This article was downloaded by: [Ondokuz Mayis Universitesine]On: 10 November 2014, At: 18:16Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

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Falcidens targatus and F. acutargatus:two species of Caudofoveata (Mollusca,Aplacophora) new for BrazilPaulo Vinicius Ferraz Corrêaab, Paola Visnardi Fassinab & FlávioDias Passosb

a Programa de Pós-Graduação em Biologia Animal, UniversidadeEstadual de Campinas, Campinas, SP, Brazilb Department of Animal Biology, Institute of Biology – University ofCampinas, Campinas, SP, BrazilPublished online: 16 Oct 2014.

To cite this article: Paulo Vinicius Ferraz Corrêa, Paola Visnardi Fassina & Flávio Dias Passos (2014):Falcidens targatus and F. acutargatus: two species of Caudofoveata (Mollusca, Aplacophora) new forBrazil, Journal of Natural History, DOI: 10.1080/00222933.2014.959575

To link to this article: http://dx.doi.org/10.1080/00222933.2014.959575

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Falcidens targatus and F. acutargatus: two species of Caudofoveata(Mollusca, Aplacophora) new for Brazil

Paulo Vinicius Ferraz Corrêaa,b, Paola Visnardi Fassinab and Flávio Dias Passosb*

aPrograma de Pós-Graduação em Biologia Animal, Universidade Estadual de Campinas,Campinas, SP, Brazil; bDepartment of Animal Biology, Institute of Biology – University ofCampinas, Campinas, SP, Brazil

(Received 19 November 2013; accepted 22 August 2014)

Two species of Falcidens Salvini-Plawen, 1968 (Chaetodermatidae) are recordedfor the first time from Campos Basin, off south-eastern Brazil. Seventeen sampleswith 176 specimens of Falcidens targatus Salvini-Plawen, 1992 were collected fromthe continental shelf, and 141 individuals of Falcidens acutargatus Salvini-Plawen,1992 were obtained in 53 samples from the slope. They are recognized by theirexternal morphology and by the details of their sclerites, radula and oral shield;further, new morphometrical data are added. Type material was also examined.As for both these species the former subgenus name Lepoderma Salvini-Plawen,1992 is a pre-occupied name by Lepoderma Looss, 1899 (Trematoda), the newsubgenus name Chiastofalcidens is proposed to replace it. The finding of F. (Ch)acutargatus from off Rio de Janeiro suggests that this species has a continuousdistribution in the slope through all the Western Atlantic. In contrast, F. (Ch)targatus appears to be more restricted in its distribution.

http://zoobank.org/urn:lsid:zoobank.org:pub:7E79F655-8468-4113-AA2D-95FDCF0CF5EA

Keywords: Chaetodermomorpha; Chaetodermatidae; distribution; biogeography;morphometry

Introduction

The Caudofoveata fauna from eastern South America are poorly known, with onlyscattered information for a few species. For the Brazilian coast, in particular, recordsof these aplacophorans are very imprecise and/or incomplete, hard to track down,with in reality some doubts about their occurrence. To date there have been only twodetailed studies on these animals from Brazil: that of Cruz et al. (1998) about thestructure of the radula of an undescribed species of Falcidens Salvini-Plawen, 1968from off Rio de Janeiro; and that of Martins (2008), who in a doctoral thesisinvestigated four new species from the south-eastern and southern coasts withoutnaming them. Rios (2009) listed Limifossor hexadentatus Salvini-Plawen, 1992 andthree other species – ‘Falcidens sp.’, ‘Limifossor sp.’ and ‘Scutopus sp.’ – but nocitations of original references or voucher material from these records were referredto. Scheltema (1990) examined one (at that time) undescribed species of Falcidensfrom off Rio de Janeiro in a discussion of the evolutionary radiation of Aplacophora.Apart from these, there are more complete records furnished by Scheltema (1985) and

*Corresponding author. Email: flaviodp@unicamp.br

Journal of Natural History, 2014http://dx.doi.org/10.1080/00222933.2014.959575

© 2014 Taylor & Francis

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Ivanov and Scheltema (2008), who obtained specimens of Chevroderma turneraeScheltema, 1985 and Spathoderma bulbosum Ivanov and Scheltema, 2008(Prochaetodermatidae) from deep waters near the north-eastern Brazilian coast.Further to the south, other caudofoveate species are known from Uruguay(Scheltema 1985; Salvini-Plawen 1992; Scarabino 2003; Ivanov and Scheltema2008) and Argentina (Ivanov and Scheltema 2008).

