. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. APLACOPHORA: PROGENETIC COELOMATES 65. Figure 7. (A-C) Chaetodermomorpha. (A. B) (.'kern'derma lurnerae. entire animal (antenor to left) and divided oral shield (I'rom Scheltema, 1985, fig. 3L, O. P). (C) Oral shield of SculOfiim (cf., Fig. 8A) (from Scheltema, 1988, fig. 6). (D. E) Neomeniomorpha. (D) Dorymenia sp. (E) A new neomenioid genus and species in the family Simrothicllidae. D and E are drawn to the same scale, anterior to left; the midgut and gonad lie between X-X and Y-Y. in its plesiomorphic state
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. APLACOPHORA: PROGENETIC COELOMATES 65. Figure 7. (A-C) Chaetodermomorpha. (A. B) (.'kern'derma lurnerae. entire animal (antenor to left) and divided oral shield (I'rom Scheltema, 1985, fig. 3L, O. P). (C) Oral shield of SculOfiim (cf., Fig. 8A) (from Scheltema, 1988, fig. 6). (D. E) Neomeniomorpha. (D) Dorymenia sp. (E) A new neomenioid genus and species in the family Simrothicllidae. D and E are drawn to the same scale, anterior to left; the midgut and gonad lie between X-X and Y-Y. in its plesiomorphic state in Aplacophora is distichous, that is, only two teeth per row (Scheltema, 1988; Schel- tema el al, 1989), a reduction in number from the doco- glossate chiton radula. Both neomenioids and chaeto- derms have a dorsoterminal sense organ (= dorsocaudal sensory pit), or sometimes several, in the epidermis. It is of unknown function, although homology to the osphra- dium has been conjectured (Spengel, 1881; Haszprunar, 1987). Whether or not this homology is correct, the po- sition of the dorsoterminal sense organ is an autapomor- phy of the Aplacophora, for there is no compelling evi- dence that this position, postulated to be primitive for the molluscan osphradium (Salvini-Plawen, 1985), is other than an apomorphy shared only by neomenioids and chaetoderms. The two aplacophoran taxa share a similar reproductive system unique among mollusks. Paired gonads, some- times fused, open directly into the pericardium, and paired U-shaped gametoducts lead from the posterior end of the pericardium, first anteriorly and then posteriorly, to the mantle cavity (Figs. 5A, 6A, 9D). Separate gonaduct openings in species of Phyllomenia (Salvini-Plawen, 1978) are interpreted here as a derived condition of that genus. The mantle cavity in both neomenioids and chaeto- derms is small and posterior, acting as little more than a cloaca. In neomenioids, the groove on either side of the foot-fold can also
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
