,1,2,4 4p
Coxal Basis Endopod Exopod 3 Maxilliped (setation)	2 8 3,1,2,5 5p	1 9 3,1,2,5 5p	1 6 2,1,2,4 5p	1 9 3,1,2,4 5p
Coxal Basis Endopod Exopod	0 4 2,1,2,4 5p	0 4 2,1,2,4 5p	0 4 2,1,2,4 5p	0 4 2,1,2,4 5p
Discussion