In the present paper, two species of Falcidens are recorded for the first time fromBrazil. Belonging to the family Chaetodermatidae Théel, 1875, this genus is among themost speciose in Caudofoveata, and was created to group species that bear a radulawith a pair of sickle-like teeth and a generally elongate, often tailed body (Salvini-Plawen 1968). This genus has grown since then, and Salvini-Plawen (1992) suggestedthe subgenus Lepoderma Salvini-Plawen, 1992 to group six species, based on thepresence of a peculiar ornamentation of the sclerites. The Brazilian species hererecorded were originally described and classified in this subgenus: Falcidens(Lepoderma) targatus Salvini-Plawen, 1992 and Falcidens (Lepoderma) acutargatusSalvini-Plawen, 1992. Apart from extending their geographic distribution in theWestern Atlantic, a discussion on their bathymetric distribution is undertaken, basedon a large-scale collecting effort. Morphologically, they are very similar and so amorphometric study was performed, emphasizing some of their distinctive features.

Materials and methods

Hundreds of bottom samples were collected in Campos Basin off the Rio de Janeiroand Espírito Santo States, south-eastern Brazil, as a part of the activities of the‘Habitats Project – Campos Basin Environmental Heterogeneity’ during 2008 and2009. These samples were obtained from 20 to 3000 m depth, fixed in buffered 4%formaldehyde and then preserved in 70% alcohol; eventually, they were sievedthrough a 0.5 mm mesh and the aplacophorans were sorted, counted, and observedunder a stereomicroscope.

Well-preserved specimens were selected for the extraction of sclerites, to beobserved in detail under a JEOL JSM-5800LV scanning electron microscope(SEM). For isolation of sclerites from each body region, the animals were firstlyplaced in a solution of 2% sodium hypochlorite for five minutes and then transferredto a 70% ethanol solution; this caused a partial dissolution of the mantle and cuticle.Then, the sclerites of the desired body region were washed and transferred ontocoverslips, which in turn were dried and placed on aluminium stubs to be gold-coated. The buccal mass of some of these specimens was further dissolved in sodiumhypochlorite solution, isolating the radula to be washed, dried and placed on stubs.Whole animals were also observed by SEM, after dehydration in an ascendingethanol series and critical point drying.

For morphometric studies, each specimen of both species was photographed by acamera coupled to a Zeiss SteREO Discovery V8 stereo microscope (Göttingen,Germany) and then five body regions were measured by using the AxioVision soft-ware version 4.8.2 (Zeiss, Göttingen, Germany): length of the anterium plus neck(neck length – NeL); length of the trunk (TrL); width of the trunk at its centralportion (TrW); length of the posterium, which is formed by a shank plus a knob(posterium length – PoL); and width of the shank at its central portion (ShW). Therelative length of the posterium (PoL/TrL), as well as the ratio between the total

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length of the animal and its diameter (ToL/TrW, where ToL is NeL + TrL + PoL),were calculated. To determine significant differences of these measurements betweenspecies t-tests were performed, and Pearson product–moment correlation coefficientswere used to verify the relationship of these relative measurements according togrowth for each species. Measurements were compared in a total of 167 individualsof F. targatus and 138 of F. acutargatus. As in caudofoveates the body can stretch andcontract axially beyond 50% (Salvini-Plawen 1968), the specimens for these measure-ments were carefully chosen to be in a similar state of body contraction.

Finally, the type material deposited in the molluscan collection of the AmericanMuseum of Natural History (AMNH), New York, was observed and compared withthe specimens obtained in Campos Basin. These lots were as follows: AMNH 265332(one individual labelled as ‘type’) and 265336 (23 specimens) of F. targatus, andAMNH 265333 (one individual labelled as ‘type’) and 265346 (fragments of an unde-termined number of individuals) of F. acutargatus. Boyko and Sage III (1996) referredto the lots ‘AMNH 265332’ and ‘265333’ as holotypes and ‘265336’ and ‘265346’ asparatypes. Three animals from the lot ‘265336’ of F. targatus were kindly provided bythe AMNH for extraction and examination of the sclerites. The specimens of CamposBasin are deposited in the following institutions: Museum of Zoology ‘Prof. Adão JoséCardoso’ of the University of Campinas (ZUEC APL 1–10 of F. targatus; and ZUECAPL 11–52 of F. acutargatus), Brazil; National Museum of Rio de Janeiro (MNRJ17463 of F. targatus; and MNRJ 17464–17467 of F. acutargatus), Brazil; andUniversity Museum of Bergen (ZMBN 94132 of F. targatus; and ZMBN 94133–94135 of F. acutargatus), Norway.

