**5. Arthropoda (Crustaceans)**

Carotenoids in the carapace of crustaceans exist as both free and esterified forms. The principal carotenoid in crustaceans is astaxanthin [6,7]. In crustaceans, astaxanthin exists as carotenoproteins such as crustacyanin, and exhibits purple, blue, and yellow colors. Many crustaceans can synthesize astaxanthin (**8**) from Άcarotene (**52**), ingested from dietary algae, via echinenone (**53**), 

3-hydroxyechinenone (**54**), canthaxanthin (**11**), and adonirubin (**12**), as shown in Figure 9 [6,7]. 

In many crustaceans, hydroxylation at C-3 (C-3ȝ) in the 4-oxo-Ά-end group is nonestereo-selective. Therefore, astaxanthin, adonixanthin, and 3-hydroxyechinenone, having a 3-hydroxy-4-oxo-Ά-end group, present in crustaceans, are comprised of a mixture of optical isomers [6,7]. 

> **Figure 9.** Metabolism of Ά-carotene in crustaceans.

**(DFKFRPSRXQGFRQVLVWVZLWKRSWLFDOLVRPHUV**

Some crustaceans can convert zeaxanthin to adonixanthin (**55**) and lutein to fritschiellaxanthin (**56**) and papyrioerythrinone (**57**) [1,6,7]. Crustaceans belonging to Isopoda can introduce a hydroxy group at C-2 in the Ά-end group. This hydroxylation is also none-stereo-selective. Therefore, Ά-caroten-2-ol (**58**) in the sea louse *Ligia exotica* exists as two optical isomers [1,6,7]. Recently, two new carotenoids, 2,3<sup>ȝ</sup>dihydroxycanthaxanthin (**59**) [27] and 2,3-dihydroserythrin (**60**) [28], were isolated from the hermit crab *Paralithodes brevipes* and crawfish *Procambarus clarkii*, respectively (Figure 10). 

> **Figure 10.** Characteristic carotenoids in crustaceans.

## **6. Echinodermata (Echinoderms)**

Echinenone is a well-known major carotenoid in the gonads of sea urchins and is an oxidative metabolite of Ά-carotene [6,7]. Echinenone from the gonads of sea urchins was found to have a 9ȝ*Z* configuration (**61**) [29]. 

Starfish are carnivorous and mainly feed on bivalves and small crustaceans. Principal carotenoids in starfish are astaxanthin (**8**), 7,8-didehydroastaxanthin (**9**), and 7,8,7<sup>ȝ</sup>,8<sup>ȝ</sup>-didehydroastaxanthin (**10**). They correspond to the oxidative metabolites of Ά-carotene, diatoxanthin, and alloxanthin, respectively. The crownof-thorns starfish *Acanthaster planci* is a large, nocturnal sea star 

that preys upon coral polyps. Recently, four new carotenoids: 4- ketodeepoxyneoxanthin (**62**), 

4-keto-4ȝ-hydroxydiatoxanthin (**63**), 3<sup>ȝ</sup>-epigobiusxanthin (**64**), and 7,8- dihydrodiadinoxanthin (**65**), were isolated from *A. planci* as minor components along with the major carotenoids 

7,8-didehydroastaxanthin, peridininol, and astaxanthin, and several other minor carotenoids including 7,8,7<sup>ȝ</sup>,8<sup>ȝ</sup>-tetrahydroastaxanthin, diadinoxanthin, diatoxanthin, and alloxanthin [30]. 

3,4,3<sup>ȝ</sup>,4<sup>ȝ</sup>-Tetrahydroxypirardixanthin 4,4ȝ-disulfate, named ophioxanthin (**66**), was reported in the brittle star *Ophioderma longicaudum* [31]. Canthaxanthin and astaxanthin were found in the 

gonads of sea cucumbers as major components. 5,6,5<sup>ȝ</sup>,6<sup>ȝ</sup>-Tetrahydro-Ά-carotene derivatives with 9*Z*, 

9ȝ*Z* configurations, termed cucumariaxanthin (**67**), were isolated from the sea cucumber 

*Cucumaria japonica* [32] (Figure 11). 

Recently, zeaxanthin, astaxanthin, and lutein were identified from spiny sea-star *Marthasterias glacialis* by HPLC-PAD-atmospheric pressure chemical ionization-MS. These carotenoids showed strong cell proliferation inhibition activity against rat basophilic leukemia 

RBL-2H3 cancer cell line [33]. 

## **7. Protochordata (Tunicates)**

As well as bivalves, tunicates are filter feeders. Carotenoids found in tunicates originate from phytoplankton such as diatoms, and are also metabolites of fucoxanthin, diatoxanthin, and alloxanthin [7,8]. 

Halocynthiaxanthin (**27**), an acetylenic analog of fucoxanthinol (**26**), and mytiloxanthinone (**68**), an oxidative metabolite of mytiloxanthin (**28**), were first isolated from the sea squirt *Halocynthia roretzi* [34]. They are widely distributed in various tunicates. Amarouciaxanthin A (**34**) and amarouciaxanthin B (**69**), having a unique 3-oxo-6-hydroxy-Ή-end group, were first isolated from the tunicate *Amaroucium pliciferum* [35] (Figure 12). Peridinin and its metabolites are also found in tunicates. 

**Figure 11.** Characteristic carotenoids in echinoderms.

**Figure 12.** Metabolic pathways of fucoxanthin in tunicates.