Taxonomy

Class CAUDOFOVEATAFamily CHAETODERMATIDAE Théel, 1875

Genus Falcidens Salvini-Plawen, 1968Subgenus Chiastofalcidens nom. nov. (pro Lepoderma Salvini-Plawen 1992,

nec Looss, 1899)Falcidens (Chiastofalcidens) targatus Salvini-Plawen, 1992

(Figures 1A–C, 2A–G, 3A, B, 4A, C)Falcidens (Chiastofalcidens) acutargatus Salvini-Plawen, 1992

(Figures 1D–F, 2H–J, 3C, 4B, D)

Chiastofalcidens is proposed to replace the species-group name (subgenus) ofLepoderma Salvini-Plawen, 1992, which is a pre-occupied name: Lepoderma Looss,1899 (Trematoda). ‘Chiastos’, derived from Greek chiasma, means intercrossed; thisnew name refers to the crossed sculpture of the sclerites, present in Falcidens loveni(Nierstrasz, 1902), F. chiastos Scheltema, 1989, F. nontargatus Salvini-Plawen, 1992,F. targotegulatus Salvini-Plawen, 1992, and F. acutargatus Salvini-Plawen, 1992, allof them related to F. targatus, the type species designated by Salvini-Plawen (1992)for Lepoderma.

Falcidens (Chiastofalcidens) targatus and F. (Ch.) acutargatus have an elongatedbody shape with three distinct regions (Figure 1): an anterior part, with an ‘anterium’

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continuous to a neck; a trunk; and a posterium with a slender shank and a terminalknob. The collar separating the trunk from the neck is well marked in most indivi-duals of both species. In F. (Ch.) targatus the neck is more prominent and theanterium can be inflated, or not (Figures 1A–C, 2A, B). Due to deposition of particlesfrom the surrounding environment, the knob is red in almost all the individuals of thisspecies (Figure 1A). In some animals the gills are partially exposed because the knobis very contracted (Figure 2C), while in others it is relaxed, showing the mantle cavityin an inflated condition (Figure 2D). In F. (Ch.) acutargatus, the knob is more distinctfrom the shank (Figures 1D–F, 2J).

The individuals of the material from the American Museum of Natural Historylabelled as ‘types’, which are considered the holotypes of both species (Boyko andSage III 1996) are quite worn (Figure 1C, F). The holotype of F. (Ch.) acutargatuscorresponds exactly to the specimen of figure 8 of Salvini-Plawen (1992). Mostspecimens of the lot of the paratypes of F. (Ch.) targatus are well preserved andone of them is very similar to one individual from Brazil (Figure 1A, B). Thefragments of the paratypes of F. (Ch.) acutargatus are not comparable. From externalview, the animals of both species from Campos Basin are very similar to thoseillustrated in figures 7 and 8 of Salvini-Plawen (1992).

The sclerites extracted from Campos Basin specimens of both species and from oneparatype of F. (Ch.) targatus are illustrated in Figures 2 and 3. In general, they are smallerin F. (Ch.) targatus than in F. (Ch.) acutargatus, being similar in shape among thesespecies, and differing only in the some details (Figure 3). In the anterium, the sclerites arevery small, with an elliptical shape and no ornamentation (Figures 2E, 3A, C). In theneck, trunk and shank they have a more slender shape in F. (Ch.) targatus (Figure 3A, B)than in F. (Ch.) acutargatus (Figure 3C); also, in the former species they have atapered tip (Figures 2F, G, 3A, B), while in the latter they are more pointed distally(Figures 2H–J, 3C). In both species, the side of the sclerites facing the body is smooth (seethe sclerites with an asterisk in Figure 3), while on the opposite surface they bear the

Figure 1. (A–C) Falcidens (Chiastofalcidens) targatus; and (D–F) Falcidens (Chiastofalcidens)acutargatus; photomicrographs of Campos Basin’s specimens from (A, D) the left and (E) right;(B) paratype and (C, F) holotypes are from the left. In A and D the different body regions areshown: anterium (a), neck (n), trunk (tr), shank (sh), and knob (k). The scale bar in C is thesame for all photos, except E.

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typical ornamentation originally described for the subgenus: on the proximal half of thesurface there are up to eight crossed ridges. On the distal half these ridges are parallel, amedian one being stronger and forming a low keel, this being particularlymore evident inF. (Ch.) acutargatus. In the neck theymeasure ~45 μm in F. (Ch.) targatus and ~120 μm inF. (Ch.) acutargatus; in the trunk, ~100 and ~140 μm; and in the shank, ~70 and ~140 μm,respectively. Throughout the body, about 1/3 of the sclerites of F. (Ch.) targatus also havea basal deep notch. In F. (Ch.) acutargatus this notch is present in about 1/4 of thesclerites, and appears to be shallower. At the knob the sclerites are elongated, ~170 μmlong in F. (Ch.) targatus and ~180 μm long in F. (Ch.) acutargatus, with the shape of longbats surrounding the mantle cavity. The extracted sclerites of the paratype of F. (Ch.)targatus (Figure 3B) are very similar to the ones obtained from Campos Basin’s speci-mens (Figure 3A).

The radula of F. (Ch.) targatus (Figure 4A) is similar to the one of F. (Ch.)acutargatus (Figure 4B). A pair of sickle-shaped teeth is present in the distal end of alarge cone-shaped support, and there is also a pair of lateral supports, which are

Figure 2. (A–G) Falcidens (Chiastofalcidens) targatus; and (H–J) Falcidens (Chiastofalcidens)acutargatus. Scanning electron micrographs of whole individuals (A, B, adults; J, juvenile), andof details of the body regions and their sclerites (C–I), all from the left side. In A and B thearrows show the collar separating the neck from the trunk. (C, D) Posterium; in C the knob iscontracted, and the gills are partially exposed; in D, the sclerites have fallen off and the mantlecavity is shown in an inflated condition. (E) Anterium; (F) trunk; (H) anterium, neck andanterior part of the trunk; (I) posterior part of the trunk and posterium. g, gills; mc, mantlecavity; os, oral shield. The scale is the same in A and B, and in H and I.

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approximately one third of the length of the central support in F. (Ch.) targatus andabout a half of its length in F. (Ch.) acutargatus. A triangular plate is placedanteriorly, connected with the teeth by an apophysis of the plate.

The oral shield is U-shaped in both species (Figure 4C, D).From a total of about 2350 specimens of caudofoveates present in the samples

collected by the Habitats Project, F. (Ch.) targatus and F. (Ch.) acutargatus are amongthe most common species, with 176 and 141 individuals, respectively (Tables 1, 2). Theformer species was only collected on the shelf, represented by 17 samples from 30 to

Figure 3. (A, B) Falcidens (Chiastofalcidens) targatus and (C) Falcidens (Chiastofalcidens)acutargatus. Scanning electron micrographs of the sclerites isolated from different body regionsof Campos Basin’s specimens (A, C) and holotype (B); the asterisks show the sclerites viewedfrom the side facing the body. a, anterium; k, knob; n, neck; sh, shank; tr, trunk. The scale baris the same for all images.

Figure 4. (A, C) Falcidens (Chiastofalcidens) targatus and (B, D) Falcidens (Chiastofalcidens)acutargatus. Scanning electron micrographs of the radula, viewed from (A) the back and (B)front, and (C, D) of the oral shield. ap, apophysis; cs, central support; ls, lateral support; rp,ridges of the triangular plate; te, teeth; tp, triangular plate. The scale bar is the same for Aand B.

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Tab

le1.

Falcidens

(Chiastofalcidens)

targatus,materialexam

ined

andstationda

ta.

Station

Position

Depth

(m)

Date

No.

specim

ens

HAB13

-A03

-R1

23°1′47.12

7″S,

41°58′29

.231″W

8028

February20

0951

HAB13

-A03

-R2

23°1′47.81

1″S,

41°58′29

.044″W

8016

March

2009

19HAB13

-A03

-R3

23°1′47.08

0″S,

41°58′29

.015″W

8016

March

2009

16HAB13

-A04

-R1

23°6′58,67

9″S,

41°53′56

,014″W

111

1March

2009

13HAB13

-A04

-R2

23°6′58.67

9″S,

41°53′56

.014″W

111

1March

2009

11HAB13

-A04

-R3

23°6′58.81

6″S,

41°53′56

.126″W

111

16March

2009

15HAB13

-B01

-R2

22°41′46

.694″S,

41°53′46

.121″W

3016

March

2009

2HAB13

-B01

-R3

22°41′47

.098″S,

41°53′46

.452″W

3016

March

2009

1HAB11

-B02

-R1

22°37′35

.319″S,

41°21′51

.590″W

5327

February20

092

HAB11

-B02

-R2

22°37′35

.330″S,

41°21′51

.788″W

5327

February20

092

HAB11

-B02

-R3

22°37′31

.874″S,

41°21′51

.734″W

5327

February20

091

HAB13

-D03

-R3

22°19′32

.127″S,

40°37′18

.980″W

7515

March

2009

1HAB13

-H05

-R3

21°42′37

.911″S,

40°8′58.91

1″W

147

10March

2009

7HAB16

-H05

-R3

21°42′37

.474″S,

40°8′59.67

7″W

147

7July

2009

4HAB17

-A03

-R2

23°1′47.43

3″S,

41°58′29

.266″W

8015

July

2009

18HAB17

-A03

-R3

23°1′48.30

9″S,

41°58′30

.289″W

8015

July

2009

1HAB17

-A04

-R3

23°6′52.26

8″S41

°55′13

.122″W

110

15July

2009

12HAB17

-B02

-R3

22°45′49

.078″S,

41°45′33

.357″W

5316

July

2009

3HAB17

-I05

-R3

21°23′2.93

3″S,

40°15′9.56

8″W

140

21July

2009

2Meandepth

85.47

Total

181

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Tab

le2.

Falcidens

(Chiastofalcidens)

acutarga

tus,materialexam

ined

andstationda

ta.

Station

Position

Depth

(m)

Date

No.

specim

ens

HAB7-B06

-R1

23°12′32

.146″S,

40°58′30

.918″W

451

04July

2008

1HAB6-B07

-R2

23°13′1.96

6″S,

40°57′36

.745″W

724.2

27June

2008

4HAB3-B08

-R1

23°13′48

.742″S,

40°55′55

.134″W

986.4

13May

2008

1HAB3-B08

-R2

23°13′47

.452″S,

40°55′56

.256″W

986.4

14May

2008

1HAB7-C06

-R1

22°59′0.28

9″S,

40°48′25

.710″W

387.4

04July

2008

1HAB7-C06

-R2

22°59′0.33

9″S,

40°48′25

.850″W

386.8

04July

2008

3HAB6-C07

-R1

22°59′51

.839″S,

40°47′42

.838″W

710.1

29June

2008

7HAB6-C07

-R2

22°59′52

.609″S,

40°47′45

.008″W

689.4

30June

2008

5HAB6-C07

-R3

22°59′52

.279″S,

40°47′45

.398″W

686.1

01July

2008

3HAB7-D06

-R1

22°33′35

.655″S,

40°26′38

.979″W

396.1

08July

2008

2HAB7-D06

-R2

22°33′36

.245″S,

40°26′39

.329″W

396.2

09July

2008

1HAB7-D06

-R3

22°33′33

.805″S,

40°26′40

.289″W

393.4

11July

2008

2HAB7-F06

-R2

22°19′11

.331″S,

40°5′44.22

1″W

403.9

08July

2008

1HAB7-F06

-R3

22°19′10

.690″S,

40°5′41.67

1″W

404.6

08July

2008

1HAB6-I07-R1

21°11′12

.183″S,

40°12′52

.020″W

693.9

17July

2008

7HAB7-I07-R2

21°11′3.02

2″S,

40°12′19

.168″W

790.2

05July

2008

3HAB7-I07-R3

21°11′2.63

2″S,

40°12′18

.218″W

792.4

05July

2008

3HAB6-CANAC07

-R2

21°47′26

.614″S,

40°2′13.76

5″W

752.5

06July

2008

1HAB9-CANAC07

-R2

21°47′26

.548″S,

40°1′55.30

1″W

780

06February20

091

HAB9-CANAC07

-R3

21°47′26

.692″S,

40°1′55.48

1″W

775

06February20

093

HAB8-A07

-R1

23°39′19

.742″S,

41°18′28

.369″W

699

28Janu

ary20

095

HAB8-A07

-R2

23°39′20

.559″S,

41°18′28

.196″W

701

28Janu

ary20

093

(Con

tinu

ed)

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Tab

le2.

(Con

tinu

ed).

Station

Position

Depth

(m)

Date

No.

specim

ens

HAB8-A07

-R3

23°39′21

.880″S,

41°18′33

.045″W

692.7

28Janu

ary20

094

HAB8-B06

-R2

23°10′23

.820″S,

40°56′45

.497″W

432

01February20

091

HAB8-B07

-R1

23°13′1.32

3″S,

40°57′37

.733″W

737.5

28Janu

ary20

093

HAB8-B07

-R2

23°13′2.79

9″S,

40°57′37

.798″W

741.6

28Janu

ary20

092

HAB8-B07

-R3

23°12′59

.638″S,

40°57′35

.825″W

761

29Janu

ary20

091

HAB8-C06

-R3

22°59′0.67

7″S,

40°48′28

.837″W

376.6

31Janu

ary20

091

HAB8-C07

-R1

22°59′52

.085″S,

40°47′43

.276″W

708

29Janu

ary20

091

HAB8-C07

-R2

22°59′53

.839″S,

40°47′45

.022″W

692

29Janu

ary20

0910

HAB8-D06

-R1

22°33′35

.276″S,

40°26′37

.585″W

400

31Janu

ary20

092

HAB8-D06

-R2

22°33′35

.143″S,

40°26′37

.449″W

401

31Janu

ary20

093

HAB8-E06

-R1

22°25′58

.821″S,

40°17′35

.352″W

380

31Janu

ary20

092

HAB8-F06

-R2

22°19′3.83

9″S,

40°5′28.58

1″W

386

30Janu

ary20

092

HAB9-H06

-R1

21°44′21

.608″S,

40°4′59.61

4″W

405

05February20

091

HAB9-H06

-R2

21°44′21

.507″S,

40°4′53.92

6″W

404

05February20

094

HAB9-H06

-R3

21°44′21

.767″S,

40°4′59.69

7″W

402

05February20

094

HAB9-I06-R1

21°13′38

.229″S,

40°14′58

.238″W

417

04February20

091

HAB9-I06-R2

21°13′38

.308″S,

40°14′57

.803″W

417

04February20

094

HAB9-I07-R1

21°11′12

.170″S,

40°12′51

.838″W

682

04February20

094

HAB9-I07-R2

21°11′12

.073″S,

40°12′52

.126″W

680

04February20

095

HAB9-I07-R3

21°11′12

.228″S,

40°12′51

.745″W

683

04February20

0911

HAB6-A07

-R1

23°39′20

.061″S,

41°18′30

.264″W

693.7

23June

2008

6HAB6-A07

-R2

23°39′19

.831″S,

41°18′30

.234″W

692.2

24June

2008

3

(Con

tinu

ed)

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Tab

le2.

(Con

tinu

ed).

HAB6-A07

-R3

23°39′19

.981″S,

41°18′30

.534″W

732.9

25June

2008

2HAB3-G08

-R2

22°7′19.66

3″S,

39°52′22

.613″W

992.6

16June

2008

1HAB7-H06

-R2

21°44′21

.564″S,

40°5′18.02

6″W

402.7

07July

2008

1HAB7-H06

-R3

21°44′21

.493″S,

40°5′18.06

6″W

401.6

07July

2008

1HAB7-H07

-R2

21°41′11

.649″S,

40°2′20.69

0″W

699.4

07July

2008

3HAB4-CANG07

-R2

21°56′10

.244″S,

39°57′43

.438″W

709.7

28May

2008

1HAB6-B07

-R1

23°13′1.39

6″S,

40°57′36

.705″W

815.5

26June

2008

1HAB8-D06

-R3

22°33′36

.014″S,

40°26′37

.171″W

383

31Janu

ary20

091

HAB8-E06

-R3

22°25′59

.389″S,

40°17′33

.343″W

387.1

31Janu

ary20

092

HAB9-I07-R3

21°11′12

.228″S,

40°12′51

.745″W

683

04February20

093

HAB9-H06

-R1

21°44′21

.608″S,

40°4′59.61

4″W

405

05February20

091

HAB8-A07

-R3

23°39′21

.880″S,

41°18′33

.045″W

692.7

28Janu

ary20

091

HAB8-A07

-R1

23°39′19

.742″S,

41°18′28

.369″W

699

28Janu

ary20

092

HAB3-H09

-R2

21°39′18

.701″S,

39°53′55

.974″W

1293

.225

June

2008

1HAB8-C08

-R2

23°1′30.86

2″S,

40°45′22

.948″W

964.8

16Janu

ary20

091

Meandepth

617.50

Total

156

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147 m depth (Figures 5, 6). Most specimens and the richest samples of F. (Ch.) targatuswere obtained in the south of the area of Campos Basin, namely in transects A and B(Figure 5). Falcidens (Chiastofalcidens) acutargatus is more common on the continentalslope, with 53 samples obtained from 376 to 1293 m depth; this species is homoge-nously distributed through all of the sampling area (Figures 5, 6).

The mean length of F. (Ch.) targatus is higher (5.34 mm), reaching up to 9.12 mm,while specimens of F. (Ch.) acutargatus have a mean length of 4.04 mm but are up to10.44 mm long. The t-test revealed statistical differences (p < 0.05) among species inrelation to the NeL, TrL, TrW and ShW (Table 3). Although the PoL was the onlyabsolute measurement that can be considered similar among species (p = 0.45), theratio PoL/TrL was not (p < 0.05). In fact, the trunk is usually twice the length of theposterium (PoL/TrL = 0.42) in F. (Ch.) targatus, while in F. (Ch.) acutargatusthe posterium is more distinct and longer when compared to the trunk (PoL/TrL = 0.63). The PoL/TrL showed no correlation with the length of the body in F.(Ch.) targatus (r = −0.15) and in F. (Ch.) acutargatus (r = −0.21) (Figure 7A).

The ratio ToL/TrW was revealed to be distinct among these species (p < 0.05). APearson product–moment coefficient showed a moderate correlation to the totallength of the body in both F. (Ch.) targatus (r = 0.77) and F. (Ch.) acutargatus(r = 0.75). This relationship is illustrated in Figure 7B.

Figure 5. Distribution of Falcidens (Chiastofalcidens) targatus and Falcidens (Chiastofalcidens)acutargatus in Campos Basin, off Rio de Janeiro (RJ) and Espírito Santo States (ES). Theactivities of the Habitats Project included sampling sites from 20 to 3000 m depths, with manyof them made along the transects shown in ‘A’ to ‘I’.

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Discussion

Members of Chaetodermatidae are ubiquitous in almost all the oceans, although theyare more commonly recorded from waters of the northern hemisphere. In the AtlanticOcean, for example, species of this family are well known from both European andNorth/Central American coasts (e.g. Heath 1911, 1918; Salvini-Plawen 1967, 1968,1972, 1975, 1992, 1996; Scheltema 1990; Schander et al. 2006; Ivanov and Scheltema2009; Ivanov et al. 2009), and scarcely registered in Africa and South America (e.g.Scheltema 1976; 1990; Salvini-Plawen 1992; Scarabino 2003). Like most aplaco-phoran species they usually inhabit subtidal to deeper waters, this certainly beingone of the main causes for them to be poorly collected in Brazil. These obstacles arenow being overcome, due to large collection efforts made by the Habitats Project.

Falcidens (Ch.) targatus was described from shallow waters (73 m) off Uruguay,where 31 specimens were obtained by the VEMA Expedition (Salvini-Plawen 1992).From the Gulf of Darien/Caribbean Sea, the same expedition collected four speci-mens of F. (Ch.) acutargatus. Until that time, these species had not been recordedfrom Brazil, but Scheltema (1990) had already had the opportunity to examineindividuals of both those of F. (Ch.) targatus from off Rio de Janeiro and those ofF. (Ch.) acutargatus from North Carolina (USA) to Guiana Basin off north-eastSouth America. She referred to them as unnamed species, and illustrated their radulaand sclerites. The upper drawings of figure 2C of Scheltema (1990) are of F. (Ch.)targatus, while the lower ones are of F. (Ch.) acutargatus. So, with the first report ofthe latter and the confirmation of the occurrence of the former in Brazilian waters,their geographical distribution can be characterized as this: F. (Ch.) targatus mustoccur from Uruguay and extend northwards up to south-eastern Brazil; and F. (Ch.)acutargatus may have a wider distribution, occurring from North Carolina to theCaribbean and possibly along the entire northern and north-eastern Brazil, down toat least its south-eastern coast, off Rio de Janeiro.

Figure 6. Depth versus number of specimens of Falcidens (Chiastofalcidens) targatus andFalcidens (Chiastofalcidens) acutargatus.

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Tab

le3.

Mean,

stan

dard

deviation(SD),minim

uman

dmaxim

ummeasurementsof

Falcidens

(Chiastofalcidens)targatus

andFalcidens

(Chiastofalcidens)

acutargatus.

NeL

(mm)

TrL

(mm)

PoL

(mm)

TrW

(mm)

ShW

(mm)

ToL

(mm)

PoL

/TrL

ToL

/TrW

Falcidens

(Chiastofalcidens)

targatus

Mean

0.75

3.33

1.26

0.65

0.35

5.33

0.39

8.24

SD0.25

1.19

0.49

0.14

0.09

1.66

0.13

2.06

Minim

um0.23

0.73

0.25

0.28

0.13

1.59

0.09

4.46

Max

imum

1.84

10.64

3.21

0.89

0.57

13.38

0.84

21.07

Falcidens

(Chiastofalcidens)

acutarga

tus

Mean

0.58

2.08

1.23

0.52

0.25

3.89

0.65

7.43

SD0.21

1.11

0.64

0.18

0.15

1.75

0.27

2.14

Minim

um0.12

0.46

0.14

0.17

0.06

0.98

0.11

4.34

Max

imum

1.34

6.17

4.31

1.12

1.86

10.44

1.90

16.85

Note:

Abb

reviations:NeL

,neck

leng

th;TrL

,trun

kleng

th;PoL

,po

sterium

leng

th;TrW

,trun

kwidth;Sh

W,shan

kwidth;ToL

,totalleng

th(=

NeL

+TrL

+PoL

).

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In Campos Basin, F. (Ch.) targatus is restricted to the shelf, and represented byfewer samples containing a higher number of specimens. In contrast, F. (Ch.) acu-targatus has a wider bathymetric distribution, occurring only from slope samples witha low number of individuals. In fact, the number of species of Caudofoveata is loweron the shelf, with a dominance of individuals of F. (Ch.) targatus, while on the slopethe species and specimen representation is more equal (personal observation). Asimilar pattern of distribution was recorded in south-eastern Australia by Scheltema(1990), who used this as evidence to suggest that most aplacophorans had an olderTethyan or pre-Tethyan broad distribution and diversification in the slope, and then,after the sea level regression events of the Pleistocene, the shelf species originated.This kind of evolutionary radiation from the slope to shelf may have caused the nowdisjunct geographical distribution observed for some groups and also the dominanceof a few species on the shelf. Members of the subgenus Chiastofalcidens nom. nov.(= Lepoderma) would represent this typical pattern of distribution: F. (Ch.) loveni,F. (Ch.) chiastos and F. (Ch.) targotegulatus occur in the Pacific Ocean, while F. (Ch.)targatus, F. (Ch.) acutargatus and F. (Ch.) nontargatus are from the Atlantic. InCampos Basin, apart from the dominance of F. (Ch.) targatus in the shelf, it isnoteworthy that this species appears to be ‘pushed’ towards the slope by the influenceof the Paraíba do Sul River delta, with lower salinities and higher sediment loads indeeper waters in the north. If this is so, this species must have a more restricteddistribution, also as a reflection of the influence of the deltas of many larger rivers ofnorth-eastern and northern Brazil (where the shelf is much narrower). These riverdeltas could act as oceanographic barriers preventing this species from being distrib-uted further to the north. In contrast, the deeper water species F. (Ch.) acutargatuscould be more widespread, as its distribution appears to be not influenced by riverdeltas. Future phylogeographical studies using specimens from other areas (includingthe north-eastern Brazilian coast), will show whether this contrasting pattern ofdistribution of F. (Ch.) targatus and F. (Ch.) acutargatus is really true and a resultof a slope-shelf direction of evolutionary radiation.

The radula and the oral shield of the species of the subgenus Chiastofalcidensnom. nov. are very similar to other Falcidens spp., but the sclerites are not; therefore,based on the peculiar sclerite structure (‘autapomorphy’ in Scheltema 1990), theproposition of a subgenus level for Chiastofalcidens nom. nov. is here maintained,as suggested by Salvini-Plawen (1992). However, the monophyly of this group is notyet tested; this depends on detailed anatomical and molecular studies, which are very

Figure 7. Total length versus (A) posterium length/trunk length, and (B) total length/trunkwidth, for Falcidens (Chiastofalcidens) targatus and Falcidens (Chiastofalcidens) acutargatus.For abbreviations see text.

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scarce for caudofoveates as a whole. From an external view, F. (Ch.) targatus and F.(Ch.) acutargatus are very similar, differing in subtle characters, such as the distinc-tiveness of the neck in the first species and the posterium in the second. The highnumber of specimens collected by the Habitats Project permitted a morphometricstudy, which showed that some measurements are also quite reliable to distinguishthese species, if specimens in a comparable state of contraction are available. Thedifference of posterium length relative to trunk length between F. (Ch.) targatus andF. (Ch.) acutargatus is particularly obvious. Differences in details of the sclerites arehere emphasized, as noted by Salvini-Plawen (1992).

Based on a review of the species of Prochaetodermatidae, Ivanov and Scheltema(2008) suggested the occurrence of a possible break of the aplacophoran diversity faunabetween the latitudes of 8° S and 36° S in the western Atlantic (like Cutler 1975). Now,with the material from Campos Basin being studied, apart from F. (Ch.) targatus andF. (Ch.) acutargatus, at least 11 other species will become known from this area, somebeing probably new species and some represented by hundreds of individuals. Thisvaluable material is thus showing that the Brazilian aplacophoran fauna is very poorlyknown and only beginning to be discovered. Comparisons with other faunas will befruitful, representing an opening of a new avenue of investigation of these molluscs.

Acknowledgements

Thanks are due to Dr A. P. Falcão, who invited F. D. Passos to participate as a taxonomist ofthe Habitats Project. Thanks are due also to A. C. S. Sprogis and S. M. F. Ferraz (Laboratoryof Microscopy – IB/UNICAMP), who provided assistance in the techniques of microscopy. Dr.M. Siddall and L. Sarfraz are acknowledged for kind reception at the AMNH and for the loanof type material of F. (C.) targatus.

The studies on the Brazilian aplacophorans were initially encouraged by ChristofferSchander, whom we specially acknowledge and to whom we dedicate this paper. And finally,we thank Dr Chistiane Todt, who has encouraged us during our aplacophoran studies. This is acontribution to the collection Who are the ‘Aculifera’? in memory of Christoffer Schander.

FundingThis work was supported by the CENPES/Petrobras; FAPESP [grant number 2011/50297-4];and FAEPEX [grant number 362/2012]. Additional financial support was provided byscholarships of FAPESP [Proc. 2011/07629-6]; and SAE/PIBIC/CNPq/UNICAMP, awardedto P. V. F. Corrêa and P. V. Fassina, respectively.

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